Contaminants in Swedish offshore sediments 2003–2021. Results from the national environmental monitoring programme.

The environmental monitoring of contaminants in offshore sediments includes organic contaminants and elements in surface sediments at 16 stations located in deeper sea areas around Sweden. The stations are placed far from the coast to reflect general pollution patterns in the environment. So far, sampling has been done four times with intervals of 5–6 years. This report summarizes the results and evaluates geographical trends. Levels of arsenic and cobalt are highest in the Gulf of Bothnia, while levels of cadmium, copper and zinc are highest in the Baltic Proper. Cadmium levels are so high that the environmental quality standard (EQS) is exceeded. These patterns depend on redox conditions, levels in bedrock/moraine in the catchment, and point sources. Levels of lead and mercury are elevated at specific stations, indicating a greater influence from point sources. Overall, metal levels are elevated compared to reference values that represent pre-industrial levels. The greatest load of organic contaminants occurs in the Baltic Proper. For most contaminants, for example PAHs, PCBs, organophosphorus compounds, TBT, and many organochlorine pesticides, the highest levels can be observed in this sea area. TOC levels are also high here. Surprisingly, levels of PFASs are markedly higher in the Gulf of Bothnia compared to other sea areas. Levels of chlorinated paraffins, measured in sediment cores from three stations, were also elevated in the Gulf of Bothnia. Levels of TBT have decreased since the start of the monitoring programme, but the EQS is still exceeded at many stations. PAHs also occur at levels that sometimes exceed thresholds. Cybutryne, which is now banned in the EU, has decreased in levels since 2008 and 2014