The Marine Management Organisation (MMO) has specific requirements regarding the analysis of Polycyclic Aromatic Hydrocarbons (PAHs) in sediments, particularly for applications concerning the disposal of dredged material at sea. This document summarizes key information based on these requirements.

The Marine Management Organisation (MMO) requires the analysis of a specific suite of polycyclic aromatic hydrocarbons (PAHs) in sediments as part of applications for the disposal of dredged material at sea. These requirements align with international conventions, particularly the OSPAR (Oslo/Paris) Convention for the Protection of the Marine Environment of the North-East Atlantic.

While the precise number and list of PAHs for any specific project are finalised within the sediment sampling plan agreed with the MMO in consultation with the Centre for Environment, Fisheries and Aquaculture Science (Cefas), a standard set of PAHs is expected to be analysed.

The OSPAR guidelines, which the MMO adheres to, explicitly define a sum of nine specific PAHs (ΣPAH9) that must be assessed. These are:

• Anthracene
• Benzo[a]anthracene
• Benzo[ghi]perylene
• Benzo[a]pyrene
• Chrysene
• Fluoranthene
• Indeno[1,2,3-cd]pyrene
• Pyrene
• Phenanthrene

Although the OSPAR guidelines explicitly list these nine PAHs, it is common practice and often implicitly required to analyse for a broader suite, typically 16 PAHs, often referred to as the US EPA (Environmental Protection Agency) 16 priority PAHs. This more comprehensive analysis allows for a more thorough assessment of potential contamination and ensures that values for other OSPAR-referenced sums, such as ΣPAH16, can be calculated.

The 16 US EPA priority PAHs generally include:

• Naphthalene
• Acenaphthylene
• Acenaphthene
• Fluorene
• Phenanthrene
• Anthracene
• Fluoranthene
• Pyrene
• Benz[a]anthracene
• Chrysene
• Benzo[b]fluoranthene
• Benzo[k]fluoranthene
• Benzo[a]pyrene
• Indeno[1,2,3-cd]pyrene
• Dibenz[a,h]anthracene
• Benzo[ghi]perylene

Cefas, which provides scientific advice to the MMO, has also historically analysed a comprehensive list of PAHs in dredged materials.

The MMO's guidance on “Chemical determinands” for sediment sampling specifies PAHs as a standard group of chemicals requiring analysis. The results of these analyses are assessed against action levels, where available, to determine the suitability of the dredged material for disposal at sea. Applicants must agree on a sediment sampling plan with the MMO, which will confirm the specific analytical requirements, including the list of PAHs to be determined.

The Marine Management Organisation (MMO) lists a standard set of polycyclic aromatic hydrocarbons (PAHs) that are potentially required for sediment characterisation as part of marine licence applications. This list is detailed on the UK government's official guidance page, “Chemical determinands.”

The MMO's PAH chemical determinands are:

• Acenapthene
• Acenapthylene
• Anthracene
• Benz[a]anthracene
• Benzo[a]pyrene
• Benzo[b]fluoranthene
• Benzo[e]pyrene
• Benzo[g,h,i]perylene
• Benzo[k]fluoranthene
• C1-Naphthalenes (alkylated naphthalenes with one additional carbon atom)
• C1-Phenanthrenes (alkylated phenanthrenes/anthracenes with one additional carbon atom)
• C2-Naphthalenes (alkylated naphthalenes with two additional carbon atoms)
• C3-Naphthalenes (alkylated naphthalenes with three additional carbon atoms)
• Chrysene
• Fluoranthene
• Fluorene
• Indeno[123-c,d]pyrene
• Naphthalene
• Perylene
• Phenanthrene
• Pyrene
• Dibenz[a,h]anthracene

This list comprises 22 specific PAHs and groups of alkylated PAHs. The guidance also specifies the limits of detection and quantification for these determinands. It's important to note that while this is the standard set, the exact requirements for a specific project will be confirmed in the sediment sampling plan agreed with the MMO.

