Retrospective study on temporal and regional variations of methylmercury concentrations in preserved umbilical cords collected from inhabitants of the Minamata area, Japan.

The present study was conducted to investigate the historical time-course changes and regional distribution of methylmercury concentrations in preserved umbilical cords collected from Minamata-area inhabitants born between 1947 and 1989. The data from Miyazaki, Tottori, Akita, Tsushima (Nagasaki), Fukuoka and Tokyo were used as controls. A total of 325 data were analyzed to estimate the temporal and spatial distribution of methylmercury among inhabitants born in the Minamata area. Elevated methylmercury concentrations (>or=1 microg/g) were mainly observed in inhabitants born between 1947 and 1968. That peak coincided with the peak of acetaldehyde production in Minamata. The methylmercury concentrations started to decrease in keeping with the decline of acetaldehyde production, which ceased in 1968, and thereafter the methylmercury levels gradually decreased to the control levels. Elevated methylmercury concentrations were first observed in the districts of Minamata, followed by Izumi, Tsunagi and Ashikita, indicating the time-course-dependent regional distributions of methylmercury pollution.