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| ==== 1.1. Significance of PAHs as Environmental Contaminants ==== | ==== 1.1. Significance of PAHs as Environmental Contaminants ==== |
| Polycyclic Aromatic Hydrocarbons (PAHs) are a complex group of organic compounds, each composed of two or more fused benzene rings arranged in various structural configurations.[1], [2] These compounds are ubiquitous in the environment and have garnered significant scientific and regulatory attention due to their persistence, potential for bioaccumulation, and, most notably, their toxicological properties.[1], [2], [[#ref3|3]], [[#ref4|4]], [[#ref5|5]], [6], [7], [8], [9] Many PAHs are recognized as carcinogenic (cancer-causing), mutagenic (causing genetic mutations), and teratogenic (causing developmental abnormalities).[2], [[#ref4|4]], [7], [[#ref10|10]], [[#ref11|11]], [[#ref12|12]], [[#ref13|13]], [[#ref14|14]], [[#ref15|15]], [16], [17], [18], [[#ref19|19]], [20], [21], [22] | Polycyclic Aromatic Hydrocarbons (PAHs) are a complex group of organic compounds, each composed of two or more fused benzene rings arranged in various structural configurations.<sup>1, 2</sup> These compounds are ubiquitous in the environment and have garnered significant scientific and regulatory attention due to their persistence, potential for bioaccumulation, and, most notably, their toxicological properties.<sup>1, 2, [[#ref3|3]], [[#ref4|4]], [[#ref5|5]], 6, 7, 8, 9</sup> Many PAHs are recognized as carcinogenic (cancer-causing), mutagenic (causing genetic mutations), and teratogenic (causing developmental abnormalities).<sup>2, [[#ref4|4]], 7, [[#ref10|10]], [[#ref11|11]], [[#ref12|12]], [[#ref13|13]], [[#ref14|14]], [[#ref15|15]], 16, 17, 18, [[#ref19|19]], 20, 21, 22</sup> |
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| PAHs are introduced into the marine environment through a wide array of pathways, which can be broadly classified into natural and anthropogenic (human-derived) sources. Natural sources include geological processes such as natural oil seeps, volcanic eruptions, and the products of natural combustion events like forest and grassland fires.[1], [2], [[#ref3|3]], [[#ref4|4]], [7], [8], [[#ref10|10]], [16], [[#ref23|23]], [24], [25], [26], [27], [28], [29], [30] Anthropogenic activities, however, are typically the dominant contributors to PAH loading in coastal and marine systems, especially in industrialized and urbanized regions. These activities include accidental oil spills during extraction and transportation, operational discharges from shipping, incomplete combustion of fossil fuels (coal, oil, and gas) by vehicles, power plants, and industrial processes, emissions from waste incineration, and runoff from paved surfaces and industrial sites.[1], [2], [[#ref3|3]], [[#ref4|4]], [6], [7], [8], [9], [[#ref10|10]], [[#ref13|13]], [16], [17], [[#ref23|23]], [24], [25], [26], [27], [28], [29], [30], [[#ref31a|31a]]/[[#ref31b|31b]], [32], [33] Atmospheric deposition of PAHs adsorbed to particulate matter also serves as a significant diffuse source to marine waters.[1], [2], [[#ref3|3]], [[#ref4|4]], [26] | PAHs are introduced into the marine environment through a wide array of pathways, which can be broadly classified into natural and anthropogenic (human-derived) sources. Natural sources include geological processes such as natural oil seeps, volcanic eruptions, and the products of natural combustion events like forest and grassland fires.<sup>1, 2, [[#ref3|3]], [[#ref4|4]], 7, 8, [[#ref10|10]], 16, [[#ref23|23]], 24, 25, 26, 27, 28, 29, 30</sup> Anthropogenic activities, however, are typically the dominant contributors to PAH loading in coastal and marine systems, especially in industrialized and urbanized regions. These activities include accidental oil spills during extraction and transportation, operational discharges from shipping, incomplete combustion of fossil fuels (coal, oil, and gas) by vehicles, power plants, and industrial processes, emissions from waste incineration, and runoff from paved surfaces and industrial sites.<sup>1, 2, [[#ref3|3]], [[#ref4|4]], 6, 7, 8, 9, [[#ref10|10]], [[#ref13|13]], 16, 17, [[#ref23|23]], 24, 25, 26, 27, 28, 29, 30, [[#ref31a|31a]]/[[#ref31b|31b]], 32, 33</sup> Atmospheric deposition of PAHs adsorbed to particulate matter also serves as a significant diffuse source to marine waters.<sup>1, 2, [[#ref3|3]], [[#ref4|4]], 26</sup> |
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| The dual origin of PAHs, being both naturally occurring substances and significant anthropogenic pollutants, presents a challenge for environmental management. While PAHs are natural components of fossil fuels like coal and oil [1], [2], [[#ref3|3]], [[#ref4|4]], [16], human activities have drastically increased their concentrations and altered their distribution patterns in the environment. Regulatory frameworks and environmental assessments must therefore differentiate between natural background levels and anthropogenic contributions that pose an unacceptable risk to ecosystem health and human well-being. Understanding the intrinsic properties of individual PAH compounds, such as their toxicity, persistence, bioaccumulation potential, and bioavailability, is paramount for prioritizing regulatory actions and remediation efforts, focusing on those PAHs that are either predominantly anthropogenic in their elevated environmental concentrations or pose the most significant ecological or health risks. | The dual origin of PAHs, being both naturally occurring substances and significant anthropogenic pollutants, presents a challenge for environmental management. While PAHs are natural components of fossil fuels like coal and oil <sup>1, 2, [[#ref3|3]], [[#ref4|4]], 16</sup>, human activities have drastically increased their concentrations and altered their distribution patterns in the environment. Regulatory frameworks and environmental assessments must therefore differentiate between natural background levels and anthropogenic contributions that pose an unacceptable risk to ecosystem health and human well-being. Understanding the intrinsic properties of individual PAH compounds, such as their toxicity, persistence, bioaccumulation potential, and bioavailability, is paramount for prioritizing regulatory actions and remediation efforts, focusing on those PAHs that are either predominantly anthropogenic in their elevated environmental concentrations or pose the most significant ecological or health risks. |
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| ==== 1.2. The Role of Sediment Analysis in Monitoring PAH Pollution ==== | ==== 1.2. The Role of Sediment Analysis in Monitoring PAH Pollution ==== |
| PAHs are characterized by their hydrophobicity (low solubility in water) and lipophilicity (high affinity for lipids and organic matter).[1], [2], [[#ref4|4]], [7], [8], [[#ref10|10]], [18], [27], [[#ref34|34]] Consequently, upon entering the aquatic environment, they tend to rapidly adsorb onto suspended particulate matter. These PAH-laden particles eventually settle, leading to the accumulation of PAHs in bottom sediments.[1], [2], [[#ref3|3]], [[#ref4|4]], [6], [7], [8], [[#ref10|10]], [[#ref13|13]], [[#ref23|23]], [25], [27], [[#ref31a|31a]]/[[#ref31b|31b]], [32], [[#ref34|34]], [[#ref35|35]] Marine sediments thus function as significant long-term reservoirs or sinks for these persistent organic pollutants, reflecting both current and historical inputs.[1], [2], [[#ref4|4]], [6], [7], [32], [36] | PAHs are characterized by their hydrophobicity (low solubility in water) and lipophilicity (high affinity for lipids and organic matter).<sup>1, 2, [[#ref4|4]], 7, 8, [[#ref10|10]], 18, 27, [[#ref34|34]]</sup> Consequently, upon entering the aquatic environment, they tend to rapidly adsorb onto suspended particulate matter. These PAH-laden particles eventually settle, leading to the accumulation of PAHs in bottom sediments.<sup>1, 2, [[#ref3|3]], [[#ref4|4]], 6, 7, 8, [[#ref10|10]], [[#ref13|13]], [[#ref23|23]], 25, 27, [[#ref31a|31a]]/[[#ref31b|31b]], 32, [[#ref34|34]], [[#ref35|35]]</sup> Marine sediments thus function as significant long-term reservoirs or sinks for these persistent organic pollutants, reflecting both current and historical inputs.<sup>1, 2, [[#ref4|4]], 6, 7, 32, 36</sup> |
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| The analysis of PAH concentrations in sediments is a cornerstone of marine environmental monitoring and assessment programs worldwide, including OSPAR's Coordinated Environmental Monitoring Programme (CEMP).[1], [2], [[#ref4|4]], [[#ref5|5]], [6], [[#ref37a|37a]]/[[#ref37b|37b]], [38], [39] Such analyses are indispensable for evaluating the health of marine ecosystems, managing natural resources effectively, assessing the potential ecological risks posed by contaminants, and determining compliance with established environmental quality standards.[1], [2], [[#ref3|3]], [[#ref4|4]], [[#ref5|5]], [6], [8], [[#ref10|10]], [[#ref11|11]], [[#ref13|13]], [[#ref19|19]], [25], [26], [27], [[#ref31a|31a]]/[[#ref31b|31b]], [32], [36], [[#ref37a|37a]]/[[#ref37b|37b]], [38], [39], [[#ref40|40]], [[#ref41|41]], [42], [43], [44], [45], [46], [47], [48], [49] Because PAHs can persist in sediments for extended periods, these matrices provide an integrated measure of contamination over time, offering insights into both recent pollution events and long-term contamination trends.[36], [48] | The analysis of PAH concentrations in sediments is a cornerstone of marine environmental monitoring and assessment programs worldwide, including OSPAR's Coordinated Environmental Monitoring Programme (CEMP).<sup>1, 2, [[#ref4|4]], [[#ref5|5]], 6, [[#ref37a|37a]]/[[#ref37b|37b]], 38, 39</sup> Such analyses are indispensable for evaluating the health of marine ecosystems, managing natural resources effectively, assessing the potential ecological risks posed by contaminants, and determining compliance with established environmental quality standards.<sup>1, 2, [[#ref3|3]], [[#ref4|4]], [[#ref5|5]], 6, 8, [[#ref10|10]], [[#ref11|11]], [[#ref13|13]], [[#ref19|19]], 25, 26, 27, [[#ref31a|31a]]/[[#ref31b|31b]], 32, 36, [[#ref37a|37a]]/[[#ref37b|37b]], 38, 39, [[#ref40|40]], [[#ref41|41]], 42, 43, 44, 45, 46, 47, 48, 49</sup> Because PAHs can persist in sediments for extended periods, these matrices provide an integrated measure of contamination over time, offering insights into both recent pollution events and long-term contamination trends.<sup>36, 48</sup> |
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| The accumulation of PAHs in sediments creates a direct exposure pathway for benthic organisms, which live in or on the sediment layer. These organisms can take up PAHs through direct contact, ingestion of sediment particles, or from porewater.[[#ref4|4]], [[#ref31a|31a]]/[[#ref31b|31b]], [32] This exposure can lead to adverse biological effects in benthic fauna and facilitate the transfer of PAHs into the broader marine food web, potentially impacting higher trophic levels, including fish, marine mammals, and humans who consume seafood. Therefore, sediment PAH concentrations are a critical indicator of the overall health of the marine environment and the potential risks to its inhabitants. | The accumulation of PAHs in sediments creates a direct exposure pathway for benthic organisms, which live in or on the sediment layer. These organisms can take up PAHs through direct contact, ingestion of sediment particles, or from porewater.<sup>[[#ref4|4]], [[#ref31a|31a]]/[[#ref31b|31b]], 32</sup> This exposure can lead to adverse biological effects in benthic fauna and facilitate the transfer of PAHs into the broader marine food web, potentially impacting higher trophic levels, including fish, marine mammals, and humans who consume seafood. Therefore, sediment PAH concentrations are a critical indicator of the overall health of the marine environment and the potential risks to its inhabitants. |
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| ==== 1.3. Overview of the Marine Management Organisation's (MMO) Requirements ==== | ==== 1.3. Overview of the Marine Management Organisation's (MMO) Requirements ==== |
| In the United Kingdom, the Marine Management Organisation (MMO) plays a key role in regulating activities in marine waters. As part of its responsibilities, particularly concerning marine licensing for activities such as the disposal of dredged material, the MMO mandates the chemical characterization of sediments. This includes the analysis of a standard suite of 22 specific Polycyclic Aromatic Hydrocarbons.[[#ref41|41]] This list is comprehensive, encompassing not only parent (non-alkylated) PAHs but also several groups of their alkylated homologues, namely C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, and C1-Phenanthrenes.[[#ref41|41]] | In the United Kingdom, the Marine Management Organisation (MMO) plays a key role in regulating activities in marine waters. As part of its responsibilities, particularly concerning marine licensing for activities such as the disposal of dredged material, the MMO mandates the chemical characterization of sediments. This includes the analysis of a standard suite of 22 specific Polycyclic Aromatic Hydrocarbons.<sup>[[#ref41|41]]</sup> This list is comprehensive, encompassing not only parent (non-alkylated) PAHs but also several groups of their alkylated homologues, namely C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, and C1-Phenanthrenes.<sup>[[#ref41|41]]</sup> |
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| The selection of these 22 determinands is designed to provide a robust assessment of PAH contamination, enabling the identification of potential sources and the evaluation of environmental risk. The inclusion of alkylated PAHs is particularly significant from a diagnostic and risk assessment perspective. Alkylated PAHs, such as methylnaphthalenes, dimethylnaphthalenes, and methylphenanthrenes, are often more prevalent in crude oils and other petrogenic sources than their unsubstituted parent compounds.[9] Furthermore, some alkylated PAHs can exhibit greater persistence in the environment and, in certain cases, enhanced toxicity compared to their parent PAHs.[9], [17], [28], [50], [51] The relative concentrations of alkylated PAHs to their parent compounds, and the distribution patterns of different alkyl homologue series, serve as valuable chemical fingerprints. These fingerprints help distinguish between petrogenic contamination (e.g., from oil spills or uncombusted fuel) and pyrogenic contamination (resulting from the incomplete combustion of organic materials).[1], [2], [[#ref4|4]], [[#ref23|23]], [24], [26], [30] By mandating the analysis of this specific suite of 22 PAHs, the MMO ensures a more thorough understanding of the nature and origin of PAH contamination, which is crucial for informed decision-making regarding the management of marine sediments. | The selection of these 22 determinands is designed to provide a robust assessment of PAH contamination, enabling the identification of potential sources and the evaluation of environmental risk. The inclusion of alkylated PAHs is particularly significant from a diagnostic and risk assessment perspective. Alkylated PAHs, such as methylnaphthalenes, dimethylnaphthalenes, and methylphenanthrenes, are often more prevalent in crude oils and other petrogenic sources than their unsubstituted parent compounds.<sup>9</sup> Furthermore, some alkylated PAHs can exhibit greater persistence in the environment and, in certain cases, enhanced toxicity compared to their parent PAHs.<sup>9, 17, 28, 50, 51</sup> The relative concentrations of alkylated PAHs to their parent compounds, and the distribution patterns of different alkyl homologue series, serve as valuable chemical fingerprints. These fingerprints help distinguish between petrogenic contamination (e.g., from oil spills or uncombusted fuel) and pyrogenic contamination (resulting from the incomplete combustion of organic materials).<sup>1, 2, [[#ref4|4]], [[#ref23|23]], 24, 26, 30</sup> By mandating the analysis of this specific suite of 22 PAHs, the MMO ensures a more thorough understanding of the nature and origin of PAH contamination, which is crucial for informed decision-making regarding the management of marine sediments. |
