Etat et tendances des teneurs en hydrocarbures aromatiques polycycliques (HAP) dans les sédiments

D8 - Teneurs en contaminants

D8.1 - Teneurs en contaminants

Message clé:

Les teneurs moyennes en hydrocarbures aromatiques polycycliques (HAP) dans les sédiments sont inférieures aux niveaux susceptibles de nuire aux espèces marines dans les zones évaluées mais sont supérieures aux teneurs ambiantes naturelles dans quatre des six zones évaluées. Les teneurs moyennes ne révèlent aucune modification significative statistiquement dans quatre zones et diminuent dans deux.

Zone Évaluée

Récapitulatif Imprimable

Contexte

Les hydrocarbures aromatiques polycycliques (HAP) sont des composants naturels du charbon et du pétrole et sont également produits lors de la combustion de combustible fossile et de matière organique. Les HAP peuvent également provenir de processus naturels tels que les incendies de forêt. Les retombées atmosphériques, les eaux de ruissellement des routes, les rejets industriels et les déversements d’hydrocarbures (indicateur commun des déversements d’hydrocarbures) sont responsables de la pénétration des HAP dans le milieu marin. Les HAP présents dans le milieu marin aboutissent souvent dans les sédiments marins, ou ils peuvent être piégés dans des couches inférieures à moins que les sédiments ne soient perturbés. On a démontré qu’il existe des rapports entre l’incidence de certaines maladies du poisson plat et les teneurs en HAP dans les sédiments qui les hébergent et les nourrissent.

La Stratégie OSPAR substances dangereuses a pour objectif, en dernier ressort, de parvenir à des teneurs dans l’environnement marin qui soient proches des teneurs ambiantes dans le cas des substances présentes à l'état naturel et proches de zéro dans celui des substances de synthèse. Des analyses des teneurs en HAP dans les sédiments et les mollusques et crustacés sont notifiées dans le cadre du Programme coordonné de surveillance de l’environnement OSPAR (CEMP) étant donné leur persistance dans le milieu marin, leur potentiel de bioaccumulation et leur toxicité. La surveillance des HAP dans les sédiments a commencé dans l’ensemble de la zone maritime OSPAR entre 1995 et 1999.

Plateforme pétrolière – Les hydrocarbures aromatiques polycycliques (HAP) peuvent pénétrer le milieu marin par l’intermédiaire des rejets industriels et des déversements d’hydrocarbures © Craig Robinson/Marine Scotland Science

Benne à sédiments– Les hydrocarbures aromatiques polycycliques (HAP) peuvent s’accumuler dans les sédiments marins © Marine Scotland Science

Polycyclic aromatic hydrocarbons (PAHs) are hydrocarbons composed of two or more fused aromatic rings, encompassing both parent (non-alkylated) compounds and alkylated homologues. Although PAHs can be produced through natural processes, they also arise from anthropogenic sources. Incomplete combustion processes are a major source of PAHs, but they can also be of petrogenic origin (crude oils or refinery products). PAHs of petrogenic origin include mainly alkylated, 2-ring and 3-ring PAHs formed as a result of diagenetic processes, whereas PAHs from pyrolytic sources mainly comprise the heavier, parent (non-alkylated) PAHs. Assessment of the PAH profile, including PAH ratios such as the phenanthrene / anthracene ratio or the fluoranthene / pyrene ratio can give an indication of the source of PAHs.

PAHs are of concern due to their persistence, potential to bioaccumulate and toxicity. They are therefore included on the OSPAR List of Chemicals for Priority Action. The analyses of PAHs in both sediment and shellfish are reported in the OSPAR Coordinated Environment Monitoring Programme (CEMP).

PAH properties will vary considerably depending on the number of rings. There are marked differences in the behaviour of PAHs in the aquatic environment between the low molecular weight compounds (e.g. naphthalene) and the high molecular weight compounds (e.g. benzo[g,h,i]perylene) as a consequence of their differing physical-chemical properties. The low molecular weight compounds are water soluble; whereas the high molecular weight compounds are relatively insoluble and hydrophobic, and can attach to both organic and inorganic particulates within the water column. PAHs derived from combustion sources may be deposited directly to the marine environment already adsorbed to atmospheric particulates, such as soot.

