Contaminants that are ecologically harmful are also referred to as pollutants or hazardous substances.

• substances that do not occur naturally in the environment, such as PCBs, DDTs, dioxins, TBT, nonylphenolethoxylates (NP/NPE), short-chained chlorinated paraffins (SCCP), brominated flame retardants (PBDEs) and certain nitromusks;

• substances occurring at concentrations exceeding natural levels, including heavy metals like lead, copper, cadmium and mercury.

Hazardous substances can accumulate in the marine food web up to levels which are toxic to marine organisms, particularly predators, and they may also represent a health risk for people. Once released into the Baltic Sea, hazardous substances can remain in the water for very long periods.

Certain contaminants may be hazardous because of their effects on hormone and immune systems, as well as their toxicity, persistence and bio-accumulating properties.

A dilute marine cocktail of contaminants

The gradual pollution of the Baltic marine environment by hazardous substances has caused a serious threat to the environment, and may even threaten the health of future generations.

Although monitoring indicates that the loads of some hazardous substances have been reduced considerably over the past 20–30 years, problems still persist. There is still too little comprehensive knowledge about the impact of the most widely used chemicals and their cocktail-like combinations on human health and the environment. Relatively few organic pollutants are fully understood or even identified today. Another problem is that the degradation and transformation of these substances in the marine environment may change their structure and reactive properties. These unknown substances could pose a considerable threat to the environment.