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.