Hazardous substances in marine organisms in Europe's seas

Hazardous substances are polluting Europe's seas, posing risks to ecosystems and human health. Nine hazardous substances were assessed in mussels and oysters between 2010 and 2022. Exceedance of safe limits was observed for benzo[a]pyrene, lindane, and polychlorinated biphenyl (PCB). Few time trends show more decreasing concentrations (improvements) than increasing ones. Therefore, further actions are essential to meeting the targets outlined in both the Marine Strategy Framework Directive and the Zero Pollution Action Plan.

Figure 1. Hazardous substances in mussels and oysters in Europe's seas

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In the marine environment, hazardous substances accumulate in fish and shellfish, which are a food source for marine life, wildlife and humans. These contaminants are toxic for marine biota. Consuming contaminated seafood may generate adverse effects on human health such as organ failure, neurological disorders and increased cancer risk.

While evidence suggests a stabilisation in concentrations, it is imperative to implement measures such as stringent regulatory enforcement and promote safe and sustainable alternatives, aimed at preventing the generation of hazardous chemicals and reducing emissions at their source. Reducing concentrations of these substances helps achieve the MSFD Good Environmental Status and the targets set in the Zero Pollution Action Plan.

Classifications of hazardous substances measured in mussels and oysters between 2010-2022 are summarised below (also Figure 1). Concentrations were classified by Environmental Quality Standards (EQS) in biota where available. OSPAR Background Assessment Concentrations (BAC) criteria and Maximum Permissible Concentrations (MPC) for humans were used to set the upper limit for the 'low' and 'moderate' classes, respectively.

The North-East Atlantic (NEA) Ocean and Mediterranean Sea demonstrate moderate to low levels of hazardous substances, with some high concentrations (PCBs for both areas, lindane and benzo[a]pyrene in addition for the Mediterranean Sea). The Baltic Sea displays moderate levels for most contaminants and high concentrations for PCB and lindane.

Overall, the NEA Ocean and Mediterranean Sea have relatively lower concentrations of certain hazardous substances compared to the Baltic Sea. Yet, the presence of high concentrations still indicates ongoing challenges. The Baltic Sea stands out with consistent moderate levels across various substances, suggesting a less favorable status compared to the NEA Ocean and Mediterranean Sea.

Time trends show decreasing concentrations are more frequent than increasing ones. Decreasing trends represent lower concentrations found in marine organisms, and an improved status. While these trends are promising, the prevalence of unknown and no discernible trends make it difficult to conclusively determine any improvements.

Assessment of one PCB (dioxin-like PCB118) showed mainly ‘high’ in all regions. A significant part of the concentrations was classified as ‘moderate’. PCBs continue to pose a threat to marine ecosystems (Figure 2).

Figure 2. Concentrations of PCB118 relative to assessment criteria

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Figure 2 shows details of assessments of PCB118 in bivalves, i.e. blue mussel (Mytilus edulis and Mytilius galloprovincialis) and oysters (almost always Crassostrea gigas), during 2010-2022, with BAC and EQS indicated. Boxplots show a large percentage ‘high’ classifications (red points) often exceeding the EQS. The Western Mediterranean, Greater North, Celtic and Baltic Seas had stations where concentrations of PCB118 in mussels were more than 10 times the EQS.

Higher concentrations result in larger risk of adverse effects for mussels and other aquatic organisms. The dioxin-like PCBs are also toxic to humans. The European Food Safety Authority set a tolerable weekly intake of dioxins and dioxin-like PCBs for humans in 2018. PCBs are typically transferred through the consumption of contaminated food, particularly meat, fish, and dairy .

Figure 2 also displays time trends for MSFD regions with ample data for assessment. The Greater North and Celtic Seas had a significant decrease in concentrations during this period. The estimate of the decrease is 20-30% per decade. For the Bay of Biscay and Baltic Sea, time series contained measurements under the detection limit, hence trends were not significant. Data were not sufficient for trend analysis in remaining areas.

Supporting information

Definition

The indicator is based on concentrations of nine hazardous substances measured in eight species of mussels and oysters. The nine substances are cadmium (Cd), mercury (Hg), lead (Pb), Copper (Cu), hexachlorobenzene (HCB), lindane (gamma-hexachlorocyclohexane, HCHG), DDT (using the breakdown product p,p'-DDE), benzo[a]pyrene (BAP) and 2,3',4,4',5-Pentachlorobiphenyl (PCB118). For each station, the 90% percentile over the 10 year period 2010-2022 was used to classify concentrations in ‘low’, ‘moderate’ and ‘high’ classes. These classifications are based on OSPAR's Background Assessment Concentrations (BAC) criteria, the Environmental Quality Standards (EQS) from the EU Water Framework Directive (WFD) and the Maximum Permissible Concentration (MPC) for food.

