Chemical characteristics of dissolved mercury in the pore water of Minamata Bay sediments

Methylmercury concentrations in fish from the historically polluted Minamata Bay remain higher than in fish from other coastal seas around Japan. To obtain a better understanding of this phenomenon, the chemical characteristics of pore water from Minamata Bay sediments were investigated. Samples were taken from two stations over a 1-year period. Total average values in the pore water at the two stations for dissolved total mercury and methylmercury concentrations were 6.64 ± 4.93 and 2.69 ± 2.07 ng/l, respectively. The pore water was centrifuged at 1000 rpm to 3000 rpm. The highest ratio of dissolved methylmercury to dissolved total mercury exceeded 60% for pore water centrifuged at 3000 rpm. Furthermore, because total average values of Log Kd of total mercury and methylmercury in sediment (St1 and St2) were 5.42 and 2.32 (L kg^{− 1}), methylmercury in Minamata Bay sediment is more eluted than other mercury species.