Variation in arsenic concentration relative to ammonium nitrogen and oxidation reduction potential in surface and groundwater

Arsenic (As), ammonium-nitrogen (N), nitrate-N concentrations, and oxidation-reduction potential (ORP) in the water samples from the river, pond, dug well, and shallow and deep tube wells (TW) were investigated in a farming village of southwestern Bangladesh. Concentrations of As and ammonium-N were the highest, whereas ORP was the lowest in the shallow TW water among the water sources. The ammonium-N concentration correlated positively with the As concentration and negatively with ORP for all samples, irrespective of the water sources. A rise in the ammonium-N concentration was hypothesized to enhance microbial activity, which in turn would lower ORP, and then As was released from sediments to the surrounding water in a reducing condition. The source of ammonium-N in the shallow TW water was identified as N fertilizer, based on the δ15N analysis. Thus, the influence of N fertilizer application on As contamination in groundwater was suggested.