PAHs can enter the marine environment through atmospheric deposition, run-off, industrial discharges and as a result of oil spills. Sediment will act as a sink for PAHs in the marine environment.

PAHs are also controlled by other international instruments, for example the United Nations Economic Commission for Europe Convention on Long-Range Transboundary Air Pollution (directed by the United Nations Economic Commission for Europe. This obliges its member countries to reduce their emissions of persistent organic pollutants such as PAHs with the ultimate objective of eliminating discharges and emissions.

In assessing polycyclic aromatic hydrocarbons (PAHs) both ‘relative’ and ‘absolute’ aspects have been analysed:

•   ‘Trend assessment’ or spatial distribution assessment to focus on relative differences and changes on spatial and temporal scales – provides information about the rates of change and whether PAH contamination is widespread or confined to specific locations; and

•   ‘Status assessment’ of the significance of the (risk of) pollution, defined as the status where PAHs are at a hazardous level, usually requires assessment criteria that take account of the possible severity of the impacts and hence require criteria that take account of the natural conditions (background concentrations) and ecotoxicology of the contaminants. For example, Environmental Assessment Criteria (EAC) are tools in this type of assessment.

OSPAR has clarified that in assessing the Co-ordinated Environmental Monitoring Programme (CEMP) data the primary assessment value used in the assessment of PAH concentrations in sediment and biota “corresponds to the achievement, or failure to achieve, statutory targets or policy objectives for contaminants in these matrices” (OSPAR, 2009). This set of assessment criteria was specifically compiled for the assessment of CEMP monitoring data on hazardous substances contributing to the Quality Status Report (QSR) 2010. The use of this set was considered an interim solution for the purposes of the QSR 2010 until more appropriate approaches to defining assessment criteria could be agreed on and implemented. These criteria have also been used in the annually recurring CEMP assessments since 2010 and will be used until OSPAR adopts improved assessment criteria and subject to the conditions set out in the agreement.

Temporal trends in PAH concentrations in sediment are presented. Two assessment criteria are used to assess PAH concentrations in sediment: Background Assessment Concentrations (BACs) and United States Environmental Protection Agency (EPA) sediment quality guidelines; Effects Range-Low (ERL).

OSPAR IA 2017 Indicator Assessment values are not to be considered as equivalent to proposed European Union Marine Strategy Framework Directive (MSFD) criteria threshold values. However, they can be used for the purposes of their MSFD obligations by those Contracting Parties that wish to do so.

Provenance and limitations of BACs

Background assessment concentrations (BACs) were developed by OSPAR for testing whether measured concentrations are near natural background levels for naturally occurring substances and close to zero for man-made substances, the ultimate aim of the OSPAR Hazardous Substances Strategy. Mean concentrations significantly below the BAC are said to be near natural background concentrations. BACs are statistical tools defined in relation to the background concentrations or low concentrations, which enable statistical testing of whether observed concentrations could be considered to be near natural background concentrations.

Background concentrations (BCs) are assessment tools intended to represent the concentrations of hazardous substances that would be expected in the North-East Atlantic if certain industrial developments had not happened. They represent the concentrations of those substances at ‘remote’ sites, or in ‘pristine’ conditions based on contemporary or historical data respectively, in the absence of significant mineralisation and / or oceanographic influences. In this way, they relate to the background values referred to in the OSPAR Hazardous Substances Strategy. BCs for man-made substances should be regarded as zero. It is recognised that natural processes such as geological variability or upwelling of oceanic waters near the coast may lead to significant variations in background concentrations of contaminants, for example trace metals. The natural variability of background concentrations should be taken into account in the interpretation of CEMP data, and local conditions should be taken into account when assessing the significance of any exceedance.

Low concentrations (LCs) are values used to assist the derivation of BACs where there have been difficulties in assembling a dataset on concentrations in remote or pristine areas from which to derive BCs. LCs have been prepared by the International Council for the Exploration of the Sea on the basis of datasets from areas that could generally be considered remote but which could not be guaranteed to be free from influence from long-range atmospheric transport of contaminants. LCs have also been used to assess concentrations in sediments from Spain due to the specific bulk composition of sediments from the coasts of the Iberian Peninsula. It is recognised that natural background concentrations may be lower than the LCs and that they may not be directly applicable across the entire Maritime Area.

