Prenatal and Postnatal Methylmercury Exposure in Niigata, Japan: FourCases Descriptive Study

Large-scale MeHg poisoning occurred in Niigata, Japan in the 1960s. Hair mercury levels were measured early in the epidemic of MeHg poisoning. The severe prenatal exposure cases with conditions resembling cerebral palsy, i.e., congenital Minamata disease are well-known, although severe prenatal and postnatal MeHg exposure cases who did not develop such severe symptoms are not well-known. We conducted follow-up neurologic examinations and interviews of four participants with a history of prenatal and postnatal MeHg exposure who had-along with their mothers undergone hair mercury measurement in June 1965. We describe their development and subjective symptoms in childhood and neurologic signs in adulthood. The hair mercury levels of the four participants ranged from 63.0 to 111.0 ppm in 1965, and maternal levels ranged from 58.0 to 275.0 ppm. Although the four participants had high prenatal and postnatal MeHg exposures, they did not develop severe symptoms resembling cerebral palsy. They had symptoms such as poor concentration and poor memory which are thought to be neuropsychological dysfunction, as well as MeHg poisoning in childhood. One was intellectually impaired (Total IQ, 79). Nearly 50 years after prenatal and postnatal MeHg exposure, they had neurologic signs such as sensory disturbances of the bilateral distal extremities and blurred vision. There are several limitations such as a possibility of selection bias, etc. in the present study. 4 cases had various signs and symptoms possibly due to prenatal and postnatal MeHg exposure such as neurologic signs and neuropsychological dysfunction during lifetime.