Surprisingly high levels of pesticides and industrial pollutants sully the snows of western Canada's stunning mountain ranges, ecologists have found. According to a study in tomorrow's Nature, these toxic compounds can waft into the atmosphere and travel hundreds of kilometers before condensing onto snow at high altitudes. As a result, the researchers suspect that cities ringed by high mountains might face an increased risk of contaminated drinking water.
No spot on the planet is free of organochlorines--pesticides such as DDT and industrial solvents called PCBs, which linger in the environment. In earlier work, toxicologists showed that such compounds build up near Earth's poles and at other high latitudes, probably after drifting as gases from warm parts of the globe and condensing in cold regions.
A team of ecologists led by David Schindler of the University of Alberta in Edmonton wondered whether organochlorines also would condense out of the air at altitudes above 2000 meters, where most of each year's snow falls. They collected snow in early 1996 at 15 sites in southern British Columbia and Alberta. Concentrations of the pollutants were up to 100 times higher at the highest site sampled (3100 meters) than at the lowest site (770 meters). "These levels are still well below toxic levels in water," Schindler says. However, he notes that the accumulation of pollutants in fish and other animals could make tinged spring runoff a concern in industrial areas nestled against high peaks, such as Denver or Mexico City.
The findings should help negotiators devise more stringent guidelines within the next 2 years on the uses of persistent pesticides and PCBs, says Andrew Hamilton, chief scientist of the Commission for Environmental Cooperation in Montreal, which is developing new environmental treaties for the United States, Canada, and Mexico under the auspices the North American Free Trade Agreement. "Now it appears that any region of the planet with high mountains will have higher levels of deposition of these compounds, and possibly toxic metals such as mercury and cadmium as well," Hamilton says. "This brings it closer to home for a lot more people."