PATHOLOGY AND TOXICOLOGY OF BELUGA WHALES FROM THE ST-LAWRENCE ESTUARY, QUEBEC, CANADA - PAST, PRESENT AND FUTURE

An indigenous population of 450-500 beluga whales (Delphinapterus leuc as) inhabiting the St. Lawrence Estuary has been exposed chronically f or more than 50 years to a complex mixture of industrial pollutants in cluding organochlorinated compounds (OC), polycyclic aromatic hydrocar bons (PAH) and heavy metals. From 1983 to 1990, we have necropsied 45 well preserved carcasses out of a total of 120 beluga whales reported dead over this period. Of these 45 animals, nine were affected by 10 m alignant neoplasms. Fifteen animals (33%) were affected by pneumonia. Milk production was compromised in eight of 17 mature females (41%), b y inflammatory changes (seven animals) and cancer (one animal) which a ffected the mammary glands. Opportunistic bacteria were found in pure culture, and/or in significant amounts in at least two organs in 20 be lugas (44%). The concentrations of both total PCBs and highly chlorina ted PCB congeners were much higher in St. Lawrence animals than in Arc tic beluga whales. OC-induced immunosuppression has been repeatedly de monstrated in a wide variety of animal species. Therefore, it is proba ble that the immune functions of St. Lawrence beluga whales are impair ed. Benzo[alpha]pyrene adducts were detected in 10 of the 11 St. Lawre nce beluga whales of which tissues (six livers, 10/11 brains) were ana lyzed by a method based on HPLC. No such adducts were found in four Ar ctic animals. Since benzo[alpha]pyrene is one of the most potent chemi cal carcinogens known to man, these compounds might be responsible for some of the cancers observed in that population. Overall, our finding s contrast vividly with those of others who found that cancers are exc eedingly rare in free-ranging odontocete populations and that the majo r causes for mortalities in these populations are bacteria, parasites, and trauma.