The Marine Management Organisation (MMO) requires the analysis of a specific list of 22 PAHs and alkylated PAH groups in sediments for several key reasons, all aimed at protecting the marine environment and ensuring consistent regulatory assessment for the disposal of dredged material at sea. These reasons include:

1. Environmental Significance (Toxicity, Persistence, and Bioaccumulation):
   1. Toxicity: Many PAHs on the list are known to be toxic, with some being carcinogenic (cancer-causing), mutagenic (causing genetic mutations), and/or teratogenic (causing birth defects) to marine organisms and potentially humans if they enter the food chain. Specific PAHs like Benzo[a]pyrene are well-known potent carcinogens.
   2. Persistence: PAHs can persist in marine sediments for long periods, resisting degradation. This longevity means they can pose a long-term risk to the marine ecosystem. Higher molecular weight PAHs, in particular, tend to be more persistent.
   3. Bioaccumulation: PAHs can accumulate in marine organisms. Hydrophobic PAHs, especially those with higher molecular weights, tend to adsorb to particulate matter and can be ingested by sediment-dwelling organisms, potentially being transferred up the food chain.

1. Source Identification and Comprehensive Characterisation:
   1. The list includes a range of PAHs, from lower molecular weight (e.g., Naphthalene and its alkylated forms) to higher molecular weight compounds (e.g., Benzo[g,h,i]perylene, Indeno[1,2,3-cd]pyrene).
   2. Crucially, it includes both parent PAHs (non-alkylated) and alkylated PAHs (e.g., C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, C1-Phenanthrenes). The relative proportions of these different types of PAHs can help indicate the source of the contamination:
      1. Petrogenic PAHs (originating from petroleum sources like crude oil or refined products) are often rich in alkylated PAHs and lower molecular weight parent PAHs.
      2. Pyrogenic PAHs (originating from the incomplete combustion of organic materials, such as fossil fuels, wood, or waste) are typically dominated by non-alkylated, higher molecular weight PAHs.
   3. Including compounds like Perylene, which can have both natural (diagenetic) and anthropogenic sources, adds to the comprehensiveness of the assessment.

1. Regulatory Consistency and Assessment against Standards:
   1. The MMO aims to ensure that sediment analysis data is consistent and comparable across different applications for disposal at sea. A standardised list of determinands is essential for this.
   2. The concentrations of these PAHs are assessed against Cefas Action Levels (where available) as part of a weight-of-evidence approach to determine the suitability of dredged material for sea disposal. Having a defined list allows for a clear framework for these regulatory decisions.

1. Alignment with International Obligations and Best Practice:
   1. Many of the PAHs on the list are recognized as priority pollutants by international bodies. For example, PAHs as a group are on the OSPAR (Oslo/Paris Convention) List of Chemicals for Priority Action due to their hazardous properties.
   2. The selection reflects a scientifically informed approach to monitoring common and hazardous PAHs found in marine environments, aligning with broader European and international monitoring strategies (e.g., requirements under the Water Framework Directive for certain PAHs).

1. Indicator Properties:
   1. Some PAHs, like Benzo[a]pyrene, are often used as markers for the presence and potential toxicity of the entire PAH mixture.
   2. The analysis of a broad suite provides a more complete picture of the overall PAH contamination burden in the sediment.

In summary, the MMO's requirement to analyse these 22 PAHs is driven by the need to comprehensively assess the potential environmental risks associated with dredged material disposal, understand the sources of contamination, ensure regulatory consistency, and meet national and international commitments for protecting the marine environment.

Ordering the 22 Polycyclic Aromatic Hydrocarbons (PAHs) required for analysis by the Marine Management Organisation (MMO) by their precise order of increasing risk to the marine environment is a complex task. “Risk” is not a single, easily quantifiable value but rather a function of several factors, including:

• Toxicity
• Persistence
• Bioaccumulation Potential
• Bioavailability
• Concentration

However, we can provide a general, indicative grouping of these PAHs from typically lower to higher concern, primarily using carcinogenic potential as a key differentiator for higher risk categories, while also considering persistence and molecular weight. This ranking is a simplification and should be interpreted with caution, as all listed PAHs are of concern to the MMO.

It's important to note that even “lower risk” PAHs can be harmful at high concentrations or to specific sensitive species. Alkylated PAHs are groups of compounds, and their properties can vary.

