Science / Medicine : Toxic Metals on Increase

The toxicity of heavy metals such as lead and mercury released into the environment as a result of human activity is now greater than the toxicity of all organic and radioactive wastes, Canadian and Norwegian researchers said last week.

Such toxic metals, which can cause nervous system damage and even death, have already significantly contaminated freshwater resources and are increasingly accumulating in the human food chain, the researchers warned in Nature magazine. But it is difficult to document whether this contamination has already had any effect on human health, said geochemist Jerome O. Nriagu of the National Water Research Institute in Burlington, Ont.

The researchers said that coal combustion, electric utilities, steel and iron manufacturing and internal combustion vehicles are the primary sources of heavy metal pollution, but that incineration of urban refuse is accounting for a growing share.

On average, the amount of arsenic, cadmium, copper, nickel and zinc released into the environment by human activity is about twice as large as the amount released by natural sources, the researchers said, but human activity releases 17 times as much lead as natural sources.