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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 2021 in mussels and oysters, all exceeded the safe limit values — especially for benzo[a]pyrene, DDE (breakdown product of DDT), and polychlorinated biphenyl (PCB). The few available time trends show that there are more decreasing trends than increasing ones, except for mercury. An overall stabilisation in concentrations suggests that upstream measures are necessary to reach Marine Strategy Framework Directive targets.
Figure 1. Hazardous substances in marine organisms in European seas
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, and consuming contaminated seafoods may generate adverse effects on human health such as organ failure and increased cancer risk. 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 2010-2021 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 the North-East Atlantic (NEA) Ocean and Mediterranean Sea, and mainly 'moderate' in the Baltic Sea. A few 'high' concentrations were found in the NEA Ocean and Mediterranean Sea.
Copper (Cu): 'moderate' or 'low' concentrations in the NEA Ocean and Mediterranean Sea. All concentrations categorised as 'moderate' for the Baltic Sea.
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): ‘low’ concentrations dominated in NEA Ocean while ‘high’ dominated in Mediterranean and Baltic Seas, and few locations 'high' in NEA Ocean. The ‘moderate’ class was found in both Baltic Sea and NEA Ocean but not in Mediterranean Sea.
Dichlorodiphenyltrichloroethane (DDT): (using the breakdown product p,p'-DDE) categorised as ‘moderate’ in NEA Ocean, Baltic and Mediterranean Seas.
Benzo[a]pyrene (BAP): ‘moderate’ in mussels from NEA Ocean and Baltic Sea. Mediterranean Sea had the largest proportion of ‘high’ concentrations, while ‘high’ percentage was low in Baltic Sea and NEA Ocean.
PCB (CB118): Assessment of one PCB (the dioxin-like CB118) showed mainly ‘high’ in all regions. Additionally, a significant part of the concentrations was classified as ‘moderate’. PCBs continue to pose a threat to marine ecosystems (Figure 2).
Time trends show that decreasing trends are more frequent than increasing trends. However, unknown and no (discernible) trends were the most frequent. Abatement policies may explain why increasing trends were not observed more often for all substances.
Figure 2. Concentrations of CB118 relative to assessment criteria
Figure 2 shows more details of assessments of CB118 during the period 2010-2021. 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, Greater North, Celtic and Baltic Seas 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 shows time trends for the MSFD regions that had enough data for the assessment of trends. The Greater North and Celtic Seas had a significant decrease in concentrations during this period. The best estimate of the decrease is ca. 25% per decade. For the Bay of Biscay and Baltic Sea, time trends could be determined, but they were not significant. For the remaining areas, the data were not sufficient for trend analysis.