Abstract

The nature, frequency and severity of the lesions observed during postmortem examination of beluga whales from a small isolated population that resides in the highly polluted St. Lawrence estuary suggested pollutants-related immunosuppression in these animals. A study was undertaken to investigate the possible relationships between environmental contamination by organo-halogens and heavy metals and a possible immunosuppression in St. Lawrence beluga whales. Since relatively little was known about marine mammal immunology, assays were developed to evaluate different immune functions in beluga whales. These assays included phagocytosis and respiratory burst, the main functions of neutrophils which are responsible for ingestion and destruction of foreign material such as bacteria, in vitro mitogen-induced lymphoblastic transformation, that measures the ability of lymphocytes to respond to stimulation, NK activity, an important non-specific defense mechanism against viral infections and tumors, and immunophenotyping of peripheral blood lymphocytes using monoclonal antibodies. Another step in this study was to evaluate the possible effects of environmental contaminants on the immune functions of belugas. The effects of in vitro exposure to eco-toxicologically relevant heavy metals and organochlorines was evaluated. Exposure to mercury and cadmium at concentrations in the range of those found in the liver of wild belugas decreased beluga lymphocytes proliferation, while lead did not. While none of six organochlorine compounds had an effect on phagocytosis at the concentrations tested, PCBs138, 180, and p,p'-DDT, but not PCBs 153, 169 nor p,p'-DDE, reduced the proliferative response of beluga lymphocytes. Also, the proliferation of beluga lymphocytes was reduced by exposure to mixtures of congeners at concentrations in the range of those observed in tissues of St. Lawrence belugas and at which they had no effect separately. In order to determine the immuno-toxic potential of naturally occurring mixtures of environmental contaminants, rats were fed blubber from either highly contaminated St. Lawrence or relatively uncontaminated Arctic belugas. Surprisingly, no differences were found in immune functions between the groups, and the possible reasons will be discussed. The effects on proliferation of beluga whale lymphocytes exposed in vitro to heavy metals and mixtures of organochlorines at concentrations in the range of those observed in tissues of St. Lawrence belugas might support the hypothesis of pollutants-induced immunosuppression in these animals. A further step will be to compare immune functions of highly polluted beluga whales from the St. Lawrence to those of relatively uncontaminated Arctic populations.