Hazardous substances in marine organisms in Europe's seas

The presence of hazardous substances in Europe's seas poses a risk to ecosystems and human health. Nine hazardous substances were assessed in mussels and oysters between 2010 and 2024. Exceedance of safe limits was observed for benzo[a]pyrene, lindane (HCHG), and polychlorinated biphenyl (PCB). Available time trends show that regions with improving (decreasing) concentrations are more prevalent than deteriorating ones. 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

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 .

While evidence suggests a stabilisation in concentrations, it is imperative to implement measures such as stringent regulatory enforcement and promote safe 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 2010-2024 are summarised below (Figure 1). Concentrations were assigned to ‘low’, ‘moderate’ and ‘high’ classes using several assessment criteria: lower limits were either in biota or OSPAR Background Assessment Concentrations (BAC). Upper limits for the 'low' and 'moderate' classes were OSPAR Environmental Assessment Criteria (EAC), EQS in biota, or Maximum Permissible Concentrations (MPC) for humans.

Few threshold exceedances were observed for Pb, Cd, DDT (p,p′-DDE), Cu and HCB. Exceedances were more frequent for benzo[a]pyrene (BaP), PCB118 and lindane, and, to a lesser extent, mercury (Hg). Overall, the Baltic Sea showed more consistently moderate contaminant levels and high concentrations of PCB118 and lindane, indicating a less favourable status than the North-East Atlantic and Mediterranean Sea. These findings demonstrate that hazardous substances remain an ongoing challenge in Europe’s seas.

Time trends largely reveal no (discernible) or unknown trend. Where trends were detected, decreasing contaminant concentrations were more common than increasing ones, indicating lower concentrations and improved status. Further actions to decrease concentrations of contaminants in “high” and “moderate” classes should be taken.

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

Figure 2 shows details of assessments of PCB118 in bivalves, i.e. blue mussel (Mytilus edulis and Mytilus galloprovincialis) and oysters (almost always Crassostrea gigas), during 2010-2024, with BAC and EAC indicated. Boxplots show a large percentage ‘high’ classifications (red points) often exceeding the EAC. The Western Mediterranean, Greater North, Celtic and Baltic Seas had stations where concentrations of PCB118 in mussels were more than 8 times the EAC.

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.

The Greater North Sea, Celtic Sea and Bay of Biscay/Iberian coast had a significant decrease in concentrations during this period. The estimate of the decrease is 20-45% per decade. For the Baltic Sea, time series contained measurements under the quantification limit (LOQ), 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 or EQS (for cadmium and mercury). The higher threshold value was either the EQS from the WFD, OSPAR EAC, or Maximum Permissible Concentration (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 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 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

Data sources and providers

Metadata

DPSIRTopicsTagsTemporal coverageGeographic coverage

TypologyUN SDGsUnit of measureFrequency of dissemination

References and footnotes

Noman, M. A., Feng, W., Zhu, G., Hossain, M. B., Chen, Y., Zhang, H. and Sun, J., 2022, 'Bioaccumulation and potential human health risks of metals in commercially important fishes and shellfishes from Hangzhou Bay, China' accessed 31 March 2025
^↵
EEA, 2011, Hazardous substances in Europe’s fresh and marine waters: an overview., Publications Office of the European Union, Luxembourg.

^↵
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.

^↵
Dietz et al_2021_A risk assessment of the effects of mercury on Baltic Sea, Greater North Sea.pdf , ( https://www.sciencedirect.com/science/article/pii/S0160412020321334/pdfft?md5=e5c7edb323d4244cae244fd7f1a8e0d2&pid=1-s2.0-S0160412020321334-main.pdf&isDTMRedir=Y ) accessed August 15, 2022.

^↵
EC, 2006, Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs (Text with EEA relevance), OJ L.

^↵
Chain (CONTAM), E. P. on C. in the F., Knutsen, H. K., Alexander, J., Barregård, L., Bignami, M., Brüschweiler, B., Ceccatelli, S., Cottrill, B., Dinovi, M., Edler, L., Grasl-Kraupp, B., Hogstrand, C., Nebbia, C. S., Oswald, I. P., Petersen, A., Rose, M., Roudot, A.-C., Schwerdtle, T., Vleminckx, C. et al., 2018, 'Risk for animal and human health related to the presence of dioxins and dioxin-like PCBs in feed and food', EFSA Journal 16(11), pp. e05333 ( https://onlinelibrary.wiley.com/doi/abs/10.2903/j.efsa.2018.5333 ) accessed August 15, 2022.

^↵
Plummer, M.; Stukalov, A.; Denwood, M. Rjags: Bayesian Graphical Models Using MCMC, 2024. (https://cran.r-project.org/web/packages/rjags/index.html) accessed 09 January 2025
^↵
European Commission. Common Implementation Strategy for the Water Framework Directive (2000/60/EC). Guidance Document No. 32 on Biota Monitoring (the Implementation of EQSbiota) under the Water Framework Directive.; Technical Report; Publications Office: Luxembourg, 2014.
^↵
European Commission. European Commission - Have your say. European Commission - Have your say. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:52022PC0540 Accessed 21 January 2025
^↵