Scientists unlock mystery of mercury's harmful effects

Martin Mittelstaedt / Toronto Globe & Mail 27mar01

Canadian scientists studying the toxic effects of mercury have made a major breakthrough, showing for the first time how the metal that gave rise to the expression "mad as a hatter" actually debilitates and destroys parts of nerve cells.

The finding, announced yesterday, is likely to raise further controversy over exposure to mercury in dental fillings and food, and provide new clues to the development of Alzheimer's disease.

Three scientists at the University of Calgary exposed the brain cells of snails to small amounts of mercury and found the damage caused by the silvery-grey metal was similar to that seen in brains of humans suffering from Alzheimer's.

The protein in snail brain cells is identical to that in the nerves of human and other higher animals.

One of the co-authors of the paper, Dr. Fritz Lorscheider of the university's faculty of medicine, said the research highlights the need to reduce public exposure to mercury. The experiments used mercury levels that are typically found in people who have a large number of amalgam fillings.

"What it really means is that we . . . need to be far more concerned about sources of mercury exposure," Dr. Lorscheider said.

A paper outlining the findings is being published as the cover story in the April issue of the British journal NeuroReport.

Almost everyone in North America is exposed to trace amounts of mercury. Fillings emit mercury vapour when people chew. Mercury concentrations have been rising in many seafoods, as fish absorb metal dispersed by coal-burning power plants and mining.

Until now, scientists have known that mercury is a potent nerve poison, causing tremors, loss of memory, insomnia, depression and personality changes, but they did not understand how.

Dr. Lorscheider and the two other researchers found that mercury attacks proteins called microtobules, which provide the structure of a nerve cell in much the same way that a skeleton provides structure for an animal.

"If your skeleton was removed, you'd be just a blob, and that's what happens with these neurons.," Dr. Lorscheider said.

The experiments were conducted with other metals, including aluminum, lead, cadmium and manganese, but they had no effect like that of mercury.

Nerves form the electrical wiring of the body, and disintegration of parts of this network could explain behavioural changes. The expression "mad as a hatter" arose when hat makers who used mercury in a felt process got the shakes and showed mental impairment.