Californians who volunteered for a nationwide study of mercury contamination had among the worst levels, with nearly one-third of those tested having concentrations in their tissues that exceeded safe levels.
The study, organized by two national environmental groups, Greenpeace and the Sierra Club, does not provide information about Californians in general because the volunteers were not a random sample.
Nonetheless, the tests of more than 6,000 people who sent hair samples to researchers provide insights into the extent and causes of mercury contamination. Details of the study were released in a report Wednesday.
Experts say that mercury exposure has little to do with proximity to pollution sources. Instead, it is determined by diet. Mercury concentrations in the study were strongly linked to how frequently the volunteers ate fish and other seafood, a finding that has been documented in other studies worldwide.
For volunteers who ate no fish, the average mercury level in hair was 0.06 parts per million, while those who consumed eight or more servings per month averaged 0.90, just below the federal government's health guideline of 1 part per million.
No link was found to dental fillings or vaccines.
"We saw a direct relationship between people's mercury levels and the amount of store-bought fish, canned tuna fish or locally caught fish people consumed," said Steve Patch, co-director of the Environmental Quality Institute at University of North Carolina-Asheville, which conducted the hair tests for the environmental groups.
Among those who volunteered for the tests, New Yorkers were the most highly contaminated. But residents of California were not far behind, with mercury levels substantially above the study's national average. Midwesterners were the least contaminated.
Asian Americans who volunteered had average levels more than twice as high as African Americans and 75% to 82% higher than whites and Latinos.
A majority of the volunteers did not exceed the 1 part per million concentration that the U.S. Environmental Protection Agency considers safe for pregnant women and children. But one out of every five women of childbearing age who volunteered for the study nationally, and one of every three in California, exceeded it.
Pregnant women are the population of greatest concern for experts, because a fetus is susceptible to mercury's toxic effects on the brain.
