Arsenic poisoning in the Ganges delta

The pollution by naturally occurring arsenic of alluvial Ganges aquifers, which are used for the public water supply in Bangladesh and West Bengal, has been discussed by Nickson et al.. We agree with their main conclusion that arsenic is released by reductive dissolution of iron oxyhydroxides, as was proposed earlier. Our observations indicate that arsenic- rich pyrite and other arsenic minerals, which were proposed in previous models (cited by Nickson et al.) to give rise to arsenic pollution, are rare or even absent in the sediments of the Ganges delta. We believe that arsenic is more likely to be co-precipitated with or scavenged by iron (III) and manganese (IV) in the sedimentary environment.