Do PAHs (toxic contaminants) cause cancer in St. Lawrence beluga whales... 

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An open debate…

Several researchers challenge the links established by Dr. Martineau and his collaborators between PAH contamination and cancers found in necropsied beluga whales. Here we present critiques prepared by two groups of researchers.

The first group is made up of Gilles Thériault of McGill University's Department of Occupational Health, Graham Gibbs of the Safety Health Environment International Consultants Corp. from Alberta and Claude Tremblay of the Institut national de santé publique du Québec. These researchers are conducting a study on lung and bladder cancer in aluminum smelter workers from the Saguenay area and their near-daily exposure to high concentrations of PAHs. This study is part of a programme funded by Alcan. In their analysis, Martineau and his collaborators draw a parallel between the fate of aluminum smelter workers and beluga whales, both of which are exposed to PAHs. According to Thériault, Gibbs and Tremblay, the cases of beluga whale and human exposure are not comparable due to the fact that exposure to PAHs occurred differently for each population: aluminum smelter workers breathed them in, while beluga whales absorbed them by ingesting contaminated prey. Martineau and his collaborators respond by stating that PAHs can provoke different types of cancers depending on vectors of exposure. It is therefore not surprising, according to them, that beluga whales develop digestive system cancer by consuming the live prey that inhabits the HAP-contaminated sediment while aluminum smelter workers develop lung and urinary bladder cancers by breathing in PAHs.

Thériault, Gibbs an Tremblay also question the correlation made by Martineau and his collaborators between the high rate of St. Lawrence beluga whale cancer and the high cancer rate of the human population living near beluga whale habitat. Martineau and his collaborators suspect that the high levels of stomach, breast and digestive tract cancer in the Saguenay area human population could be linked to the contamination of drinking water—most of it drawn from surface sources such as lakes and rivers—by PAHs discharged into the atmosphere by local aluminum smelters. Thériault, Gibbs and Tremblay challenge the cancer rate used by Martineau and his collaborators as it inflates statistics by not excluding aluminum workers. Also, according to Thériault, Gibbs and Tremblay, there is no known connection between PAHs and the stomach cancers of smelter workers, even though they consume local drinking water. Finally, it is highly unlikely, again according to Thériault, Gibbs and Tremblay, that high cancer rates in the Saguenay population are linked to PAH contaminated drinking water because PAH levels measured in both treated and non-treated water meet Environment Ministry norms.

The second group of researchers to challenge the Martineau et al. publication is made up of Mike Hammill and Véronique Lesage, of Fisheries and Oceans Canada’s Maurice-Lamontagne Institute, and Michael Kingsley of the Greenland Institute of Natural Resources. According to these researchers, the population size that was used to calculate the cancer rate is too low and thus inflates statistics. In light of new science, a total population value of 1100 beluga whales should be used, instead of 650. Martineau and his collaborators reply that they used the population size that was published and accepted when they published their study. Furthermore, Kingsley, one of the co-authors of the critique, had already mentioned that the mortality rate that had been used to calculate the annual cancer rate (1.4 percent) was particularly low. Yet, according to Martineau and his collaborators, by using the new value for population size and a more realistic cancer rate of 6 percent the annual cancer rate would be even higher than the one presented in their article.

Hammill, Lesage and Kingsley also question Martineau and his collaborator’s conclusions concerning how beluga whales become contaminated by PAHs, that is to say by consuming marine invertebrates in the Saguenay River, a major source of PAHs. According to them, the Saguenay is not used intensively by all beluga whales. Furthermore, data used to determine beluga whale diet is from a study that was conducted in 1936 in the Ouelle River area, far from the zone that is presently occupied by St. Lawrence beluga whales. Yet, Martineau and his collaborators specify that a study carried out by Robert Michaud demonstrated that 5 percent of beluga whales could be found in the Saguenay River during the summer and that there is no reason to believe that beluga whales avoid eating prey found in this river. Finally, Hammill, Lesage and Kingsley estimate that the importance of cancer as cause of death could be overestimated, considering the difficulty in evaluating other causes of death, such as ship strikes and malnutrition.

Cancers noted in St Lawrence beluga whales are complex and worthy of concern. Although the critiques formulated by various groups of researchers have shed doubt on some of the numbers put forward in the study carried out by Daniel Martineau and his collaborators, the coincidence between the high rates of cancer found in St. Lawrence beluga whales and the human population in the Saguenay area remains intriguing. These critiques should lead to a better understanding of this nebulous issue and urge further investigation. What is the nature of the link between high concentrations of contaminants—PAHs and others—measured in St. Lawrence beluga whales and the types of cancer that have been detected? The causes of these cancers have yet to be determined.