Concentration of arsenic in groundwater was investigated at three villages (Chong Prek, Prek Tameng and Prek Thom) in the Kandal Province of Cambodia, which ranged from 80.9 μg/L (in Prek Tameng village) to 1420 μg/L (in Prek Thom village), with average and median concentrations of 463.16 and 217 μg/L, respectively. Iron concentration was also determined. Nearly all the twenty-five samples contained arsenic and iron concentrations exceeding the WHO drinking water guidelines (100% As > 10 μg/L, 100% Fe > 300 10 μg/L) and the Cambodian legal limits of drinking water (100%  As  >  50  μg/L,  100%  Fe  >  1000  μg/L).  The
sources of arsenic occurrence were studied trying to explain in terms of geogenic origin based on the available data. The As release into groundwater may result from the reductive dissolution of metal oxides under reducing condition at circum-neutral pH, in particular iron sulfide (pyrite), according to the evidences of iron, sulfate, phosphate, nitrate and nitrite in the groundwater, measured by ICP-AES and IC. This study showed that the occurrence of arsenic in Kandal Province poses a health threat to the villagers in Kandal Province and appropriate treatment of groundwater must be implemented.