Epizootier som drabbat marina däggdjur och lett till storskaliga dödsfall har uppmärksammats runt om i världen de senaste decennierna. Höga halter av persistenta miljökontaminanter såsom DDT (diklordifenyltrikloretan) och PCB (Polyklorerade bifenyler) har uppmätts hos djur som drabbats. Detta har lett till tankar om att miljökontaminanter, i den nivå de finns i våra akvatiska ekosystem idag, kan vara en bidragande orsak till den ökade mottagligheten för infektioner och den ökade mortaliteten hos marina däggdjur. I denna litteraturstudie sammanställs resultaten från försök, både på laboratoriedjur och marina däggdjur, som tyder på att kontaminanter med fokus på PCB kan orsaka immunosuppression och därmed vara en bakomliggande orsak till allvarligheten i dessa epizootier. Resultat från studier visar på att PCB kan orsaka immunosuppression genom att ge nedsatt proliferativt svar hos T-lymfocyter under stimulering med mitogener, minskad aktivitet hos NK-celler, nedsatt antikroppsproduktion, minskad antigen-specifik proliferation och minskat DTH (delayed-type hypersensitivity) svar.

Polychlorinated biphenyls, PCBs, were used in elastic sealants in buildings during the years1956-1973. Studies of PCB have revealed that it is harmful for humans and animals,especially water-living predators and other top-predators. It is also a persistent organicpollutant and remains in the environment for a very long time. To reduce the levels of PCB inthe environment, it has to be removed from the buildings. According to Swedish law, theproperty holder has to decontaminate sealants with a PCB level of 500 mg/kg or above.

Environmental chemicals are transported to the Arctic through the air and oceans, once within the Arctic they spread through rivers, lakes and other watercourses. Polar bears and sledge dogs in-gest high concentrations of environmental chemicals since many of the chemicals are fat-soluble and their diet mainly consists of marine mammals. The aim of this study is to describe how environmental chemicals spread in nature, how they reach the polar bears, and finally how they affect the animals reproduction, with reproductive hormones and genitals in focus. The animals are exposed to a cocktail effect which complicates the assessment of the chemicals impact on the reproduction. Studies show that the genitals can decrease in size or become malformed, sexual maturation can be affected and the reproductive hormones can be disturbed.