Etat et tendances des polychlorobiphényles (PCB) dans les sédiments

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).

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.

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).

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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