Etat et tendances des polychlorobiphényles (PCB) dans les sédiments

D8 - Teneurs en contaminants

D8.1 - Teneurs en contaminants

Message clé:

Les polychlorobiphényles (PCB) ont été interdits dans de nombreux pays au milieu des années 1980. Dès lors, des problèmes locaux subsistent mais les teneurs moyennes en PCB dans les sédiments ont diminué dans trois des cinq zones d’évaluation des contaminants OSPAR. Les teneurs dans les sédiments, à l’exception de celles du congénère le plus toxique (CB118), sont inférieures au niveau susceptible de présenter un risque intolérable pour le milieu marin.

Zone Évaluée

Récapitulatif Imprimable

Contexte

La Stratégie substances dangereuses OSPAR a pour but, 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.

Les polychlorobiphényles (PCB) sont des composés chimiques de synthèse qui ont été interdits au milieu des années 1980, leur toxicité, leur persistance et leur bioaccumulation potentielle dans l’environnement causant des préoccupations. Depuis les années 1980, des mesures mondiales ont entraîné des réductions importantes des rejets et les stocks restants ont été supprimés progressivement. En dépit des mesures européennes et mondiales cependant les rejets se poursuivent par l’intermédiaire d’émissions diffuses dans l’air et l’eau provenant de chantiers et de matériaux industriels. Les sources restantes sont notamment le matériel électrique et hydraulique contenant des PCB, l’élimination des déchets, la redistribution des sédiments marins contaminés historiquement et les sous-produits de processus thermiques et chimiques. 

Les PCB ne se dégradent pas facilement dans l’environnement et ne sont pas métabolisés aisément par l’homme ou les animaux. Ils sont extrêmement toxiques pour les animaux et l’homme. Les PCB « de type dioxine » sont un sous-groupe plus toxique que d’autres congénères des PCB.

Sept congénères des PCB ont été sélectionnés comme indicateurs de la contamination d’ensemble par les PCB étant donné leurs teneurs et effets toxiques relativement élevés.

Armoires électriques pour chemin de fer abandonnées contenant des teneurs élevées en polychlorobiphényles (PCB).

Polychlorinated biphenyls (PCBs) (Figure a) are industrial compounds with multiple industrial and commercial uses. It has been estimated that globally 1.3 million tonnes of PCB compounds have been produced (Breivik et al., 2007). PCBs have been used as coolants and lubricants in transformers, capacitors, and other electrical equipment. PCBs have also been used in adhesives, paints, inks and as plasticisers and sealing agents in products such as rubber and especially in polyvinyl chloride plastics used to coat electrical wiring.

Figure a. Chemical structure of polychlorinated biphenyls

Although usage of PCBs was banned in most forms over 30 years ago (PARCOM, 1992), they still exist in old electrical equipment and environmental media to which humans can be exposed. PCBs are expected to be present in electronic waste streams from which they can leach into the environment (Menad et al., 1998). Humans are exposed mainly via food, mostly from contaminated animal fats. Indoor air can also contribute to human exposure. Worldwide monitoring programmes have shown that PCBs are present in most samples of human breast milk (Pietrzak-Fiecko et al., 2005).

PCBs do not burn easily and are good insulators (Bergman et al., 2012). These properties contribute greatly to PCBs having become environmental contaminants, which are regulated by the Stockholm Convention on Persistent Organic Pollutants (2004, amended 2007). The chemical inertness and heat stability properties that make PCBs desirable for industry also enable PCB residues to persist in the environment for long periods and to be transported worldwide associated with particulate matter as this is dispersed through waters, precipitation, wind, and other physical forces (Jaward et al., 2004; Eckhardt et al., 2007; Gioia et al., 2008).

Of the 209 PCB congeners, the most toxic are the so-called ‘dioxin-like’ PCBs. These are the four non-ortho PCBs (CB77, CB81, CB126, CB169) and eight mono-ortho PCBs (CB105, CB114, CB118, CB123, CB156, CB157, CB167, CB189).

