Investigation of Mercury Concentration and Existence Form in River Waters in Niigata Prefecture

Abstract

The mercury concentration of river waters in Niigata Prefecture was studied for regional distribution, fluctuation factors, and speciation. We investigated 11 rivers in Niigata Prefecture four times a year. As a result, average concentrations of total mercury (T-Hg), and dissolved T-Hg in the river waters were 1.7 ng/L, and 0.29 ng/L, respectively. The average ratio of dissolved alkyl mercury concentrations to dissolved T-Hg concentrations were about 15%. The dissolved T-Hg concentrations had no observable regional differences. On the other hand, the T-Hg concentration in suspended solids (SS) was highest in the Seki River. The average T-Hg concentration in SS (SS-Hg) in the Seki River was 0.34 μg/g, whereas those in the other rivers ranged from 0.11 to 0.23 μg/g. The factor that increased SS-Hg concentration in the Seki River is considered to be the sediment originated from volcano. We investigated long-term fluctuations of T-Hg concentration in the Shinkawa River during April 2017 to March 2019. As a result, the average concentrations of dissolved T-Hg and particulate T-Hg in the Shinkawa River were 0.40 ng/L and 2.3 ng/L, respectively. The particulate T-Hg concentration was highly correlated with SS concentration.