ARSENIC RELEASE PROCESSES INTO CONFINED AQUIFERS OF THE SEINO BASINS, NOBI PLAIN, JAPAN

Abstract

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.