• Group 1: Generally Considered Lower Risk (especially regarding carcinogenicity; may still pose acute toxicity risks, particularly at high concentrations)

These are often Lower Molecular Weight (LMW) PAHs (2-3 rings) or PAHs with low carcinogenic potency according to common Toxic Equivalency Factor (TEF) schemes. LMW PAHs can be more water-soluble and cause acute toxicity.

1. Naphthalene
2. C1-Naphthalenes
3. C2-Naphthalenes
4. C3-Naphthalenes
5. Acenaphthylene
6. Acenaphthene
7. Fluorene
8. Phenanthrene
9. C1-Phenanthrenes (and anthracenes)
10. Anthracene
11. Perylene (Often has natural sources too, generally low toxicity compared to potent carcinogens)
12. Fluoranthene (Low carcinogenic TEF, but can have other toxic effects)
13. Pyrene (Low carcinogenic TEF, but can have other toxic effects)
14. Benzo[e]pyrene (Generally considered to have low or no carcinogenic TEF)

• Group 2: Moderate or Variable Concern

These PAHs may have some carcinogenic potential (moderate TEFs), or be notably persistent and bioaccumulative.

1. Chrysene (TEF varies, can be significant; persistent)
2. Benz[a]anthracene (Recognised carcinogen, moderate TEF)
3. Benzo[g,h,i]perylene (High Molecular Weight (HMW) PAH, very persistent and a marker of pyrogenic sources, but usually assigned a low/zero carcinogenic TEF)

• Group 3: Generally Considered Higher Risk (primarily due to higher carcinogenic potency, persistence, and bioaccumulation)

These are typically High Molecular Weight (HMW) PAHs (4-6 rings) that are known or probable human carcinogens and have significant TEF values relative to Benzo[a]pyrene.

1. Benzo[k]fluoranthene (Recognised carcinogen, significant TEF)
2. Benzo[b]fluoranthene (Recognised carcinogen, significant TEF)
3. Indeno[1,2,3-cd]pyrene (Recognised carcinogen, significant TEF, persistent)
4. Benzo[a]pyrene (Reference compound for PAH carcinogenicity, high TEF of 1, known human carcinogen, persistent, bioaccumulative)
5. Dibenz[a,h]anthracene (Often has one of the highest TEF values, sometimes even higher than Benzo[a]pyrene; potent carcinogen, persistent)

• Alkylated PAHs: The groups C1, C2, C3-Naphthalenes and C1-Phenanthrenes represent multiple individual compounds. Alkylation can sometimes increase persistence and toxicity compared to the parent PAH, particularly for LMW PAHs. They are key indicators of petrogenic (oil-related) pollution.
• Mixtures: PAHs almost always occur as complex mixtures in the environment. The combined effect of these mixtures (synergistic, additive, or antagonistic) is a critical aspect of risk assessment that a simple ranking of individual compounds cannot capture.
• Acute vs. Chronic Effects: LMW PAHs, while often less carcinogenic, can be more acutely toxic to aquatic organisms than HMW PAHs, which tend to cause chronic effects like cancer.
• Site-Specific Conditions: The actual risk posed by these PAHs at a specific location depends on their concentrations, the sediment characteristics, water conditions, and the local marine ecosystem.

The MMO's requirement to analyse all 22 of these PAHs allows for a comprehensive characterisation of sediment contamination, enabling a more informed assessment of the potential risks associated with the disposal of dredged material at sea, rather than implying that all 22 pose an identical level of risk.

Creating definitive, strictly ordered lists of the 22 PAHs required by the Marine Management Organisation (MMO) for increasing toxicity, persistence, bioaccumulation potential, bioavailability, and natural abundance is highly challenging. These properties are influenced by numerous factors. However, based on general scientific understanding, we can provide indicative groupings. The alkylated PAHs (e.g., C1-Naphthalenes) are groups of isomers, and their properties are generally considered based on the parent compound or lower alkylated forms.

The 22 PAHs referred to are: Acenapthene, Acenapthylene, Anthracene, Benz[a]anthracene, Benzo[a]pyrene, Benzo[b]fluoranthene, Benzo[e]pyrene, Benzo[g,h,i]perylene, Benzo[k]fluoranthene, C1-Naphthalenes, C1-Phenanthrenes (and/or anthracenes), C2-Naphthalenes, C3-Naphthalenes, Chrysene, Fluoranthene, Fluorene, Indeno[1,2,3-cd]pyrene, Naphthalene, Perylene, Phenanthrene, Pyrene, Dibenz[a,h]anthracene.

