BS3 Harmful substances

>> Background information

Development

PCBs and DDT are chlorinated organic compounds which have polluted the Baltic Sea for decades. The use of PCBs in electronic insulators and cooling systems began already in the 1920s. DDT is an insecticide developed and used since 1940s. The use of PCBs and DDT has been prohibited in most countries since the 1970s because of their severe toxicity.

The monitoring data from 1985 to present shows a significant decrease in the amounts PCBs and DDT in all sampling points. Present values are merely traces of the peaks of the 1970s. The toxin levels have been generally higher in the Gulf of Finland and Åland than in the Gulf of Bothnia. The data consist of PCB and DDT concentrations in the muscles of Baltic Herrings.

Impact on biodiversity

Harmful substances often have a strong tendency to accumulate in organisms as well as in food webs. It has been observed that PCBs and DDT as well as mercury are enriched in Baltic Herring in a way that in ten year old individuals the concentrations are five times higher than in two year olds. Accumulation in the food web leads to enrichment of these compounds in especially top predators, which may receive harmful or even lethal amounts of toxins. A well-known example of the accumalation of toxic compunds is the case of seals (see BS9).