BACs are calculated according to the method set out in Section 4 of the CEMP Assessment Manual (OSPAR, 2008). The outcome of this method is that, on the basis of what is known about variability in observations, there is a 90% probability that the observed mean concentration will be below the BAC when the true mean concentration is at the BC. Where this is the case, the true concentrations can be regarded as ’near background’ (for naturally occurring substances) or ’close to zero’ (for man-made substances).

BACs are calculated on the basis of variability within the CEMP dataset currently available through databases held by the ICES Data Centre and will be refined at the working level by the relevant assessment group as further CEMP monitoring data are collected.

Provenance and limitations of ERLs

Because OSPAR has not yet established Environmental Assessment Criteria (EACs) for PAHs in sediment, an alternative means of assessment is required. ‘Effects range’ values were developed by the United States Environmental Protection Agency (EPA) as sediment quality guidelines for assessing the ecological significance of contaminant concentrations in sediment to protect against the potential for adverse biological effects on organisms. Concentrations below the Effects Range-Low (ERL) level rarely cause adverse effects in marine organisms.

The ERL value is defined as the lower tenth percentile of the data set of concentrations in sediments which were associated with biological effects. Adverse effects on organisms are rarely observed when concentrations fall below the ERL value, and the ERL therefore has some parallels with the philosophy underlying the OSPAR EACs and the Environmental Quality Standards (EQSs) of the European Union Water Framework Directive. The procedure by which ERL criteria are derived is very different from the methods used to derive EACs and EQSs, and so precise equivalence between the two sets of criteria should not be expected. ERL values are to be used in sediment assessments of PAHs as an interim solution where recommended EACs are not available.

Assessment methods

For each PAH compound at each monitoring site, the time series of concentration measurements was assessed for temporal trends and status using the methods described in the contaminants online assessment tool (http://dome.ices.dk/osparmime2016/main.html). The results from these individual time series were then synthesised at the assessment area scale in a series of meta-analyses.

For temporal trends, those monitoring sites that were representative of general conditions were considered and those monitoring sites impacted due to a point source and baseline monitoring sites where temporal trends would not be expected were excluded. Analysis was also restricted to assessment areas where there were at least three monitoring sites with trend information and where those monitoring sites had reasonable geographic spread.

The temporal trend for each PAH compound at each monitoring site was summarised by the estimated annual change in log concentration, with its associated standard error. The annual change in log concentration was then modelled by a linear mixed model with a fixed effect:

            ~ OSPAR contaminants assessment area

and random effects:

            ~ compound + compound: OSPAR contaminants assessment area + monitoring site + compound: monitoring site + within-series variation

The choice of fixed and random effects was motivated by the assumption that the PAH compounds would have broadly similar temporal trends, since they have similar sources. Thus, the fixed effect measures the common temporal trend in PAH compounds in each assessment area and the random effects measure variation in trends:

  • between compounds common across contaminants assessment area (compound);
  • between compounds within contaminants assessment area (compound: contaminants assessment area);
  • between monitoring sites common across compounds (monitoring site); and
  • residual variation (compound: monitoring site + within-series variation).

There are two residual terms. Within-series variation is the variation associated with the estimate of the temporal trend from the individual time series and is assumed known (and given by the square of the standard error). Compound: monitoring site allows for any additional residual variation.

Evidence of temporal trends in PAH concentration at the assessment area scale was then assessed by plotting the estimated fixed effects with point-wise 95% confidence intervals. Differences between compounds were explored by plotting the predicted trend for each compound and for each compound / assessment area combination with point-wise 95% confidence intervals.

Similar analyses explored status at the assessment area. Two summary measures were considered: the log ratio of the fitted concentration in the last monitoring year to the ERL; and the log ratio of the fitted concentration in the last monitoring year to the BAC. Baseline monitoring sites were also included in these analyses.

Finally, concentration profiles across compounds at the assessment area scale were explored using the fitted log concentration in the last monitoring year.

