報告書番号

U02024

タイトル（和文）

メチル水銀の健康影響とリスクアセスメントに関する調査

タイトル（英文）

Review of health effects and the risk assessment of methylmercury

概要 （図表や脚注は「報告書全文」に掲載しております）

近年、メチル水銀の低濃度暴露による健康影響が懸念されている。本調査では、その健康影響とリスクアセスメントに関する知見をまとめ、影響評価研究の現状と問題点を明らかとした。メチル水銀暴露による影響は主に中枢神経系障害である。毒性は暴露量と暴露期間に大きく依存し、年齢、性別等により異なるが、特に胎児は感受性が高い。幾つかの疫学研究では、魚摂取による妊娠中の水銀暴露量とその小児の神経行動学的所見に関連があり、胎児期暴露が小児の脳機能に影響を及ぼすことが示唆された。しかし相反する報告もあり今後も大規模な信頼性の高い疫学研究、および動物実験やメカニズム解明が不可欠である。また、各国、各機関によりリスクアセスメントの手法が異なるため基準値が異なることが明らかとなった。胎児期曝露に基づいたリスクアセスメントが進むにつれ、国際的に基準値が厳しくなる可能性があることが示唆された。

概要 （英文）

The combustion of fossil fuels is a major anthropogenic source of mercury (Hg) emissions to the atmosphere. Methylmercury (MeHg), one organic form of Hg, is accumulated in predatory fish by the aquatic food chain. Concern and awareness are growing over the health effects of chronic, low-dose MeHg exposure from contaminated fish and seafood. The authors review the epidemiological and biological researches and risk assessment of MeHg. MeHg is a potent neurotoxicant to human and animal. Both epidemiological and laboratory data suggest that the developing nervous system is more susceptible to MeHg neurotoxicity than the adult nervous system. The most severe effect reported in human was seen following high dose poisoning episodes in Japan and Iraq. Recently, some of large epidemiological studies have indicated that chronic, low-dose prenatal MeHg exposure from maternal consumption of fish has been associated with subtle end points of neurotoxicity in children. Those end points include poor performance on neurobehavioral tests, particularly attention, motor function, language, visual-spatial abilities, and verbal memory. Based on risk assessments and other societal considerations, several countries and international organizations have recommended acceptable levels of Hg exposure. The most recent, comprehensive risk evaluation on MeHg was performed in the USA. In 2001, U.S. EPA revised reference dose (RfD) of 0.1μg/kg/day based on the recent epidemiological results. In Japan, a tolerable weekly intake of 0.17 mg/50 kg body weight as MeHg was established based on the adult data of Minamata disease in 1973. The varieties in guideline levels among the countries are due to the differences of data sets used, risk-assessment methods, and mandates of each country.Further research on low-dose human and animal exposure to MeHg are needed to clarify the developmental neurotoxicity and its mechanisms and factors that might influence biological responses, such as age, sex, health status, and nutrition. It is also important to improve the methods for MeHg risk assessment.

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