Etat et tendances des métaux lourds (mercure, cadmium et plomb) dans le poisson et les mollusques et crustacés

D8 - Teneurs en contaminants

D8.1 - Teneurs en contaminants

Message clé:

Dans la plupart des zones évaluées (depuis 2009) les teneurs en mercure, cadmium et plomb dans la moule et le poisson sont supérieures aux niveaux ambiants. Toutes les teneurs sont néanmoins inférieures aux limites pour les denrées alimentaires de la Commission européenne. Les teneurs sont en baisse ou ne révèlent aucune modification significative dans toutes les zones évaluées; à l’exception du cadmium dans quelques sites de la mer du Nord et de la mer d’Irlande.

Zone Évaluée

Récapitulatif Imprimable

Contexte

L’objectif stratégique d’OSPAR est de prévenir la pollution de la zone maritime OSPAR en réduisant sans relâche les rejets, émissions et pertes de substances dangereuses. Les métaux sont des substances dangereuses omniprésentes dans l’environnent et se trouvent dans la moule et le poisson dans toutes les régions OSPAR. Le mercure, le cadmium et le plomb sont les métaux les plus toxiques pour l’homme et les animaux, ce sont des métaux lourds, tous présents à l'état naturel dans l’environnent.

Le mercure, le cadmium et le plomb pénètrent le milieu marin par l’intermédiaire d’un certain nombre de processus naturels, agricoles et industriels (voir l’évaluation de l’indicateur des apports de métaux lourds), du transport atmosphérique à longue distance, des apports fluviaux ou des eaux de ruissellement à terre et, dans certains cas, d’apports directs. Certains métaux utilisés en tant que produits chimiques antisalissures (cuivre essentiellement) et les anodes sacrificielles (zinc essentiellement), par exemple, sont laissés intentionnellement dans le milieu marin, étant utilisés sur la coque des navires ou les installations marines et sont la cause de points chauds des teneurs en métaux dans les ports et à proximité.

Le mercure est extrêmement toxique. Le mercure et le cadmium s’accumulent dans la chaîne trophique mais le plomb ne s’accumule pas par l’intermédiaire de la chaîne trophique.

Les métaux lourds ne disparaissent pas au fil du temps et peuvent être piégés dans les niveaux plus profonds des sédiments jusqu'à ce que des processus miniers, géologiques ou biologiques les libèrent et ils peuvent alors affecter le milieu vivant. 

Les accumulateurs au plomb-acide abandonnés dans un port, juste au-dessous du niveau de la marée haute sont une source d’apports de plomb dans le milieu marin (© Martin M. Larsen)

Des teneurs naturelles en métaux lourds se trouvent dans toutes les eaux, les sédiments, la moule et le poisson, il s’agit des teneurs ambiantes. OSPAR utilise les limites maximales de concentration, pour les métaux lourds dans le poisson et la moule, déterminées par la Commission européenne à titre de valeurs de remplacement pour les critères d’évaluation environnementale (EAC).

The most toxic metals to fish and animals are mercury, cadmium and lead. Although other metals are also included in the OSPAR Coordinated Environmental Monitoring Programme, these are the three priority heavy metals.

Mercury has the potential to evaporate and be transported as a gas through the air; other heavy metals are mainly transported as fine particles or bound to other particles. Heavy metals can be trapped in deeper levels of sediment until mining, geological or biological processes release them, at which point they may affect biota.

Mercury and cadmium accumulate in the food chain and are considered the most toxic of the three heavy metals. The effects of high concentrations of heavy metals on humans can include: decreased learning ability (lead and mercury); reduced strength of bones (cadmium); and damage to the central nervous system (mercury). This has led to restrictions on most uses of cadmium and lead, and strict bans on mercury use.

In the Roman empire lead was used for water pipes, as sweetener in wine (lead-acetate) and as colouring for skin-cream. In modern times it is still being used in car batteries and until 2000 in leaded fuel as an engine lubricant, the major source of lead pollution in air and water during the 1970s until its ban (Larsen et. al, 2012). It has also been used as a softener in PVC piping.

Mercury has been used in medicine as an antibacterial agent and as a liquid anode in electrolysis in the paper industry. It has also been used in dental fillings, in thermometers and other scientific instruments. The Minamata Convention adopted in 2013 but still to enter into force, is a global treaty to protect human health and the environment from the adverse effects of mercury (http://www.zeromercury.org).

