Direct and indirect arsenic release from soaps by unhygienic use in tubewells

Abstract

Microorganisms have been implicated in the release of arsenic into drinking water involving bio-electrochemical reactions. Iron reducer has been shown to release captive arsenic from insoluble ferric oxyhydroxide- arsenic oxide adduct. Sulphate reducing bacteria (SRB) and Enterobacteriaceae may play a similar role by releasing hydrogen sulphide. The case of arsenic mobilization in water may be complex and varied. Arsenic contamination in Kanpur, northern India, 1000 km upstream of the Gangetic delta, added a new dimension to understanding the cause of its release in water. We propose that passive arsenic carried by the Ganges in the soil for centuries may be activated by unhygienic use of tubewells during the past three decades. We modelled the soil redox-chemistry prevalent under such conditions. We show that SRB grow in the vicinity of tubewells due to the availability of abundant food as fatty acids and sulphate as electron acceptors from soaps and detergents to release arsenic. In the absence of soap, Enterobacteriaceae play the same role. We also show that 26 commonly used soaps and detergents in India contain alarmingly high concentration of soluble arsenic, contaminating surface water.