Etat et tendances des métaux lourds (mercure, cadmium et plomb) dans les sédiments

D8 - Teneurs en contaminants

D8.1 - Teneurs en contaminants

Message clé:

Les teneurs moyennes en mercure, cadmium et plomb dans les sédiments marins sont en baisse ou ne révèlent aucune modification significative dans la majorité des zones évaluées. Les teneurs sont néanmoins supérieures aux teneurs ambiantes naturelles dans toutes les zones et supérieures aux niveaux pour lesquels on ne peut pas exclure des effets négatifs dans quatre des six zones évaluées.

Area assessed

Printable Summary

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 les sédiments marins de 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, tels que les émissions provenant de centrales électriques au charbon, du transport atmosphérique à longue distance, des apports fluviaux ou des eaux de ruissellement à terre (évaluation de l’indicateur des apports de métaux lourds). Certains métaux utilisés en tant que produits chimiques antisalissures (cuivre essentiellement) et les anodes sacrificielles (zinc essentiellement) sont laissés intentionnellement dans le milieu marin, étant utilisés sur la coque des navires ou par des installations marines et sont la cause de points chauds des teneurs en ces métaux dans les ports et à proximité.

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

Coal-fired power station in Scotland, an example of a potential source of heavy metals

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.

Des teneurs naturelles en métaux lourds se trouvent dans toutes les eaux, les sédiments et le milieu vivant marin, il s’agit des teneurs ambiantes. OSPAR utilise les lignes directrices pour l’évaluation de l’importance écologique des teneurs en contaminants dans les sédiments de la National Oceanic and Atmospheric Administration des Etats-Unis (gammes de concentrations occasionnellement associées à des effets toxiques (ERL)) à titre de remplacement des 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 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 cadmium and mercury are suspected carcinogens.

In assessing heavy metals 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 confined to specific locations; and

•     ‘Status’ assessment of the significance of the (risk of) pollution, defined as the status where 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, (Effects Range-Low (ERL) values are used by OSPAR as proxy Environmental Assessment Criteria (EAC).

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 sediment are presented. Two assessment criteria are used to assess the status of heavy metal concentrations in sediment: Background Assessment Concentrations (BACs) and United States National Oceanic and Atmospheric Administration (NOAA) sediment quality guidelines; Effects Range-Low (ERL) (NOAA, 1999).

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 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 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. 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 at the working level by the relevant assessment group as further CEMP monitoring data are collected.

Provenance and limitations of ERLs

OSPAR has not yet established EACs for heavy metals in sediment. Therefore a proxy means of assessment has been used. ‘Effects range’ values were developed by the United States National Oceanic and Atmospheric Administration (NOAA) 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 used in sediment assessments of contaminants as an interim solution where recommended EACs are not available.

Assessment Methods

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 OSPAR 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 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 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. 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 (heavy 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 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.

BAC assessment criteria differ spatially. The BACs and ERL assessment criteria used to assess sediment are set out in Table a and the number of monitoring sites with time series used for status and trend assessments are set out in Table b.

Table a: Assessment criteria used for heavy metals in sediment. BAC, Background Assessment Concentrations (normalised to 5% all, except for Iberian Sea and Gulf of Cadiz); ERL, Effects Range-Low (O’Conner, 2004); dw, dry weight
BAC BAC ERL
mg/kg dw All OSPAR assessment areas except Iberian Sea and Gulf of Cadiz Iberian Sea and Gulf of Cadiz All OSPAR assessment areas
Cadmium 0.31 0.129 1.2
Mercury 0.07 0.091 0.15
Lead 38 22.4 47

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 site was presented.

Résultats

La surveillance des métaux lourds dans les sédiments est réalisée régulièrement dans le cadre du Programme coordonné de surveillance de l’environnement OSPAR (CEMP), dans 65 à 125 sites de surveillance (Figure 1) selon le métal lourd surveillé. L’évaluation se fonde sur les sites surveillés depuis 2009 au moins; certains étant surveillés depuis 1989. Les tendances temporelles sont évaluées à partir des données de surveillance pour une période de dix ans (c’est-à-dire 2005–2015) et la tendance est déterminée à partir des cinq dernières années de données.

Les teneurs en mercure, cadmium et plomb ont été comparées aux teneurs ambiantes d’évaluation (BAC) et aux valeurs des gammes de concentrations occasionnellement associées à des effets toxiques (ERL). Les teneurs en mercure et en plomb dans les sédiments sont égales ou supérieures aux BAC dans toutes les zones d’évaluation des contaminants. Les teneurs moyennes en cadmium sont inférieures aux BAC (Figure 2) dans trois des six zones évaluées: la mer du Nord septentrionale, les côtes ouest irlandaise et écossaise et la mer d’Irlande.

Les teneurs en mercure dans les sédiments sont égales ou supérieures aux ERL dans trois des six zones d’évaluation (Figure 3). Les teneurs en cadmium dans les sédiments sont inférieures aux ERL dans toutes les zones d’évaluation. Les teneurs en plomb sont égales ou supérieures aux ERL dans cinq des six zones d’évaluation, et inférieures aux ERL seulement dans la zone des côtes ouest irlandaise et écossaise.

