Environmental poisons never play by the rules. Just when you think you've got them figured out and rounded up, they give you the slip. Get the lead out of gasoline, and it comes at you through aging pipes. Bury waste and toxins in landfills, and they seep into groundwater. Mercury, at least, we thought we understood. For all its toxic power, as long as we avoided certain kinds of fish in which contamination levels were particularly high, we'd be fine. And not even everyone had to be careful, just children and women of childbearing age.
But mercury is famously slippery stuff, and a series of recent studies and surveys suggests that the potentially deadly metal is nearly everywhere--and more dangerous than most of us appreciated. Researchers testing birds in the Northeast have found creeping mercury levels in the blood of more than 175 once clean species. Others have found the metal for the first time in polar bears, bats, mink, otters, panthers and more.
Just as alarming are new discoveries about unexpected sources of mercury contamination. While coal-fired power plants and chemical factories are familiar culprits, a recent study reveals that wetlands are mercury time bombs; if hit by wildfire, they release centuries' worth of accumulated toxin in a single, sudden blaze. In addition, there's a growing body of research that reveals the extent to which medium to high levels of exposure to the metal can harm adults as well as children, causing a wide range of ills--including fatigue, tremors, vision disorders and brain, kidney and circulatory damage. All told, "the breadth of the problem has expanded greatly," says biologist David Evers of the BioDiversity Research Institute in Gorham, Maine. "It's far more prevalent and at higher levels than considered even a couple years ago."
Mercury has to work hard to do all the damage it does. In its pure state, it is only moderately toxic because it passes quickly through the body, leaving little to be absorbed. Not so the mercury we pump into the skies. Smokestack mercury exists in either particle form--which falls relatively quickly back to earth--or aerosol form, which can travel anywhere around the globe. Either way, when it lands, trouble begins. On the ground or especially in the low-oxygen environment of the oceans, mercury is consumed by bacteria that add a bit of carbon to convert it to methylmercury, a metabolically stickier form that stays in the body a long time. That is bad news for the food chain, since every time a bigger animal eats a smaller animal, it consumes a heavy dose of its prey's mercury load. That's why such large predatory fish as shark, swordfish, mackerel, tilefish and albacore tuna are so heavily contaminated. Less publicized but still problematic is toxic mercury vapor, which can be odorlessly emitted from factories and dumps where batteries, fluorescent lamps, jewelry, paints, electrical switches and other mercury-containing products are manufactured or discarded.