Mercury pollution may dwarf published levels.

Each year, tons of mercury, a potent neurotoxin, disappear from industry record books, according to a new study. In their forthcoming book, Accounting for Resource Use, environmental economists Robert Ayres and James Cummings-Saxton take an auditor's approach to the industrial use of mercury and other materials, and discover that the intake and output data don't come anywhere near balancing.

Small amounts of mercury occur naturally in the environment, weathering out of terrestrial deposits or evaporating from the oceans, but industrial use has greatly increased the metal's presence. Once airborne, mercury is highly mobile and accumulates readily in the upper links of the food chain. Mercury breaks down protein in both plants and animals; because it's a nerve poison, chronic exposure in humans leads to permanent brain damage.

Mercury is used in batteries, paint, dental fillings, and electrical devices, but its main use may be in the electrolysis of brine to produce chlorine. Mercury is also a widespread contaminant of fossil fuels. Conventional analysis attributes about a third of all airborne mercury to human activity, but the new study argues that the real figure may be as high as 50 to 75 percent.

The actual amount of mercury in the environment will remain a mystery until we know with greater certainty what is happening to the mercury in use. In a review of American chlorine production, for example, the authors found an intake of 209 metric tons of mercury in 1992, while the fullest account of the industry's output for that year cited only 13.2 tons as transferred to other uses or released as emissions. The statistics, from the U.S. Bureau of Mines and the Environmental Protection Agency's Toxic Release Inventory (TRI), left nearly 94 percent of the industry's mercury unaccounted for. Since chlorine producers buy substantial amounts of mercury every year, the missing material is not likely to be in storage. Much of it probably ended up in "off-site treatment and/or disposal," a category that took in 108 tons of mercury from all industrial uses that year. Accounting for chlorine producers' share of this, however, still leaves a lode of missing mercury that dwarfs the industry's reported emissions. Nor are the statistics any better on a national level: of the 621 tons of mercury that the United States consumed in 1992, the TRI can account for only 134 tons.

Such findings suggest that U.S. environmental regulations may be based on a dangerously inadequate understanding of how materials move through the economy. And the implications for other countries may be worse: the authors found the American statistics "grossly incomplete" - but better than those collected in the other countries they studied.