BURLINGTON, Vt. (AP) - A study of Californians who loaded their lunch and dinner menus with fish shows 89 percent wound up with elevated mercury levels in their bodies.

The research, presented Saturday by San Francisco internist Dr. Jane Hightower at a symposium of environmental health experts in Vermont, is one of the first studies to document mercury levels in Americans who eat more fish than the Environmental Protection Agency recommends.

Doctors are increasingly interested in the possible risks of eating too much mercury-tainted fish, and the Environmental Protection Agency and the Food and Drug Administration are trying to better inform the public about the subject.

It is a thorny problem because of the widely recognized benefits of fish, a high quality protein source loaded with heart-protecting Omega 3 fatty acids.

Conference participants didn't seem panicked about the findings: The majority ordered salmon for dinner Saturday - though salmon is considered among the safest types of fish to eat.

"We are not talking about whether or not to eat fish," said the EPA's Kathryn Mahaffey, one of the conference organizers.

Hightower screened 720 patients from March 2000 to March 2001, then tested the mercury levels of patients who reported eating more than two servings of fish a week. That's the maximum the EPA recommends for pregnant women and small children.

The tests showed that of 116 patients who had their blood tested, 89 percent showed mercury levels greater than the 5 parts per million recognized as safe by the National Academy of Sciences.

Of that group, 63 people had blood mercury levels more than twice the recommended level and 19 showed blood mercury levels four times the level considered safe. Four people had mercury levels 10 times as high as the government recommends.

The peer-reviewed study is slated for publication Nov. 1 in the journal Environmental Health Perspectives.

The study monitored 67 patients as they reduced their fish intake and subsequently their bodies' mercury levels. Within 41 weeks, all but two had reduced their blood mercury levels to below government-recommended thresholds, according to Hightower.

The study did not address physical symptoms such as fatigue or memory loss associated with mercury poisoning. Some patients did report such problems, but Hightower's study did not seek to correlate symptoms with mercury levels.

Still, Alan Stern, a New Jersey public health official at the conference, said any mercury study focusing on people who eat a lot of fish is a sort of "holy grail" for the field.

Too much mercury damages the nervous system, especially in children and fetuses, but scientists are not certain how much mercury-tainted fish is needed to trigger health problems.

The FDA currently recommends that pregnant women and young children limit their fish intake to two 6-ounce cans of tuna per week if it's the only fish they eat, and to one can per week if they also eat other fish. The agency says they should not eat any swordfish, shark, king mackerel or tilefish.

About 78 percent of patients with high mercury levels reported eating canned tuna more than three times a month; 74 percent ate salmon more than four times a month; and 72 percent said they had swordfish more than once a month. Other fish commonly eaten by the patients included halibut, ahi, sea bass and sushi.

Hightower recommended that doctors concerned about patients' mercury exposure take dietary histories including fish consumption to help identify people at risk of accumulating too much mercury.

She also recommended that state and federal government agencies make the results of mercury testing in fish available wherever fish are sold, along with the details of consumption advisories.

Mercury is a naturally occurring element that makes its way into the environment when oil- and coal-fired power plants burn those fossil fuels. Rain washes it into waterways, where it settles and is eaten by microorganisms, which are eaten by fish.

The Vermont conference was organized by the American Fisheries Society and the EPA.

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On the Net:

American Fisheries Society: www.fisheries.org

Environmental Protection Agency: www.epa.gov