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| ==== 1.4. Report Objectives ==== | ==== 1.4. Report Objectives ==== |
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| ==== 2.1. Definitive List of MMO PAHs ==== | ==== 2.1. Definitive List of MMO PAHs ==== |
| The Marine Management Organisation (MMO) of the United Kingdom stipulates a standard set of 22 Polycyclic Aromatic Hydrocarbons (PAHs) that are potentially required for the chemical characterisation of sediment, particularly in the context of marine licensing applications such as those for dredged material disposal.[[#ref41|41]] The analysis of these specific compounds allows for a comprehensive assessment of PAH contamination. The definitive list, along with key structural information, is presented in Table 2.1. | The Marine Management Organisation (MMO) of the United Kingdom stipulates a standard set of 22 Polycyclic Aromatic Hydrocarbons (PAHs) that are potentially required for the chemical characterisation of sediment, particularly in the context of marine licensing applications such as those for dredged material disposal.<sup>[[#ref41|41]]</sup> The analysis of these specific compounds allows for a comprehensive assessment of PAH contamination. The definitive list, along with key structural information, is presented in Table 2.1. |
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| **Table 2.1: The Marine Management Organisation's 22 Target PAHs for Sediment Analysis.[[#ref41|41]]** | **Table 2.1: The Marine Management Organisation's 22 Target PAHs for Sediment Analysis.<sup>[[#ref41|41]]</sup>** |
| ^ No. ^ PAH Name ^ Abbreviation (Common) ^ Molecular Weight (g/mol)<sup>a</sup> ^ Number of Aromatic Rings<sup>b</sup> ^ Classification ^ | ^ No. ^ PAH Name ^ Abbreviation (Common) ^ Molecular Weight (g/mol)<sup>a</sup> ^ Number of Aromatic Rings<sup>b</sup> ^ Classification ^ |
| | 1 | Naphthalene | Nap | 128.17 | 2 | LMW | | | 1 | Naphthalene | Nap | 128.17 | 2 | LMW | |
| <sup>a</sup> Molecular weights are for the parent (unsubstituted) PAH or representative isomer for alkylated groups (e.g., methylnaphthalene for C1-Naphthalenes). | <sup>a</sup> Molecular weights are for the parent (unsubstituted) PAH or representative isomer for alkylated groups (e.g., methylnaphthalene for C1-Naphthalenes). |
| <sup>b</sup> Number of aromatic rings refers to true fused benzene rings unless otherwise specified. | <sup>b</sup> Number of aromatic rings refers to true fused benzene rings unless otherwise specified. |
| <sup>c</sup> These LMW PAHs contain a five-membered ring fused to a naphthalene or biphenyl system, contributing to their three-ring classification in some contexts.[[#ref19|19]] | <sup>c</sup> These LMW PAHs contain a five-membered ring fused to a naphthalene or biphenyl system, contributing to their three-ring classification in some contexts.<sup>[[#ref19|19]]</sup> |
| <sup>d</sup> Fluoranthene and Indeno[1,2,3-cd]pyrene contain a five-membered ring in addition to their fused benzene rings. | <sup>d</sup> Fluoranthene and Indeno[1,2,3-cd]pyrene contain a five-membered ring in addition to their fused benzene rings. |
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| ==== 2.2. Classification of PAHs (LMW vs. HMW) ==== | ==== 2.2. Classification of PAHs (LMW vs. HMW) ==== |
| PAHs are commonly categorized into two main groups based on their molecular structure and weight: Low Molecular Weight (LMW) PAHs and High Molecular Weight (HMW) PAHs.[[#ref19|19]], [[#ref40|40]] This classification is pivotal as it often correlates with significant differences in their physical-chemical properties, environmental fate, and toxicological profiles. | PAHs are commonly categorized into two main groups based on their molecular structure and weight: Low Molecular Weight (LMW) PAHs and High Molecular Weight (HMW) PAHs.<sup>[[#ref19|19]], [[#ref40|40]]</sup> This classification is pivotal as it often correlates with significant differences in their physical-chemical properties, environmental fate, and toxicological profiles. |
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| * **Low Molecular Weight (LMW) PAHs:** These compounds typically consist of two or three fused aromatic rings.[[#ref19|19]], [[#ref40|40]] Examples from the MMO list include Naphthalene, C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, C1-Phenanthrenes, and Anthracene. LMW PAHs are generally more water-soluble, more volatile, and more susceptible to biodegradation compared to HMW PAHs.[1], [2], [27], [[#ref34|34]] They are often associated with acute toxicity to aquatic organisms [1], [2], [[#ref13|13]], [[#ref19|19]], [20], [27], [[#ref34|34]], [[#ref52|52]] and are predominant in petrogenic (oil-derived) sources.[1], [2], [[#ref4|4]], [[#ref23|23]], [24], [29], [30], [[#ref40|40]] | * **Low Molecular Weight (LMW) PAHs:** These compounds typically consist of two or three fused aromatic rings.<sup>[[#ref19|19]], [[#ref40|40]]</sup> Examples from the MMO list include Naphthalene, C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, C1-Phenanthrenes, and Anthracene. LMW PAHs are generally more water-soluble, more volatile, and more susceptible to biodegradation compared to HMW PAHs.<sup>1, 2, 27, [[#ref34|34]]</sup> They are often associated with acute toxicity to aquatic organisms <sup>1, 2, [[#ref13|13]], [[#ref19|19]], 20, 27, [[#ref34|34]], [[#ref52|52]]</sup> and are predominant in petrogenic (oil-derived) sources.<sup>1, 2, [[#ref4|4]], [[#ref23|23]], 24, 29, 30, [[#ref40|40]]</sup> |
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| * **High Molecular Weight (HMW) PAHs:** These compounds contain four or more fused aromatic rings.[[#ref19|19]], [[#ref40|40]] From the MMO list, HMW PAHs include Fluoranthene, Pyrene, Benz[a]anthracene, Chrysene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[e]pyrene, Benzo[a]pyrene, Perylene, Indeno[1,2,3-cd]pyrene, Dibenz[a,h]anthracene, and Benzo[g,h,i]perylene. HMW PAHs are characterized by lower water solubility, lower volatility, and greater persistence in the environment.[1], [2], [7], [8], [[#ref15|15]], [27], [[#ref34|34]] They tend to adsorb more strongly to sediment particles and organic matter. Many HMW PAHs are of greater concern for their carcinogenic potential.[2], [[#ref13|13]], [[#ref15|15]], [16], [27], [[#ref34|34]] Pyrogenic sources, such as the combustion of fossil fuels and biomass, are major contributors of HMW PAHs to the environment.[1], [2], [[#ref4|4]], [[#ref23|23]], [24], [29], [30], [33] | * **High Molecular Weight (HMW) PAHs:** These compounds contain four or more fused aromatic rings.<sup>[[#ref19|19]], [[#ref40|40]]</sup> From the MMO list, HMW PAHs include Fluoranthene, Pyrene, Benz[a]anthracene, Chrysene, Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[e]pyrene, Benzo[a]pyrene, Perylene, Indeno[1,2,3-cd]pyrene, Dibenz[a,h]anthracene, and Benzo[g,h,i]perylene. HMW PAHs are characterized by lower water solubility, lower volatility, and greater persistence in the environment.<sup>1, 2, 7, 8, [[#ref15|15]], 27, [[#ref34|34]]</sup> They tend to adsorb more strongly to sediment particles and organic matter. Many HMW PAHs are of greater concern for their carcinogenic potential.<sup>2, [[#ref13|13]], [[#ref15|15]], 16, 27, [[#ref34|34]]</sup> Pyrogenic sources, such as the combustion of fossil fuels and biomass, are major contributors of HMW PAHs to the environment.<sup>1, 2, [[#ref4|4]], [[#ref23|23]], 24, 29, 30, 33</sup> |
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| This LMW versus HMW classification provides a foundational framework for anticipating trends in the environmental properties discussed in the following sections. For instance, one would generally expect HMW PAHs to be more persistent and have higher bioaccumulation potential due to their increased hydrophobicity, while LMW PAHs might exhibit greater bioavailability from the dissolved phase and higher acute toxicity. | This LMW versus HMW classification provides a foundational framework for anticipating trends in the environmental properties discussed in the following sections. For instance, one would generally expect HMW PAHs to be more persistent and have higher bioaccumulation potential due to their increased hydrophobicity, while LMW PAHs might exhibit greater bioavailability from the dissolved phase and higher acute toxicity. |
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| === 3.1.1. Definition and Metrics of PAH Toxicity === | === 3.1.1. Definition and Metrics of PAH Toxicity === |
| PAH toxicity encompasses a spectrum of adverse biological effects, including carcinogenicity (cancer-causing), mutagenicity (causing genetic mutations), teratogenicity (causing developmental malformations), and acute toxicity to aquatic organisms.[7], [[#ref10|10]], [[#ref11|11]], [[#ref14|14]], [[#ref15|15]], [16], [17] The primary metric used for comparing the carcinogenic potency of different PAHs is the **Toxic Equivalency Factor (TEF)**. TEFs express the toxicity of an individual PAH compound relative to that of Benzo[a]pyrene (BaP), which is a well-studied and potent carcinogen assigned a TEF of 1.0.[[#ref14|14]], [21], [[#ref35|35]], [[#ref41|41]], [53], [54], [55], [56], [57], [58], [59], [60], [61], [62], [63], [64], [65], [66], [67] The concentration of a PAH multiplied by its TEF yields its Benzo[a]pyrene equivalent concentration (BaP-TEQ). Different TEF schemes exist (e.g., developed by Nisbet and LaGoy, 1992; U.S. EPA), which may assign slightly different values to the same PAH. For consistency in this report, TEF values primarily based on the Nisbet and LaGoy (1992) scheme will be used where available for the MMO PAHs, as it is frequently cited for a broad range of compounds. EPA TEFs will be used supplementally. | PAH toxicity encompasses a spectrum of adverse biological effects, including carcinogenicity (cancer-causing), mutagenicity (causing genetic mutations), teratogenicity (causing developmental malformations), and acute toxicity to aquatic organisms.<sup>7, [[#ref10|10]], [[#ref11|11]], [[#ref14|14]], [[#ref15|15]], 16, 17</sup> The primary metric used for comparing the carcinogenic potency of different PAHs is the **Toxic Equivalency Factor (TEF)**. TEFs express the toxicity of an individual PAH compound relative to that of Benzo[a]pyrene (BaP), which is a well-studied and potent carcinogen assigned a TEF of 1.0.<sup>[[#ref14|14]], 21, [[#ref35|35]], [[#ref41|41]], 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67</sup> The concentration of a PAH multiplied by its TEF yields its Benzo[a]pyrene equivalent concentration (BaP-TEQ). Different TEF schemes exist (e.g., developed by Nisbet and LaGoy, 1992; U.S. EPA), which may assign slightly different values to the same PAH. For consistency in this report, TEF values primarily based on the Nisbet and LaGoy (1992) scheme will be used where available for the MMO PAHs, as it is frequently cited for a broad range of compounds. EPA TEFs will be used supplementally. |
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| While TEFs are invaluable for assessing carcinogenic risk, it is important to note that LMW PAHs, which often have low or zero TEFs for carcinogenicity, can exhibit significant acute toxicity to marine life.[1], [2], [[#ref13|13]], [[#ref19|19]], [20], [27], [[#ref34|34]], [[#ref52|52]] This report's toxicity ranking will primarily focus on carcinogenic potency via TEFs due to the availability of comparative data, but the acute toxicity of LMW PAHs will be acknowledged. | While TEFs are invaluable for assessing carcinogenic risk, it is important to note that LMW PAHs, which often have low or zero TEFs for carcinogenicity, can exhibit significant acute toxicity to marine life.<sup>1, 2, [[#ref13|13]], [[#ref19|19]], 20, 27, [[#ref34|34]], [[#ref52|52]]</sup> This report's toxicity ranking will primarily focus on carcinogenic potency via TEFs due to the availability of comparative data, but the acute toxicity of LMW PAHs will be acknowledged. |
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| Sediment Quality Guidelines (SQGs) such as Effects Range Low (ERL) and Effects Range Median (ERM) values are also used to assess the potential ecological risks of PAHs in sediments.[2], [[#ref4|4]], [6], [[#ref11|11]], [[#ref31a|31a]]/[[#ref31b|31b]], [38], [[#ref40|40]], [49] ERLs represent concentrations below which adverse effects are rarely observed, while ERMs indicate concentrations above which adverse effects are frequently observed. While these are crucial for sediment risk assessment, they are concentration thresholds in sediment rather than intrinsic toxicity values of the PAHs themselves, and thus are not the primary basis for ranking the PAHs against each other for inherent toxicity in this section. | Sediment Quality Guidelines (SQGs) such as Effects Range Low (ERL) and Effects Range Median (ERM) values are also used to assess the potential ecological risks of PAHs in sediments.<sup>2, [[#ref4|4]], 6, [[#ref11|11]], [[#ref31a|31a]]/[[#ref31b|31b]], 38, [[#ref40|40]], 49</sup> ERLs represent concentrations below which adverse effects are rarely observed, while ERMs indicate concentrations above which adverse effects are frequently observed. While these are crucial for sediment risk assessment, they are concentration thresholds in sediment rather than intrinsic toxicity values of the PAHs themselves, and thus are not the primary basis for ranking the PAHs against each other for inherent toxicity in this section. |
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| === 3.1.2. Toxicity Data for MMO PAHs === | === 3.1.2. Toxicity Data for MMO PAHs === |