Owing to their persistence, potential to bioaccumulate and toxicity they have been included on the OSPAR List of Chemicals for Priority Action (OSPAR, 2007). Six PCB congeners were recommended for monitoring by the European Commission (2001). As the most toxic PCB, CB118 is also monitored. As per the OSPAR Coordinated Environmental Monitoring Programme (CEMP) (OSPAR, 2016), Contracting Parties are required to monitor the seven PCB congeners CB28, CB52, CB101, CB118, CB138, CB153, and CB180 (OSPAR, 1997) on a mandatory basis in biota (fish and mussels) and sediments for temporal trends and spatial distribution. Marine sediments, in particular those with a high organic carbon content, may accumulate hydrophobic compounds like PCBs to considerably higher concentrations than surrounding waters. The sampling strategy is defined by the purpose of the monitoring programme and the natural conditions of the region to be monitored (OSPAR, 1997). Typically sampling approaches include fixed-monitoring site sampling, stratified random sampling, or stratified fixed sampling. Muddy sediments, namely those containing a high proportion of fine material, are preferable for organic contaminant monitoring, although sieving of sediments may be an alternative (OSPAR, 2002).

In assessing contaminants 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 contamination is widespread or rather confined to specific locations; and

•   ‘Status’ assessment of the significance of the (risk of) pollution, defined as the status where chemicals are at a hazardous level, usually requires assessment criteria that take account of the possible severity of the impacts and hence requires criteria that take account of the natural conditions (background concentrations) and the ecotoxicology of the contaminant. 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 contaminant concentrations in sediment and biota, “corresponds to the achievement, or failure to achieve, statutory targets or policy objectives for contaminants in these matrices” (OSPAR, 2009a). This set of assessment criteria was specifically compiled for the assessment of CEMP monitoring data on hazardous substances contributing to the 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 upon and implemented. These criteria have also been used in the annually recurring CEMP assessments since 2010 and will be used until OSPAR agrees on the adoption of improved assessment criteria and subject to the conditions set out in the agreement.

Two assessment criteria are used to assess PCB concentrations in sediment: background assessment concentrations (BACs) and environmental assessment criteria (EACs).

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

BACs were developed by OSPAR for testing whether measured concentrations are near background levels for naturally occurring substances and close to zero for synthetic substances, the ultimate aim of the OSPAR Hazardous Substances Strategy. Mean concentrations significantly below the BAC are said to be near background (naturally occurring 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 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 synthetic, 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 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 Convention area.

BACs are calculated according to the method set out in Section 4 of the CEMP Assessment Manual (OSPAR, 2008). The outcome 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 by the relevant assessment group as further CEMP monitoring data are collected.

Provenance and limitations of EACs

Environmental Assessment Criteria were developed by OSPAR and ICES for assessing the ecological significance of sediment and biota concentrations. Some EAC values were specifically compiled for the assessment of CEMP monitoring data on hazardous substances contributing to the QSR 2010 (OSPAR Agreement 2009-2). EACs do not represent target values or legal standards under the OSPAR Convention and should not be used as such. The EAC values were set so that hazardous substance concentrations in sediment and biota below the EAC should not cause chronic effects in sensitive marine species, including the most sensitive species, nor should concentrations present an unacceptable risk to the environment and its living resources. However, the risk of secondary poisoning is not always considered. EACs continue to be developed for use in data assessments.

As concentrations below the EAC are considered to present no significant risk to the environment, in most cases EAC are considered analogous to the Environmental Quality Standards applied to concentrations of contaminants in water or biota, for example under the European Union Water Framework Directive.

For PCBs in biota, equilibrium concentrations were calculated from sediment concentrations and partition coefficients based on the assumption of equilibrium between PCBs in lipids of biota and in sediment (OSPAR, 2009a,b). Thus, the EACs for PCBs in sediment were used to calculate concentrations of PCBs in fish liver (on a lipid weight basis) and in mussels, in equilibrium with sediment containing PCB concentrations equal to the EAC in sediment.

