Women told to be wary of fish diet
By Jan TenBruggencate
Advertiser Science Writer
Women in the Islands who are pregnant or might become pregnant should limit consumption of certain seafoods, particularly broadbill swordfish and shark, because of the danger of brain-function damage to the fetus from mercury, according to the U.S. Food and Drug Administration.
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Gary Gill is working to enhance FDA guidance in Hawai'i.
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Honolulu tests found both mako and thresher sharks at muscle levels of 1 part per million of mercury right at the federal warning level. Broadbill swordfish are nearly at the same level, ranking 0.80 part per million.
"The levels that we are seeing are consistent with the Mainland numbers," said Barbara Brooks, toxicologist with the Department of Health's Hazard Evaluation and Emergency Response Branch.
The state is preparing a study on mercury contamination in seafood around Hawai'i and is reviewing available fish-mercury test data, which date back to 1991 and 1992, to determine whether to conduct further studies.
"We agree with the FDA guidance. We are trying to further enhance the guidance with local data," said Gary Gill, deputy director for the environment under the state Department of Health.
The FDA in March issued a recommendation that pregnant women and those of childbearing age avoid eating more than one monthly serving of four types of seafood that are high in mercury content: tilefish, swordfish, king mackerel and shark.
Mercury is a potent poison in higher doses. Its first symptom in adults is tingling or numbing in the fingers and toes. It can go on to cause other neurological damage such as balance problems and, in the highest doses, death.
Furthermore, children whose mothers were exposed during pregnancy to high levels of mercury perform worse on tests of brain function than others.
"There is no doubt that when humans are exposed to high levels of methyl mercury, poisoning and problems in the nervous system can occur," FDA toxicologist Mike Bolger said.
Elemental mercury the silvery liquid substance recently found contaminating some homes on O'ahu can be dangerous when its fumes are inhaled but not as dangerous when consumed. Another form, methyl mercury, is an organic compound that builds up in fish tissue, and can be dangerous to humans.
The National Academy of Sciences, which issued a report on mercury in seafood last year, says that while all humans have some mercury in their systems, seafood is the main source of methyl mercury in the human diet.
The report estimated that as many as 60,000 children in the United States may be born with neurological deficits as a result of mercury exposure before birth.
Most of the mercury that enters the atmosphere is from natural sources, but about a third is believed to come from human-
produced sources. Bolger said between 2,700 and 6,000 tons of mercury are released into the atmosphere annually as a result of natural releases from the planet's crust and oceans. Another 2,000 to 3,000 tons are released through human activity such as the burning of waste and fossil fuels, notably coal.
Some of that mercury enters the oceans, where bacteria can convert it to methyl mercury. Fish take the compound into their systems through eating or from the water passing over their gills. Predators can get higher concentrations because they ingest the methyl mercury from their prey.
The FDA recommends that pregnant women and those of childbearing age who may become pregnant eat shark or swordfish no more than once a month. The first trimester of pregnancy is most important in terms of fetal exposure to mercury, since the early part of pregnancy is a period of rapid brain growth.
The agency also recommends that other people limit their consumption of fish such as shark and swordfish to no more than seven ounces per week.
The agency, which notes that fish is a healthful food, does not want people to stop eating it altogether. It recommends other types of seafood, including catfish, cod, crabs, flatfish, pollock, salmon, scallops, shrimp and canned tuna, all of which have lower levels of mercury. The FDA's suggested weekly limit of these forms of seafood is 2.2 pounds.
The FDA says its proposed action level for mercury of 1 part per million is 10 times lower than the lowest levels at which any kind of adverse effect has been seen.
The 1991-92 state Department of Health Hawai'i Food and Drug Branch tests found these levels in Hawai'i deep-sea fish: mako shark, 1.0; thresher shark, 1.0; broadbill swordfish, 0.8; bigeye tuna, 0.6; Pacific blue marlin, 0.5; yellowfin tuna, 0.5; moonfish, 0.4; striped marlin, 0.3; and ono, 0.2.