CHEMICAL SPECIATION AND RELEASE OF ARSENIC TO GROUNDWATER IN SEINO BASINS, NOBI PLAIN

Abstract

 Arsenic has been frequently detected with more than the Japanese environmental standard (0.01mg/L) in groundwater in south of Seino Basins, which locates in western part of Nobi Plain. Total content and chemical speciation of arsenic was evaluated by use of drilling samples of these area. The mechanisms of arsenic releasing to groundwater was investigated by some kinds of leaching experiments response to redox condition and pH.
 The water soluble arsenic concentration was higher in the Nobi formation distributed at south-west part of the plain than in the Nan-yo formation of north-west. Dominant arsenic speciation in Nobi layer was As sorbed Fe- and/or Mn-oxides. Total arsenic content in the profile was correlated with total carbon and total ferric content in this part of the plane. These results suggested that As sorbed on to Fe- and/or Mnoxides in Nobi layer was the one of the origin of the arsenic dissolution to groundwater. The arsenic leaching experiments suggested that slightly high pH value of groundwater and dissolved organic carbon leaching from Nobi layer enhance arsenic release to groundwater.