Groundwater contamination of arsenic has
been acknowledged as a major public
health issue by the World Health Organization
(WHO) based on its prevalence
worldwide [1]. In natural waters, arsenic
exists as arsenite [As(III)], arsenate [As(V)],
monomethylarsonic acid (MMA) and
dimethylarsinic acid (DMA), and as various
organoarsenicals (Fig. 1). Among these,
As(III) and As(V) are the predominant
species in most natural waters. MMA and
DMA occur at levels of a few lg/L in some
groundwaters and surface waters [2].
However, in reducing environments and in
contaminated sites, MMA and DMA occur
at levels above those of inorganic species. In
seawater, besides inorganic and methylated
species, various organoarsenicals exist
[3]. In geothermal waters, besides arsenic