BACs and / or ERLs are available for the PAHs shown in Table a.

Table a: Background Assessment Concentrations (BACs) and Effects-Range Low (ERLs) for polycyclic aromatic hydrocarbons (PAHs) in sediment. Dw, dry weight
Abbreviation BAC (μg/kg dw) BAC (μg/kg dw) ERL (μg/kg dw)
All assessment areas except Iberian Sea and Gulf of Cadiz Iberian Sea and Gulf of Cadiz All OSPAR assessment areas
Naphthalene 8 160
Phenanthrene PA 32 7.3 240
Anthracene ANT 5 1.8 85
Dibenzothiophene 190
Fluoranthene FLU 39 14.4 600
Pyrene PYR 24 11.3 665
Benz[a]anthracene BAA 16 7.1 261
Chrysene (including triphenylene) CHR 20 8.0 384
Benzo[a]pyrene BAP 30 8.2 430
Benzo[g,h,i]perylene BGHIP 80 6.9 85
Indeno[123-c,d]pyrene ICDP 103 8.3 240

Table a notes:

  • BACs are normalised to 2.5% organic carbon in all assessment areas except the Iberian Sea and Gulf of Cadiz, where BACs are not normalised.

The number of time series used in each OSPAR region and assessment area is shown in Table b.

Differences in methodology used for the IA 2017 compared to the QSR 2010

For the IA 2017, a meta-analysis is used to synthesise the individual time series results and provide an assessment of status and temporal trend at the assessment area level. Meta-analyses take into account both the estimate of status or temporal trend in each time series and the uncertainty in that estimate. They provide a more objective regional assessment than was possible in the QSR 2010, where a simple tabulation of the trend and status at each monitoring site was presented.

Résultats

Les teneurs en hydrocarbures aromatiques polycycliques (HAP) ont été mesurées dans les échantillons de sédiments prélevés entre 1995 et 2015 dans les sites de surveillance dans la plus grande partie de la mer du Nord au sens large, des mers Celtiques, du golfe de Gascogne et de la côte ibérique (Figure 1), à des fréquences allant de tous les ans à tous les cinq ans.

Le nombre des sites de surveillance varie grandement d’une zone d’évaluation des contaminants OSPAR à l’autre, la mer du Nord au sens large en possédant le plus. Seules les zones d’évaluation possédant au moins trois sites de surveillance et une répartition géographique raisonnable figurent dans l’évaluation de l’état et des tendances temporelles.

Figure 1: Sites de surveillance utilisés pour l’évaluation des teneurs en HAP dans les sédiments par zone d’évaluation des contaminants OSPAR (lignes blanches)

déterminés selon des principes hydro géographiques et des connaissances d’expert plutôt que des limites internes OSPAR

Figure 2: La teneur moyenne en HAP dans les sédiments dans chaque zone d’évaluation des contaminants OSPAR relative à la gamme de concentrations occasionnellement associées à des effets toxiques (ERL) (avec des limites de confiance supérieures de 95%),

lorsque la valeur 1 signifie que la teneur moyenne est égale à l’ERL. Bleu: la teneur moyenne est nettement inférieure statistiquement (p <0,05) à la teneur ambiante d’évaluation (BAC) et l’ERL. Vert: la teneur moyenne est nettement inférieure statistiquement à l’ERL mais pas nettement inférieure statistiquement à la BAC

Figure 3: Modification du pourcentage annuel des teneurs en HAP dans chaque zone d’évaluation des contaminants OSPAR.

Tendances temporelles nettement à la baisse statistiquement (p <0,05) (triangle inversé), aucune modification nette (p <0,05) (cercle). Limites de confiance de 95% (lignes)

Les teneurs en HAP ont été comparées par rapport à deux critères d’évaluation: les teneurs ambiantes d’évaluation OSPAR (BAC) et la gamme de concentrations occasionnellement associées à des effets toxiques (ERL) de l'Agence américaine pour la protection de l'environnement. On relève rarement des effets négatifs sur les organismes marins lorsque les teneurs sont inférieures à la valeur de l’ERL.