| TEF values for the parent PAHs on the MMO list have been compiled from various sources within the provided research material.[[#ref14|14]], [21], [[#ref35|35]], [53], [54], [56], [57], [60], [61], [62], [63], [64], [65], [66], [67] For the alkylated PAH groups (C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, C1-Phenanthrenes), specific TEFs for the entire group are generally not defined. Following the approach suggested in [[#ref14|14]], where the TEF of 2-methylnaphthalene (0.001) is applied to 1-methylnaphthalene and also to dimethyl- and trimethylnaphthalenes, a TEF of 0.001 will be assigned to C1-Naps, C2-Naps, and C3-Naps. Similarly, C1-Phenanthrenes will be assigned a TEF of 0.001, consistent with the TEF for the parent Phenanthrene in many schemes. Perylene is generally considered non-carcinogenic or to have very low carcinogenic potential, often assigned a TEF of 0.001 or is not listed in carcinogenic assessments.[68], [69] Benzo[e]pyrene is also typically assigned a TEF of 0.001 or 0.01 in some schemes, reflecting its lower carcinogenicity compared to Benzo[a]pyrene.[20], [54], [62], [63], [70] | TEF values for the parent PAHs on the MMO list have been compiled from various sources within the provided research material.<sup>[[#ref14|14]], 21, [[#ref35|35]], 53, 54, 56, 57, 60, 61, 62, 63, 64, 65, 66, 67</sup> For the alkylated PAH groups (C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, C1-Phenanthrenes), specific TEFs for the entire group are generally not defined. Following the approach suggested in <sup>[[#ref14|14]]</sup>, where the TEF of 2-methylnaphthalene (0.001) is applied to 1-methylnaphthalene and also to dimethyl- and trimethylnaphthalenes, a TEF of 0.001 will be assigned to C1-Naps, C2-Naps, and C3-Naps. Similarly, C1-Phenanthrenes will be assigned a TEF of 0.001, consistent with the TEF for the parent Phenanthrene in many schemes. Perylene is generally considered non-carcinogenic or to have very low carcinogenic potential, often assigned a TEF of 0.001 or is not listed in carcinogenic assessments.<sup>68, 69</sup> Benzo[e]pyrene is also typically assigned a TEF of 0.001 or 0.01 in some schemes, reflecting its lower carcinogenicity compared to Benzo[a]pyrene.<sup>20, 54, 62, 63, 70</sup> |
| |
| It is important to recognize that TEF values can vary between different assessment schemes. For example, Dibenz[a,h]anthracene is assigned a TEF of 1 by the EPA [53] but a TEF of 5 by Nisbet and LaGoy (1992).[54] This report will primarily use the Nisbet and LaGoy (1992) values where available for consistency, as they are widely cited for a broader range of PAHs, and note significant discrepancies. | It is important to recognize that TEF values can vary between different assessment schemes. For example, Dibenz[a,h]anthracene is assigned a TEF of 1 by the EPA <sup>53</sup> but a TEF of 5 by Nisbet and LaGoy (1992).<sup>54</sup> This report will primarily use the Nisbet and LaGoy (1992) values where available for consistency, as they are widely cited for a broader range of PAHs, and note significant discrepancies. |
| |
| === 3.1.3. Ordered List of MMO PAHs by Increasing Toxicity (Carcinogenic Potency) === | === 3.1.3. Ordered List of MMO PAHs by Increasing Toxicity (Carcinogenic Potency) === |
| **Table 3.1.1: MMO PAHs Ordered by Increasing Carcinogenic Potency (TEF values relative to Benzo[a]pyrene).** | **Table 3.1.1: MMO PAHs Ordered by Increasing Carcinogenic Potency (TEF values relative to Benzo[a]pyrene).** |
| ^ Rank ^ PAH Name ^ Number of Rings ^ Assigned TEF<sup>a</sup> ^ Source of TEF (Primary) ^ | ^ Rank ^ PAH Name ^ Number of Rings ^ Assigned TEF<sup>a</sup> ^ Source of TEF (Primary) ^ |
| | 1 | Naphthalene | 2 | 0.001 | Nisbet & LaGoy, 1992 [21], [57] | | | 1 | Naphthalene | 2 | 0.001 | Nisbet & LaGoy, 1992 <sup>21, 57</sup> | |
| | 2 | C1-Naphthalenes | 2 | 0.001 | Surrogate (2-MN) [[#ref14|14]] | | | 2 | C1-Naphthalenes | 2 | 0.001 | Surrogate (2-MN) <sup>[[#ref14|14]]</sup> | |
| | 3 | C2-Naphthalenes | 2 | 0.001 | Surrogate (2-MN) [[#ref14|14]] | | | 3 | C2-Naphthalenes | 2 | 0.001 | Surrogate (2-MN) <sup>[[#ref14|14]]</sup> | |
| | 4 | C3-Naphthalenes | 2 | 0.001 | Surrogate (2-MN) [[#ref14|14]] | | | 4 | C3-Naphthalenes | 2 | 0.001 | Surrogate (2-MN) <sup>[[#ref14|14]]</sup> | |
| | 5 | Acenaphthylene | 3<sup>b</sup> | 0.001 | Nisbet & LaGoy, 1992 [57] | | | 5 | Acenaphthylene | 3<sup>b</sup> | 0.001 | Nisbet & LaGoy, 1992 <sup>57</sup> | |
| | 6 | Acenaphthene | 3<sup>b</sup> | 0.001 | Nisbet & LaGoy, 1992 [57] | | | 6 | Acenaphthene | 3<sup>b</sup> | 0.001 | Nisbet & LaGoy, 1992 <sup>57</sup> | |
| | 7 | Fluorene | 3<sup>b</sup> | 0.001<sup>d</sup> | Larsen et al., 1998 / Nisbet & LaGoy, 1992 [57] | | | 7 | Fluorene | 3<sup>b</sup> | 0.001<sup>d</sup> | Larsen et al., 1998 / Nisbet & LaGoy, 1992 <sup>57</sup> | |
| | 8 | Phenanthrene | 3 | 0.001<sup>d</sup> | Larsen et al., 1998 / Nisbet & LaGoy, 1992 [21], [57] | | | 8 | Phenanthrene | 3 | 0.001<sup>d</sup> | Larsen et al., 1998 / Nisbet & LaGoy, 1992 <sup>21, 57</sup> | |
| | 9 | C1-Phenanthrenes | 3 | 0.001 | Surrogate (Phe) [21] | | | 9 | C1-Phenanthrenes | 3 | 0.001 | Surrogate (Phe) <sup>21</sup> | |
| | 10 | Anthracene | 3 | 0.01 | Nisbet & LaGoy, 1992 / EPA [21], [53] | | | 10 | Anthracene | 3 | 0.01 | Nisbet & LaGoy, 1992 / EPA <sup>21, 53</sup> | |
| | 11 | Fluoranthene | 4<sup>c</sup> | 0.001 | Nisbet & LaGoy, 1992 / EPA [21], [53] | | | 11 | Fluoranthene | 4<sup>c</sup> | 0.001 | Nisbet & LaGoy, 1992 / EPA <sup>21, 53</sup> | |
| | 12 | Pyrene | 4 | 0.001 | Nisbet & LaGoy, 1992 / EPA [21], [53] | | | 12 | Pyrene | 4 | 0.001 | Nisbet & LaGoy, 1992 / EPA <sup>21, 53</sup> | |
| | 13 | Chrysene | 4 | 0.001<sup>e</sup> | Nisbet & LaGoy, 1992 / EPA [21], [[#ref35|35]], [53], [56] | | | 13 | Chrysene | 4 | 0.001<sup>e</sup> | Nisbet & LaGoy, 1992 / EPA <sup>21, [[#ref35|35]], 53, 56</sup> | |
| | 14 | Benzo[e]pyrene | 5 | 0.01 | Estimated (literature consensus) [20], [54], [62], [63], [70] | | | 14 | Benzo[e]pyrene | 5 | 0.01 | Estimated (literature consensus) <sup>20, 54, 62, 63, 70</sup> | |
| | 15 | Perylene | 5 | 0.01<sup>f</sup> | Estimated (literature consensus) [68], [69] | | | 15 | Perylene | 5 | 0.01<sup>f</sup> | Estimated (literature consensus) <sup>68, 69</sup> | |
| | 16 | Benzo[g,h,i]perylene | 6 | 0.01 | Nisbet & LaGoy, 1992 [21], [54] | | | 16 | Benzo[g,h,i]perylene | 6 | 0.01 | Nisbet & LaGoy, 1992 <sup>21, 54</sup> | |
| | 17 | Benz[a]anthracene | 4 | 0.1 | Nisbet & LaGoy, 1992 / EPA [21], [[#ref35|35]], [53], [54] | | | 17 | Benz[a]anthracene | 4 | 0.1 | Nisbet & LaGoy, 1992 / EPA <sup>21, [[#ref35|35]], 53, 54</sup> | |
| | 18 | Benzo[b]fluoranthene | 5 | 0.1 | Nisbet & LaGoy, 1992 / EPA [21], [[#ref35|35]], [53], [54], [71] | | | 18 | Benzo[b]fluoranthene | 5 | 0.1 | Nisbet & LaGoy, 1992 / EPA <sup>21, [[#ref35|35]], 53, 54, 71</sup> | |
| | 19 | Benzo[k]fluoranthene | 5 | 0.1<sup>g</sup> | Nisbet & LaGoy, 1992 / EPA [21], [[#ref35|35]], [53], [54], [71] | | | 19 | Benzo[k]fluoranthene | 5 | 0.1<sup>g</sup> | Nisbet & LaGoy, 1992 / EPA <sup>21, [[#ref35|35]], 53, 54, 71</sup> | |
| | 20 | Indeno[1,2,3-cd]pyrene | 6<sup>c</sup> | 0.1 | Nisbet & LaGoy, 1992 / EPA [21], [[#ref35|35]], [53], [54], [71] | | | 20 | Indeno[1,2,3-cd]pyrene | 6<sup>c</sup> | 0.1 | Nisbet & LaGoy, 1992 / EPA <sup>21, [[#ref35|35]], 53, 54, 71</sup> | |
| | 21 | Benzo[a]pyrene | 5 | 1 | Reference Compound [21], [[#ref35|35]], [53], [54], [71] | | | 21 | Benzo[a]pyrene | 5 | 1 | Reference Compound <sup>21, [[#ref35|35]], 53, 54, 71</sup> | |
| | 22 | Dibenz[a,h]anthracene | 5 | 1<sup>h</sup> (or 5) | EPA / Nisbet & LaGoy, 1992 [21], [[#ref35|35]], [53], [54], [71] | | | 22 | Dibenz[a,h]anthracene | 5 | 1<sup>h</sup> (or 5) | EPA / Nisbet & LaGoy, 1992 <sup>21, [[#ref35|35]], 53, 54, 71</sup> | |
| |
| //Notes on Table 3.1.1:// | //Notes on Table 3.1.1:// |
| <sup>b</sup> Contains a five-membered ring in addition to two benzene rings. | <sup>b</sup> Contains a five-membered ring in addition to two benzene rings. |
| <sup>c</sup> Contains a five-membered ring in addition to fused benzene rings. | <sup>c</sup> Contains a five-membered ring in addition to fused benzene rings. |
| <sup>d</sup> Some sources [57] suggest TEF 0.0005 for Fluorene and Phenanthrene; 0.001 is also widely used. | <sup>d</sup> Some sources <sup>57</sup> suggest TEF 0.0005 for Fluorene and Phenanthrene; 0.001 is also widely used. |
| <sup>e</sup> EPA TEF for Chrysene is 0.001 [53], while Nisbet & LaGoy (1992) also use 0.01.[54] The more conservative (lower) value of 0.001 is used for ranking. | <sup>e</sup> EPA TEF for Chrysene is 0.001 <sup>53</sup>, while Nisbet & LaGoy (1992) also use 0.01.<sup>54</sup> The more conservative (lower) value of 0.001 is used for ranking. |
| <sup>f</sup> Perylene is often considered non-carcinogenic or having very low carcinogenic potential; some sources assign a TEF of 0.001 or 0.01.[68] | <sup>f</sup> Perylene is often considered non-carcinogenic or having very low carcinogenic potential; some sources assign a TEF of 0.001 or 0.01.<sup>68</sup> |
| <sup>g</sup> EPA TEF for Benzo[k]fluoranthene is 0.01 [53], while Nisbet & LaGoy (1992) use 0.1.[54] The higher value is used here reflecting some schemes. | <sup>g</sup> EPA TEF for Benzo[k]fluoranthene is 0.01 <sup>53</sup>, while Nisbet & LaGoy (1992) use 0.1.<sup>54</sup> The higher value is used here reflecting some schemes. |
| <sup>h</sup> EPA TEF for Dibenz[a,h]anthracene is 1 [53], while Nisbet & LaGoy (1992) use 5.[54] Ranked based on EPA value, with Nisbet & LaGoy value noted as it would place it highest. | <sup>h</sup> EPA TEF for Dibenz[a,h]anthracene is 1 <sup>53</sup>, while Nisbet & LaGoy (1992) use 5.<sup>54</sup> Ranked based on EPA value, with Nisbet & LaGoy value noted as it would place it highest. |
| |
| === 3.1.4. Insights and Implications for Toxicity === | === 3.1.4. Insights and Implications for Toxicity === |
| The ranking by TEFs highlights a wide range in carcinogenic potency among the MMO PAHs. Many LMW PAHs and some HMW PAHs like Fluoranthene, Pyrene, and Chrysene have very low TEFs (0.001), indicating significantly lower carcinogenic potential compared to BaP. Conversely, BaP itself and Dibenz[a,h]anthracene (especially with a TEF of 5) are the most potent carcinogens on the list. This differentiation is critical for risk assessment, as simple summation of PAH concentrations without applying TEFs can grossly misrepresent the actual carcinogenic risk of a PAH mixture.[53] | The ranking by TEFs highlights a wide range in carcinogenic potency among the MMO PAHs. Many LMW PAHs and some HMW PAHs like Fluoranthene, Pyrene, and Chrysene have very low TEFs (0.001), indicating significantly lower carcinogenic potential compared to BaP. Conversely, BaP itself and Dibenz[a,h]anthracene (especially with a TEF of 5) are the most potent carcinogens on the list. This differentiation is critical for risk assessment, as simple summation of PAH concentrations without applying TEFs can grossly misrepresent the actual carcinogenic risk of a PAH mixture.<sup>53</sup> |
| |
| The use of surrogate TEFs for alkylated PAH groups introduces an element of uncertainty. While pragmatic due to limited data on individual alkylated isomers, it is a simplification. Individual isomers within an alkylated group can exhibit varying toxicities, and future research may lead to more refined TEFs for these groups. The current approach, however, acknowledges their presence and assigns a conservative, low carcinogenic potential based on their parent structures or representative congeners like 2-methylnaphthalene.[[#ref14|14]] | The use of surrogate TEFs for alkylated PAH groups introduces an element of uncertainty. While pragmatic due to limited data on individual alkylated isomers, it is a simplification. Individual isomers within an alkylated group can exhibit varying toxicities, and future research may lead to more refined TEFs for these groups. The current approach, however, acknowledges their presence and assigns a conservative, low carcinogenic potential based on their parent structures or representative congeners like 2-methylnaphthalene.<sup>[[#ref14|14]]</sup> |
| |
| It is also crucial to remember that this ranking focuses on carcinogenicity. LMW PAHs such as Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, and Anthracene, despite their low TEFs, are recognized for their acute toxicity to aquatic organisms.[1], [2], [[#ref13|13]], [[#ref19|19]], [20], [27], [[#ref34|34]], [[#ref52|52]] Therefore, a low TEF value does not imply a complete absence of ecological risk, particularly for these LMW compounds which can cause different types of biological harm. A comprehensive risk assessment should consider both carcinogenic potential (primarily from HMW PAHs) and acute toxicity (often associated with LMW PAHs). | It is also crucial to remember that this ranking focuses on carcinogenicity. LMW PAHs such as Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, and Anthracene, despite their low TEFs, are recognized for their acute toxicity to aquatic organisms.<sup>1, 2, [[#ref13|13]], [[#ref19|19]], 20, 27, [[#ref34|34]], [[#ref52|52]]</sup> Therefore, a low TEF value does not imply a complete absence of ecological risk, particularly for these LMW compounds which can cause different types of biological harm. A comprehensive risk assessment should consider both carcinogenic potential (primarily from HMW PAHs) and acute toxicity (often associated with LMW PAHs). |
| |
| ==== 3.2. Persistence Ranking (in Marine Sediment) ==== | ==== 3.2. Persistence Ranking (in Marine Sediment) ==== |
| |
| === 3.2.1. Definition and Metrics of PAH Persistence === | === 3.2.1. Definition and Metrics of PAH Persistence === |
| Persistence refers to the ability of a chemical to remain in an environmental compartment, such as marine sediment, over time without undergoing degradation or transformation.[1], [2], [[#ref3|3]], [[#ref4|4]], [6], [7], [8], [9], [17], [72], [73] The primary metric for quantifying persistence is the **half-life (t<sub>1/2</sub>)**, which is the time required for 50% of the initial concentration of a substance to degrade or dissipate from the specified medium.[[#ref15|15]], [22], [42], [[#ref74|74]], [75], [76], [77], [78], [79], [80], [81], [82], [83], [84], [85], [86], [87], [88], [89], [90], [91], [92], [93], [94], [95], [96], [97], [98], [99], [100], [101], [102], [103] A longer half-life signifies greater persistence. | Persistence refers to the ability of a chemical to remain in an environmental compartment, such as marine sediment, over time without undergoing degradation or transformation.<sup>1, 2, [[#ref3|3]], [[#ref4|4]], 6, 7, 8, 9, 17, 72, 73</sup> The primary metric for quantifying persistence is the **half-life (t<sub>1/2</sub>)**, which is the time required for 50% of the initial concentration of a substance to degrade or dissipate from the specified medium.<sup>[[#ref15|15]], 22, 42, [[#ref74|74]], 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103</sup> A longer half-life signifies greater persistence. |
| |
| PAH persistence in marine sediments is influenced by several factors: | PAH persistence in marine sediments is influenced by several factors: |
| * **Molecular Structure:** Generally, persistence increases with increasing molecular weight and the number of aromatic rings. HMW PAHs are more resistant to degradation than LMW PAHs.[7], [8], [[#ref15|15]], [77] Alkylation can also increase persistence compared to the parent PAH.[9], [17] | * **Molecular Structure:** Generally, persistence increases with increasing molecular weight and the number of aromatic rings. HMW PAHs are more resistant to degradation than LMW PAHs.<sup>7, 8, [[#ref15|15]], 77</sup> Alkylation can also increase persistence compared to the parent PAH.<sup>9, 17</sup> |
| * **Sediment Characteristics:** The organic carbon content of the sediment is a critical factor, as PAHs adsorb to organic matter, which can protect them from degradation. The presence of black carbon (soot, char) can lead to even stronger sorption and reduced degradation rates.[[#ref10|10]], [[#ref31a|31a]]/[[#ref31b|31b]] | * **Sediment Characteristics:** The organic carbon content of the sediment is a critical factor, as PAHs adsorb to organic matter, which can protect them from degradation. The presence of black carbon (soot, char) can lead to even stronger sorption and reduced degradation rates.<sup>[[#ref10|10]], [[#ref31a|31a]]/[[#ref31b|31b]]</sup> |
| * **Environmental Conditions:** Oxygen availability is paramount; anaerobic (anoxic) conditions, common in deeper or highly organic sediments, significantly slow down PAH biodegradation compared to aerobic conditions.[[#ref15|15]], [[#ref74|74]], [83], [104] Temperature and microbial community composition also play vital roles.[43], [[#ref74|74]], [84] | * **Environmental Conditions:** Oxygen availability is paramount; anaerobic (anoxic) conditions, common in deeper or highly organic sediments, significantly slow down PAH biodegradation compared to aerobic conditions.<sup>[[#ref15|15]], [[#ref74|74]], 83, 104</sup> Temperature and microbial community composition also play vital roles.<sup>43, [[#ref74|74]], 84</sup> |
| * **Bioavailability:** Processes that reduce bioavailability, such as strong sorption or aging, can indirectly increase persistence by making PAHs less accessible to degrading microorganisms.[85], [105], [106] | * **Bioavailability:** Processes that reduce bioavailability, such as strong sorption or aging, can indirectly increase persistence by making PAHs less accessible to degrading microorganisms.<sup>85, 105, 106</sup> |
| |
| === 3.2.2. Persistence Data for MMO PAHs in Marine Sediment === | === 3.2.2. Persistence Data for MMO PAHs in Marine Sediment === |
| |
| * **LMW PAHs (2-3 rings):** Generally less persistent. | * **LMW PAHs (2-3 rings):** Generally less persistent. |
| * Naphthalene: t<sub>1/2</sub> ~20-21 days (San Francisco Estuary model [77]); 2.3-130 days in GW/Soil (slowest inf (3851) days) [94]; 0.13-inf (88) days in Sed/GW.[94] | * Naphthalene: t<sub>1/2</sub> ~20-21 days (San Francisco Estuary model <sup>77</sup>); 2.3-130 days in GW/Soil (slowest inf (3851) days) <sup>94</sup>; 0.13-inf (88) days in Sed/GW.<sup>94</sup> |
| * Acenaphthene: Uptake t<sub>1/2</sub> onto microplastics ~10 hours [78], not degradation in sediment. No specific degradation t<sub>1/2</sub> in marine sediment found in provided snippets, but generally considered less persistent than HMW PAHs. Howard Handbook data (via OEHHA [107]) gives an average soil half-life for PAHs as 570 days, but this is a very broad average. | * Acenaphthene: Uptake t<sub>1/2</sub> onto microplastics ~10 hours <sup>78</sup>, not degradation in sediment. No specific degradation t<sub>1/2</sub> in marine sediment found in provided snippets, but generally considered less persistent than HMW PAHs. Howard Handbook data (via OEHHA <sup>107</sup>) gives an average soil half-life for PAHs as 570 days, but this is a very broad average. |
| * Acenaphthylene: Similar to Acenaphthene, expected to be relatively less persistent. | * Acenaphthylene: Similar to Acenaphthene, expected to be relatively less persistent. |
| * Fluorene: t<sub>1/2</sub> ~32-60 days reported.[80] | * Fluorene: t<sub>1/2</sub> ~32-60 days reported.<sup>80</sup> |
| * Phenanthrene: t<sub>1/2</sub> ~63 days (San Francisco Estuary model [77]); 16-126 days (soil/sediment [[#ref15|15]]); 4.5-137 days (diesel-contaminated sediment [100]); 1.5-2.8 weeks (landscaping material [84]). | * Phenanthrene: t<sub>1/2</sub> ~63 days (San Francisco Estuary model <sup>77</sup>); 16-126 days (soil/sediment <sup>[[#ref15|15]]</sup>); 4.5-137 days (diesel-contaminated sediment <sup>100</sup>); 1.5-2.8 weeks (landscaping material <sup>84</sup>). |
| * Anthracene: t<sub>1/2</sub> 57-210 days (unacclimatised sediments), 5-7 days (oil-treated sediments) [76]; experimental sediment t<sub>1/2</sub> "days to months", calculated 80.2 years.[82] | * Anthracene: t<sub>1/2</sub> 57-210 days (unacclimatised sediments), 5-7 days (oil-treated sediments) <sup>76</sup>; experimental sediment t<sub>1/2</sub> "days to months", calculated 80.2 years.<sup>82</sup> |
| * **HMW PAHs (4+ rings):** Generally more persistent. | * **HMW PAHs (4+ rings):** Generally more persistent. |
| * Fluoranthene: t<sub>1/2</sub> ~302 days (San Francisco Estuary model [77]); 2.4-39 weeks (landscaping material [84]). | * Fluoranthene: t<sub>1/2</sub> ~302 days (San Francisco Estuary model <sup>77</sup>); 2.4-39 weeks (landscaping material <sup>84</sup>). |
| * Pyrene: t<sub>1/2</sub> ~9-16 years (Gulf sediments [[#ref74|74]]); 2.7-52 weeks (landscaping material [84]). | * Pyrene: t<sub>1/2</sub> ~9-16 years (Gulf sediments <sup>[[#ref74|74]]</sup>); 2.7-52 weeks (landscaping material <sup>84</sup>). |
| * Benz[a]anthracene: t<sub>1/2</sub> ~338 days (San Francisco Estuary model [77]). | * Benz[a]anthracene: t<sub>1/2</sub> ~338 days (San Francisco Estuary model <sup>77</sup>). |
| * Chrysene: t<sub>1/2</sub> 372-993 days (soil [83]); 22-198 weeks (landscaping material [84]). | * Chrysene: t<sub>1/2</sub> 372-993 days (soil <sup>83</sup>); 22-198 weeks (landscaping material <sup>84</sup>). |
| * Benzo[b]fluoranthene: t<sub>1/2</sub> ~5.6 years (San Francisco Estuary model [77], [108]); 360 days - 1.67 years (aerobic soil [85]). Resistant to degradation in some studies.[84] | * Benzo[b]fluoranthene: t<sub>1/2</sub> ~5.6 years (San Francisco Estuary model <sup>77, 108</sup>); 360 days - 1.67 years (aerobic soil <sup>85</sup>). Resistant to degradation in some studies.<sup>84</sup> |
| * Benzo[k]fluoranthene: No specific marine sediment t<sub>1/2</sub> found, but as an isomer of BbF, expected to be very persistent. EPA data indicates soil t<sub>1/2</sub> of 360 days - 1.67 years for Benzo(b)fluoranthene [85], BkF likely similar. | * Benzo[k]fluoranthene: No specific marine sediment t<sub>1/2</sub> found, but as an isomer of BbF, expected to be very persistent. EPA data indicates soil t<sub>1/2</sub> of 360 days - 1.67 years for Benzo(b)fluoranthene <sup>85</sup>, BkF likely similar. |
| * Benzo[e]pyrene: No specific marine sediment t<sub>1/2</sub> found. Expected to be very persistent, similar to BaP. | * Benzo[e]pyrene: No specific marine sediment t<sub>1/2</sub> found. Expected to be very persistent, similar to BaP. |
| * Benzo[a]pyrene: t<sub>1/2</sub> 229->1400 days (soil/sediment [[#ref15|15]]); EPA data: 57-522 days (aerobic soil [87]), 85-inf (2100) days (sediment [94]). | * Benzo[a]pyrene: t<sub>1/2</sub> 229->1400 days (soil/sediment <sup>[[#ref15|15]]</sup>); EPA data: 57-522 days (aerobic soil <sup>87</sup>), 85-inf (2100) days (sediment <sup>94</sup>). |
| * Perylene: Primarily diagenetic, so its "persistence" reflects formation and stability over geological timescales rather than degradation of recent inputs.[89], [90], [98], [109], [110] Biodegradation t<sub>1/2</sub> of 3.4 days reported in a yeast consortium study, but this is under optimal lab conditions, not representative of sediment.[89] | * Perylene: Primarily diagenetic, so its "persistence" reflects formation and stability over geological timescales rather than degradation of recent inputs.<sup>89, 90, 98, 109, 110</sup> Biodegradation t<sub>1/2</sub> of 3.4 days reported in a yeast consortium study, but this is under optimal lab conditions, not representative of sediment.<sup>89</sup> |
| * Indeno[1,2,3-cd]pyrene: Biodegradation t<sub>1/2</sub> ~330-331 days (EPA CompTox [91]). | * Indeno[1,2,3-cd]pyrene: Biodegradation t<sub>1/2</sub> ~330-331 days (EPA CompTox <sup>91</sup>). |
| * Dibenz[a,h]anthracene: t<sub>1/2</sub> ~5.7 years (San Francisco Estuary model [77]). | * Dibenz[a,h]anthracene: t<sub>1/2</sub> ~5.7 years (San Francisco Estuary model <sup>77</sup>). |
| * Benzo[g,h,i]perylene: t<sub>1/2</sub> ~5.7 years (San Francisco Estuary model [77]); EPA data: 590-650 days (aerobic soil [85]). | * Benzo[g,h,i]perylene: t<sub>1/2</sub> ~5.7 years (San Francisco Estuary model <sup>77</sup>); EPA data: 590-650 days (aerobic soil <sup>85</sup>). |
| * **Alkylated PAHs:** Generally more persistent than their parent compounds.[9], [17] | * **Alkylated PAHs:** Generally more persistent than their parent compounds.<sup>9, 17</sup> |
| * C1-C3 Naphthalenes: Expected to be more persistent than Naphthalene. [100] reports rapid metabolism of naphthalenes in diesel-contaminated sediments, but this includes parent and alkylated. [50] notes alkylated PAHs (including naphthalenes) are abundant and their movement understudied. | * C1-C3 Naphthalenes: Expected to be more persistent than Naphthalene. <sup>100</sup> reports rapid metabolism of naphthalenes in diesel-contaminated sediments, but this includes parent and alkylated. <sup>50</sup> notes alkylated PAHs (including naphthalenes) are abundant and their movement understudied. |
| * C1-Phenanthrenes: Expected to be more persistent than Phenanthrene. [111] notes C1-Phenanthrene can be an evaluation index for oil pollution release. [100] indicates rapid metabolism of phenanthrenes in diesel-contaminated sediments. | * C1-Phenanthrenes: Expected to be more persistent than Phenanthrene. <sup>111</sup> notes C1-Phenanthrene can be an evaluation index for oil pollution release. <sup>100</sup> indicates rapid metabolism of phenanthrenes in diesel-contaminated sediments. |
| |
| === 3.2.3. Ordered List of MMO PAHs by Increasing Persistence in Marine Sediment === | === 3.2.3. Ordered List of MMO PAHs by Increasing Persistence in Marine Sediment === |
| **Table 3.2.1: MMO PAHs Ordered by Estimated Increasing Persistence (Half-life in Sediment).** | **Table 3.2.1: MMO PAHs Ordered by Estimated Increasing Persistence (Half-life in Sediment).** |
| ^ Rank ^ PAH Name ^ Number of Rings ^ Estimated Half-life in Sediment (Range / Value) ^ Primary Data Source(s) / Comment ^ | ^ Rank ^ PAH Name ^ Number of Rings ^ Estimated Half-life in Sediment (Range / Value) ^ Primary Data Source(s) / Comment ^ |
| | 1 | Naphthalene | 2 | 20 - 100 days | [77], [94]; LMW, relatively volatile and biodegradable. | | | 1 | Naphthalene | 2 | 20 - 100 days | <sup>77, 94</sup>; LMW, relatively volatile and biodegradable. | |
| | 2 | Acenaphthylene | 3<sup>b</sup> | Days to Weeks | Estimated based on LMW nature, similar to Acenaphthene. | | | 2 | Acenaphthylene | 3<sup>b</sup> | Days to Weeks | Estimated based on LMW nature, similar to Acenaphthene. | |
| | 3 | Acenaphthene | 3<sup>b</sup> | Days to Weeks | [78], [95]; LMW, more degradable than HMW. | | | 3 | Acenaphthene | 3<sup>b</sup> | Days to Weeks | <sup>78, 95</sup>; LMW, more degradable than HMW. | |
| | 4 | Fluorene | 3<sup>b</sup> | 30 - 90 days | [80]; LMW. | | | 4 | Fluorene | 3<sup>b</sup> | 30 - 90 days | <sup>80</sup>; LMW. | |
| | 5 | C1-Naphthalenes | 2 | Weeks to Months | Estimated > Naphthalene due to alkylation.[9], [17] | | | 5 | C1-Naphthalenes | 2 | Weeks to Months | Estimated > Naphthalene due to alkylation.<sup>9, 17</sup> | |
| | 6 | Anthracene | 3 | 60 - 210 days (highly variable) | [76], [82]; Can be rapid in oil-treated, slower in unacclimatised. | | | 6 | Anthracene | 3 | 60 - 210 days (highly variable) | <sup>76, 82</sup>; Can be rapid in oil-treated, slower in unacclimatised. | |
| | 7 | Phenanthrene | 3 | 60 - 180 days | [[#ref15|15]], [77], [84], [100]; LMW but more stable than Naphthalene. | | | 7 | Phenanthrene | 3 | 60 - 180 days | <sup>[[#ref15|15]], 77, 84, 100</sup>; LMW but more stable than Naphthalene. | |
| | 8 | C2-Naphthalenes | 2 | Months | Estimated > C1-Naphthalenes due to increased alkylation.[9], [17] | | | 8 | C2-Naphthalenes | 2 | Months | Estimated > C1-Naphthalenes due to increased alkylation.<sup>9, 17</sup> | |
| | 9 | C3-Naphthalenes | 2 | Months to >1 Year | Estimated > C2-Naphthalenes due to further alkylation.[9], [17] | | | 9 | C3-Naphthalenes | 2 | Months to >1 Year | Estimated > C2-Naphthalenes due to further alkylation.<sup>9, 17</sup> | |
| | 10 | C1-Phenanthrenes | 3 | Months to >1 Year | Estimated > Phenanthrene due to alkylation.[9], [17], [111] | | | 10 | C1-Phenanthrenes | 3 | Months to >1 Year | Estimated > Phenanthrene due to alkylation.<sup>9, 17, 111</sup> | |
| | 11 | Fluoranthene | 4<sup>c</sup> | ~300 days (up to 1 year) |.[77], [84] | | | 11 | Fluoranthene | 4<sup>c</sup> | ~300 days (up to 1 year) |.<sup>77, 84</sup> | |
| | 12 | Pyrene | 4 | 1 - 9 years (highly variable) | [[#ref74|74]], [84]; Can be very persistent. | | | 12 | Pyrene | 4 | 1 - 9 years (highly variable) | <sup>[[#ref74|74]], 84</sup>; Can be very persistent. | |
| | 13 | Benz[a]anthracene | 4 | ~340 days (up to 1-2 years) |.[77] | | | 13 | Benz[a]anthracene | 4 | ~340 days (up to 1-2 years) |.<sup>77</sup> | |
| | 14 | Chrysene | 4 | 1 - 3 years |.[83], [84] | | | 14 | Chrysene | 4 | 1 - 3 years |.<sup>83, 84</sup> | |
| | 15 | Indeno[1,2,3-cd]pyrene | 6<sup>c</sup> | ~1 year (up to several years) |.[91], [92] | | | 15 | Indeno[1,2,3-cd]pyrene | 6<sup>c</sup> | ~1 year (up to several years) |.<sup>91, 92</sup> | |
| | 16 | Benzo[e]pyrene | 5 | Years | Estimated based on HMW structure, similar to BaP/BbF. | | | 16 | Benzo[e]pyrene | 5 | Years | Estimated based on HMW structure, similar to BaP/BbF. | |
| | 17 | Benzo[a]pyrene | 5 | 0.5 - >4 years (highly variable) | [[#ref15|15]], [87], [88], [94]; Very persistent. | | | 17 | Benzo[a]pyrene | 5 | 0.5 - >4 years (highly variable) | <sup>[[#ref15|15]], 87, 88, 94</sup>; Very persistent. | |
| | 18 | Benzo[k]fluoranthene | 5 | Years | Estimated based on HMW structure, similar to BbF.[85] | | | 18 | Benzo[k]fluoranthene | 5 | Years | Estimated based on HMW structure, similar to BbF.<sup>85</sup> | |
| | 19 | Perylene | 5 | Very High (Diagenetic Origin) | [89], [90], [98], [109], [110]; Persistence reflects stability post-formation. | | | 19 | Perylene | 5 | Very High (Diagenetic Origin) | <sup>89, 90, 98, 109, 110</sup>; Persistence reflects stability post-formation. | |
| | 20 | Benzo[b]fluoranthene | 5 | ~1 - 5.6 years | [77], [84], [85]; Very persistent. | | | 20 | Benzo[b]fluoranthene | 5 | ~1 - 5.6 years | <sup>77, 84, 85</sup>; Very persistent. | |
| | 21 | Benzo[g,h,i]perylene | 6 | ~1.6 - 5.7 years | [77], [85]; Very persistent. | | | 21 | Benzo[g,h,i]perylene | 6 | ~1.6 - 5.7 years | <sup>77, 85</sup>; Very persistent. | |
| | 22 | Dibenz[a,h]anthracene | 5 | ~5.7 years | [77]; Very persistent. | | | 22 | Dibenz[a,h]anthracene | 5 | ~5.7 years | <sup>77</sup>; Very persistent. | |
| |
| //Notes on Table 3.2.1:// | //Notes on Table 3.2.1:// |
| The data clearly indicate that PAH persistence in marine sediments varies dramatically, spanning from days for some LMW compounds to many years, or even decades under certain conditions, for HMW compounds. This wide range has significant implications for long-term ecological risk and the selection of sediment management strategies. | The data clearly indicate that PAH persistence in marine sediments varies dramatically, spanning from days for some LMW compounds to many years, or even decades under certain conditions, for HMW compounds. This wide range has significant implications for long-term ecological risk and the selection of sediment management strategies. |
