Hazardous substances in marine organisms in European seas

Hazardous substances pollute European seas. When these substances exceed certain limits in marine organisms, a risk is posed to ecosystems and human health through the food chain. Of nine hazardous substances monitored between 2010 and 2019, all exceeded the safe limit values — especially benzo[a]pyrene, dichlorodiphenyltrichloroethane (DDT) and polychlorinated biphenyl (PCB). The few available time trends show that there are more decreasing trends than increasing ones (with the exception of mercury). An overall stabilisation in concentrations suggests that upstream measures are necessary to reach Marine Strategy Framework Directive targets.

In the marine environment, hazardous substances accumulate in fish and shellfish, which are a food source for marine wildlife and humans. The contaminants are toxic for marine biota, and consuming contaminated seafoods may generate detrimental effects on human health such as structural damage or failure of organs and increased cancer risk. Reducing concentrations of these substances helps achieve the MSFD Good Environmental Status and the Zero Pollution Action Plan targets.

Classifications of hazardous substances measured in mussels and oysters between 2010-2019 are summarised below and in Figure 1. Concentrations were classified by Environmental Quality Standards (EQS) in biota where available; and 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.

Cadmium (Cd): ‘moderate’ or ‘low’ in all regions. A few ‘high’ concentrations were found in the North-East Atlantic (NEA) Ocean and the Baltic Sea.

Copper (Cu): ‘moderate’ or ‘low’ in all regions.

Lead (Pb): ‘moderate’ or ‘low’ in all regions. ‘High’ concentrations were found in a small proportion of NEA Ocean and Mediterranean stations.

Mercury (Hg): ‘moderate’ in a majority of NEA Ocean and Baltic Sea locations, while generally ‘low’ in mussels from the Mediterranean. In the case of mercury, ‘moderate’ is above the Environmental Quality Standard.

Hexachlorobenzene (HCB): ‘low’ for the majority of NEA Ocean locations and ‘moderate’ for the majority of Baltic Sea and Mediterranean Sea locations.

Lindane (HCHG): Most concentrations in the Mediterranean Sea (64%) and the Baltic Sea (77%) were classified as “high”. In the NEA Ocean, most concentrations (60%) were “low”, but also here some locations (12%) had “high” concentrations.

Dichlorodiphenyltrichloroethane (DDT): (using the breakdown product p,p'-DDE; DDE) ‘moderate’ in the NEA Ocean, Baltic Sea and Mediterranean Sea.

Benzo[a]pyrene (BAP): ‘moderate’ in mussels from the NEA Ocean and the Baltic Sea. The Mediterranean Sea had the highest proportion of ‘high’ concentrations, while in the Baltic Sea and the NEA Ocean, the ‘high’ proportion was low.

PCB (CB118): Unlike in previous years, an assessment of one particular PCB (the dioxin-like CB118) was carried out. This PCB was mainly classified as ‘high’ in all regions. In addition, a large part of the concentrations was classified as ‘moderate’.

Time trends show that decreasing trends were more frequent than increasing trends. However, unknown and no trends were most frequent. Abatement policies may explain why increasing trends weren’t observed more often for all substances.

Figure 2 shows more details of assessments of CB118 during the period 2010-2019. The OSPAR evaluation criteria, BAC, and Environmental Quality Standards (EQS) are indicated. At the same time, the boxplots show that a large percentage of the ‘high’ classifications (red points) exceed the EAC many times. The Western Mediterranean Sea, Greater North Sea, Celtic Seas and Baltic Sea all had stations where concentrations of CB118 in mussels were more than ten times the EAC. The higher concentrations likely result in a higher risk of adverse effects for mussels and other aquatic organisms. The dioxin-like PCBs are also toxic to humans, and in 2018, the European Food Safety Authority set a tolerable weekly intake of dioxins and dioxin-like PCBs for humans .

The figure also shows time trends for the MSFD regions that had enough data to enable trend assessments. There were significant decreases in concentrations between 2010 and 2019 in the Greater North Sea and the Celtic Seas. The best estimate of the decreases is around 25% per decade. For the Bay of Biscay/Iberian coast and the Baltic Sea, time trends could be determined, but they were not significant. For the remaining areas, the data were not sufficient to enable trend analysis.

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; DDEPP), benzo[a]pyrene (BAP) and 2,3',4,4',5-Pentachlorobiphenyl (CB118). For each station, the 90% percentile over the 10-year period 2010-2019 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 in mussels in the spring are affected by spawning. For status, the 90% percentile over the 10-year period 2010-2019 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 1 year (Mediterranean) or 3 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 data series had no median concentrations under LOQ, we used linear regression; otherwise, a Bayesian model (with non-informative priors) implemented in JAGS (Plummer 2021) was used.

Database extractions taken in early 2021 were used. However, due to the time lag in reporting, most data series stop in 2019 — so the analysis was restricted to the period 2010-2019. Even so, we do not expect that including later data would have substantially changed the conclusions.

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 uncertaintiesData sources and providers

Metadata

DPSIRTopicsTagsTemporal coverageGeographic coverage

TypologyUN SDGsUnit of measureFrequency of disseminationContact

References and footnotes

EEA, 2011, Hazardous substances in Europe’s fresh and marine waters: an overview., Publications Office of the European Union, Luxembourg.

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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.

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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.

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In organisms, DDT is quite rapidly metabolised to DDE (which also is toxic); therefore, almost all monitoring programs measure DDE as a proxy of DDT.
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