November 2, 1999

New Efforts to Uncover the Dangers of Mercury

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    A panel convened by the National Academy of Sciences is determining whether mercury threatens the health of Americans. Coal-fired power plants, like this one near Moundsville, W.Va., are a leading source of emissions.
    Most people think of mercury as the shiny liquid metal in thermometers. But it has other forms, and it is a less visible, and very toxic, kind -- methylmercury -- that is troubling scientists, environmentalists and government officials.

    Methylmercury is formed from the mercury discharged into the air by coal-burning power plants, incinerators, mining and other sources. The mercury rains down onto the land and leaches into waterways; there, having been converted by bacteria into methylmercury, it collects in the fatty tissues of fish and the animals that prey on them.

    Its concentration rises at each step up the food chain until it is consumed by people.

    While most industrial uses of mercury are declining, concentrations are nevertheless increasing in the environment and in the food chain. Airborne mercury is estimated to be three to six times the level it was in pre-industrial times.

    The toxicity of methylmercury at low concentrations is a matter of intense debate. As a result, scientists and government officials are making new efforts to determine how much mercury is safe to consume and whether new limits on power-plant emissions are needed.

    The National Academy of Sciences has established a committee to investigate the mercury toxicity issue, but its work is difficult.

    Recent studies of the effects of low-level mercury exposure, primarily from eating contaminated fish, have produced differing results. One showed neurological damage; the other did not. The committee's study, sponsored by the Environmental Protection Agency, began last December and is scheduled for completion next June.

    Dr. Robert Goyer, the panel's chairman, says its top priority is to determine the effects of prenatal mercury exposure. "Methylmercury, the type of mercury found in fish people eat, kills nerve cells because it is transported readily across the cell membranes," said Dr. Goyer, a pathologist who is professor emeritus at the University of Western Ontario.

    "The bottom line for the N.A.S. study is determining the minimum amount of mercury that will affect the most sensitive member of our population, the unborn child.

    The current data from different studies are not consistent."

    The panel's conclusions could have big implications for the coal-burning plants of the electric power industry. The Environmental Protection Agency estimates that it would cost about $2 billion a year to control mercury emissions from those plants; Congress has required the environmental agency to wait for the National Academy of Sciences' study before proposing additional mercury regulations for power plants.

    Death and illness from mercury poisoning have been documented since the 16th century in Europe. The expression "mad as a hatter" came into the language because hat makers were poisoned by mercury salts used to make felt for fancy hats. They were well known for their symptoms: shaking, stumbling and muttering to themselves. And in the 1960's and 70's, consumption of food heavily contaminated with methylmercury resulted in death or serious illness to thousands of people in Japan and Iraq.

    But subtle, mostly neurological, effects of low doses are now emerging as the long-term legacy of mercury. Slower reflexes, reduced coordination and poorer vision are evident in people ingesting small amounts of mercury in fish. But the effects are difficult to measure and despite decades of study, experts disagree on the levels of mercury that are safe in air, water and food.

    "It is a frustrating issue," said Dr. David C. Bellinger, an associate professor of neurology at the Harvard Medical School and member of the National Academy of Sciences committee. "With mercury, we have only a few major studies." He said more mercury studies were needed to form a better foundation for regulatory change.

    Dr. Donna Mergler, a professor of neurophysiology at the University of Quebec at Montreal, says that in many respects, the situation with mercury is similar to what it was years ago for lead.

    "Why take lead out of gasoline and paint?" she said.

    "No one was getting sick or writhing on the ground. But lead did lower the I.Q. of kids.

    Subtle effects for toxins like lead and mercury are sometimes difficult to see in the individual, but can be seen in a group portrait where we compare the functioning of groups of people exposed to different levels."

    But in some respects, mercury is a more serious contaminant than lead.

    Because mercury can exist in vapor form, it can spread around the globe far more easily than lead. Also, "mercury accumulates more efficiently than lead in the aquatic food chain, especially in larger predatory fish," said Dr. William H. Farland, director of E.P.A.'s National Center for Environmental Assessment.

    Even minute additions of mercury to a lake can substantially increase the amount in the fish people eat.

    Regional effects of mercury have been observed by teams of Canadian and Brazilian researchers working along the Amazon River since 1994. They have concluded that the small amounts of mercury naturally occurring in local soils can substantially raise the concentration of methylmercury in fish when the soil erodes into the river after clear-cutting of the adjacent forests. Neurological testing has shown that local people have been affected.

    "Coordination and vision tests showed a shift to lower performance at higher levels of mercury exposure from fish eating," said Dr. Mergler, one of the researchers working in Brazil.

    "This lower level of performance makes the people less able to do things, which is important in a world which is expecting them to develop." Programs are under way to reduce mercury exposure there by encouraging consumption of fish species with lower mercury levels.

    Fish consumption was also examined in two major studies under way since the late 1980's. One, in the Seychelles, in the Indian Ocean, found that general performance on intelligence tests was not affected by exposure to methylmercury; the other, in the Faroe Islands, northwest of Scotland, found deficits in memory, attention and language.

    The studies differed in many respects, including eating patterns in pregnancy, ethnic or genetic makeup, and testing methodology. They are now under review by the national academy's panel.

    A question about how much exposure to a dangerous chemical is safe.

    Mercury enters the body in a number of ways, including diet, dental fillings, pharmaceuticals and contact with mercury metal or its compounds.

    But it is fish -- "brain food" -- that is the major dietary source of methylmercury to humans.

    Nonetheless, the Food and Drug Administration continues to recommend consumption of as much as 1 kilogram (2.2 pounds) of fish and shellfish a week and has not changed the mercury level it considers safe: 1 part per million in seafood. (Another government agency, the Agency for Toxic Substances and Disease Registry in the Centers for Disease Control and Prevention, has a similar recommendation; under it, a 150-pound person could safely eat four ounces of canned tuna a day.) The top 10 seafood species, making up 80 percent of the commercial market, all average well below that.

    Shark and swordfish, both top predator fish, may have mercury concentrations above 1 part per million, and the F.D.A. continues to recommend no more than one weekly serving of these two fish for most people, and no more than one serving a month for pregnant or nursing women, or those who may become pregnant.

    The push to lower overall exposure to mercury has continued on many fronts.

    In June, the E.P.A. announced that fluorescent bulbs, which contain mercury, could now be recycled to keep them out of waste dumps. On Sept. 14, the National Wildlife Federation released a study blaming coal-burning power plants for more than half of excess mercury in rain in several Midwestern cities.

    On Sept. 24, the E.P.A. announced a plan to severely restrict the direct discharge of mercury and other chemicals that accumulate in fish in the Great Lakes.

    Despite all this activity, it will be difficult to gain full protection of human health and a comprehensive understanding of mercury's effects in the human body and the environment. Dr. Farland said the Academy of Sciences panel would have more information than the C.D.C. did in making its recommendations, but he added:

    "They will still not have complete information.

    Over all, we are looking at what to do to avoid adding more mercury to the environment and how controls on mercury sources may improve human heath."

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