Arsenic release processes into confined aquifers of the Seino Basins, Nobi Plain, Japan

To understand the mechanisms of arsenic release from the sediment of the Seino Basins, Nobi Plain, Japan, the present study investigated the characteristics of arsenic dissolution and arsenic phases in the sediments of the G₁ and G₂ aquifers and their upper layers. No significant, direct positive relationship between the total and water-soluble arsenic was found. The results of sequential extraction showed that the main sources of water-soluble arsenic were the non-specifically and weakly bound arsenic phases. In addition, a small portion of the arsenic specifically sorbed on the surface of the sediment was dissolved by water extraction. Multiple regression analyses demonstrated that high pH, total arsenic content, and water-soluble organic carbon (WSOC) content strongly contributed to the enhancement of arsenic release from the specifically bound arsenic fraction. These results suggest that high levels of total and non-specifically bound arsenic are responsible for higher levels of arsenic release. In addition, high pH and WSOC content facilitate arsenic release.