Cadmium is used in batteries and electronics and previously in some red paints and plastics. It is found in minerals mined for zinc, copper and lead, and is a minor constituent of all products of these heavy metals. As it is taken up from soil by plants, it is also concentrated in plants, especially tobacco leaves, sunflower and linseed.

Both mercury and cadmium are suspected carcinogens.

In assessing heavy metals both ‘relative’ and ‘absolute’ aspects have been

  • ‘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 confined to specific locations; and
  • ‘Status’ assessment of the significance of the (risk of) pollution, defined as the status where heavy metals 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 heavy metals. For example, the European Commission (EC) maximum concentration limits for heavy metals in seafood (fish and mussels) are used by OSPAR as proxy Environmental Assessment Criteria (EACs).

OSPAR has clarified that in assessing the Co-ordinated Environmental Monitoring Programme (CEMP) data the primary assessment value used in the assessment of heavy metal 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 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 agrees on the adoption of improved assessment criteria and subject to the conditions set out in the agreement.

Trends in heavy metal concentrations in biota are presented. Two assessment criteria are used to assess the status of heavy metal concentrations in biota: Background Assessment Concentrations (BACs) and European Commission maximum levels for fish and seafood (EC, 2006).

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 background 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 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) 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 heavy 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 the influence of long-range atmospheric transport of contaminants.

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 International Council for the Exploration of the Sea (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 EC maximum levels in fish and seafood

OSPAR has not yet established EACs for heavy metals in biota. Therefore the European Commission maximum levels in fish and seafood (EC, 2006) have been used as a proxy means for assessing the ecological significance of biota concentrations of heavy metals. EC maximum levels are applied in European Union Member States’ control of foodstuffs with the aim to protect public health by excluding the most contaminated food from the market. The limits are set on the basis of the diet of the ‘average’ European consumer, and should according to Regulation 1881/2006 be set at “a strict level which is reasonably achievable by following good agricultural, fishery and manufacturing practices and taking into account the risk related to the consumption of the food”. So if there are improvements in the practices (i.e. a decrease in the levels of environmental contaminants) the EC maximum levels may be reviewed. If the EC maximum food levels for fish and mussels are exceeded, the catch should not be put on the market.

The maximum EC levels for lead, mercury and cadmium in fish muscle and bivalve molluscs are used as alternatives to EACs for heavy metals in both fish and shellfish species. These values are firmly established by EC regulation, but have the disadvantage that the standards for cadmium and lead have not been directly designed for all the matrix/contaminant combinations required for the assessment. In general, it is recognised that the use of dietary standards is not fully satisfactory for assessing environmental risk, and that these values and their use to draw conclusions concerning the heavy metals in biota common indicator assessment should be treated with care. They are used as an interim solution to address the need for criteria until a more appropriate approach can be defined and agreed.

Assessment method

Concentrations of heavy metals in biota are monitored on a yearly basis in the CEMP monitoring programme at 304 monitoring sites (Figure 1).

For each heavy metal 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 area 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 and 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 metal 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 fixed effects:

    ~ heavy metal: OSPAR contaminants assessment areas

and random effects:

    ~ monitoring site + metal: monitoring site + within-series variation

The choice of fixed and random effects was motivated by the assumption that the heavy metals could have very different trends as they have different sources and are metabolised differently. Thus, the fixed effects measure the trend in each heavy metal in each OSPAR contaminants assessment area and the random effects measure variation in trends:

  • between monitoring sites common across heavy metals (monitoring site); and
  • residual variation (metal: 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). Heavy metal: monitoring site allows for any additional residual variation.

Evidence of trends in heavy metal concentrations at the assessment area scale was then assessed by plotting the estimated fixed effects 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 EC maximum levels; 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.

For heavy metals, BACs have been developed for mussels and fish. The upper limit for good status is set as the EC maximum levels in fish and seafood for the heavy metals, which might not be precautionary for the most sensitive species. An EC Environmental Quality Standard of 20 µg/kg ww for mercury has been developed for whole fish, but is not used as it requires re-calculation of the results to a top predator level in the food chain, resulting in all measurements failing to comply (OSPAR, 2016). It is also below what is considered a natural background concentration of mercury.

