Arsenic Pollution in Nagae River after Volcanic Eruption of Mt. Iou

The water quality of the river basins situated in volcanic areas and exposed to volcanic activity can be affected by the acidic water, resulting in the pollution of surface water. On April 19th, 2018, the first eruption in 250 years of Mt. Iou, one of the Kirishima volcanos, caused the discharge of mud and acidic water into the Nagae River, contaminating the water with arsenic at a high concentration that exceeded the environmental standard （ 10 µg L -1 ） . In this study, we investigated the changes in arsenic concentration in the streamflow process, the relationship between pH and Electrical Conductivity （ EC ） , and the runoff characteristics through a continuous observation. The results indicate that the river water was diluted and improved during the streamflow process owing to dilution as a result of influx of water from tributaries, the arsenic concentration has a correlation with pH and EC, particularly, in the upstream area and on nonrainy days, and the arsenic concentration correlates with iron, aluminum, and manganese concentrations. Consequently, arsenic accumulates at the bottom of the riverbed on nonrainy days, and its concentration becomes high owing to the resuspension of the river sediment on rainy days.