Caution should be exercised in using these generic environmental assessment criteria in specific situations. Their use does not preclude the use of common sense and expert judgement when assessing environmental effects and/or the potential for them.

Assessment method

For each PCB compound at each monitoring site, the time series of concentration measurements was assessed for 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 areas scale in a series of meta-analyses.

Trend assessments included those monitoring sites that were representative of general conditions, and excluded those monitoring sites impacted due to a point source as well as baseline monitoring sites where trends would not be expected. The 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 trend in each congener 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 areas

and random effects:

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

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

  • between congeners common across OSPAR contaminants assessment areas (congener);
  • between congeners within OSPAR contaminants assessment areas (congener: contaminants assessment area);
  • between monitoring sites common across congeners (monitoring site); and
  • residual variation (congener: monitoring site + within-series variation).

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

Evidence of trends in PCB concentrations at the contaminants assessment area scale was then assessed by plotting the estimated fixed effects with point-wise 95% confidence intervals. Differences between congeners were explored by plotting the predicted trend for each congener and for each congener / assessment area combination with point-wise 95% confidence intervals.

Similar analyses explored status at the assessment area scale. Two summary measures were considered: the log ratio of the fitted concentration in the last monitoring year to the EAC; 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 congeners at the assessment area scale were explored using the fitted log concentration in the last monitoring year.

BACs and EACs are available for the following PCBs in sediment (Table a).

Table a: Background Assessment Concentration (BACs) and Environmental Assessment Criteria (EAC) for polychlorinated biphenyls (PCBs) in sediment. Dw, dry weight
BAC (μg/kg dw) EAC (μg/kg dw)
All OSPAR assessment areas except Iberian Sea and Gulf of Cadiz All OSPAR assessment areas
CB28 0.22 1.7
CB52 0.12 2.7
CB101 0.14 3.0
CB118 0.17 0.6
CB138 0.15 7.9
CB153 0.19 40
CB180 0.10 12

Table a notes: BACs are normalised to 2.5% organic carbon; BACs are under development for the Iberian Sea and Gulf of Cadiz, where concentrations are only assessed against the EAC.

The number of monitoring sites used to assess trends and status by assessment area is shown in Tables b and c.

Table b: Status data for regional assessment: number of monitoring sites and time series by OSPAR contaminants assessment area
OSPAR contaminants assessment areas Monitoring sites CB28 CB52 CB101 CB118 CB138 CB153 CB180
Northern North Sea 21 8 16 17 16 17 19 15
Southern North Sea 42 39 31 41 42 42 41 37
English Channel 34 11 16 27 32 3 34 22
Irish and Scottish West Coast 9 6 4 6 6 8 8 3
Irish Sea 19 17 16 17 19 19 18 16
Celtic Sea 1 1 1 1 1 1 1 1
Iberian Sea 15 15 15 15 15 15 15 15
Gulf of Cadiz 14 13 13 14 14 14 14 14
Table c: Trend data for regional assessment: number of monitoring sites and time series by OSPAR contaminants assessment area
OSPAR contaminants assessment area Monitoring sites CB28 CB52 CB101 CB118 CB138 CB153 CB180
Northern North Sea 17 5 8 12 12 11 15 8
Southern North Sea 33 29 22 32 31 32 31 27
Channel 2 0 0 2 2 2 2 1
Irish and Scottish West Coast 7 2 4 5 6 6 6 3
Irish Sea 10 9 9 10 10 10 10 8
Celtic Sea 1 1 1 1 1 1 1 1
Gulf of Cadiz 9 4 8 3 4 5 8 4

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 trend at the assessment area level. Meta-analyses take into account both the estimate of status or 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 station was presented.

