CONTAMINANT-INDUCED IMMUNOTOXICITY IN HARBOR SEALS - WILDLIFE AT RISK

Persistent, lipophilic polyhalogenated aromatic hydrocarbons (PHAHs) a ccumulate readily in the aquatic food chain and are found in high conc entrations in seals and other marine mammals. Recent mass mortalities among several marine mammal populations have been attributed to infect ion by morbilliviruses, but a contributing role for immunotoxic PHAHs, including the polychlorinated biphenyls (PCBs), polychlorinated diben zo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) was no t ruled out. We addressed this issue by carrying out a semi-field stud y in which captive harbour seals were fed herring from either the rela tively uncontaminated Atlantic Ocean or the contaminated Baltic Sea fo r 2 years, We present here an overview of results obtained during this study, An impairment of natural killer (NK) cell activity, in vitro T -lymphocyte function, antigen-specific in vitro lymphocyte proliferati ve responses, and in vivo delayed-type hypersensitivity and antibody r esponses to ovalbumin was observed in the seals fed the contaminated B altic herring. Additional feeding studies in PVG rats using the same h erring batches suggested that an effect at the level of the thymus may be responsible for changes in cellular immunity, that virus-specific immune responses may be impaired, and that perinatal exposure to envir onmental contaminants represents a greater immunotoxic threat than exp osure as a juvenile or adult. Together with the pattern of TCDD toxic equivalents of different PHAHs in the herring, these data indicate tha t present levels of PCBs in the aquatic food chain are immunotoxic to mammals. A review of contaminant levels in free-ranging harbour seals inhabiting polluted areas of Europe and North America suggests that ma ny populations may be at risk to immunotoxicity. This could result in diminished host resistance and an increased incidence and severity of infectious disease.