| |
| A critical factor emerging from the data is the substantial variability in reported half-lives for the same PAH. This variability underscores that persistence is not an intrinsic property of the chemical alone but is heavily influenced by site-specific environmental conditions such as sediment organic matter content, the presence of black carbon, oxygen levels (aerobic vs. anaerobic), microbial community structure, and temperature.[[#ref74|74]], [76], [82], [84], [93], [94] For example, anaerobic conditions, common in buried or highly organic sediments, drastically reduce degradation rates for most PAHs.[[#ref15|15]], [[#ref74|74]], [83], [104] Therefore, a single half-life value for a PAH may not be universally applicable. | A critical factor emerging from the data is the substantial variability in reported half-lives for the same PAH. This variability underscores that persistence is not an intrinsic property of the chemical alone but is heavily influenced by site-specific environmental conditions such as sediment organic matter content, the presence of black carbon, oxygen levels (aerobic vs. anaerobic), microbial community structure, and temperature.<sup>[[#ref74|74]], 76, 82, 84, 93, 94</sup> For example, anaerobic conditions, common in buried or highly organic sediments, drastically reduce degradation rates for most PAHs.<sup>[[#ref15|15]], [[#ref74|74]], 83, 104</sup> Therefore, a single half-life value for a PAH may not be universally applicable. |
| |
| Despite this variability, a consistent trend is the markedly greater persistence of HMW PAHs (those with four or more rings) compared to LMW PAHs (two to three rings).[7], [8], [[#ref15|15]] This is attributed to their lower water solubility, stronger sorption to sediment particles, and greater resistance to microbial degradation. This principle is fundamental in predicting the relative persistence of PAHs when specific half-life data are scarce. | Despite this variability, a consistent trend is the markedly greater persistence of HMW PAHs (those with four or more rings) compared to LMW PAHs (two to three rings).<sup>7, 8, [[#ref15|15]]</sup> This is attributed to their lower water solubility, stronger sorption to sediment particles, and greater resistance to microbial degradation. This principle is fundamental in predicting the relative persistence of PAHs when specific half-life data are scarce. |
| |
| The inclusion of alkylated PAHs in the MMO list is particularly relevant to persistence. Alkylated PAHs are generally found to be more resistant to degradation than their parent (unsubstituted) compounds.[9], [17] This increased persistence, combined with their often high abundance in petrogenic sources, means that alkylated PAHs can contribute significantly to the long-term PAH burden and associated risks in contaminated sediments. The ranking reflects this by placing alkylated PAHs as more persistent than their respective parent compounds. | The inclusion of alkylated PAHs in the MMO list is particularly relevant to persistence. Alkylated PAHs are generally found to be more resistant to degradation than their parent (unsubstituted) compounds.<sup>9, 17</sup> This increased persistence, combined with their often high abundance in petrogenic sources, means that alkylated PAHs can contribute significantly to the long-term PAH burden and associated risks in contaminated sediments. The ranking reflects this by placing alkylated PAHs as more persistent than their respective parent compounds. |
| |
| Perylene's persistence is a special case. Its high concentrations in some sediments, particularly deeper layers, are often attributed to its //in situ// diagenetic formation from natural organic precursors rather than direct anthropogenic input and subsequent degradation.[[#ref34|34]], [89], [90], [98], [109], [110] Thus, its "persistence" reflects its inherent stability once formed and the continuous nature of its formation process over long timescales, distinguishing it from the environmental persistence of externally introduced PAHs. | Perylene's persistence is a special case. Its high concentrations in some sediments, particularly deeper layers, are often attributed to its //in situ// diagenetic formation from natural organic precursors rather than direct anthropogenic input and subsequent degradation.<sup>[[#ref34|34]], 89, 90, 98, 109, 110</sup> Thus, its "persistence" reflects its inherent stability once formed and the continuous nature of its formation process over long timescales, distinguishing it from the environmental persistence of externally introduced PAHs. |
| |
| ==== 3.3. Bioaccumulation Potential Ranking ==== | ==== 3.3. Bioaccumulation Potential Ranking ==== |
| |
| === 3.3.1. Definition and Metrics of PAH Bioaccumulation === | === 3.3.1. Definition and Metrics of PAH Bioaccumulation === |
| Bioaccumulation refers to the process by which organisms accumulate chemical substances in their tissues to concentrations higher than those in the surrounding environment (water, sediment, or food).[1], [2], [[#ref3|3]], [[#ref4|4]], [[#ref5|5]], [6], [8], [[#ref15|15]], [99], [108], [[#ref112|112]], [[#ref113|113]], [114], [115], [116], [117], [118], [119], [120], [121], [122], [123], [124], [125], [126], [127], [128], [129], [130], [131], [132], [133], [134], [135], [136], [137], [138], [139], [140], [141] For PAHs, which are lipophilic (fat-loving), accumulation primarily occurs in the lipid-rich tissues of organisms. | Bioaccumulation refers to the process by which organisms accumulate chemical substances in their tissues to concentrations higher than those in the surrounding environment (water, sediment, or food).<sup>1, 2, [[#ref3|3]], [[#ref4|4]], [[#ref5|5]], 6, 8, [[#ref15|15]], 99, 108, [[#ref112|112]], [[#ref113|113]], 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141</sup> For PAHs, which are lipophilic (fat-loving), accumulation primarily occurs in the lipid-rich tissues of organisms. |
| |
| Key metrics for assessing bioaccumulation potential include: | Key metrics for assessing bioaccumulation potential include: |
| * **Octanol-Water Partition Coefficient (Log K<sub>ow</sub>):** This is a measure of a chemical's hydrophobicity. A higher Log K<sub>ow</sub> value indicates a greater tendency for the chemical to partition from water into octanol (a surrogate for lipids), and thus a higher potential for bioaccumulation in fatty tissues.[99], [[#ref112|112]], [[#ref113|113]], [114], [115], [116], [118], [124], [125], [126], [142], [143] | * **Octanol-Water Partition Coefficient (Log K<sub>ow</sub>):** This is a measure of a chemical's hydrophobicity. A higher Log K<sub>ow</sub> value indicates a greater tendency for the chemical to partition from water into octanol (a surrogate for lipids), and thus a higher potential for bioaccumulation in fatty tissues.<sup>99, [[#ref112|112]], [[#ref113|113]], 114, 115, 116, 118, 124, 125, 126, 142, 143</sup> |
| * **Bioconcentration Factor (BCF):** This is the ratio of the concentration of a chemical in an organism to its concentration in the surrounding water, specifically considering uptake from water across respiratory surfaces (e.g., gills).[99], [108], [[#ref112|112]], [[#ref113|113]], [114], [115], [116], [117], [118], [119], [120], [121], [122], [123], [124], [125], [126], [127], [128], [129], [130], [131], [132], [133], [134], [135], [136], [137], [138], [139], [140], [141], [142], [143] | * **Bioconcentration Factor (BCF):** This is the ratio of the concentration of a chemical in an organism to its concentration in the surrounding water, specifically considering uptake from water across respiratory surfaces (e.g., gills).<sup>99, 108, [[#ref112|112]], [[#ref113|113]], 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143</sup> |
| * **Bioaccumulation Factor (BAF):** This is similar to BCF but accounts for uptake from all exposure routes, including water, diet (ingestion of contaminated food), and direct contact with contaminated sediment.[[#ref112|112]], [[#ref113|113]], [114], [116], [117], [118], [122], [123], [125], [126], [127], [142], [143] | * **Bioaccumulation Factor (BAF):** This is similar to BCF but accounts for uptake from all exposure routes, including water, diet (ingestion of contaminated food), and direct contact with contaminated sediment.<sup>[[#ref112|112]], [[#ref113|113]], 114, 116, 117, 118, 122, 123, 125, 126, 127, 142, 143</sup> |
| |
| For regulatory purposes, such as under REACH, BCF values are often used to categorize substances: Not Bioaccumulative (nB, BCF < 2000 L/kg), Bioaccumulative (B, BCF 2000-5000 L/kg), and Very Bioaccumulative (vB, BCF > 5000 L/kg).[114] This report will focus on marine invertebrates (e.g., mussels, crustaceans) for BCF/BAF data, as they generally exhibit higher PAH accumulation than fish due to their limited metabolic capacity to break down PAHs.[2], [[#ref5|5]], [32], [[#ref52|52]], [114], [118], [119], [122], [124], [125], [137], [139] | For regulatory purposes, such as under REACH, BCF values are often used to categorize substances: Not Bioaccumulative (nB, BCF < 2000 L/kg), Bioaccumulative (B, BCF 2000-5000 L/kg), and Very Bioaccumulative (vB, BCF > 5000 L/kg).<sup>114</sup> This report will focus on marine invertebrates (e.g., mussels, crustaceans) for BCF/BAF data, as they generally exhibit higher PAH accumulation than fish due to their limited metabolic capacity to break down PAHs.<sup>2, [[#ref5|5]], 32, [[#ref52|52]], 114, 118, 119, 122, 124, 125, 137, 139</sup> |
| |
| === 3.3.2. Bioaccumulation Data for MMO PAHs === | === 3.3.2. Bioaccumulation Data for MMO PAHs === |
| Log K<sub>ow</sub> values were systematically extracted from PubChem entries (experimental if available, otherwise computed XLogP3 values). BCF data for marine invertebrates were primarily sourced from the RIVM report [114] and supplemented by other provided snippets. | Log K<sub>ow</sub> values were systematically extracted from PubChem entries (experimental if available, otherwise computed XLogP3 values). BCF data for marine invertebrates were primarily sourced from the RIVM report <sup>114</sup> and supplemented by other provided snippets. |
| |
| * **Naphthalene (Nap):** XLogP3 = 3.3.[144], [145] BCF in crustaceans 131-736 L/kg.[114] Category: nB. | * **Naphthalene (Nap):** XLogP3 = 3.3.<sup>144, 145</sup> BCF in crustaceans 131-736 L/kg.<sup>114</sup> Category: nB. |
| * **C1-Naphthalenes (C1-Naps):** (e.g., 1-Methylnaphthalene, 2-Methylnaphthalene) XLogP3 = 3.9.[146], [147], [148], [149], [150], [151] Expected BCF < 2000 L/kg. Category: nB. | * **C1-Naphthalenes (C1-Naps):** (e.g., 1-Methylnaphthalene, 2-Methylnaphthalene) XLogP3 = 3.9.<sup>146, 147, 148, 149, 150, 151</sup> Expected BCF < 2000 L/kg. Category: nB. |
| * **C2-Naphthalenes (C2-Naps):** (e.g., Dimethylnaphthalenes) XLogP3 = 4.3.[152], [153], [154], [155], [156] Expected BCF < 2000 L/kg. Category: nB. | * **C2-Naphthalenes (C2-Naps):** (e.g., Dimethylnaphthalenes) XLogP3 = 4.3.<sup>152, 153, 154, 155, 156</sup> Expected BCF < 2000 L/kg. Category: nB. |
| * **C3-Naphthalenes (C3-Naps):** (e.g., Trimethylnaphthalenes) XLogP3 = 4.7.[157], [158] Expected BCF potentially approaching 2000 L/kg. Category: nB to B. | * **C3-Naphthalenes (C3-Naps):** (e.g., Trimethylnaphthalenes) XLogP3 = 4.7.<sup>157, 158</sup> Expected BCF potentially approaching 2000 L/kg. Category: nB to B. |
| * **Acenaphthylene (Acy):** Experimental Log K<sub>ow</sub> = 3.93 [108]; XLogP3 = 3.7.[108], [159], [160], [161], [162] BCF in carp 560 L/kg (lipid norm.).[137] Category: nB. | * **Acenaphthylene (Acy):** Experimental Log K<sub>ow</sub> = 3.93 <sup>108</sup>; XLogP3 = 3.7.<sup>108, 159, 160, 161, 162</sup> BCF in carp 560 L/kg (lipid norm.).<sup>137</sup> Category: nB. |
| * **Acenaphthene (Ace):** Experimental Log K<sub>ow</sub> = 3.92.[163], [164] BCF (invertebrates) < 2000 L/kg (e.g., Nereis BDL [132]). Category: nB.[114] | * **Acenaphthene (Ace):** Experimental Log K<sub>ow</sub> = 3.92.<sup>163, 164</sup> BCF (invertebrates) < 2000 L/kg (e.g., Nereis BDL <sup>132</sup>). Category: nB.<sup>114</sup> |
| * **Fluorene (Flu):** XLogP3 = 4.2.[165], [166], [167] BCF in Daphnia magna 506 L/kg.[114] Category: nB. | * **Fluorene (Flu):** XLogP3 = 4.2.<sup>165, 166, 167</sup> BCF in Daphnia magna 506 L/kg.<sup>114</sup> Category: nB. |
| * **Phenanthrene (Phe):** XLogP3 = 4.5.[140], [168], [169] BCF in some crustaceans (Diporeia, Pontoporeia) > 5000 L/kg; molluscs < 2000 L/kg.[114] Category: vB in some invertebrates. | * **Phenanthrene (Phe):** XLogP3 = 4.5.<sup>140, 168, 169</sup> BCF in some crustaceans (Diporeia, Pontoporeia) > 5000 L/kg; molluscs < 2000 L/kg.<sup>114</sup> Category: vB in some invertebrates. |
| * **C1-Phenanthrenes (C1-Phe/Ant):** XLogP3 = 5.1.[170], [171], [172] Expected BCF > Phenanthrene, likely vB in sensitive invertebrates. | * **C1-Phenanthrenes (C1-Phe/Ant):** XLogP3 = 5.1.<sup>170, 171, 172</sup> Expected BCF > Phenanthrene, likely vB in sensitive invertebrates. |
| * **Anthracene (Ant):** XLogP3 = 4.4.[173], [174], [175], [176], [177] BCF in molluscs (Perna) 19000 L/kg; crustaceans (Pontoporeia) 16800-40000 L/kg.[114] Category: vB. | * **Anthracene (Ant):** XLogP3 = 4.4.<sup>173, 174, 175, 176, 177</sup> BCF in molluscs (Perna) 19000 L/kg; crustaceans (Pontoporeia) 16800-40000 L/kg.<sup>114</sup> Category: vB. |
| * **Fluoranthene (Flt):** XLogP3 = 5.2.[178], [179], [180], [181], [182] BCF in molluscs (Mytilus) 5920 L/kg, (Perna) 12250 L/kg; crustaceans (Diporeia) 15136-58884 L/kg.[114] Category: vB. | * **Fluoranthene (Flt):** XLogP3 = 5.2.<sup>178, 179, 180, 181, 182</sup> BCF in molluscs (Mytilus) 5920 L/kg, (Perna) 12250 L/kg; crustaceans (Diporeia) 15136-58884 L/kg.<sup>114</sup> Category: vB. |
| * **Pyrene (Pyr):** XLogP3 = 4.9.[134], [183], [184] BCF in molluscs (Dreissena) 13000-77000 L/kg, (Perna) 44550 L/kg; crustaceans (Pontoporeia) 166000 L/kg.[114] Category: vB. | * **Pyrene (Pyr):** XLogP3 = 4.9.<sup>134, 183, 184</sup> BCF in molluscs (Dreissena) 13000-77000 L/kg, (Perna) 44550 L/kg; crustaceans (Pontoporeia) 166000 L/kg.<sup>114</sup> Category: vB. |
| * **Benz[a]anthracene (BaA):** XLogP3 = 5.8.[185], [186], [187], [188] BCF in crustaceans (Daphnia, Pontoporeia) 10109-63000 L/kg.[114] Category: vB. | * **Benz[a]anthracene (BaA):** XLogP3 = 5.8.<sup>185, 186, 187, 188</sup> BCF in crustaceans (Daphnia, Pontoporeia) 10109-63000 L/kg.<sup>114</sup> Category: vB. |
| * **Chrysene (Chr):** Experimental Log K<sub>ow</sub> ~5.6-5.86; XLogP3 (for dione) = 3.9 [189], (for perhydro) = 7.4.[190] For Chrysene itself, XLogP3 is typically ~5.8. BCF in Daphnia magna 6088 L/kg.[114] Category: vB. | * **Chrysene (Chr):** Experimental Log K<sub>ow</sub> ~5.6-5.86; XLogP3 (for dione) = 3.9 <sup>189</sup>, (for perhydro) = 7.4.<sup>190</sup> For Chrysene itself, XLogP3 is typically ~5.8. BCF in Daphnia magna 6088 L/kg.<sup>114</sup> Category: vB. |
| * **Benzo[b]fluoranthene (BbF):** Experimental Log K<sub>ow</sub> = 5.78-6.12 [179], [191], [192], [193]; XLogP3 = 6.4. No reliable BCF data for categorization in [114], but high Log K<sub>ow</sub> suggests vB potential. | * **Benzo[b]fluoranthene (BbF):** Experimental Log K<sub>ow</sub> = 5.78-6.12 <sup>179, 191, 192, 193</sup>; XLogP3 = 6.4. No reliable BCF data for categorization in <sup>114</sup>, but high Log K<sub>ow</sub> suggests vB potential. |
