SAN FRANCISCO, March 11 (Xinhua) -- A new study shows detailed consumption advisories have a role in recent years when fish consumption has increased while blood mercury concentrations have decreased among women of childbearing age in the United States.
The research, published in the journal Environmental Health by researchers with Oregon State University (OSU), looked at fish consumption patterns with regard to blood mercury levels in U.S. women of childbearing age from 1999 to 2010 using data from the ongoing U.S. National Health and Nutrition Examination Survey.
Food from the ocean has a unique nutritional profile. Among seafood's many benefits are the omega-3 fatty acids that promote neurodevelopment, therefore are especially important for pregnant women to pass on to developing fetuses. But the main way people are exposed to toxic methylmercury, a mercury atom with a methyl group, CH3, attached to it, is through eating seafood.
Comparatively less-toxic elemental mercury enters the ocean from natural sources such as volcanic eruptions and also from human activities like the burning of fossil fuels, which accounts for about two-thirds of the mercury that goes into the water.
Once in the ocean, the mercury is methylated, diffuses into phytoplankton and passes up the food chain, accumulating along the way. A scallop or a shrimp, for example, can have a mercury concentration of less than 0.003 parts per million. A large predator like a tuna, on the other hand, can contain roughly 10 million times as much methylmercury as the water that surrounds it and have a concentration of many parts per million.
Thus, said Leanne Cusack, a postdoctoral scholar in OSU's College of Public Health and Human Sciences and the corresponding author of the study, fish consumption advisories need to be precise and nuanced.
These advisories are often aimed at women of childbearing age because a developing fetus has greater sensitivity to the neurotoxic effects of methylmercury. The U.S. Environmental Protection Agency (EPA) and the Food and Drug Administration (FDA) recommend women in that group eat two meals of low-mercury fish per week.
"We also found total monthly fish consumption by women of reproductive age was higher than it had been in recent years, with women consuming more marine fish and shellfish but with no appreciable difference in the mean consumption of freshwater fish, tuna, swordfish and shark," Cusack was quoted as saying in a news release. "That's encouraging because marine and shellfish are associated with smaller increases in blood mercury. And also encouragingly, an average women who'd eaten fish nine or more times in the previous month had lower blood mercury levels than women who'd had fish at the same rate in 1999-2000."
Among ethnic groups in the United States, Asian Americans, Pacific Islanders, Alaska Natives and Native Americans ate fish the most often and showed the most mercury, and Mexican Americans consumed fish the least often and showed the smallest concentration of mercury.
Cusack said the differences in consumption and mercury levels by race and region illustrate the need for tailored fish advisories.