Levels of contaminants in many parts of the Baltic Sea are elevated compared with most European seas. The overall contamination status has not changed markedly in the past two decades. Generally the levels of some contaminants that were previously of concern are improved today, for example hexachlorocyclohexane (HCH, lindane) and dichlorodiphenyltrichloroethane (DDT) and its metabolites. Contaminants that degrade very slowly and are expected to be long-lasting in the ecosystem include mercury, flame retardants (PBDEs), dioxins, and PCBs. The latter two are of special concern for the fishing sector and for food provision.
Generally, there is a long recovery time in the environment for contamination that has taken place in the past, with a continuous risk that sediment-deposited contaminants will be remobilized.
Oil spills have decreased in all sub-basins of the Baltic Sea over the past decades. However, increasing maritime traffic leads to continued risk that single oil spills introduce large amounts of oil to the environment.
Caesium (Cs-137), deposited after the accident at the Chernobyl nuclear power plant in 1986, is now at acceptable levels in some sub-basins and can be expected to be so in all of the Baltic Sea by 2020.