Contaminant-induced immunosuppression and mass mortalities among harbor seals

Virus-associated mass mortalities among seals inhabiting northwestern Europ e have generated an interest in immunotoxicology in this species. A morbill ivirus has been isolated from victims, but a contribution of immunotoxic co ntaminants to the severity of the outbreaks could not be ruled out. Fish-ea ting seals occupy high trophic levels in the aquatic food chain, and accumu late high levels of contaminants including polychlorinated biphenyls (PCBs) , polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofur ans (PCDFs). Such chemicals have been found to be immunotoxic at low doses in studies of laboratory animals. We carried out an immunotoxicological stu dy, in which captive harbor seals (Phoca vitulina) were fed herring from ei ther relatively uncontaminated sites of the Atlantic Ocean, or from the hig hly contaminated Baltic Sea. In this report we summarize the contaminant-re lated immunosuppression observed in the captive group of seals fed herring from the Baltic Sea. In addition, we describe two parallel studies, in whic h laboratory rats are exposed as adults or perinatally to the contaminants in the Baltic Sea herring, exhibiting immunotoxicity. On the basis of these studies we conclude that complex mixtures of environmental contaminants in cluding PCBs, PCDFs, and PCDDs may represent a real immunotoxic risk to fre e-ranging seals. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved .