A national study that tested mercury levels found that one in five women of childbearing age included in the voluntary survey had levels higher than the Environmental Protection Agency's recommended limit and suggests that Hawai'i residents may be at even greater risk.

Of 46 Hawai'i residents who submitted hair samples in the study, 36 had mercury levels exceeding the EPA's recommended limit of one part per million. Of nine Hawai'i women in the study who were of childbearing age, seven had elevated mercury levels.

Nationwide, researchers at the University of North Carolina-Asheville's Environmental Quality Institute said the consumption of fish was the single most significant factor in predicting mercury levels. The Hawai'i data does not represent the entire Island population, both because the sample is small and participation was not random — respondents volunteered to participate.

The hair sample mercury study, backed by Greenpeace and the Sierra Club, included a total of 6,600 people from all 50 states. The childbearing bracket included 2,834 women, ages 16 to 49, and found that 22.6 percent of that group had mercury levels greater than 1 part per million.

When grouped by geographic region, the study found that participants in Pacific and Western states had the highest adjusted median mercury levels, with an average of .56 parts per million. The average among Northeastern participants was .53 ppm, while Southeastern and Midwestern averages were .49 ppm and .34 ppm, respectively.

The Sierra Club said the statistics are a wake-up call for women who could become pregnant. Mercury exposure in the womb can affect a child's neurological development. But the data do not support avoiding seafood altogether, according to health and fisheries sources.

Seafood consultant John Kaneko, a fisheries biologist and veterinarian with PacMar in Honolulu, said the EPA's caution level is very conservative, and that the benefits of eating fish typically far outweigh a level of safety obtained by excluding seafood from a regular diet.

Furthermore, for teenagers and adults who are unlikely to become pregnant, there is effectively no risk of eating even those kinds of fish rated high in mercury, Kaneko said. Open-ocean fish — as opposed to freshwater fish from industrial regions where toxic chemicals may enter the water — are high in beneficial products, such as omega-3 fatty acids, he said.

"Avoiding fish altogether puts your body at risk. You need healthy fish oils," Kaneko said.

A state Department of Health's online pamphlet on the subject concurs, adding: "Fish is a good food and part of a healthy diet. Don't stop eating fish."

In a press release, the Sierra Club said that the coal-fired power plants produce the largest proportion of the nation's mercury pollution, which finds its way into lakes streams and eventually oceans.

Kaneko said, however, there is little evidence that industrial mercury is a significant factor in mid-Pacific fish stocks, where natural sources of mercury appear to dominate. He pointed to a study involving Hawai'i yellowfin tuna in 1971 and in 1998 that showed no significant change in mercury levels.

Different fish have dramatically different levels of mercury. For example, yellowfin tuna have about half the level of bigeye tuna, and just a third the amount of high-mercury fish, such a swordfish and shark.

The Los Angeles Times reported that nationally, Asians had average levels more than twice as high as blacks and 75 percent to 82 percent higher than Caucasians and Hispanics.

The Times reported that mercury concentrations in the study were strongly linked to how frequently the volunteers ate fish and other seafood, a finding that also has been documented in many other studies. The more fish eaten, the more likely was a higher mercury level.

On a related issue, Kaneko said that most fishcake sold in markets today is made with low-mercury pollock. Fishcake once was primarily made of shark, but the contents of the processed product have changed, he said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.