BACs and EC levels are available for three heavy metals only, cadmium, mercury and lead (Table a)

Table a: Assessment criteria used in for heavy metals in fish and shellfish: BAC are Background Assessment Concentrations developed by OSPAR, EC levels are European Commission maximum levels in fish and seafood. Ww, wet weight; dw, dry weight
NoneBACEC levels
musselsoystersfishall species
μg/kg dwμg/kg dwμg/kg wwμg/kg ww
Mercury9018035500
Cadmium9603000261000
Lead13001300261500

Table a notes:

  • BACs for mussels and oysters are expressed as μg/kg dw (dry weight) and BACs for fish and EC levels are expressed as μg/kg ww (wet weight);
  • Cadmium and lead are monitored in fish liver, for which no food standard exists; concentrations in fish liver are naturally higher than in fish muscle, so the food standards for fish muscle are not used; instead the food standards for shellfish are used as a proxy; and
  • BACs and EC levels are converted to other bases (wet, dry or lipid weight) using species-specific conversion factors.

Differences in methodology used for the IA 2017 compared with 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 site was presented.

Résultats

Diverses espèces de poisson et de mollusques et crustacés sont surveillées pour déterminer les teneurs en métaux dans la zone maritime OSPAR. La surveillance dans les sites côtiers porte principalement sur la moule bleue. L’huître est surveillée dans le golfe de Gascogne et la côte irlandaise. La surveillance dans les sites de surveillance restants, pour la plupart en haute mer, porte principalement sur le poisson flat (Figure 1).

Il existe 22 sites de surveillance dans les eaux Arctiques qui ne sont pas notifiés car ils ne sont pas représentatifs, sur le plan géographique, de la région dans son ensemble. Ils comprennent de six à huit sites de surveillance des tendances temporelles dans la mer de Barents, selon les métaux lourds surveillés, et aucun métal lourd ne révèle une tendance à la hausse des teneurs.

Figure 1: Sites de surveillance utilisés pour l’évaluation des teneurs en métaux lourds dans le poisson et les mollusques et crustacés par zone d’évaluation OSPAR

(lignes blanches) déterminés selon des principes hydrogéographiques et des connaissances d’expert plutôt que des limites internes OSPAR

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

Les teneurs maximales en métaux lourds de la CE dans le poisson et les mollusques et crustacés sont au moins cinq fois supérieures aux teneurs ambiantes. Les teneurs moyennes en métaux lourds sont inférieures aux teneurs maximales de la CE dans toutes les régions OSPAR évaluées depuis 2009.

Les teneurs en mercure dans le milieu vivant sont égales ou supérieures aux teneurs ambiantes dans toutes les zones d’évaluation des contaminants (Figure 2). Les teneurs les plus élevées, étant égales à environ deux fois les teneurs ambiantes, se trouvent dans la fosse norvégienne, la mer du Nord septentrionale, la mer du Nord méridionale et la mer d’Irlande.

Les teneurs en cadmium dans le milieu vivant sont supérieures aux teneurs ambiantes dans neuf des douze zones d’évaluation; à l’exception de la Manche, du golfe de Gascogne septentrional et de la mer Ibérique. Les teneurs dans le milieu vivant dans la mer de Barents et la mer du Nord méridionale sont entre deux à cinq fois supérieures aux teneurs ambiantes (Figure 2).

Les teneurs en plomb dans le milieu vivant sont supérieures aux teneurs ambiantes, sauf sur les côtes ouest irlandaise et écossaise (Figure 2). Les teneurs moyennes dans la mer de Barents, le Skagerrak, le Kattegat, et le golfe de Gascogne septentrional sont inférieures aux teneurs ambiantes mais les limites supérieures de confiance sont supérieures aux limites ambiantes. Les teneurs en plomb dans la mer du Nord septentrionale, la mer d’Irlande et le golfe de Cadix sont toutes entre deux à cinq fois supérieures aux teneurs ambiantes.

