Beluga whales' mercurial status.

Beluga whales in the St. Lawrence River estuary have gained renown for their ill health. At autopsy, the animals' internal organs frequently show evidence of opportunistic diseases, suggesting immune damage--perhaps by environmental pollutants. Moreover, notes Julie M. Gauthier, a marine mammal toxicologist at the University of Quebec in Montreal, the cancer rate in this population of highly protected whales exceeds that in most human or animal populations: Each year, 1 in every 500 of these belugas develops a tumor.

A new study by Gauthier's team hints that mercury pollution might help foster the tumors.

The researchers examined cells derived from the skin of a beluga that had been harvested for consumption by Hudson Bay Inuits. The Quebec scientists incubated these cells with elemental or methyl mercury, pollutants found in the St. Lawrence and other North American waterways (SN: 3/9/91, p. 152).

After the treated cells divided once, the researchers looked for micronuclei: whole or fragmentary chromosomes that failed to become incorporated into the nuclei of newly formed cells. Micronuclei serve as markers of genetic damage and cancer risk.

In the December 1998 Environmental Toxicology and Chemistry, Gauthier's group reports that about 15 percent of cells exposed to low concentrations of the mercury pollutants had micronuclei, twice the rate seen in unexposed cells. As concentrations of the pollutants climbed, so did micronuclei rates--eventually reaching a quadrupling of background values.

Moreover, Gauthier notes, the pollutant concentrations causing "significant DNA damage" in the new tests were comparable to what could be expected in the blood and skin of at least some St. Lawrence belugas. As such, she says, these pollutants--especially the methyl mercury discharged by plants along the river producing the chemical chloralkali--warrant further study as one possible factor underlying the high rate of cancers in these whales.