Eating lots of fish tied to high mercury levels
Jane Kay, Chronicle Environment Writer
Thursday, October 21, 2004
A study sponsored by an environmental group has produced new evidence linking high fish consumption to potentially unsafe levels of mercury.
Scientists at the University of North Carolina at Asheville tested hair samples from 1,449 people nationwide who volunteered to participate in the study after hearing about it through Greenpeace USA and other groups.
About 1 in 5 had mercury levels exceeding Environmental Protection Agency safety guidelines. Almost half of the volunteers who had consumed large amounts of fish exceeded the EPA guideline.
The study wasn't designed to estimate what percentage of the U.S. population may exceed the mercury guidelines, the authors said.
The study is one of the first to examine the relationship between mercury levels and the consumption of three categories of fish: canned tuna, locally caught fish, and fresh or frozen fish sold in stores and restaurants.
Richard Maas, a co-author and professor of environmental science at the University of North Carolina, noted that among those consuming the most fish, mercury levels were several times greater than the safety guidelines.
Among the findings:
-- About 50 percent of the participants who ate seven or more 6-ounce servings a month of fish purchased in restaurants or stores exceeded the safety guideline of 1 part per million.
-- Almost 33 percent of those who ate four or more servings a month of canned tuna had mercury exceeding the guideline. The study questionnaire didn't differentiate between different types of tuna. The U.S. Food and Drug Administration warns that canned albacore has three times the mercury as chunk light.
-- Almost 36 percent of the people who ate three or more 6-ounce servings a month of locally caught fish exceeded the guideline.
Coal-fired power plant emissions and natural rock formations release mercury into the environment. The largest single source of exposure in the United States comes from fish in the diet.
Health officials agree that fish offers health benefits, and the FDA recommends 12 ounces a week of fish, while warning that women of child-bearing age and children should avoid swordfish, shark, king mackerel and tilefish. Mercury, which is toxic to the human nervous system, is linked to learning and behavioral problems in children. In adults, mercury can cause tremors, memory loss and other health problems.
The study was advertised at Greenpeace events and in an e-mail campaign. Interested parties sent $25 for a kit, then sent their hair and a questionnaire to the scientists.
"I would expect there to be some bias in our survey because the participants were self-selected,'' said Steven Patch, statistics professor at the University of North Carolina, a study co-author.
Patch said he believes the study may overrepresent people who eat a lot of fish, and may underrepresent those consuming locally caught fish.
The study also examined correlations between mercury levels in the hair samples and other sources of exposure, including dental amalgams, flu shots in which mercury is used as a preservative, workplace exposure or hair dyes.
"The effects -- if any -- were much lower than the effects from fish consumption of store-bought fish, canned tuna or locally caught fish,'' Patch said.
Data gathered in 1999-2000 by the U.S. Centers for Disease Control and Prevention based on a national nutrition survey showed that 12 percent of women of childbearing age had mercury levels above the safety guidelines.
E-mail Jane Kay at jkay@sfchronicle.com.
http://sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2004/10/21/MNGKH9D3KO1.DTL
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