An Exposure Assessment for Methylmercury from Seafood for Consumers in the United States. C. D. Carrington and P. M. Bolger, US Food and Drug Administration, DC
An exposure model was developed to relate seafood consumption to levels of mercury in blood and hair in the U.S. population, and two subpopulations (children and adult women). Seafood consumption was initially modeled using 3 day U.S. consumption surveys. Since longer exposure periods include more eaters with a lower daily mean intake, the consumption distribution was adjusted by broadening the distribution to include more eaters and reducing the distribution mean to keep total population intake constant. The estimate for the total number of eaters was based on long-term purchase diaries. Levels of mercury in canned tuna, swordfish, and shark were based on FDA survey data. A composite lognormal distribution for levels of mercury in other species was based on reported mean levels, with each species weighted by market share. The distribution was then broadened in order to reflect additional variation among individual fish in each species. These distributions were integrated with a simulation that estimated average daily intake over a 360 day period. The results of this simulation were then used as an input to a second simulation that modeled levels of mercury in blood and hair. The relationship between dietary intake and mercury blood in a population was modeled from data obtained from a 90 day study with controlled seafood intake, while the blood to hair relationship was based on survey data. The biomarker simulation results were then compared to the recent National Health and Nutrition Examination Survey (NHANES) that tabulated blood and hair mercury levels in a cross section of the U.S. population. The output of the model and NHANES were quite similar for adult women with overlap in the confidence intervals. However, the exposure model clearly over-predicted levels for children. This result may be from the use of observations of adults for parts of the model that are not representative of children (e.g., seafood consumption patterns, pharmacokinetic relationships).
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