Effects of dry and heavy rainfall periods on arsenic species and behaviour in the aquatic environment adjacent a mining area in South Korea

This study investigated the spatiotemporal variation of arsenic (As) distribution, species and its behaviour in the aquatic environment changed by extended dry and heavy rainfall periods in the area adjacent an abandoned gold mine, South Korea. As appears to be transported from the mine wastes to Guryong stream through groundwater baseflow and leachate. The oxidation-reduction potential (ORP) conditions changed spatially and temporally following dry and heavy rainfall periods, and rainfalls caused decrease in the stream pH. As mainly existed as arsenates (AsO43-) bound with H, Ca, and Fe in water. In groundwater, the lower the pH and the ORP, the higher the proportions of acid species of arsenate (HAsO42-, H2AsO4-) and arsenite (H3AsO3), resulting in increased As mobility and toxicity, respectively. In stream, the primary influencing factor of As variation is the ORP. Under oxidizing conditions, As in stream could precipitate as amorphous FeAsO4.2HH(2)O and FeOOH in the streambed. Then, the ORP decrease could remobilize As by redissolution and desorption of As bound to bed sediments. Thus, streambed sediments acted as a temporary sink-and-source for As, and extension of source areas accompanied with physical transport after heavy rainfalls.

Automated summary

This study investigated the changes in the distribution, species, and behavior of arsenic (As) in the aquatic environment near an abandoned gold mine in South Korea, caused by extended dry and heavy rainfall periods. The results showed that As is transported from mine wastes to Guryong stream through groundwater baseflow and leachate. The oxidation-reduction potential (ORP) conditions and stream pH vary spatially and temporally, with heavy rainfall leading to a decrease in pH. Arsenic mainly exists as arsenates (AsO43-) bound with H, Ca, and Fe in water. In groundwater, lower pH and ORP levels result in higher proportions of acid species of arsenate and arsenite, increasing As mobility and toxicity, respectively. The primary factor influencing As variation in the stream is ORP. Under oxidizing conditions, As can precipitate as amorphous FeAsO4.2HH(2)O and FeOOH in the streambed, and a decrease in ORP can remobilize As through redissolution and desorption from bed sediments. Streambed sediments act as temporary sinks and sources for As, and the extension of source areas occurs after heavy rainfalls.