Methodology

Concentrations of the nine hazardous substances were collected from two databases: ICES (www.ices.dk) and EMODNET Chemistry (https://www.emodnet-chemistry.eu/). The databases contain measurements for a large number of species, but to achieve a relatively homogenous dataset, only data from bivalves of the following species were used: Cerastoderma edule (common cockle), Mya arenaria (softshell clam), Ruditapes philippinarum (Manila clam), Mytilus edulis (blue mussel), M. galloprovincialis (Mediterranean mussel), Crassostrea gigas (Pacific oyster), Ostrea edulis (native oyster) and Macoma balthica (Baltic clam). This left us with approximately 300,000 measurements. Approximately 10% of the stations had data in both databases and needed database cleaning to avoid using the same measurement from both databases. Furthermore, only data from the late summer and autumn were used, as concentrations of mussels in the spring are affected by spawning. For status, the 90% percentile over the 10 year period 2010-2022 was used to classify concentrations in 'low', 'moderate', and 'high' classes using two threshold values per contaminant (some thresholds also differ between blue mussels and oysters). The lower of the two thresholds was mostly OSPAR's BAC criterion; the EQS for cadmium and mercury was used. The higher threshold value was either the EQS from the WFD or MPC for seafood security. In order to calculate status, at least one year (Mediterranean) or three years (other areas) of data since 2010 were needed. For trends, dry-weight concentrations for metals and wet-weight concentrations for organic substances were used. Data before 2005 were excluded and trends were calculated for time series of 5-10 years that ended in 2015 or later. If the data series had no median concentrations under LOQ, we used linear regression; otherwise, a Bayesian model (with non-informative priors) implemented in JAGS was used.

Policy/environmental relevance

The MSFD websitestates that ‘human activities affect the marine environment through the release of chemical contaminants, which degrade the state of marine waters and can cause serious damage to its functioning’. The indicator is based on bivalves, which live as water filterers and are very effective ‘harvesters’ of any contaminants found in the water. In our process of selecting contaminants, we wanted to have contaminants that have been recorded in as many parts of Europe as possible — as well as contaminants that span a range of sources and behave differently in the environment. For instance, mercury is very volatile, which makes the atmosphere (including rain) an important source. Many of the other contaminants are mostly found in the aquatic environment. Many of the contaminants — such as DDT, lindane — represent ‘legacy’ contaminants. These are now largely banned but still exist in the environment, including in ocean sediments.

Accuracy and uncertainties

There is a large variation in coverage between regions and parameters — with especially low coverage in the Black Sea. It is important to use sensitive analytical measurements that have sufficiently quantification levels. Of the 182 species in the databases, there were 86 fish species, and species monitored vary between regions (e.g. there were 64 fish species in the Atlantic region, but only four fish species in the Mediterranean). Assessment of contaminants in fish from high trophic levels are important supplement to mussel data for identifying risks to human health. Possibly normalisation to lipid content or dry weight as described in the implementation strategy for the Water Framework Directive could be used to get an overview.

Also, ‘novel’ contaminants such as per- and polyfluoroalkyl substances (PFAS) were not included in the indicator because there was no coverage in the Mediterranean and Black Sea regions. PFAS were analysed by only a limited number of countries of which PFOS was the most common PFAS reported. There was high variation in species, tissue and coverage of different PFAS analysed. A direct comparison of levels between regions is therefore challenging. Exceedances of the current EQS for PFOS was observed for mammals, birds and fish. The highest exceedances were observed for polar bears with 100 times exceedances of EQS. The current EQS for PFOS will probably be replaced by a proposed and much lower EQS for the sum of 24 PFAS

Data sources and providers

Metadata

DPSIRTopicsTagsTemporal coverageGeographic coverage

TypologyUN SDGsUnit of measureFrequency of dissemination

References and footnotes

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<div class="csl-bib-body" style="line-height: 1.35; "> <div class="csl-entry">EU, 2013, Directive 2013/39/EU of the European Parliament and of the Council of 12 August 2013 amending Directives 2000/60/EC and 2008/105/EC as regards priority substances in the field of water policy, OJ L 226, 24.8.2013, p. 1–17.</div> </div>
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