Résultats

Les teneurs en polychlorobiphényles (PCB) sont mesurées dans les échantillons de sédiment prélevés tous les ans (ou à quelques années d’intervalle) de sites de surveillance dans la majeure partie de la mer du Nord au sens large, des mers Celtiques, de la côte ibérique et du golfe de Gascogne (Figure 1).

Les séries temporelles utilisées pour informer cette évaluation ont débuté en 1995. Les données permettent d’étudier les tendances des teneurs en PCB au cours de la période de 1995 à 2015 et de comparer les teneurs à deux séries de valeurs d’évaluation: les teneurs ambiantes d’évaluation (BAC) et les critères d’évaluation environnementale (EAC). Les teneurs inférieures aux EAC ne devraient pas avoir des effets chroniques sur les espèces marines sensibles et ne devraient donc présenter aucun risque significatif pour l’environnement. Les BAC permettent d’évaluer si les teneurs sont proches de zéro pour les substances synthétiques, but ultime de la Stratégie substances dangereuses OSPAR.

Evaluation des tendances

Les teneurs en PCB diminuent dans la mer du Nord septentrionale, la mer du Nord méridionale et le golfe de Cadix. Par contraste les teneurs ne révèlent aucune modification significative statistiquement sur les côtes ouest irlandaise et écossaise et dans la mer d’Irlande (Figure 2).

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

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

Evaluation de l’état

Les teneurs de six des sept congénères des PCB dans les sédiments sont inférieures aux EAC dans toutes les zones d’évaluation des contaminants OSPAR (Figure 3) au cours de la période de 1995 à 2015. Il existe cependant des différences entre les congénères, les teneurs en CB118 dans les sédiments, l’un des PCB les plus toxiques, étant proches des, ou supérieures aux, EAC dans trois zones d’évaluation (Manche, mer du Nord méridionale et mer d’Irlande), indiquant des effets négatifs possibles sur le milieu vivant marin dans ces zones. Les teneurs en CB118 dans les sédiments dans les zones d’évaluation des côtes ouest irlandaise et écossaise, de la mer du Nord septentrionale et du golfe de Cadix, sont inférieures aux EAC mais encore supérieures aux BAC. Les teneurs en CB28 dans les zones d’évaluation des côtes ouest irlandaise et écossaise sont les seules teneurs mesurées dans les sédiments inférieures aux BAC.

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

Figure 2: Modification du pourcentage annuel des teneurs en PCB dans les sédiments (1995–2015) dans chaque zone d’évaluation des contaminants OSPAR.

Aucune modification significative statistiquement (p <0,05) de la teneur moyenne (cercle), la teneur moyenne diminue nettement (triangle inversé). Les régions manquantes possèdent trop peu de sites de surveillance pour une évaluation

Figure 3: Teneurs moyennes en PCB dans les sédiments par congénère (1995–2015) dans chaque zone d’évaluation des contaminants OSPAR, par rapport aux EAC (avec des limites de confiance supérieures de 95%)

lorsque la valeur 1 signifie que la teneur moyenne est égale aux EAC. Bleu: teneur moyenne nettement inférieure statistiquement (p <0,05) aux teneurs ambiantes d’évaluation (BAC) du congénère. Vert, teneur moyenne supérieure aux BAC du congénère significative statistiquement mais inférieure aux critères d’évaluation environnementale (EAC). Rouge: teneur moyenne pas nettement inférieure statistiquement aux EAC.

Regional Assessment Results

Contamination from polychlorinated biphenyls (PCBs) is widespread and persists in the marine environment, especially in biological systems. There are few areas where concentrations are close to zero.

PCB concentrations are lowest in the Northern North Sea, the Irish and Scottish West Coast and the Gulf of Cadiz. However, PCBs are not yet at concentrations close to zero even at monitoring stations remote from industrial activity. In three assessment areas (English Channel, Southern North Sea, Irish Sea) there are locations where concentrations of the most toxic PCB congener (CB118) pose a risk of pollution effects.

