In Europe, the Baltic Sea is an important sink of PCBs and dioxins. However, recent studies have revealed a major problem at localised spots, due to the production and use of chlorophenols for impregnation of timber. In the most contaminated regions the concentration of PCDDs and PCDFs in soil and sediments appears to be incredibly high. The decrease in environmental concentrations is due to cessation of PCB use and improved incineration technology. Dioxins and some PCBs cause multiple toxic effects.
Dioxins bring about a wide spectrum of biochemical and toxic effects in experimental animals.
These effects depend on species, strain, gender, age and tissue. TCDD serves as a surrogate for the whole group of chemicals. For the most part, the mechanisms of these impacts are still obscure. This hampers rational risk assessment. Some of the most toxic PCBs have dioxin-like toxicity based on AH receptor, but e.g. some effects of PCBs on the nervous system are believed to have a different mechanism.