| * **Benzo[k]fluoranthene (BkF):** Experimental Log K<sub>ow</sub> = 6.0-6.12 [194]; XLogP3 = 6.4.[86], [194], [195], [196], [197], [198], [199] BCF in Daphnia magna 13225 L/kg.[114] Category: vB. | * **Benzo[k]fluoranthene (BkF):** Experimental Log K<sub>ow</sub> = 6.0-6.12 <sup>194</sup>; XLogP3 = 6.4.<sup>86, 194, 195, 196, 197, 198, 199</sup> BCF in Daphnia magna 13225 L/kg.<sup>114</sup> Category: vB. |
| * **Benzo[e]pyrene (BeP):** Experimental Log K<sub>ow</sub> = 6.25-6.57 [134], [135], [200]; XLogP3 = 6.4. BCF for marine invertebrates not specified in [114], but high Log K<sub>ow</sub> suggests vB potential. | * **Benzo[e]pyrene (BeP):** Experimental Log K<sub>ow</sub> = 6.25-6.57 <sup>134, 135, 200</sup>; XLogP3 = 6.4. BCF for marine invertebrates not specified in <sup>114</sup>, but high Log K<sub>ow</sub> suggests vB potential. |
| * **Benzo[a]pyrene (BaP):** Experimental Log K<sub>ow</sub> = 5.97-6.13 [75], [87], [88], [135]; XLogP3 = 6.0.[71], [135], [201], [202], [203] BCF in molluscs (Dreissena) 24000-273000 L/kg, (Perna) 8500 L/kg; crustaceans (Daphnia, Pontoporeia) 8496-73000 L/kg.[114] Category: vB. | * **Benzo[a]pyrene (BaP):** Experimental Log K<sub>ow</sub> = 5.97-6.13 <sup>75, 87, 88, 135</sup>; XLogP3 = 6.0.<sup>71, 135, 201, 202, 203</sup> BCF in molluscs (Dreissena) 24000-273000 L/kg, (Perna) 8500 L/kg; crustaceans (Daphnia, Pontoporeia) 8496-73000 L/kg.<sup>114</sup> Category: vB. |
| * **Perylene (Per):** Experimental Log K<sub>ow</sub> = 6.25-6.30 [98], [204]; XLogP3 = 5.8. BCF for marine invertebrates not specified in [114], but high Log K<sub>ow</sub> suggests vB potential. | * **Perylene (Per):** Experimental Log K<sub>ow</sub> = 6.25-6.30 <sup>98, 204</sup>; XLogP3 = 5.8. BCF for marine invertebrates not specified in <sup>114</sup>, but high Log K<sub>ow</sub> suggests vB potential. |
| * **Indeno[1,2,3-cd]pyrene (IP):** Experimental Log K<sub>ow</sub> = 6.50-7.66 [91], [92], [205], [206], [207]; XLogP3 = 7.0. No reliable BCF data for categorization in [114], but high Log K<sub>ow</sub> suggests vB potential. | * **Indeno[1,2,3-cd]pyrene (IP):** Experimental Log K<sub>ow</sub> = 6.50-7.66 <sup>91, 92, 205, 206, 207</sup>; XLogP3 = 7.0. No reliable BCF data for categorization in <sup>114</sup>, but high Log K<sub>ow</sub> suggests vB potential. |
| * **Dibenz[a,h]anthracene (DBA):** Experimental Log K<sub>ow</sub> = 6.75-7.10 [208], [209], [210]; XLogP3 = 6.5.[211] BCF in Daphnia magna 50119 L/kg.[114] Category: vB. | * **Dibenz[a,h]anthracene (DBA):** Experimental Log K<sub>ow</sub> = 6.75-7.10 <sup>208, 209, 210</sup>; XLogP3 = 6.5.<sup>211</sup> BCF in Daphnia magna 50119 L/kg.<sup>114</sup> Category: vB. |
| * **Benzo[g,h,i]perylene (BghiP):** Experimental Log K<sub>ow</sub> = 6.50-7.23 [212], [213], [214], [215], [216], [217]; XLogP3 = 6.6. BCF in Daphnia magna 28288 L/kg.[114] Category: vB. | * **Benzo[g,h,i]perylene (BghiP):** Experimental Log K<sub>ow</sub> = 6.50-7.23 <sup>212, 213, 214, 215, 216, 217</sup>; XLogP3 = 6.6. BCF in Daphnia magna 28288 L/kg.<sup>114</sup> Category: vB. |
| |
| === 3.3.3. Ordered List of MMO PAHs by Increasing Bioaccumulation Potential === | === 3.3.3. Ordered List of MMO PAHs by Increasing Bioaccumulation Potential === |
| |
| //Notes on Table 3.3.1:// | //Notes on Table 3.3.1:// |
| <sup>a</sup> BCF Categories based on RIVM [114] for invertebrates where available: nB (BCF < 2000 L/kg), B (BCF 2000-5000 L/kg), vB (BCF > 5000 L/kg). "Estimated" indicates categorization based on Log K<sub>ow</sub> trends where specific BCF data for invertebrates was lacking in the primary review document. | <sup>a</sup> BCF Categories based on RIVM <sup>114</sup> for invertebrates where available: nB (BCF < 2000 L/kg), B (BCF 2000-5000 L/kg), vB (BCF > 5000 L/kg). "Estimated" indicates categorization based on Log K<sub>ow</sub> trends where specific BCF data for invertebrates was lacking in the primary review document. |
| <sup>b</sup> Contains a five-membered ring in addition to two benzene rings. | <sup>b</sup> Contains a five-membered ring in addition to two benzene rings. |
| <sup>c</sup> Contains a five-membered ring in addition to fused benzene rings. | <sup>c</sup> Contains a five-membered ring in addition to fused benzene rings. |
| |
| === 3.3.4. Insights and Implications for Bioaccumulation === | === 3.3.4. Insights and Implications for Bioaccumulation === |
| The Log K<sub>ow</sub> value serves as a strong primary indicator for the bioaccumulation potential of PAHs, with higher values generally correlating with increased partitioning into organism lipids.[99], [[#ref112|112]], [[#ref113|113]], [114], [115], [116], [118], [124], [125], [126], [142], [143] However, this relationship is not always linear across the entire range of PAHs. Factors such as very large molecular size can hinder membrane permeation, and the metabolic capacity of the organism can significantly reduce the actual accumulated concentration, particularly in vertebrates like fish which possess efficient enzyme systems (e.g., cytochrome P450) for metabolizing PAHs.[2], [[#ref5|5]], [32], [[#ref52|52]], [114], [118], [119], [122], [124], [125], [137], [139] | The Log K<sub>ow</sub> value serves as a strong primary indicator for the bioaccumulation potential of PAHs, with higher values generally correlating with increased partitioning into organism lipids.<sup>99, [[#ref112|112]], [[#ref113|113]], 114, 115, 116, 118, 124, 125, 126, 142, 143</sup> However, this relationship is not always linear across the entire range of PAHs. Factors such as very large molecular size can hinder membrane permeation, and the metabolic capacity of the organism can significantly reduce the actual accumulated concentration, particularly in vertebrates like fish which possess efficient enzyme systems (e.g., cytochrome P450) for metabolizing PAHs.<sup>2, [[#ref5|5]], 32, [[#ref52|52]], 114, 118, 119, 122, 124, 125, 137, 139</sup> |
| |
| This is why marine invertebrates, such as bivalve molluscs (e.g., mussels) and crustaceans, are often better indicators of PAH bioaccumulation in the environment. Their generally lower metabolic capacity for PAHs allows these compounds to accumulate to higher concentrations in their tissues, reflecting environmental exposure levels more directly.[2], [[#ref5|5]], [32], [[#ref52|52]], [114], [118], [119], [122], [124], [125], [137], [139] The RIVM report [114] confirms that many HMW PAHs are categorized as "very bioaccumulative" in invertebrates, even if they are less so in fish. | This is why marine invertebrates, such as bivalve molluscs (e.g., mussels) and crustaceans, are often better indicators of PAH bioaccumulation in the environment. Their generally lower metabolic capacity for PAHs allows these compounds to accumulate to higher concentrations in their tissues, reflecting environmental exposure levels more directly.<sup>2, [[#ref5|5]], 32, [[#ref52|52]], 114, 118, 119, 122, 124, 125, 137, 139</sup> The RIVM report <sup>114</sup> confirms that many HMW PAHs are categorized as "very bioaccumulative" in invertebrates, even if they are less so in fish. |
| |
| Alkylation tends to increase the Log K<sub>ow</sub> of PAHs. For example, C1-Naphthalenes (Log K<sub>ow</sub> ~3.9) are more hydrophobic than Naphthalene (Log K<sub>ow</sub> ~3.3), and this trend continues with C2- and C3-Naphthalenes (Log K<sub>ow</sub> ~4.3 and ~4.7, respectively). This suggests an increased intrinsic potential for bioaccumulation with increasing alkylation, assuming metabolic processes do not counteract this effect. The data for C1-Phenanthrenes (Log K<sub>ow</sub> ~5.1) compared to Phenanthrene (Log K<sub>ow</sub> ~4.5) also supports this. The ranking reflects this by generally placing alkylated PAHs higher in bioaccumulation potential than their parent compounds within the same ring-size category. | Alkylation tends to increase the Log K<sub>ow</sub> of PAHs. For example, C1-Naphthalenes (Log K<sub>ow</sub> ~3.9) are more hydrophobic than Naphthalene (Log K<sub>ow</sub> ~3.3), and this trend continues with C2- and C3-Naphthalenes (Log K<sub>ow</sub> ~4.3 and ~4.7, respectively). This suggests an increased intrinsic potential for bioaccumulation with increasing alkylation, assuming metabolic processes do not counteract this effect. The data for C1-Phenanthrenes (Log K<sub>ow</sub> ~5.1) compared to Phenanthrene (Log K<sub>ow</sub> ~4.5) also supports this. The ranking reflects this by generally placing alkylated PAHs higher in bioaccumulation potential than their parent compounds within the same ring-size category. |
| |
| === 3.4.1. Definition and Factors Influencing PAH Bioavailability from Sediment === | === 3.4.1. Definition and Factors Influencing PAH Bioavailability from Sediment === |
| Bioavailability, in the context of sediment contaminants, refers to the fraction of the total amount of a PAH present in the sediment that is accessible for uptake by, and can cause an effect in, an organism.[7], [9], [17], [20], [22], [[#ref31a|31a]]/[[#ref31b|31b]], [32], [49], [51], [85], [99], [105], [106], [118], [124], [[#ref218|218]], [219] It is a critical concept because not all of the PAH mass measured in a bulk sediment sample is necessarily available to cause harm. | Bioavailability, in the context of sediment contaminants, refers to the fraction of the total amount of a PAH present in the sediment that is accessible for uptake by, and can cause an effect in, an organism.<sup>7, 9, 17, 20, 22, [[#ref31a|31a]]/[[#ref31b|31b]], 32, 49, 51, 85, 99, 105, 106, 118, 124, [[#ref218|218]], 219</sup> It is a critical concept because not all of the PAH mass measured in a bulk sediment sample is necessarily available to cause harm. |
| |
| Key factors influencing PAH bioavailability from sediment include: | Key factors influencing PAH bioavailability from sediment include: |
| * **PAH Physicochemical Properties:** | * **PAH Physicochemical Properties:** |
| * **Water Solubility & Log K<sub>ow</sub>:** LMW PAHs, with their relatively higher water solubility and lower Log K<sub>ow</sub> values, are generally more readily available from the sediment porewater (the water filling spaces between sediment particles).[1], [2], [27], [[#ref34|34]] HMW PAHs, being more hydrophobic (higher Log K<sub>ow</sub>), have very low concentrations in porewater and their bioavailability is often more linked to the ingestion of sediment particles by benthic organisms.[1], [2], [27], [32], [[#ref34|34]], [118] | * **Water Solubility & Log K<sub>ow</sub>:** LMW PAHs, with their relatively higher water solubility and lower Log K<sub>ow</sub> values, are generally more readily available from the sediment porewater (the water filling spaces between sediment particles).<sup>1, 2, 27, [[#ref34|34]]</sup> HMW PAHs, being more hydrophobic (higher Log K<sub>ow</sub>), have very low concentrations in porewater and their bioavailability is often more linked to the ingestion of sediment particles by benthic organisms.<sup>1, 2, 27, 32, [[#ref34|34]], 118</sup> |
| * **Sediment Characteristics:** | * **Sediment Characteristics:** |
| * **Organic Carbon (OC) Content:** PAHs strongly adsorb to the organic carbon fraction of sediments. Higher OC content generally leads to stronger binding and lower concentrations of freely dissolved (and thus readily bioavailable via aqueous uptake) PAHs in porewater.[[#ref4|4]], [[#ref10|10]], [[#ref31a|31a]]/[[#ref31b|31b]] | * **Organic Carbon (OC) Content:** PAHs strongly adsorb to the organic carbon fraction of sediments. Higher OC content generally leads to stronger binding and lower concentrations of freely dissolved (and thus readily bioavailable via aqueous uptake) PAHs in porewater.<sup>[[#ref4|4]], [[#ref10|10]], [[#ref31a|31a]]/[[#ref31b|31b]]</sup> |
| * **Black Carbon (BC) Content:** Black carbon, which includes materials like soot, char, and coal particles, has an exceptionally strong affinity for PAHs, binding them much more tightly than natural amorphous organic carbon. The presence of BC significantly reduces PAH bioavailability.[[#ref31a|31a]]/[[#ref31b|31b]], [106], [[#ref218|218]], [219] PAHs sorbed to coal-derived particles are noted to have minimal biodegradation and slow release rates.[[#ref218|218]], [219] | * **Black Carbon (BC) Content:** Black carbon, which includes materials like soot, char, and coal particles, has an exceptionally strong affinity for PAHs, binding them much more tightly than natural amorphous organic carbon. The presence of BC significantly reduces PAH bioavailability.<sup>[[#ref31a|31a]]/[[#ref31b|31b]], 106, [[#ref218|218]], 219</sup> PAHs sorbed to coal-derived particles are noted to have minimal biodegradation and slow release rates.<sup>[[#ref218|218]], 219</sup> |
| * **Grain Size:** Finer sediments (silt and clay) have a larger surface area per unit mass and often higher organic carbon content, which can lead to higher bulk PAH concentrations. However, PAHs associated with the clay/silt fraction might be more mobile or available under certain conditions compared to those strongly bound to coarser, black carbon-rich particles.[[#ref10|10]], [[#ref31a|31a]]/[[#ref31b|31b]], [[#ref218|218]] | * **Grain Size:** Finer sediments (silt and clay) have a larger surface area per unit mass and often higher organic carbon content, which can lead to higher bulk PAH concentrations. However, PAHs associated with the clay/silt fraction might be more mobile or available under certain conditions compared to those strongly bound to coarser, black carbon-rich particles.<sup>[[#ref10|10]], [[#ref31a|31a]]/[[#ref31b|31b]], [[#ref218|218]]</sup> |
| * **Aging and Weathering:** Over time (aging), PAHs can become more strongly sequestered within the sediment matrix, diffusing into micropores or becoming more intimately associated with organic matter. This process generally reduces their extractability and bioavailability.[51], [105] Weathering processes also preferentially remove more soluble and degradable PAHs, leaving behind a more recalcitrant mixture. | * **Aging and Weathering:** Over time (aging), PAHs can become more strongly sequestered within the sediment matrix, diffusing into micropores or becoming more intimately associated with organic matter. This process generally reduces their extractability and bioavailability.<sup>51, 105</sup> Weathering processes also preferentially remove more soluble and degradable PAHs, leaving behind a more recalcitrant mixture. |
| * **Organism-Specific Factors:** The feeding strategy (e.g., deposit feeder, filter feeder), habitat, and physiology of benthic organisms also influence their actual exposure and uptake of sediment-bound PAHs. | * **Organism-Specific Factors:** The feeding strategy (e.g., deposit feeder, filter feeder), habitat, and physiology of benthic organisms also influence their actual exposure and uptake of sediment-bound PAHs. |
| |
| |
| === 3.4.4. Insights and Implications for Bioavailability === | === 3.4.4. Insights and Implications for Bioavailability === |
