1. Mercury morass

2. Danger signs

3. Mercury mystery

4. Safety: in eye of beholder?

Clean sampling techniques are needed to measure mercury when there's less than a nanogram in a liter of water. Photo: USGS

Once upon a time, mercury was a valued medicine. Photo: Courtesy New Orleans Pharmacy Museum

Changes in mercury deposition measured in sediments in two ponds in the Adirondack region of New York from 1820 to the present. The levels echo changes in mercury emissions and deposition. When mercury emissions go down, ditto sediment levels. Courtesy David Sleeper et al, see "Letter to...." in the bibliography.

Incinerators are another big source, but controls on mercury are working to reduce pollution. Photo: USGS

But we could look to an expert group that interpreted the conflicting results from the three studies we've examined. In 2000, the National Research Council concluded that the Faeroes study was most relevant.

As the report's executive summary explained: "...there do not appear to be any serious flaws in the design and conduct of the Seychelles, Faeroe Islands and New Zealand studies that would preclude their use in a risk assessment. However, because there is a large body of scientific evidence showing adverse neurodevelopmental effects, including well-designed epidemiological studies, the committee concludes that an RfD dose [the amount that a person could tolerate for a lifetime without harm] should not be derived from a study, such as the Seychelles study, that did not observe any associations with" methylmercury.

Lynda Knobeloch, of the Wisconsin Bureau of Environmental Health, served on the NRC panel. She told us the statisticians confirmed an association between "low levels of mercury and learning. It was a few IQ points, not something you could see in an individual child, but something you could see in groups."

Eat safe
Aposhian, another NRC panel member, says based on the "studies that were available to us at that time, the committee came up with a reference dose of 0.1 microgram per kilogram of body weight per day." This, he says, agreed with the existing EPA reference dose, and was only slightly lower than safe doses established by two other government agencies -- the Food and Drug Administration and the Agency for Toxic Substances and Disease Registry.

As previously mentioned, the EPA says each year, mercury in their mothers' blood threatens 300,000 American infants with birth defects and brain problems.

Up to this point, we've concentrated on those risks, but Knobeloch says data are also emerging linking low levels of mercury with cardiovascular risks. "Heart attacks are a very bad outcome," she says. "They kill half the people who have them. The irony is that men are being told to eat a lot of fish because it's very good for the heart. That's true if it's very low in mercury, but if you are telling people with heart disease to eat fish, they better be careful which ones they eat."

Curious about the latest federal advice on fish?

Signs of success
Amidst the ongoing debate about mercury, here's another irony: Pollution controls work. Air-pollution devices that trap sulfur dioxide also trap some mercury. Driscoll, of Syracuse University, says studies in Minnesota and Florida have linked reductions in mercury precipitation, lake water and fish to pollution controls, especially on incinerators.

Gochfeld says incinerator controls are also working in New Jersey. "We had battery recycling and collection ... and we saw a 90 percent drop in incinerator emissions. Everybody said it couldn't be done, but of course it could be done, and it's the same thing with power plants now."

"We certainly think it's technologically feasible, and do believe it's cost-effective," says Jon Heinrich, who tracks mercury pollution control at the Wisconsin Department of Natural Resources. New coal-burning plants, especially if they burn eastern coal, can achieve huge reductions, Heinrich says: A 1,200 megawatt plant by Wisconsin Energy, scheduled to operate around 2010, is projected to reduce mercury emissions by 90 percent.

But refitting older plants is tougher, Heinrich adds. "With new facilities, we traditionally can do a better job, because we do the design and construction from the ground up." With existing plants, he says, it's necessary to cram pollution controls into existing spaces, and that cuts the effectiveness of controls.

Most of the people who study mercury seem to agree that it's time to move forward with stringent controls -- for the sake of the wildlife and the people who eat wildlife. Even Gary Myers, who found that mercury seemed harmless in the Seychelles, says "There are two ways to look at it. One is science and the interpretation of science. Two is common sense. Polluting your environment is not a wise thing to do. Whether or not it causes these problems, we know mercury is toxic at some point. Whether we close to that point or not, common sense tells you you can't put it in the environment forever without causing some effects."

No ill effects in our bibliography.

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