Figure 2: Teneurs moyennes de chacun des métaux lourds dans le milieu vivant, dans chaque zone d’évaluation des contaminants OSPAR, par rapport aux teneurs ambiantes d’évaluation (BAC) (avec des limites de confiance supérieures de 95%),

lorsque la valeur 1 signifie que les teneurs moyennes sont égales aux BAC. Bleu: teneurs moyennes nettement inférieures statistiquement (p <0,05) aux teneurs ambiantes d’évaluation (BAC) et aux teneurs maximales dans les denrées alimentaires de la Commission européenne, orange: teneurs moyennes égales aux BAC (si la limite de confiance dépasse le 1) ou supérieures aux BAC mais nettement inférieures aux teneurs maximales dans les denrées alimentaires de la CE. Les teneurs maximales de la CE sont en général plus de cinq fois supérieures aux BAC et ne sont donc pas illustrées

Figure a: Percentage yearly change in heavy metal concentrations in fish and shellfish in each OSPAR contaminant assessment area

No statistically significant (p <0.05) change in mean concentration (circle), mean concentration is significantly decreasing (downward triangle), mean concentration is significantly increasing (upward triangle) trends, 95% confidence limits (lines)

Mercury concentrations in biota show no statistically significant change in all assessment areas except for the Iberian Sea where there is a downward trend (Figure a). In contrast, lead concentrations are declining in seven of the ten assessment areas and show no significant change at three.

The only assessment area where concentrations are increasing is the Southern North Sea, for cadmium (Figure a). Here, half of the monitoring sites show upward trends for cadmium, resulting in a yearly increase in concentration of approximately 2%.

Individual Time Series Results per Monitoring Site

A summary of individual time series results at monitoring sites across the OSPAR Maritime Area for heavy metal concentrations in biota is presented here http://dome.ices.dk/osparmime2016/regional_assessment_biota_metals.html. In total, mean concentrations of heavy metals in biota are above EC limits for foodstuffs in 36 out of 1130 time series. In 88 out of 904 time series where trend assessments have been undertaken, 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 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 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 methods.

Conclusion

Le but, en dernier ressort, de la Stratégie substances dangereuses OSPAR est que les teneurs en métaux lourds dans le milieu vivant soient égales aux teneurs ambiantes naturelles. Les teneurs en métaux lourds dans le milieu vivant sont cependant supérieures aux teneurs ambiantes naturelles.

Les teneurs moyennes en métaux lourds dans les mollusques et crustacés et le poisson sont inférieures aux limites maximales pour les denrées alimentaires de la Commission européenne dans toutes les régions OSPAR. Les teneurs en mercure ne révèlent aucune modification significative ou révèlent une tendance à la baisse dans la plupart des zones d’évaluation. La mer du Nord méridionale est la seule zone d’évaluation révélant une tendance à la hausse des teneurs en métaux dans le milieu vivant, il s’agit du cadmium.

Les teneurs en mercure, cadmium et plomb dans les mollusques et crustacés et le poisson sont inférieures aux limites maximales pour les denrées alimentaires de la CE dans toutes les zones évaluées mais l’on peut potentiellement réduire les teneurs en métaux lourds dans le milieu vivant afin de parvenir aux teneurs ambiantes naturelles.

Lacunes des connaissances

Les critères d’évaluation sont basés sur les teneurs ambiantes et les limites maximales pour les denrées alimentaires de la Commission européenne, plutôt que sur les limites environnementales.

La Commission européenne n’a dérivé des critères de qualité environnementale pour le poisson que pour le mercure, ils sont inférieurs aux teneurs ambiantes et devront être étudiés à nouveau. Il faudra développer des critères d’évaluation environnementale pour tous les métaux lourds dans la moule et le poisson.

Il faudra étudier les raisons de l’augmentation des teneurs en cadmium dans la mer du Nord méridionale afin d’en identifier les sources.

EC (2006). European Union: Commission Regulation (EC) No. 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs

Larsen M.M., Blusztajn J.S., Andersen O., Dahllöf I. (2012). Lead isotopes in marine surface sediments reveal historical use of leaded fuel. Journal of Environmental Monitoring, 2012:14, 2893-2901. DOI: 10.1039/c2em30579h

OSPAR (2008). OSPAR Publication 2008-379 CEMP Assessment Manual: Co-ordinated Environmental Monitoring Programme Assessment Manual for contaminants in sediment and biota

OSPAR (2009). OSPAR Publication 2009-461 Background Document on CEMP Assessment Criteria for the QSR 2010

OSPAR (2016). OSPAR Publication 2016-679 Assessment criteria comparison (EAC/EQS) for mercury