Harmful substances deriving from human activity reach the Baltic Sea from many different sources. Oil spills release large amounts of hydrocarbons into the sea. Radioactive fallout reaches the Baltic either airborne or carried by sea currents.
Heavy metals such as cadmium, lead and mercury are directly harmful to the environment. They accumulate on the sea bottom in sediments and can be converted into a soluble form, released into the water and returned to the nutrient chain when conditions on the sea bottom change through oxygen depletion
Harmful substances also accumulate in organisms. The Finnish Environment Institute is conducting studies on the accumulation of toxic organic compounds (PCB and DDT compounds) in Baltic herring and on heavy metals.