Les teneurs moyennes en HAP dans les sédiments sont nettement inférieures statistiquement à l’ERL dans tous les contaminants des zones d’évaluation (Figure 2). Des effets biologiques négatifs sur les espèces marines sont donc peu probables. Les teneurs les plus basses se trouvent dans les sédiments du golfe de Cadix et des côtes ouest irlandaise et écossaise et sont au niveau ambiant (c’est-à-dire nettement inférieures statistiquement à la BAC). Dans les quatre autres zones d’évaluation les teneurs moyennes sont inférieures à l’ERL mais pas nettement inférieures statistiquement aux BAC.

Les tendances temporelles des teneurs en HAP dans les sédiments ont été évaluées pour la période allant de la date de surveillance la plus ancienne (1995-1999) et 2015. Les HAP dans les sédiments ont été évalués dans six zones lorsque des données étaient disponibles pour cinq ans au moins (Figure 3). Les teneurs en HAP diminuent dans le golfe de Cadix et la Manche. Les teneurs relevées dans les quatre autres zones d’évaluation ne révèlent aucune tendance significative statistiquement.

La méthodologie d’évaluation et d’échantillonnage et les données utilisées inspirent une confiance élevée.

Regional Assessment Results

Polycyclic aromatic hydrocarbon (PAH) concentrations are measured in sediment samples taken annually (or every few years) from monitoring sites throughout much of the Greater North Sea, Celtic Seas, and Bay of Biscay and Iberian coast (Figure 3). The number of monitoring sites varies widely between assessment areas, with the Greater North Sea having the most. Only assessment areas with at least three monitoring sites and a reasonable geographic spread were included in the assessment of status and temporal trends (Table b). All monitoring sites in the Iberian Sea were classed as impacted (close to a point source) and therefore were not included in the area assessments of status and temporal trends.

PAH concentrations were compared against two assessment criteria: the OSPAR Background Assessment Concentration (BAC) and the United States Environmental Protection Effects Range-Low (ERL). Mean PAH concentrations (normalised to organic carbon in the Greater North Sea and Celtic Seas) relative to the BAC for each assessment area are shown in Figure a. Mean PAH concentrations in sediment were lowest in the Gulf of Cadiz and in the Irish and Scottish West Coast sediments. Concentrations were statistically significantly below the BACs for all individual PAHs in the Gulf of Cadiz and for six of the nine PAH compounds in the Irish and Scottish West Coast. Concentrations were also statistically significantly below BACs for two individual PAHs in the English Channel and Southern North Sea. The Irish Sea and Northern North Sea concentrations are not statistically significantly below the BACs for any PAHs.

Figure a: Mean PAH concentration in sediment in each OSPAR contaminants assessment area, relative to the background assessment concentration (BAC) (with 95% upper confidence limits)

Value of 1 means that the mean concentration equals the BAC. Blue, mean concentration is statistically significantly (p <0.05) below the BAC. Green, mean concentration is statistically significantly below the Effects Range-Low (ERL), but not significantly below the ERL. Orange, there is no ERL and the mean concentration is not significantly below the BAC. ICDP, indeno[123-cd]pyrene; BGHIP, benzo[ghi]perylene; BAP, benzo[a]pyrene; CHR, chrysene (including triphenylene); BAA, benz[a]anthracene; PYR, pyrene; FLU, fluoranthene; ANT, anthracene; PA, phenanthrene

Mean PAH concentrations (normalised to organic carbon in the Greater North Sea and Celtic Seas) relative to the ERL for each assessment area are shown in Figure b.

Figure b: Mean PAH concentration in sediment in each OSPAR contaminants assessment area, relative to the Effects Range-Low (ERL) value by assessment area and compound (with 95% upper confidence limits)

Value of 1 means that the mean concentration equals the ERL. Green, mean concentration is statistically significantly (p <0.05) below the ERL but not significantly below the Background Assessment Concentration (BAC). Blue, mean concentration is statistically significantly below the ERL and the BAC. ICDP, indeno[123-cd]pyrene; BGHIP, benzo[ghi]perylene; BAP, benzo[a]pyrene; CHR, chrysene (including triphenylene); BAA, benz[a]anthracene; PYR, pyrene; FLU, fluoranthene; ANT, anthracene; PA, phenanthrene

All individual PAH concentrations in sediment are significantly below the ERL in all assessment areas. Therefore, adverse biological effects in marine species are unlikely in the assessed areas. The PAH profile in all assessment areas was typical of pyrolytic sources, being dominated by the heavier 4-ring to 6-ring PAH compounds.

