Epidemiological update of methylmercury and minamata disease

Abstract

The first epidemic of Minamata disease was observed in Minamata and surrounding areas mainly from the mid-1950s to the mid-1970s, and the second one in the Agano River basin mainly in the 1960s. There are some difficulties in conducting epidemiological study on the health effects of methylmercury among residents of the previously contaminated site. The evaluation of the past exposure level is difficult for methylmercury that has a relatively short biological half-life of 50-70 days in the human body. The limited data on hair mercury concentration obtained in the early 1960s, difference assumed in the exposure level among subpopulations and areas of residence, or methylmercury concentrations of preserved umbilical cord have been used in studies on the health effects of the past exposure. Subjective complaints are important to be considered as possible outcomes on the effects of chronic exposure to methylmercury. However, diagnostic or selection bias should not be underestimated, especially given the possibility of linkage with the compensation of patients. Despite these limitations, epidemiological studies have clarified associations between methylmercury exposure and a variety of health impairments including nonspecific clinical manifestations.