Figure 1: Sites de surveillance utilisés pour l’évaluation des teneurs en métaux lourds dans les sédiments au sein des zones d’évaluation des contaminants OSPAR

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

Figure 2: Teneurs moyennes en trois métaux lourds dans les sédiments dans les zones 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 BAC et aux ERL. Orange: teneurs moyennes égales ou supérieures aux BAC mais nettement inférieures statistiquement aux gammes de concentrations occasionnellement associées à des effets toxiques (ERL). Rouge: les teneurs moyennes sont supérieures aux BAC et égales ou supérieures aux ERL

Figure 3: Teneurs moyennes en métaux lourds dans les sédiments par rapport aux teneurs des gammes de concentrations occasionnellement associées à des effets toxiques (ERL) (avec des limites de confiance supérieures de 95%),

lorsque la valeur 1 signifie que les teneurs moyennes sont égales aux ERL. Bleu: teneurs moyennes nettement inférieures statistiquement (p <0,05) aux teneurs ambiantes d’évaluation (BAC) et aux ERL. Orange: teneurs moyennes nettement inférieures aux ERL mais égales ou supérieures aux BAC. Rouge: les teneurs moyennes sont supérieures aux BAC et égales ou supérieures aux ERL

Les tendances temporelles (moyennes dans l’ensemble) des teneurs en métaux lourds dans les sédiments (Figure 4) révèlent des teneurs en mercure en baisse dans cinq des six zones d’évaluation et aucune modification significative statistiquement des teneurs dans la Manche. Les teneurs en cadmium ne révèlent aucune modification significative statistiquement dans cinq zones d’évaluation mais sont en baisse dans la mer du Nord méridionale. Les teneurs en plomb ne révèlent aucune modification significative statistiquement dans quatre zones d’évaluation et une tendance à la baisse dans la mer du Nord méridionale. La tendance des teneurs en plomb est à la hausse dans le golfe de Cadix.

Ceci diffère de la situation dans le milieu vivant, dans lequel la plupart des teneurs en mercure ne révèlent aucune modification significative statistiquement et les teneurs en plomb sont en baisse dans la plupart des sites de surveillance (indicateur commun des métaux lourds dans le poisson et les mollusques et crustacés). On s’attend à ce que les sédiments réagissent, aux mesures prises pour réduire les métaux lourds, plus lentement que le milieu vivant car la couche supérieure des sédiments (les quelques centimètres supérieurs) échantillonnés pour l’analyse peut représenter plusieurs années de sédimentation et donc intègrent des apports en métaux lourds durant la période correspondante.

Figure 4: Modification du pourcentage annuel des teneurs en métaux lourds dans les sédiments dans six zones d’évaluation des contaminants OSPAR.

Aucune modification significative statistiquement des teneurs moyennes (cercle), les teneurs moyennes sont nettement en baisse (triangle inversé), les teneurs moyennes sont nettement en hausse (triangle), limites de confiance de 95% (lignes)

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

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 sediment is presented here http://dome.ices.dk/osparmime2016/regional_assessment_sediment_metals.html. In total, mean concentrations of heavy metals in sediment are above the ERL in 243 out of 479 time series. In 90 out of 308 time series where trend assessments have been undertaken, mean concentrations have increased over the assessment period (since 2005). 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 method.

Conclusion

Le but, en dernier ressort, de la Stratégie substances dangereuses OSPAR est que les teneurs en métaux lourds dans les sédiments soient égales aux teneurs ambiantes naturelles. Les teneurs en métaux lourds dans les sédiments sont cependant supérieures aux teneurs ambiantes naturelles dans la plupart des zones d’évaluation. Les teneurs les plus élevées en mercure et cadmium dans les sédiments se trouvent dans la Manche. Les teneurs les plus élevées en plomb dans les sédiments se trouvent dans le golfe de Cadix. Les teneurs les plus faibles en métaux lourds se trouvent sur les côtes ouest irlandaise et écossaise.

Les teneurs en mercure dans les sédiments sont supérieures aux ERL dans la moitié des zones d’évaluation et les teneurs en plomb sont égales ou supérieures aux ERL dans cinq des six sites de surveillance. Ceci signifie que l’on ne peut pas exclure des effets négatifs dans ces zones d’évaluation. Par contre, les teneurs en cadmium sont inférieures aux ERL dans les six zones d’évaluation.

Les tendances à la baisse générales des teneurs en mercure ne se retrouvent pas dans les teneurs en cadmium et en plomb; la plupart des teneurs en cadmium et en plomb dans les sédiments ne révèlent aucune modification significative statistiquement.

Lacunes des connaissances

Les données écotoxicologiques sont insuffisantes pour pouvoir développer de nouveaux critères d’évaluation basés sur les principes de la Directive cadre sur l'eau de l’Union européenne ou des critères d’évaluation environnementale OSPAR (EAC), afin de remplacer les critères actuels des gammes de concentrations occasionnellement associées à des effets toxiques (ERL). Le nombre des sites de surveillance dans les eaux Arctiques est trop faible pour pouvoir réaliser une évaluation de cette zone.

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

NOAA (1999). Sediment Quality Guidelines developed for the National Status and Trends Program. National Oceanic and Atmospheric Administration, US Department of Commerce, United States of America. 12pp

O’Conner, T.P. (2004): Marine Pollution Bulletin 49, 383–385

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