Comparative Evaluation on Human Infants Dietary Mercury Exposure through Consumption of Fish and Rice Products

Abstract

Human exposure to methylmercury (MeHg) through diets (e.g., fish and rice) is a global health concern. Although MeHg exposure through fish consumption has long been considered the major route of mercury health risks, studies concerning the long-term changes in MeHg exposure from fish remain lacking. In sharply contrast to the fish MeHg issue, the presence of MeHg in rice has only been reported recently and its implications on MeHg exposure, albeit probably important, are still in infancy. Focusing on the discrepancies in the studies of MeHg exposure through fish and rice consumption, this study was aimed to assess the MeHg exposure of human infants through consumption of rice cereals and to evaluate the long-term changes in fish MeHg. The presence of MeHg in rice prompted the studies on MeHg concentrations and bioaccessibility in rice cereals and potential infant dietary exposure to MeHg through cereal consumption, which is believed to be the first of its kind. The analysis of a variety of infant cereals sampled from the common markets in the United States and China showed that the concentrations of MeHg in the cereals ranged from 0.07 to 13.9 µg/kg with a mean of 1.61 µg/kg. On the basis of these MeHg concentrations, the daily intake vii of MeHg through rice cereal consumption for infants was estimated to be 4-122% of the reference dose (RfD). The MeHg bioaccessibility in the cereals, determined using an in vitro digestion method, ranged from 25 to 74% with a mean of 48±16%. A further examination on these results, however, revealed the occurrence of MeHg re-adsorption during extraction steps, which leads to the underestimation of MeHg bioaccessibility and warrants cautions to be exercised when using these procedures to evaluate bioaccessibility in general. The long-term changes in fish MeHg were investigated through conducting a comprehensive data analysis on datasets for the Everglades, a well-studied aquatic ecosystem for Hg contamination. The results showed a clear decline of MeHg in mosquitofish in the Everglades during the past two decades, which was probably related to changes in environmental conditions (e.g., periphyton, dissolve organic matter, and sulfate) instead of mercury deposition. viii