Toxic Compounds and Health and Reproductive Effects in St. Lawrence Beluga Whales

Abstract

An epidemiologic study was carried out over a period of 9 years on an isolated population of beluga whales ( Delphinapterus leucas) residing in the St. Lawrence estuary (Quebec, Canada). More than 100 individual deaths were aged, and/or autopsied and analyzed for toxic compounds, and the population was surveyed for size and structure. Arctic belugas and other species of whales and seals from the St. Lawrence were used for comparison. Population dynamics: Population size appeared to be stable and modeling showed this stable pattern to result from low calf production and/or low survival to adulthood. Toxicology: St. Lawrence belugas had higher or much higher levels of mercury, lead, PCBs, DDT, Mirex, benzo[a]pyrene metabolites, equivalent levels of dioxins, furans, and PAH metabolites, and much lower levels of cadmium than Arctic belugas. In other St. Lawrence cetaceans, levels of PCBs and DDT were inversely related to body size, as resulting from differences in metabolic rate, diet, and trophic position, compounded by length of residence in the St. Lawrence basin. St. Lawrence belugas had much higher levels than predicted from body size alone; levels increased with age in both sexes, although unloading by females through the placenta and/or lactation was evidenced by overall lower levels in females and very high burdens in some calves. No PCDDs and only low levels of some PCDFs were detected in St. Lawrence belugas, while proportions of toxic non-ortho (coplanar) PCBs were low relative to proportions seen in other species. At least ten different PCB methylsulphone metabolites were detected in St. Lawrence belugas. Levels of B[a]P adducts to DNA in St. Lawrence beluga brain and liver approached those associated with carcinogenis in small laboratory animals. Pathology: St. Lawrence belugas were not emaciated, and major findings were: a high prevalence of tumors (40% of animals) including eight malignant neoplasms; a high incidence of lesions to the digestive system (53%), to the mammary glands (45% of adult females), and to other glandular structures (11%); some evidence of immuno-suppression; frequent tooth loss and periodontitis. Two animals had severe ankylosing spondylosis and another was a true bilateral hermaphrodite. No such lesions were observed in 36 necropsies of Arctic belugas and of seals and cetaceans from the St. Lawrence.