summarized in Table 3 could reflect more accurately the fractions
introduced by external sources and are bioavailable compared to
total arsenic contents. Arsenate was found to be the major inorganic
arsenic species, while ASA was the major organoarsenic species
in the surface soils and sediments. The concentrations of
arsenite in the sediments were relatively high compared to surface
soils, which was probably caused by the more reducing environment.
The fact that arsenic is first methylated to MMA, and then
to DMA explains the higher concentrations of MMA relative to
those of DMA in the soils and sediments (Tamaki and
Frankenberger, 1992; Tlustoš et al., 2004).