| The bioavailability of PAHs from sediment is a highly complex and dynamic property, influenced by an interplay of chemical, sediment, and biological factors. It is not an intrinsic property of the PAH alone but rather a result of these interactions.[[#ref10|10]], [[#ref31a|31a]]/[[#ref31b|31b]], [105], [106], [[#ref218|218]], [219] This complexity makes a universal, quantitative ranking of bioavailability challenging. The provided qualitative ranking is based on general principles of solubility, sorption behavior (inferred from Log K<sub>ow</sub> and molecular structure), and typical exposure pathways for benthic organisms. | The bioavailability of PAHs from sediment is a highly complex and dynamic property, influenced by an interplay of chemical, sediment, and biological factors. It is not an intrinsic property of the PAH alone but rather a result of these interactions.<sup>[[#ref10|10]], [[#ref31a|31a]]/[[#ref31b|31b]], 105, 106, [[#ref218|218]], 219</sup> This complexity makes a universal, quantitative ranking of bioavailability challenging. The provided qualitative ranking is based on general principles of solubility, sorption behavior (inferred from Log K<sub>ow</sub> and molecular structure), and typical exposure pathways for benthic organisms. |
| |
| A critical factor is the nature of the sediment itself. The amount and type of organic carbon significantly control PAH partitioning. While higher total organic carbon (TOC) generally reduces the freely dissolved PAH concentration in porewater, the presence of black carbon (e.g., soot, coal particles from industrial or combustion sources) has a disproportionately strong effect, binding PAHs much more tenaciously than amorphous organic carbon and thereby drastically reducing their bioavailability.[[#ref31a|31a]]/[[#ref31b|31b]], [106], [[#ref218|218]], [219] Studies have shown that PAHs sorbed to such carbonaceous materials exhibit minimal biodegradation and slow release rates, effectively locking them away from biological uptake.[[#ref218|218]], [219] Conversely, PAHs associated with finer sediment fractions like clay and silt, which may have higher amorphous organic carbon, might be relatively more mobile and bioavailable under certain conditions.[[#ref218|218]] | A critical factor is the nature of the sediment itself. The amount and type of organic carbon significantly control PAH partitioning. While higher total organic carbon (TOC) generally reduces the freely dissolved PAH concentration in porewater, the presence of black carbon (e.g., soot, coal particles from industrial or combustion sources) has a disproportionately strong effect, binding PAHs much more tenaciously than amorphous organic carbon and thereby drastically reducing their bioavailability.<sup>[[#ref31a|31a]]/[[#ref31b|31b]], 106, [[#ref218|218]], 219</sup> Studies have shown that PAHs sorbed to such carbonaceous materials exhibit minimal biodegradation and slow release rates, effectively locking them away from biological uptake.<sup>[[#ref218|218]], 219</sup> Conversely, PAHs associated with finer sediment fractions like clay and silt, which may have higher amorphous organic carbon, might be relatively more mobile and bioavailable under certain conditions.<sup>[[#ref218|218]]</sup> |
| |
| The concept of "aging" is also crucial. Over time, PAHs in sediment can become more strongly sequestered, diffusing into micropores within sediment particles or becoming more intimately incorporated into the organic matrix.[105] This aging process generally leads to a decrease in their extractability by mild solvents and, consequently, a reduction in their bioavailability to organisms. This implies that recently deposited PAHs may pose a greater immediate bioavailable risk than older, historically contaminated sediments, even if bulk concentrations are similar. | The concept of "aging" is also crucial. Over time, PAHs in sediment can become more strongly sequestered, diffusing into micropores within sediment particles or becoming more intimately incorporated into the organic matrix.<sup>105</sup> This aging process generally leads to a decrease in their extractability by mild solvents and, consequently, a reduction in their bioavailability to organisms. This implies that recently deposited PAHs may pose a greater immediate bioavailable risk than older, historically contaminated sediments, even if bulk concentrations are similar. |
| |
| While LMW PAHs are generally more water-soluble and thus potentially more bioavailable from porewater, their higher volatility and faster degradation rates (as discussed in Section 3.2) can reduce their long-term presence in the bioavailable fraction. HMW PAHs, although less soluble and more strongly sorbed, are also more persistent. Their bioavailability is often linked to the direct ingestion of contaminated sediment particles by deposit-feeding benthic organisms. Therefore, the "most bioavailable" PAH depends on the specific exposure route and organism being considered. For organisms primarily exposed via porewater, LMW PAHs might dominate uptake, whereas for sediment ingestors, persistent HMW PAHs on particles can be a significant source of exposure. | While LMW PAHs are generally more water-soluble and thus potentially more bioavailable from porewater, their higher volatility and faster degradation rates (as discussed in Section 3.2) can reduce their long-term presence in the bioavailable fraction. HMW PAHs, although less soluble and more strongly sorbed, are also more persistent. Their bioavailability is often linked to the direct ingestion of contaminated sediment particles by deposit-feeding benthic organisms. Therefore, the "most bioavailable" PAH depends on the specific exposure route and organism being considered. For organisms primarily exposed via porewater, LMW PAHs might dominate uptake, whereas for sediment ingestors, persistent HMW PAHs on particles can be a significant source of exposure. |
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| **Natural Sources of PAHs:** | **Natural Sources of PAHs:** |
| * **Diagenesis:** The slow, low-temperature transformation of sedimentary organic matter by geological and microbial processes over long periods. This is a primary natural source for Perylene.[[#ref34|34]], [89], [90], [98], [109], [110] | * **Diagenesis:** The slow, low-temperature transformation of sedimentary organic matter by geological and microbial processes over long periods. This is a primary natural source for Perylene.<sup>[[#ref34|34]], 89, 90, 98, 109, 110</sup> |
| * **Natural Pyrolysis:** Incomplete combustion of organic matter from natural events like forest fires and volcanic eruptions.[1], [2], [[#ref3|3]], [[#ref4|4]], [7], [9], [[#ref10|10]], [16], [17], [[#ref23|23]], [24], [25], [26], [27], [28], [29], [30] These processes generate a range of PAHs, often dominated by unsubstituted HMW PAHs. | * **Natural Pyrolysis:** Incomplete combustion of organic matter from natural events like forest fires and volcanic eruptions.<sup>1, 2, [[#ref3|3]], [[#ref4|4]], 7, 9, [[#ref10|10]], 16, 17, [[#ref23|23]], 24, 25, 26, 27, 28, 29, 30</sup> These processes generate a range of PAHs, often dominated by unsubstituted HMW PAHs. |
| * **Petroleum Seeps:** Natural seepage of crude oil and gas from underwater geological formations into the marine environment. These seeps release a mixture of PAHs, typically rich in LMW and alkylated PAHs.[1], [2], [[#ref4|4]], [8], [9], [[#ref10|10]], [24], [26], [28], [[#ref31a|31a]]/[[#ref31b|31b]] | * **Petroleum Seeps:** Natural seepage of crude oil and gas from underwater geological formations into the marine environment. These seeps release a mixture of PAHs, typically rich in LMW and alkylated PAHs.<sup>1, 2, [[#ref4|4]], 8, 9, [[#ref10|10]], 24, 26, 28, [[#ref31a|31a]]/[[#ref31b|31b]]</sup> |
| |
| **Anthropogenic Sources of PAHs:** | **Anthropogenic Sources of PAHs:** |
| * **Pyrogenic Sources:** These involve high-temperature processes, primarily the incomplete combustion of organic materials. Major sources include the burning of fossil fuels (coal, oil, and gas for power generation, industry, and transportation – including shipping emissions), wood burning (domestic heating, biomass burning), and waste incineration.[1], [2], [[#ref3|3]], [[#ref4|4]], [7], [9], [[#ref10|10]], [[#ref13|13]], [16], [17], [[#ref23|23]], [24], [25], [26], [27], [28], [29], [30], [33] These sources typically produce mixtures dominated by unsubstituted HMW PAHs. | * **Pyrogenic Sources:** These involve high-temperature processes, primarily the incomplete combustion of organic materials. Major sources include the burning of fossil fuels (coal, oil, and gas for power generation, industry, and transportation – including shipping emissions), wood burning (domestic heating, biomass burning), and waste incineration.<sup>1, 2, [[#ref3|3]], [[#ref4|4]], 7, 9, [[#ref10|10]], [[#ref13|13]], 16, 17, [[#ref23|23]], 24, 25, 26, 27, 28, 29, 30, 33</sup> These sources typically produce mixtures dominated by unsubstituted HMW PAHs. |
| * **Petrogenic Sources:** These relate to uncombusted petroleum and its products. Sources include crude oil spills, operational discharges from oil tankers and platforms, runoff contaminated with lubricating oils and fuels, and releases from asphalt and creosote-treated wood.[1], [2], [[#ref4|4]], [7], [8], [9], [[#ref10|10]], [[#ref12|12]], [16], [17], [[#ref23|23]], [24], [25], [26], [27], [28], [29], [30], [[#ref31a|31a]]/[[#ref31b|31b]], [33] Petrogenic mixtures are characterized by a higher proportion of LMW PAHs and, importantly, abundant alkylated PAH homologues.[1], [2], [[#ref4|4]], [9], [17], [[#ref23|23]], [24], [28], [30] | * **Petrogenic Sources:** These relate to uncombusted petroleum and its products. Sources include crude oil spills, operational discharges from oil tankers and platforms, runoff contaminated with lubricating oils and fuels, and releases from asphalt and creosote-treated wood.<sup>1, 2, [[#ref4|4]], 7, 8, 9, [[#ref10|10]], [[#ref12|12]], 16, 17, [[#ref23|23]], 24, 25, 26, 27, 28, 29, 30, [[#ref31a|31a]]/[[#ref31b|31b]], 33</sup> Petrogenic mixtures are characterized by a higher proportion of LMW PAHs and, importantly, abundant alkylated PAH homologues.<sup>1, 2, [[#ref4|4]], 9, 17, [[#ref23|23]], 24, 28, 30</sup> |
| |
| The ranking for natural abundance will order PAHs from those whose presence is most strongly indicative of anthropogenic activity (low natural background relative to typical pollution levels) to those with more significant or dominant natural sources. | The ranking for natural abundance will order PAHs from those whose presence is most strongly indicative of anthropogenic activity (low natural background relative to typical pollution levels) to those with more significant or dominant natural sources. |
| |
| === 3.5.2. Natural Abundance Data for MMO PAHs === | === 3.5.2. Natural Abundance Data for MMO PAHs === |
| * **Perylene:** Uniquely among the MMO PAHs, Perylene is widely recognized as having a predominantly diagenetic origin in many sedimentary environments. Its presence and concentration are often linked to the in-situ transformation of terrestrial or aquatic organic matter under specific (often anoxic) conditions, rather than direct input from combustion or petroleum sources.[30], [[#ref34|34]], [89], [90], [98], [109], [110] | * **Perylene:** Uniquely among the MMO PAHs, Perylene is widely recognized as having a predominantly diagenetic origin in many sedimentary environments. Its presence and concentration are often linked to the in-situ transformation of terrestrial or aquatic organic matter under specific (often anoxic) conditions, rather than direct input from combustion or petroleum sources.<sup>30, [[#ref34|34]], 89, 90, 98, 109, 110</sup> |
| * **Alkylated PAHs (C1-C3 Naphthalenes, C1-Phenanthrenes):** These groups are characteristic of petrogenic sources. While crude oil is a natural substance and natural seeps contribute these PAHs to the marine environment [8], [9], the widespread and high concentrations often encountered in contaminated areas are typically due to anthropogenic petroleum spills, fuel combustion, or industrial releases of petroleum products. The ratio of alkylated PAHs to their parent compounds is a key indicator of petrogenic versus pyrogenic sources, with petrogenic sources showing a dominance of alkylated forms.[1], [2], [[#ref4|4]], [24], [26], [30] | * **Alkylated PAHs (C1-C3 Naphthalenes, C1-Phenanthrenes):** These groups are characteristic of petrogenic sources. While crude oil is a natural substance and natural seeps contribute these PAHs to the marine environment <sup>8, 9</sup>, the widespread and high concentrations often encountered in contaminated areas are typically due to anthropogenic petroleum spills, fuel combustion, or industrial releases of petroleum products. The ratio of alkylated PAHs to their parent compounds is a key indicator of petrogenic versus pyrogenic sources, with petrogenic sources showing a dominance of alkylated forms.<sup>1, 2, [[#ref4|4]], 24, 26, 30</sup> |
| * **LMW Parent PAHs (Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene):** These PAHs can originate from both petrogenic (crude oil, natural seeps) and pyrogenic sources (natural fires, anthropogenic combustion). Their natural background levels can be variable, but significant elevations are often linked to anthropogenic inputs.[1], [2], [[#ref4|4]], [[#ref19|19]], [[#ref23|23]], [24], [27], [29], [30], [33], [[#ref34|34]], [[#ref40|40]] | * **LMW Parent PAHs (Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene):** These PAHs can originate from both petrogenic (crude oil, natural seeps) and pyrogenic sources (natural fires, anthropogenic combustion). Their natural background levels can be variable, but significant elevations are often linked to anthropogenic inputs.<sup>1, 2, [[#ref4|4]], [[#ref19|19]], [[#ref23|23]], 24, 27, 29, 30, 33, [[#ref34|34]], [[#ref40|40]]</sup> |
| * **HMW Parent PAHs (Fluoranthene, Pyrene, BaA, Chrysene, BbF, BkF, BeP, BaP, IP, DBA, BghiP):** These are primarily associated with pyrogenic processes. Natural sources like forest fires and volcanic activity do produce these HMW PAHs. However, the extensive and elevated concentrations found in many marine sediments, particularly in urban and industrial areas, are overwhelmingly attributed to anthropogenic combustion of fossil fuels and biomass.[1], [2], [7], [[#ref13|13]], [16], [[#ref23|23]], [24], [26], [27], [29], [30], [33], [[#ref34|34]] Some of these, like Benzo[a]pyrene, are often used as markers for anthropogenic combustion. | * **HMW Parent PAHs (Fluoranthene, Pyrene, BaA, Chrysene, BbF, BkF, BeP, BaP, IP, DBA, BghiP):** These are primarily associated with pyrogenic processes. Natural sources like forest fires and volcanic activity do produce these HMW PAHs. However, the extensive and elevated concentrations found in many marine sediments, particularly in urban and industrial areas, are overwhelmingly attributed to anthropogenic combustion of fossil fuels and biomass.<sup>1, 2, 7, [[#ref13|13]], 16, [[#ref23|23]], 24, 26, 27, 29, 30, 33, [[#ref34|34]]</sup> Some of these, like Benzo[a]pyrene, are often used as markers for anthropogenic combustion. |
| |
| === 3.5.3. Ordered List of MMO PAHs by Increasing Natural Abundance === | === 3.5.3. Ordered List of MMO PAHs by Increasing Natural Abundance === |
| |
| === 3.5.4. Insights and Implications for Natural Abundance === | === 3.5.4. Insights and Implications for Natural Abundance === |
