Mad About Mercury

By Pat Hemminger, Common Ground. Posted September 15, 2004.

Last April, at the first federally sponsored symposium on mercury and public health, Dr Jane Hightower of San Francisco's California Pacific Medical Center presented some alarming findings: nine out of 10 Bay Area residents who ate fish regularly had elevated blood-mercury levels and associated health complaints.

"People are having symptoms just like the hatters," says Hightower alluding to the 19th and early 20th century "mad hatters" who were exposed to mercury nitrate used to process fur pelts. "They have weakness, headache, stomach upsets, hair loss, allergy symptoms, and there's a question of autoimmune disease."

Hightower is not the only medical professional who is worried about mercury. Recently, many Bay Area physicians have begun questioning their patients about fish intake and measuring blood-mercury levels. Dr. Laurie Green of the Pacific Women's Obstetrics and Gynecology Medical Group now asks her patients to record not only what fish they eat but how much: "I've been astounded at how many patients have high mercury levels and underestimate their fish intake," she writes. Green was amazed to discover "how much better they feel once they cut out the contaminated food."

Public Health Crisis?

Concern over toxic mercury levels in the general population is growing. The dangerous poison is showing up everywhere: not just in smokestacks, lakes and oceans, fish, dental amalgams and vaccines, but also in Arctic sunrises, wildfire smoke, landfill emissions and homes. Coal-burning power plants – the largest source of industrial mercury pollution – spew out mercury that ends up in lakes and oceans, where bacteria convert it to methylmercury.

This potent neurotoxin bioaccumulates in freshwater fish and seafood and is especially dangerous to the developing fetus. The Environmental Protection Agency warned in January that one in six children born annually may be at risk from high exposure to methylmercury in the womb.

"We have some exposures occurring now in the United States that have produced blood mercury a lot higher than anything we would have expected to see," says Kate Mahaffey of the EPA's Office of Prevention, Pesticides and Toxic Substances. "And this appears to be related to consumption of larger amounts of fish that are higher in mercury than we had anticipated."

How Much Fish is Safe?

Everyone agrees that mercury is toxic. The question is how much mercury poses a risk? Scientific uncertainty has spawned heated debate over whether the EPA's March 19 advisory to pregnant and nursing women is adequate. The advisory cautions against eating shark, swordfish, king mackerel and tilefish because of their high mercury content but allows up to 12 ounces a week of shrimp, canned light tuna and salmon.

While no one doubts the benefits of eating fish, evidence is mounting that methylmercury not only harms the developing fetal brain but could also play a role in common adult complaints like insomnia, fatigue, and serious heart and autoimmune diseases.

Dr. Paul Dantzig of Columbia University's School of Medicine has linked a distinctive skin rash to mercury exposures at levels well below the EPA "safe" limit. Dantzig (who encounters two or three patients a week with mercury poisoning) reports that the rash disappears when people stop eating fish or undergo chelation therapy to reduce mercury levels. "When it comes to mercury," Dantzig says, "there is no safe level."

The EPA had set the "safe" exposure level at 5.8 micrograms of mercury per liter of blood, which is thought to be protective of fetal development. Some scientists think the level should be higher although a recent analysis of umbilical cord blood suggests it should be lower. And so far no one knows exactly what blood mercury level triggers problems in adults.

Mercury's toxicity was vividly illustrated in the 1950s by the deaths and deformities resulting from the release of methylmercury into Minamata Bay in Japan. Hundreds more died in Iraq in 1972 after eating bread made from seeds treated with methylmercury.

Pat Hemminger, a science and environmental writer in New York, was associate editor of "Pollution A-Z" (MacMillan, 2003).

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