IMPAIRED IMMUNITY IN HARBOR SEALS (PHOCA-VITULINA) EXPOSED TO BIOACCUMULATED ENVIRONMENTAL CONTAMINANTS - REVIEW OF A LONG-TERM FEEDING STUDY

Mass mortalities among seals and dolphins inhabiting contaminated mari ne regions have led to speculation about a possible involvement of imm unosuppression associated with environmental pollution. To evaluate wh ether contaminants at ambient environmental levels can affect immune f unction of seals, we carried out an immunotoxicological study under se mifield conditions. Two groups of 11 harbour seals (Phoca vitulina) or iginating from a relatively uncontaminated area were fed herring from either the highly polluted Baltic Sea or the relatively uncontaminated Atlantic Ocean. Changes in immune function were monitored over a 2 1/ 2-year period. The seals that were fed contaminated Baltic herring dev eloped significantly higher body burdens of potentially immunotoxic or ganochlorines and displayed impaired immune responses as demonstrated by suppression of natural killer cell activity and specific T-cell res ponses. During a 2-week lasting experiment performed at the end of the feeding study, mobilization of organochlorines from the blubber did n ot lead to a strong increase of contaminant levels in the blood, and n o enhancement of the existing immunosuppression was observed. These re sults demonstrate that chronic exposure to environmental contaminants accumulated through the food chain affects immune function in harbour seals, whereas short-term fasting periods, which are normal for seals, do not seem to pose an additional risk. The seals of this study were not exposed perinatally to high levels of environmental chemicals, and body burdens of organochlorines measured near the end of the study we re lower than those generally observed in free-ranging seals inhabitin g many contaminated regions. Therefore, it may be expected that enviro nmental contaminants adversely affect immune function of free-ranging seals inhabiting contaminated regions at least as seriously as observe d in these studies.