St. Lawrence beluga whales, the river sweepers? (Correspondence).

Many polycyclic aromatic hydrocarbons (PAHs), among which the most extensively studied is benzo[a]pyrene (BAP), are carcinogenic in mammals (1,2). Because humans are also mammals, these PAHs are reasonably anticipated to be human carcinogens (3-5).

Further support for PAH carcinogenicity in humans has been provided by epidemiologic studies such as those carried out in aluminum workers of the Saguenay-Lac Saint-Jean region of Canada (6-8). In these studies, the epidemiologic association between exposure to PAHs and lung and urinary bladder cancers has been strong enough to warrant the compensation of affected workers by the Quebec Health and safety Workers Compensation Board (6-8).

The types and sites of cancer induced by PAHs depend on the route of exposure (1,2,9). Thus, it should be no surprise that PAHs cause lung and urinary bladder cancer in aluminium workers who inhale these compounds and that PAHs may cause cancer of the digestive system in belugas, because these animals ingest fish that feed on plankton and invertebrates living in the contaminated sediments of the Saguenay river (10).

Advanced age is related to the high incidence of cancer. Thus, the high rate of cancer in SLE belugas might have been associated with the old age of stranded belugas, but this is not the case. Belugas that died as a result of being hunted in Alaska and belugas found stranded in the SLE were used to infer the age structures of the respective populations (Figure 1), following accepted procedures in field population biology that are appropriate to each case (11-15). The records (13-15) show that age-specific mortality rates in classes 18 and above are consistently higher in the SLE than in Alaska; thus, "St. Lawrence estuary beluga die at an earlier age," as we stated in our paper (16). Further, the age distribution of adult belugas that died of cancer is the same as adult belugas that died from other causes (16). The hypothesis that the SLE population includes a large proportion of animals in the age groups with elevated cancer rates is not supported by the data (13-15). Within the 18-30-year age group--the age group of SLE belugas with intestinal cancer (16)--there are more belugas in the Alaska population (19.8%) than in the SLE population (18.9%) (Figure 1).

[FIGURE 1 OMITTED]

The data in our paper relating to pet animals (17) were collected from animals seen in veterinary colleges and thus comprise a large proportion of sick animals, where cancer is most likely more prevalent than in the general population of domestic animals.

Smith and Levy (18) estimated that, downwind of the smelters, 40,000 tons of PAHs had accumulated in the Saguenay watershed by 1980; 20 tons of the accumulated PAHs are released annually, of which 3% is BAP (18). They stated that this represents a serious, chronic hazard to this environment and its inhabitant (18). The smelter company estimated that 100-200 tons of PAHs were released annually between 1964 and 1976 through the liquid waste discharged directly into the Saguenay River from the scrubber of one plant [Alcan, personal communication, cited in (19)]. Smith and Levy (18) more conservatively estimated that 80 tons of PAHs were discharged in the Saguenay before 1976 from that plant.

In the 1990s two studies were carried out by the Quebec Environment Ministry, each using a different norm (20,21). The Quebec Environment Ministry classified 16 PAlls as "group 1 PAHs," which comprises PAHs that are possibly and probably carcinogenic and those for which there is sufficient evidence of carcinogenicity. The first study was carried out on surface waters from 1997 to 1999 (20) using a norm from the U.S. Environmental Protection Agency (5); this norm of 4.4 ng/L (group 1 PAHs), which was designed to protect an individual who drank this water for his/her life time and ate aquatic organisms containing bioaccumulated material from water contaminated at the determined level, was exceeded in this study. For instance, 1 km downstream of the drinking water intake of LaBaie city, "Riviere a Mars" contained up to 19.7 ng/L in 1997 (n = 2) and 16.4 ng/L in 1999 of group 1 PAHs. Total PAH levels were much higher--up to 83 ng/L--in Riviere Chicoutimi in 1997 (20).

Cancer, the ultimate result of a progressive accumulation of mutations over a long period, requires exposure to mutagens over a significant proportion of the life span of animals and people (22). In marked contrast, PAH levels in the surface waters of the Saguenay-Lac Saint-Jean area have been measured only twice over a short and recent period (1997-2000) (20,21).

The smelter company claims that, in 2002, PAH emissions have been reduced 88% from the 1983 levels (23). This implies that PAH emissions were about 8 times higher in 1983 and that, in 1983 and over the previous decades, PAH levels in the surface waters, downwind of the smelters, were most likely elevated in the same proportion. Supporting this inference, Picard-Berube et al. (24) reported in 1983 that the initial BAP levels of blue mussels transplanted from a nonpolluted area to various sites along the fjord increased 200 times within 1 month (24). Aluminium workers, predominantly male, have been exposed to airborne PAHs (6-8). A significant part of the daily water intake of aluminium workers has occurred at work, as opposed to the spouses whose water intake has been largely at home.

Although no attempts have been made to detect PAHs in the tissues of people living in that region, the Quebec worker compensation board compensates aluminium workers affected with urinary bladder cancer based on their exposure to PAHs (8). In contrast, such attempts--which have demonstrated PAH contamination--have been made in terrestrial and aquatic wildlife of that region (25,26). The results and observations presented in our paper (16) warrant undertaking studies that would address this gap.

REFERENCES AND NOTES

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Daniel Martineau
Karin Lemberger
Andre Dallaire
Pascal Michel
Faculte de Medecine Veterinaire
Departement de Pathologie et Microbiologie
Universite de Montreal
Montreal, Quebec, Canada
E-mail: [e-mail]

Pierre Beland
St. Lawrence National Institute of
Ecotoxicology
Montreal, Quebec, Canada

Philippe Labelle
University of California, Davis
Veterinary Medical Teaching Hospital
Davis, California

Thomas P. Lipscomb
Department of Veterinary Pathology
Armed Forces Institute of Pathology
Washington, DC