Methylmercury (MeHg) is an environmental pollutant with neurotoxic effects on the central nervous system. The major exposure route of MeHg to humans is via consumption of fish and shellfish which accumulate the chemical through the food web in an aquatic environment. We have been conducting a survey on hair mercury contents among general populations from different districts to estimate the current Japanese MeHg exposure level. In Japan, a provisional regulatory standard of mercury and MeHg in fish and shellfish was determined in 1973 based on the assumption of a safe intake limit of 0.17 mg/person/week (0.48 μg/kg/day). On the other hand, the US EPA issued a revised reference dose based on a cohort study conducted in the Faroe Islands. Recently, a provisional tolerable weekly intake (PTWI) of MeHg was revised to 1.6 μg/kg/week in 61st Joint FAO/WHO Expert Committee on Food Additives (JECFA), which was about half that of the Japanese standard. The distribution of hair mercury levels in Japanese populations currently obtained from 10 districts indicated that 25% of the Japanese females of child-bearing age were estimated to be exposed to MeHg over the PTWI level. This would reflect the high Japanese consumption of marine products. Not only mercury contamination, but also the nutritional benefit may have to be considered when discussing the risk involved in the current level of fish and shellfish consumption in Japan.
2004 by The Pharmaceutical Society of Japan