| The concept of "natural abundance" for PAHs is nuanced because many of these compounds, while having natural origins, are also produced and released in much larger quantities by human activities. The ranking aims to reflect the relative significance of natural formation or release pathways compared to anthropogenic inputs for each PAH typically found in marine sediments. OSPAR's strategy, for instance, aims to achieve concentrations in the marine environment near natural background values for naturally occurring substances.[1], [2], [[#ref4|4]], [6] Understanding which PAHs have a substantial natural background is key to interpreting monitoring data and setting realistic environmental targets. | The concept of "natural abundance" for PAHs is nuanced because many of these compounds, while having natural origins, are also produced and released in much larger quantities by human activities. The ranking aims to reflect the relative significance of natural formation or release pathways compared to anthropogenic inputs for each PAH typically found in marine sediments. OSPAR's strategy, for instance, aims to achieve concentrations in the marine environment near natural background values for naturally occurring substances.<sup>1, 2, [[#ref4|4]], 6</sup> Understanding which PAHs have a substantial natural background is key to interpreting monitoring data and setting realistic environmental targets. |
| |
| Perylene is a standout compound due to its predominantly diagenetic origin in many aquatic sediments.[[#ref34|34]], [89], [90], [98], [109], [110] Its presence and concentration profile in sediment cores can provide insights into past environmental conditions and organic matter sources rather than solely indicating direct anthropogenic pollution like other PAHs. This unique characteristic means that high perylene concentrations do not necessarily equate to high anthropogenic impact in the same way they might for, say, Benzo[a]pyrene. | Perylene is a standout compound due to its predominantly diagenetic origin in many aquatic sediments.<sup>[[#ref34|34]], 89, 90, 98, 109, 110</sup> Its presence and concentration profile in sediment cores can provide insights into past environmental conditions and organic matter sources rather than solely indicating direct anthropogenic pollution like other PAHs. This unique characteristic means that high perylene concentrations do not necessarily equate to high anthropogenic impact in the same way they might for, say, Benzo[a]pyrene. |
| |
| Alkylated PAHs (C1-C3 Naphthalenes, C1-Phenanthrenes) are strongly indicative of petrogenic sources.[1], [2], [[#ref4|4]], [9], [17], [[#ref23|23]], [24], [28], [30] Crude oil is a natural substance, and natural petroleum seeps are a significant natural source of these alkylated compounds to the marine environment.[8] However, the widespread, high concentrations of alkylated PAHs often found in contaminated coastal and marine areas are typically the result of anthropogenic activities such as oil spills or chronic releases of uncombusted fuels and lubricants. The relative abundance of different alkylated homologues (e.g., C1-, C2-, C3-naphthalenes) versus their parent PAH (Naphthalene) is a critical diagnostic tool for distinguishing petrogenic sources from pyrogenic sources, with petrogenic sources generally showing a higher proportion of alkylated compounds.[1], [2], [[#ref4|4]], [24], [26], [30] | Alkylated PAHs (C1-C3 Naphthalenes, C1-Phenanthrenes) are strongly indicative of petrogenic sources.<sup>1, 2, [[#ref4|4]], 9, 17, [[#ref23|23]], 24, 28, 30</sup> Crude oil is a natural substance, and natural petroleum seeps are a significant natural source of these alkylated compounds to the marine environment.<sup>8</sup> However, the widespread, high concentrations of alkylated PAHs often found in contaminated coastal and marine areas are typically the result of anthropogenic activities such as oil spills or chronic releases of uncombusted fuels and lubricants. The relative abundance of different alkylated homologues (e.g., C1-, C2-, C3-naphthalenes) versus their parent PAH (Naphthalene) is a critical diagnostic tool for distinguishing petrogenic sources from pyrogenic sources, with petrogenic sources generally showing a higher proportion of alkylated compounds.<sup>1, 2, [[#ref4|4]], 24, 26, 30</sup> |
| |
| Most HMW parent PAHs (e.g., Benzo[a]pyrene, Indeno[1,2,3-cd]pyrene, Dibenz[a,h]anthracene) are primarily formed during combustion processes. While natural fires (forest fires, volcanic activity) contribute to their presence in the environment, the levels found in industrialized and urbanized coastal zones are usually dominated by anthropogenic combustion of fossil fuels and biomass.[1], [2], [7], [[#ref13|13]], [16], [[#ref23|23]], [24], [26], [27], [29], [30], [33], [[#ref34|34]] For these compounds, the natural background is often significantly lower than concentrations observed in impacted areas, making them strong indicators of anthropogenic pollution. | Most HMW parent PAHs (e.g., Benzo[a]pyrene, Indeno[1,2,3-cd]pyrene, Dibenz[a,h]anthracene) are primarily formed during combustion processes. While natural fires (forest fires, volcanic activity) contribute to their presence in the environment, the levels found in industrialized and urbanized coastal zones are usually dominated by anthropogenic combustion of fossil fuels and biomass.<sup>1, 2, 7, [[#ref13|13]], 16, [[#ref23|23]], 24, 26, 27, 29, 30, 33, [[#ref34|34]]</sup> For these compounds, the natural background is often significantly lower than concentrations observed in impacted areas, making them strong indicators of anthropogenic pollution. |
| |
| ===== 4. Integrated Discussion and Implications ===== | ===== 4. Integrated Discussion and Implications ===== |
| |
| * **Number of Aromatic Rings:** As the number of fused aromatic rings increases (i.e., moving from LMW to HMW PAHs): | * **Number of Aromatic Rings:** As the number of fused aromatic rings increases (i.e., moving from LMW to HMW PAHs): |
| * **Toxicity (Carcinogenic):** Generally increases, with many 4- to 6-ring PAHs having higher TEFs.[[#ref13|13]], [16] | * **Toxicity (Carcinogenic):** Generally increases, with many 4- to 6-ring PAHs having higher TEFs.<sup>[[#ref13|13]], 16</sup> |
| * **Persistence:** Significantly increases due to greater chemical stability and resistance to microbial degradation.[7], [8], [[#ref15|15]] | * **Persistence:** Significantly increases due to greater chemical stability and resistance to microbial degradation.<sup>7, 8, [[#ref15|15]]</sup> |
| * **Bioaccumulation Potential (Log K<sub>ow</sub>/BCF):** Increases due to greater hydrophobicity and lipophilicity.[[#ref112|112]], [[#ref113|113]], [114], [118] | * **Bioaccumulation Potential (Log K<sub>ow</sub>/BCF):** Increases due to greater hydrophobicity and lipophilicity.<sup>[[#ref112|112]], [[#ref113|113]], 114, 118</sup> |
| * **Water Solubility:** Decreases sharply, which in turn affects bioavailability from the dissolved phase.[1], [2], [27], [[#ref34|34]] | * **Water Solubility:** Decreases sharply, which in turn affects bioavailability from the dissolved phase.<sup>1, 2, 27, [[#ref34|34]]</sup> |
| * **Volatility:** Decreases, reducing atmospheric transport in the gas phase but increasing association with particulate matter. | * **Volatility:** Decreases, reducing atmospheric transport in the gas phase but increasing association with particulate matter. |
| |
| * **Alkylation:** The addition of alkyl groups (e.g., methyl, ethyl) to a parent PAH structure typically: | * **Alkylation:** The addition of alkyl groups (e.g., methyl, ethyl) to a parent PAH structure typically: |
| * **Persistence:** Often increases resistance to degradation compared to the parent compound.[9], [17] | * **Persistence:** Often increases resistance to degradation compared to the parent compound.<sup>9, 17</sup> |
| * **Bioaccumulation Potential (Log K<sub>ow</sub>):** Increases hydrophobicity and thus Log K<sub>ow</sub>, suggesting higher intrinsic bioaccumulation potential.[119], [124] | * **Bioaccumulation Potential (Log K<sub>ow</sub>):** Increases hydrophobicity and thus Log K<sub>ow</sub>, suggesting higher intrinsic bioaccumulation potential.<sup>119, 124</sup> |
| * **Toxicity:** The effect of alkylation on toxicity is complex and can vary. Some alkylated PAHs may exhibit increased toxicity or different toxic mechanisms compared to their parent compounds.[[#ref4|4]], [17] For carcinogenic TEFs, alkylated PAHs are often conservatively assumed to have similar or slightly lower potency than their parent if specific data are lacking.[[#ref14|14]] | * **Toxicity:** The effect of alkylation on toxicity is complex and can vary. Some alkylated PAHs may exhibit increased toxicity or different toxic mechanisms compared to their parent compounds.<sup>[[#ref4|4]], 17</sup> For carcinogenic TEFs, alkylated PAHs are often conservatively assumed to have similar or slightly lower potency than their parent if specific data are lacking.<sup>[[#ref14|14]]</sup> |
| * **Source Indication:** The presence and relative abundance of alkylated PAHs are key indicators of petrogenic (petroleum-derived) contamination, as crude oils are rich in these compounds, whereas combustion sources tend to produce predominantly parent PAHs.[1], [2], [[#ref4|4]], [9], [17], [[#ref23|23]], [24], [28], [30], [[#ref40|40]] | * **Source Indication:** The presence and relative abundance of alkylated PAHs are key indicators of petrogenic (petroleum-derived) contamination, as crude oils are rich in these compounds, whereas combustion sources tend to produce predominantly parent PAHs.<sup>1, 2, [[#ref4|4]], 9, 17, [[#ref23|23]], 24, 28, 30, [[#ref40|40]]</sup> |
| |
| ==== 4.3. Considerations for Environmental Risk Assessment and Management ==== | ==== 4.3. Considerations for Environmental Risk Assessment and Management ==== |
| |
| * **Prioritization:** PAHs that exhibit a combination of high toxicity, high persistence, and high bioaccumulation potential (e.g., Dibenz[a,h]anthracene, Benzo[a]pyrene, and other carcinogenic HMW PAHs) should be prioritized in monitoring programs and risk management strategies. Their long residence time in sediments and ability to accumulate in biota pose significant long-term threats. | * **Prioritization:** PAHs that exhibit a combination of high toxicity, high persistence, and high bioaccumulation potential (e.g., Dibenz[a,h]anthracene, Benzo[a]pyrene, and other carcinogenic HMW PAHs) should be prioritized in monitoring programs and risk management strategies. Their long residence time in sediments and ability to accumulate in biota pose significant long-term threats. |
| * **Source Apportionment:** The inclusion of alkylated PAHs (C1-C3 Naphthalenes, C1-Phenanthrenes) in the MMO list is critical. Analyzing the full suite allows for more robust source apportionment, distinguishing between pyrogenic (combustion) and petrogenic (oil) inputs. This is vital for identifying pollution sources and implementing targeted control measures. For example, a high proportion of alkylated naphthalenes and phenanthrenes relative to their parent compounds would strongly suggest petroleum contamination.[1], [2], [[#ref4|4]], [24], [30] | * **Source Apportionment:** The inclusion of alkylated PAHs (C1-C3 Naphthalenes, C1-Phenanthrenes) in the MMO list is critical. Analyzing the full suite allows for more robust source apportionment, distinguishing between pyrogenic (combustion) and petrogenic (oil) inputs. This is vital for identifying pollution sources and implementing targeted control measures. For example, a high proportion of alkylated naphthalenes and phenanthrenes relative to their parent compounds would strongly suggest petroleum contamination.<sup>1, 2, [[#ref4|4]], 24, 30</sup> |
| * **Sediment Quality Guidelines (SQGs):** Understanding the varying toxicities (TEFs) and bioaccumulation potentials (BCFs) is essential when applying or developing SQGs. Generic SQGs based on total PAH concentrations can be misleading if the mixture composition and relative potencies of individual PAHs are not considered. The TEF approach provides a more refined method for assessing the carcinogenic risk of PAH mixtures.[53] | * **Sediment Quality Guidelines (SQGs):** Understanding the varying toxicities (TEFs) and bioaccumulation potentials (BCFs) is essential when applying or developing SQGs. Generic SQGs based on total PAH concentrations can be misleading if the mixture composition and relative potencies of individual PAHs are not considered. The TEF approach provides a more refined method for assessing the carcinogenic risk of PAH mixtures.<sup>53</sup> |
| * **Bioavailability Considerations:** Risk assessments must acknowledge that not all PAHs measured in bulk sediment are bioavailable.[[#ref31a|31a]]/[[#ref31b|31b]], [105], [106], [[#ref218|218]] Factors like organic carbon content, black carbon presence, and aging significantly modify bioavailability. Site-specific assessments may require more sophisticated approaches, such as equilibrium partitioning models or direct measurement of freely dissolved PAH concentrations in porewater, to better estimate actual exposure and risk.[[#ref31a|31a]]/[[#ref31b|31b]] | * **Bioavailability Considerations:** Risk assessments must acknowledge that not all PAHs measured in bulk sediment are bioavailable.<sup>[[#ref31a|31a]]/[[#ref31b|31b]], 105, 106, [[#ref218|218]]</sup> Factors like organic carbon content, black carbon presence, and aging significantly modify bioavailability. Site-specific assessments may require more sophisticated approaches, such as equilibrium partitioning models or direct measurement of freely dissolved PAH concentrations in porewater, to better estimate actual exposure and risk.<sup>[[#ref31a|31a]]/[[#ref31b|31b]]</sup> |
| * **Management of Alkylated PAHs:** Given their potential for increased persistence and abundance in petrogenic spills, specific attention should be paid to the alkylated PAHs on the MMO list. Their distinct environmental behavior warrants their individual consideration in risk assessments rather than solely relying on data for parent PAHs. | * **Management of Alkylated PAHs:** Given their potential for increased persistence and abundance in petrogenic spills, specific attention should be paid to the alkylated PAHs on the MMO list. Their distinct environmental behavior warrants their individual consideration in risk assessments rather than solely relying on data for parent PAHs. |
| |
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| <wrap #ref220>220. Vliz (279011.pdf) [[https://www.vliz.be/imisdocs/publications/279011.pdf|Vliz 279011.pdf]]</wrap> | <wrap #ref220>220. Vliz (279011.pdf) [[https://www.vliz.be/imisdocs/publications/279011.pdf|Vliz 279011.pdf]]</wrap> |
| | |
| <wrap #ref221>221. NTP NIEHS (polycyclicaromatichydrocarbons.pdf) [[https://ntp.niehs.nih.gov/sites/default/files/ntp/roc/content/profiles/polycyclicaromatichydrocarbons.pdf|NTP NIEHS PAHs]]</wrap> | <wrap #ref221>221. NTP NIEHS (polycyclicaromatichydrocarbons.pdf) [[https://ntp.niehs.nih.gov/sites/default/files/ntp/roc/content/profiles/polycyclicaromatichydrocarbons.pdf|NTP NIEHS PAHs]]</wrap> |
| |
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