Methylmercury exposure and mortality in southern Japan: a close look at causes of death

This study examines mortality patterns by cause of death to investigate the effect of exposure to methylmercury in a small area of Minamata City (Kumamoto Prefecture, Japan), which has the highest concentration of patients with Minamata disease. Standardised mortality ratios (SMRs) are computed by cause of death for the study area, using the age specific rates of the entire city as a standard. The SMRs for liver cancer and chronic liver disease in the study area are significantly higher than unity and are consistent with the mortality patterns of registered Minamata disease patients. While an excess mortality is observed for cerebral haemorrhage, mortality from cerebral infarction and other cerebrovascular diseases is considerably lower in the study area. The multiple risk factors of liver related diseases and a possible explanation for the cerebrovascular mortality patterns are discussed to suggest further investigation.