Persistence generally increases with molecular size and complexity.

• Lower Persistence (Relatively more degradable, volatile, or soluble):
  1. Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene
  2. C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, C1-Phenanthrenes
• Moderate Persistence:
  1. Fluoranthene, Pyrene
• Higher Persistence:
  1. Benz[a]anthracene, Chrysene, Benzo[e]pyrene
• Very High Persistence (Highly resistant to degradation):
  1. Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[a]pyrene, Indeno[1,2,3-cd]pyrene, Dibenz[a,h]anthracene, Benzo[g,h,i]perylene, Perylene

Bioaccumulation potential generally increases with Kow and molecular size.

• Lower Bioaccumulation Potential (Lower Kow):
  1. Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene
• Moderate Bioaccumulation Potential:
  1. C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, C1-Phenanthrenes
  2. Fluoranthene, Pyrene
• Higher Bioaccumulation Potential:
  1. Benz[a]anthracene, Chrysene, Benzo[e]pyrene
• Very High Bioaccumulation Potential (Higher Kow):
  1. Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[a]pyrene, Indeno[1,2,3-cd]pyrene, Dibenz[a,h]anthracene, Benzo[g,h,i]perylene, Perylene

Bioavailability from water is generally higher for more soluble PAHs. This list considers general potential for uptake from water or desorption.

• Lower Bioavailability (Tend to be strongly bound to sediment, low water solubility):
  1. Indeno[1,2,3-cd]pyrene, Dibenz[a,h]anthracene, Benzo[g,h,i]perylene, Perylene
  2. Benzo[a]pyrene, Benzo[b]fluoranthene, Benzo[k]fluoranthene
• Moderate-Low Bioavailability:
  1. Benzo[e]pyrene, Chrysene, Benz[a]anthracene
• Moderate-High Bioavailability:
  1. Fluoranthene, Pyrene
  2. C1-Phenanthrenes, C3-Naphthalenes
• Higher Bioavailability (Higher water solubility, weaker sediment binding):
  1. Acenaphthene, Fluorene, Phenanthrene, Anthracene
  2. C1-Naphthalenes, C2-Naphthalenes, Acenaphthylene, Naphthalene

This ranking considers a combination of acute aquatic toxicity and carcinogenic/chronic toxicity.

• Relatively Lower Overall Toxic Concern (but not harmless):
  1. Perylene
  2. Benzo[e]pyrene
• Primarily Acute Toxicants / Lower Carcinogenic Concern (LMW PAHs):
  1. Naphthalene, C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes
  2. Acenaphthylene, Acenaphthene, Fluorene
  3. Phenanthrene, C1-Phenanthrenes, Anthracene
  4. Fluoranthene, Pyrene
• Increasing Carcinogenic and Chronic Toxicity Concern (HMW PAHs):
  1. Benzo[g,h,i]perylene
  2. Chrysene
  3. Benz[a]anthracene
  4. Benzo[k]fluoranthene
  5. Benzo[b]fluoranthene
  6. Indeno[1,2,3-cd]pyrene
  7. Benzo[a]pyrene
  8. Dibenz[a,h]anthracene

“Natural abundance” here refers to contributions from sources other than direct anthropogenic industrial discharges, such as natural geological processes or natural combustion events.

• Lowest Natural Abundance (Predominantly from anthropogenic combustion/industrial sources):
  1. Dibenz[a,h]anthracene
  2. Benzo[a]pyrene
  3. Indeno[1,2,3-cd]pyrene
  4. Benzo[b]fluoranthene
  5. Benzo[k]fluoranthene
  6. Benzo[g,h,i]perylene
  7. Benz[a]anthracene
  8. Chrysene
  9. Benzo[e]pyrene
• Low to Moderate Natural Input (From broader combustion sources including natural fires, some geological):
  1. Fluoranthene
  2. Pyrene
• Moderate Natural Input (Can have sources from natural seeps, biomass combustion, some diagenesis):
  1. Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene
  2. C1-Naphthalenes, C2-Naphthalenes, C3-Naphthalenes, C1-Phenanthrenes
• Highest Potential for Natural Contribution Among this List:
  1. Perylene

Important Disclaimer: These lists provide generalised orderings. The actual properties and effects of these PAHs can vary significantly. For regulatory purposes and detailed risk assessment, specific data and context are crucial.

