The spatial distribution of total mercury in sediments in the Yatsushiro Sea, Japan

The Yatsushiro Sea in Japan is contaminated with mercury in wastewater discharge from the Chisso Company, which produced acetaldehyde from 1932 onwards. In this study, we investigated the current spatial distribution of total mercury (T-Hg) in sediments, both at the surface and at different depths, using 43 sediment cores and 22 surface sediment samples collected from the Yatsushiro Sea in August 2017. Altogether, 821 surface and core samples were analyzed for their T-Hg concentrations. Most of the mercury that was discharged from Chisso remained either in, or around the exit of, Minamata Bay, but some had been transported from Minamata Bay to the Nagashima Sea. We estimated that almost 51 and 6 tons of mercury had accumulated in the Yatsushiro and the Amakusa Sea areas, respectively. The amount of acetaldehyde produced in Chisso over time was correlated with the T-Hg concentrations in the sediments from the Yatsushiro Sea.