Trace Element Concentrations in Arsenic (As) Contaminated Drinking Water in Nepal Reflect Sediment Surface-Ground Water Interactions

Since more than a decade it is known that in a variety of countries in South East Asia, arsenic (As) contamination of ground water used for drinking poses a serious health hazard. In ground water of these countries, the concentrations of the highly toxic elements frequently exceed the World Health Organization (WHO) drinking water guideline of 10 μg/L. According to a widely accepted hypothesis, a reductive dissolution of Fe-bearing minerals releases As-oxyanions. As the concentrations of As and Fe in ground water in the lowlands (Terai) of Nepal are highly variable as a function of location and a clear de-coupling of As and Fe resulting in a loss of correlation between these two elements, the mentioned hypothesis has to be questioned. Major trace element analysis of the ground water depicts a low concentration of Fe but substantial amount of Na, K, Li, B and Mo in these waters. All these elements are positively correlated with As; therefore, pointing to clayey sediments mainly consisting of micas and other clay minerals as the hosts of As. This specific pattern of trace element distribution is related to a so far underestimated original source of As as the peraluminous leucogranites found ubiquitously in the Nepalese Himalayas.