Temporal trends in PAH concentrations were assessed in areas where there were at least five years of data. The percentage yearly change for each PAH in each assessment area is shown in Figure c.

Figure c: Mean annual trends in PAH concentration in sediment by OSPAR contaminants assessment area and compound.

No statistically significant (p <0.05) change (circle), statistically significant downward trends (downward triangle). ICDP, indeno[123-cd]pyrene; BGHIP, benzo[ghi]perylene; PYR, pyrene; BAA, benz[a]anthracene; BAP, benzo[a]pyrene; PA, phenanthrene; ANT, anthracene; CHR, chrysene (including triphenylene); FLU, fluoranthene

Individual Time Series Results per Monitoring Site

A summary of individual time series results per monitoring site (across the OSPAR Maritime Area) for PAH concentrations in sediments is presented here http://dome.ices.dk/osparmime2016/regional_assessment_sediment_pah_(parent).html. In summary, at 184 out of 1597 monitoring sites across the OSPAR Maritime Area, mean concentrations of PAH in sediment are above the ERL. At 35 out of 1104 monitoring sites, mean concentrations have increased over the assessment period. It should be noted that not all individual time series results are included in the assessments (see number of time series used in each assessment area in Table b), due to the criteria set out in the assessment methods.

Confidence Assessment

There is high confidence in the quality of the data used for this assessment. The data have been collected over many years using established sampling methodologies. There is sufficient temporal and spatial coverage and no significant data gaps in the areas assessed over the relevant time periods. Although synthesis of monitoring site data for the assessment area scale uses new methods they are based on established and internationally recognised protocols for monitoring and assessment per monitoring site, therefore there is also high confidence in the methodology.

Conclusion

Les teneurs moyennes en hydrocarbures aromatiques polycycliques (HAP) dans les sédiments sont aux niveaux ambiants dans deux des six zones d’évaluation des contaminants. Les teneurs moyennes en HAP sont inférieures à la gamme de concentrations occasionnellement associées à des effets toxiques (ERL) dans toutes les zones d’évaluation et il est donc peu probable qu’elles aient des effets négatifs sur les organismes marins.

Il faudra cependant surveiller les teneurs en HAP dans les sédiments car les teneurs sont supérieures aux niveaux ambiants dans quatre zones d’évaluation. Les teneurs ne révèlent aucune tendance significative statistiquement dans quatre régions et sont en déclin dans la Manche et le golfe de Cadix seulement.

Les HAP proviennent de sources naturelles et seront donc toujours présents dans le milieu marin mais une meilleure utilisation des technologies de contrôle des émissions dans les processus de combustion pourrait améliorer encore plus la situation et réduire les teneurs pour les ramener aux niveaux naturels.

Offshore oil and gas extraction can release PAHs. The OSPAR assessment of discharges, spills and emissions from the offshore oil and gas industry has shown a reduction in oil discharged in produced water, due to measures put in place by OSPAR, but no statistically significant temporal trend in the number of oil spills or the quantity of oil spilled (Common indicator Discharges, Spills and Emissions).

Lacunes des connaissances 

On relève l’absence de données de la surveillance des hydrocarbures aromatiques polycycliques (HAP) dans les sédiments, en particulier pour les eaux arctiques et certaines parties de la mer du Nord au sens large, des mers Celtiques, du golfe de Gascogne et de la côte ibérique. Une coopération entre OSPAR et le Programme de surveillance et d’évaluation de l’Arctique (AMAP) permettrait un meilleur accès aux données sur les eaux arctiques.

La gamme de concentrations occasionnellement associées à des effets toxiques (ERL) développée par l'Agence américaine pour la protection de l'environnement a été utilisée dans l’évaluation car aucun critère d’évaluation environnementale (EAC) OSPAR n’est disponible actuellement. Il y a lieu de développer des EAC pour les HAP alkylés et les HAP parents dans les sédiments.

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