Identifying the source of a mixture of the 22 Polycyclic Aromatic Hydrocarbons (PAHs) required by the Marine Management Organisation (MMO) involves “fingerprinting” techniques that compare the specific composition of PAHs in a sample to known source profiles. The comprehensive list of 22 PAHs provides a robust dataset for these methods.

Here are some of the best methods:

1. PAH Ratios (Diagnostic Ratios):
   1. Principle: Relies on the fact that certain PAHs are formed in different proportions depending on the source. Ratios of specific PAH isomers or related compounds are calculated and compared to established ranges.
   2. Commonly Used Ratios:
      1. Low Molecular Weight (LMW) PAHs / High Molecular Weight (HMW) PAHs: Petrogenic sources tend to have higher LMW proportions; pyrogenic sources are HMW dominated.
      2. Anthracene / (Anthracene + Phenanthrene) (ANT/[ANT+PHE]): Values <0.1 often suggest petrogenic sources, while values >0.1 suggest pyrogenic sources.
      3. Fluoranthene / (Fluoranthene + Pyrene) (FLA/[FLA+PYR]): Helps distinguish petroleum (<0.4), petroleum combustion (0.4-0.5), and biomass/coal combustion (>0.5).
      4. Benz[a]anthracene / (Benz[a]anthracene + Chrysene) (BaA/[BaA+CHR]): Values <0.2 may indicate petrogenic; 0.2-0.35 mixed/petroleum combustion; >0.35 combustion.
      5. Indeno[1,2,3-cd]pyrene / (Indeno[1,2,3-cd]pyrene + Benzo[g,h,i]perylene) (IcdP/[IcdP+BghiP]): Can help differentiate petroleum combustion (0.2-0.5) from grass/wood/coal combustion (>0.5).
   3. Benefit of the 22 PAH list: Provides all necessary parent PAHs for these ratios.

1. Alkylated vs. Parent PAH Profiles:
   1. Principle: Petrogenic PAHs are rich in alkylated homologues. Pyrogenic PAHs are dominated by parent (non-alkylated) PAHs.
   2. Application: The MMO's list includes C1, C2, C3-Naphthalenes and C1-Phenanthrenes.
      1. High proportions of alkylated PAHs relative to parent PAHs strongly suggest petrogenic contamination.
      2. Low proportions of alkylated PAHs point to pyrogenic sources.
   3. Benefit of the 22 PAH list: Explicit inclusion of alkylated series is crucial.

1. Homologue and Isomer Patterns:
   1. Principle: Detailed examination of the distribution of specific isomers within an alkylated series or the relative abundance of different parent PAHs can provide further clues.
   2. Benefit of the 22 PAH list: Comprehensive analysis allows detailed pattern recognition.

1. Multivariate Statistical Analysis:
   1. Principle: Techniques like Principal Component Analysis (PCA), Positive Matrix Factorization (PMF), or cluster analysis can be applied to the full dataset of 22 PAH concentrations.
   2. Application: PCA can group samples with similar PAH profiles. PMF can attempt to quantitatively apportion source contributions.
   3. Benefit of the 22 PAH list: More comprehensive data leads to more robust statistical analyses.

1. Comparison with Source Libraries:
   1. Principle: The PAH profile of the unknown sample is compared to a library of PAH fingerprints from known specific sources.
   2. Application: Requires access to a relevant source library.

• Weathering: Environmental processes can alter PAH profiles over time, making source identification challenging.
• Mixed Sources: Sediments often contain PAHs from multiple sources, complicating interpretation.
• Regional Variability: PAH fingerprints for a source type can vary regionally.
• Analytical Accuracy: Accurate quantification of individual PAHs is critical.

By using a combination of these methods, leveraging the detailed information from the analysis of all 22 MMO-required PAHs, environmental scientists can make more robust identifications of PAH contamination sources.