Mercury exposure: medical and public health issues.

Mercury exposure is widespread in the United States with methylmercury as the predominant chemical species and fish and shellfish as the source. Use of more advanced diagnostic techniques and application of population-based risk assessment methodologies have assisted in addressing the impact of mercury exposure on the United States population. Biomonitoring, particularly through analyses of blood mercury, provides both population-based data and exposure information that can be informative for physicians. Data from the National Health and Nutrition Examination Survey (NHANES) beginning in 1999 provide population-based exposure estimates for United States overall. Methylmercury exposures among women of childbearing age are of particular concern because of methylmercury's developmental neurotoxicity. Exposures of concern among women are estimated to occur in between approximately 6% to 8% of the 16-to-49-year-old age group based on data from NHANES; and in approximately 15% of this age and sex group if physiological factors such as the degree of transplacental transport of methylmercury are taken into consideration. Subgroups with high fish consumption (e.g., many island and coastal populations, some persons of Asian ethnicity, some individuals following "healthy" diets) can have methylmercury exposures substantially higher than those reported among the NHANES examinees. These subpopulations are not likely to be aware of their blood mercury concentrations or the possible health outcomes associated with such high blood mercury levels. The American Medical Association has adopted policies that express concerns about methylmercury exposure, and advise patient education. Non-neurological risks for adults associated with methylmercury, including the potential for adverse cardiac outcomes, have not yet been incorporated into risk assessments.