Arsenic in groundwater: The chemical behavior, source and relevant problems

摘要

In the last decade, arsenic contaminated groundwater (>0.01 mg/L) has frequently been detected from place to place in Japan, and has caused serious social problems. The comprehensive surveys and researches have demonstrated that arsenic of natural origin dissolves from the aquifer to groundwater under specific environmental conditions. Concerning the aquifer geology, the arsenic-bearing groundwater is divided into S-type (sediment hosted type) and M-type (metamorphic rock hosted type). Meanwhile, from the viewpoint of dissociation mechanism, the arsenic contamination is classified into three types; Type 1: Reductive dissolution of iron oxyhydroxide (goethite) and release of adsorbed arsenic into groundwater; Type 2: Oxidation of arsenic pyrite, and Type 3: Arsenic release by the decomposition of organic matter in an alluvial peat layer under reducing condition of the aquifer. Because arsenic takes various forms as source and sink in nature and is sensitive to the environmental conditions, it is important that we should consider the geochemical cycle of arsenic for elucidating the dissolution mechanism and also for the remediation of groundwater at the contaminated sites.