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Signs Of Uncertain Times
Mercury alert notable for what was left out

By John Krist
February 27, 2003

Shoppers at Trader Joe's, Whole Foods, Kroger's, Albertson's and Safeway stores may have been alarmed last week to find ominous signs posted near the fish counters.  

"WARNING!" the signs say. "Nearly all fish and seafood contain some amount of mercury and related compounds ... Pregnant and nursing women, women who may become pregnant, and young children should not eat the following fish: SWORDFISH, SHARK, KING MACKEREL, TILEFISH. They should also limit their consumption of other fish, including fresh or frozen tuna."

Although health advocates hailed the warnings as a landmark in their battle to protect consumers from a potent environmental contaminant, the somewhat vague alerts merely serve to underscore continuing uncertainty about the severity of the threat. Several recent reports suggest mercury exposure is more pervasive than previously believed, but it is still not clear whether people are being harmed by it.

The warnings are also notable for what they do not say about canned tuna, the most widely consumed fish product in America.

The signs were posted as an interim step toward settlement of a lawsuit filed last month by the California Attorney General's Office against the five grocery chains, alleging that they were violating Proposition 65 by failing to warn consumers that fish contain mercury and mercury compounds.

Mercury ends up in the environment in a number of ways. Some sources are natural -- volcanic eruptions and erosion, for example -- but vast amounts are emitted by modern industrial activities, such as coal combustion in power plants. Once in the water, mercury can be converted by microbial action into methylmercury, the most dangerous form, and enter the food chain. It accumulates and magnifies in living organisms, reaching high levels in big predatory fish.

Proposition 65, also known as the Safe Drinking Water and Toxic Enforcement Act of 1986, requires businesses to provide customers "clear and reasonable warning" before exposing them to chemicals known to the state of California to cause cancer and reproductive harm. Many types of freshwater fish and seafood contain methylmercury, which is a potent toxin capable of producing neurological damage in fetuses and young children. By failing to warn consumers that fish may contain this neurotoxin, the lawsuit argues, the grocery stores were violating the law.

Two years ago, while researching a series of stories about the emerging threat posed by mercury contamination, I was struck by the uncertain state of knowledge regarding the risk to human health. Although the danger of severe exposure is clear, there are no good data regarding the effect of chronic, low-level exposure. Nor was it particularly clear how many people might be at risk.

I was able to cite three estimates: the EPA's 1997 Mercury Study Report to Congress, which suggested 1 percent to 3 percent of American women of childbearing age eat enough fish to be at risk of excessive mercury exposure; a 2001 report by the National Academy of Sciences that concluded 60,000 children born each year in the United States are at increased risk of brain damage because their mothers consume mercury-contaminated fish; and a 2001 report by the Centers for Disease Control and Prevention, which found that 10 percent of women of childbearing age have mercury levels in their bodies high enough to pose a potential threat to their fetuses.

Those findings have been reinforced in recent months by several new studies. Two months ago, the CDC released the second of its reports on human exposure to environmental contaminants, this one more comprehensive than the report I cited two years ago. The newest study found that about 8 percent of women of childbearing age have blood mercury levels high enough to pose a risk to the fetus. That statistic was echoed by the Environmental Protection Agency in a report released Monday.

And in a study published Nov. 1 in the journal Environmental Health Perspectives, a San Francisco physician found that patients who ate a lot of swordfish and tuna had blood mercury levels higher than the EPA considers safe. One of those patients, a child who consumed two cans of tuna a week, actually exhibited signs of low-level mercury poisoning.

The Proposition 65 warnings posted last week by five of California's biggest grocery chains are absent from the canned-tuna aisles. That's because the major canned-seafood companies asked that the signs be kept away from their products, and promised to defend the grocers against any legal action that might result.

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John Krist is a senior reporter and Opinion page columnist for The Star. His e-mail address is krist@insidevc.com.

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