Health Effects of Methylmercury in Coastal Areas of the Yatsushiro Sea, Far from Minamata

Minamata disease, caused by ingesting seafood contaminated with methylmercury dumped by corporations, was discovered in 1956; however, there has been no continued investigation to determine the full extent of the damage. Since 2004, it has been discovered that affected patients can be found in areas further away from Minamata than previously known. In the present study, we investigated various symptoms and somatosensory disturbances in western Miyanokawachi District, northern Himedo District, southwestern Nagashima District, and the uncontaminated Amami district and calculated the proportion of patients with sensory disturbances as a percentage of the population in each area. Both touch and pain sensations, with a predominance of the peripheral extremities, were observed in 58.6% of patients in Miyanokawachi, 53.9% in Himedo, 37.8% in Nagashima, and 1.4% in Amami. The lowest estimates of attributable fractions of the exposed group for four-limb-predominant sensory disturbance in the population of the contaminated districts were 94.1% in Miyanokawachi, 94.6% in Himedo, and 91.4% in Nagashima, and general and perioral sensory disturbances were also high. This suggests that the presence or absence of these sensory disturbances is useful in the diagnosis of Minamata disease, even in more distant parts of the Yatsushiro Sea area.