Let’s start with a straightforward fact: Mercury is unimaginably toxic and dangerous. A single drop on a human hand can be irreversibly fatal. A single drop in a large lake can make all the fish in it unsafe to eat.
Often referred to as quicksilver, mercury is the only common metal that is liquid at room temperature. Alchemists, including the young Sir Isaac Newton, believed it was the source of gold. In the modern era, it became a common ingredient of paints, diuretics, pesticides, batteries, fluorescent lightbulbs, skin creams, antifungal agents, vaccines for children, and of course, thermometers. There is probably some in your mouth right now: So-called silver dental fillings are half mercury.
Mercury is also a by-product of many industrial processes. In the United States coal-fired power plants alone pump about 50 tons of it into the air each year. That mercury rains out of the sky into oceans, lakes, rivers, and streams, where it becomes concentrated in the flesh of fish, shellfish, seals, and whales. Last year the Food and Drug Administration determined there is so much mercury in the sea that women of childbearing age should severely limit their consumption of larger ocean fish. The warning comes too late for many mothers. A nationwide survey by the Centers for Disease Control shows that one in 12 women of childbearing age already have unsafe blood levels of mercury and that as many as 600,000 babies in the United States could be at risk. But that begs a critical question: At risk for what?
Infants born to mothers contaminated by mercury in Japan’s Minamata Bay in 1956 had profound neurological disabilities including deafness, blindness, mental retardation, and cerebral palsy. In adults, mercury poisoning can cause numbness, stumbling, dementia, and death. “It’s no secret that mercury exposure is highly toxic,” says toxicologist Alan Stern, a contributor to a 2000 National Research Council report on mercury toxicity. But high-level exposures like those at Minamata cannot help scientists determine whether six silver fillings and a weekly tuna-salad sandwich will poison you or an unborn child. “The question is, what are the effects at low levels of exposure?” he says.
Data now suggest effects might occur at levels lower than anyone suspected. Some studies show that children who were exposed to tiny amounts of mercury in utero have slower reflexes, language deficits, and shortened attention spans. In adults, recent studies show a possible link between heart disease and mercury ingested from eating fish. Other groups claim mercury exposure is responsible for Parkinson’s disease, multiple sclerosis, Alzheimer’s, and the escalating rate of autism.
