Saint Lawrence belugas
Lesions and contaminants
Contaminants
Polycyclic aromatic hydrocarbons (PAH)
Polycyclic aromatic hydrocarbons constitute a family of compounds whose members are abundant in the environment of Saint Lawrence beluga. PAHs result from the incomplete combustion of fossil fuels. These compounds are produced for instance by forest fires, active volcanoes, cigarette smoking and many industrial processes such as some used in aluminum production. Most PAHs found in the Saguenay River, a major part of the Saint Lawrence beluga habitat, originate from the aluminum plant located upstream. They are released in the atmosphere during the reduction of alumina, in large electrolytic cells ("the pots"). Electrolysis of alumina is carried out with a negative electrode (cathode) composed of a steel shell lined with carbon, and with a positive electrode (anode), which is a baked mixture of coke and petroleum pitch suspended over the electrolytic bath. During the reaction, the burning anode generates particles and gases rich in PAHs (coal tar pitch volatile).
Workers in the aluminum plants upstream of the Saguenay River are affected by a high prevalence of lung and urinary bladder cancer that are clearly related with exposure to coal tar pitch volatiles (from the burning anode). affected workers are now compensated by the Quebec worker's compensation board (CSST). Importantly, it has been demonstrated that chronic ingestion of coal tar mixtures causes small intestinal cancer in mice.
Carcinogens are also present in the environment of Saint Lawrence beluga and beluga likely ingest these compounds. Sediments in the Saguenay River, part of the beluga habitat, contain 500-4500 ppb of total PAH (dry weight) originating for the most part from the aluminum factories located upstream. Invertebrates living in sediments contaminated by PAH accumulate these compounds, in contrast to vertebrates. In summer, beluga are known to feed in significant amounts on bottom invertebrates. In addition, field observations suggest that these whales dig into sediments. Benzopyrene DNA adducts were detected in the brain of stranded Saint Lawrence beluga brain tissue. (Exposure to benzopyrene is often used as a marker for exposure to PAHs because it is the most abundant and one of the most carcinogenic PAH). However, in a different study where stranded Saint Lawrence beluga liver was analyzed using a different technique, no difference was observed between Arctic and Saint Lawrence beluga tissues. These apparently conflicting results are not surprising given the different methods and tissues that were used in the two studies.
Considered together, these observations suggest that Saint Lawrence beluga ingest carcinogenic compounds accumulated by benthic invertebrates, which may contribute to the etiology of digestive tract cancers. The concomitant role of viruses in the etiology of these cancers cannot be ruled out since in the bovine species, both the ingestion of a carcinogen (bracken fern) and infection with bovine papillomavirus type 4 are necessary to cause small intestinal cancer. In addition, genetic factors may also contribute to the etiology of these cancers.
Organochlorinated compounds (OC)
Each adult beluga whale carries between 20 and 30 grams of pure PCBs, enough to cover the bottom of your average peanut butter jar! Adult females are slightly less contaminated than adult males because they get rid of PCBs and DDT through their milk. Unfortunately newborns ingest these contaminants. Thus, the beluga herd moves between 14 and 21 kilograms of pure BPC around the St Lawrence Estuary, that is almost a full average sized bucket. This corresponds to the amount carried by the whole bovine population of Canada, that is around twenty millions animals.
Saint Lawrence beluga are affected with lesions and infectious agents compatible with immunosuppression. Numerous collaborators, among whom Drs. P. Béland, S. De Guise, C. Desjardins, S. Lair, I. Mikaelian, D. Martineau, R. Norstrom and L. Shugart, have demonstrated that these animals are contaminated by high levels of organochlorinated compounds (a family of compounds with powerful immunosuppressive effects). Dr. S. De Guise (currently professor at University of Connecticut) studied the immune system of beluga whales during the course of a Ph.D. program in the laboratory of Dr. M. Fournier at Université du Québec à Montréal (UQAM). He demonstrated that, in vitro, the normal proliferation of immune cells of Arctic beluga decreased when these cells were exposed to a mixture of OC compounds at concentrations similar to those observed in the tissues of Saint Lawrence beluga.
Heavy metals
Heavy metals, of which several are immunosuppressive, are also found in high concentrations in the tissues of Saint Lawrence beluga. Dr S. De Guise demonstrated in vitro that mercury concentrations found in Saint Lawrence beluga liver were sufficient to decrease the proliferative response of immune cells from Arctic beluga. Dr Julie Gauthier, while a Ph.D. candidate in Dre. H. Dubeau's laboratory, at UQAM, demonstrated that toxaphene (an OC insecticide) and mercury break down the nuclei of beluga cells in culture.
Again, this negative effect was observed when beluga cells were exposed to pollutant concentrations similar to those measured in Saint Lawrence beluga tissue. (Interestingly, Dr Gauthier developed this cell line from a juvenile beluga dead since several days). Because these compounds damage the genetic material of beluga (contained in nuclei), they could be involved in the etiology of the various types of cancer observed in that population.
Tributyltins
Beluga tissues provided by B. Doidge, D. Leclair, I. Mikaelian, and D. Martineau and analyzed by R. St-Louis, R. S. deMora, and E. Pelletier were found to be contaminated by tributyltins, highly toxic compounds used to paint the hulls of large ships. (Approximately 6,500 ships cross annually the Saint Lawrence beluga habitat). This compound kills mollusks that would grow on unprotected hulls. Curiously, the use of tributyltins in antifouling paint is illegal in Canada only for boats shorter than 25 m.
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