Owing to their slow breakdown in the environment, PCBs will persist in marine sediments for many years to come.

Individual Time Series Results per Monitoring Site

A summary of individual time series results at monitoring sites across the OSPAR Maritime Area for PCB concentrations in sediment is presented here http://dome.ices.dk/osparmime2016/regional_assessment_sediment_chlorobiphenyls.html. In total, mean concentrations of PCBs in sediment are above the EAC in 207 out of 1016 time series. In 27 out of 563 time series, mean concentrations have increased over the assessment period (1996–2015). It should be noted that not all individual time series results are included in the regional assessments (see number of time series used in each OSPAR region and assessment area in Tables b and c), due to the criteria set out in the assessment methodology.

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 period (1995–2015). The methods are based on established and internationally recognised protocols for monitoring and assessment per monitoring site, with a new secondary step of synthesising monitoring site data at the assessment area scale. Therefore there is also high confidence in the methodology.

Conclusion

Plus de 25 ans après l’interdiction de l’utilisation des polychlorobiphényles (PCB) ceux-ci risquent encore d’avoir des effets négatifs sur le milieu vivant marin dans certaines parties de la zone maritime OSPAR.

Les PCB se trouvent dans tous les sédiments marins. Les teneurs diminuent dans la mer du Nord au sens large et le golfe de Cadix mais elles ne révèlent aucune modification significative statistiquement dans les mers Celtiques. Les teneurs en tous les congénères des PCB dans les sédiments, à l’exception de celles du congénère le plus toxique (CB118), sont inférieures au niveau susceptible de présenter un risque intolérable pour l’environnement. Les teneurs moyennes en CB118 dans les sédiments sont égales ou supérieures à ce niveau dans trois des six zones d’évaluation évaluées.

Les PCB subsistent dans les sédiments pendant de longues périodes et peuvent potentiellement s’accumuler dans le milieu vivant et se bioamplifier le long des chaînes trophiques. Il faudra attendre plusieurs autres décennies pour que les teneurs soient proches de zéro, but en dernier ressort de la Stratégie substances dangereuses OSPAR, étant donné les utilisations industrielles antérieures et la persistance des PCB dans l’environnement.

Historic contamination of the environment by polychlorinated biphenyls (PCBs) means there are limited possibilities for addressing the issue of PCB concentrations in sediment.

In parallel to reduced PCB emissions in areas of former use, studies have recorded surprisingly high concentrations of PCBs in areas far from the traditional source regions (Jaward et al., 2004; Gioia et al., 2008, 2011). There are indications that primary emission sources of PCBs are increasing from some African countries, where PCBs have not been commercially produced and used. Major sources of PCBs in African countries include transformers, continuing import of e-waste from other countries, shipwrecks, and biomass burning (Gioia et al., 2013).

Lacunes des connaissances

Des données de surveillance sont absentes pour certaines parties de la zone maritime OSPAR, en particulier dans les eaux Arctiques, certaines parties des mers Celtiques et de la côte ibérique et du golfe de Gascogne.

Des recherches supplémentaires sont nécessaires pour pouvoir apprécier la mesure dans laquelle la réduction des teneurs en polychlorobiphényles (PCB) dans des zones d’usages antérieurs se produit au détriment des niveaux dans les zones où les PCB n’ont pas été produits et utilisés commercialement, telles que l’Afrique, qui reçoivent des PCB sous forme de produits obsolètes et de déchets.

Further research is required to define diffuse inputs from terrestrial sources. Modelling work to understand atmospheric transport from remaining sources could also be undertaken. Landfill and waste deposit sites may also still be leaking PCB contaminated material as they are unable to provide the very high temperatures needed to destroy PCBs. Demolition of buildings containing PCB sealants and redistribution of sediments via dredging may be remobilising PCBs which were locked away (Jepson and Law, 2016).

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