Arsenic speciation in natural waters

Speciation studies are necessary to understand the biogeochemical cycling of arsenic in aquatic systems. The species of arsenic present, their behaviour and toxicity will change depending on the biotic and abiotic conditions in the water. In groundwater, arsenic is predominantly present as arsenite (As-III) and arsenate (As-V). The major arsenic species in freshwater are As-III and As-V and minor amounts of MMA, DMA and methylated As-III have also be detected. In seawater, the arsenic speciation differs in the surface and deep zone. In addition to the above species, uncharacterized arsenic species may constitute a significant portion of the total arsenic present in some water and the identification of these compounds is necessary to fully understand the arsenic biogeochemistry in water.