Level of arsenic contamination in drinking and irrigation water in the Narayani irrigation command area, Nepal

Abstract

Background Arsenic contamination in groundwater and its threat to human health is relatively new for Nepal. Groundwater is the main source for drinking and irrigation in the Tarai region of Nepal, where the arsenic risk population has been increased since the last few years. Efforts have been made by the government to harness the groundwater for year round irrigation for increasing agricultural crops in the Tarai. Since the groundwater is found to be contaminated with arsenic, continuous use of groundwater for both drinking and irrigation appears to be health catastrophe to the Tarai’s communities. Objective This study examines the arsenic state and classifies water availability in the Narayani Irrigation Command (NIC) area. Methods The arsenic test for this study report has been based on two spatial levels. The first level includes total tube well samples for all three districts of Parsa, Bara and Rautahat lying in the command area of Narayani Irrigation System. At the second level, the data and information on the water samples of the tube wells were gathered at Village Development Committee (VDC) of those districts. The analysis of the data has been schematically presented through GIS Map. Based on the samples, the households consuming arsenic contaminated water above Nepal Interim Standard (50μg/L) were classified as risk households. Among the risk household members, the Arsenicosis patients were identified based on clinical examination. Arsenicosis prevalence rate is computed as the ratio between symptomatic patients and total risk population, expressed in terms of percent. Water Availability Index (WAI) was assigned to classify water availability situation in NIC area. Results Of the total 2,389 tube wells sampled in the Narayani Irrigation Command area, 4.5 percent are above the Nepal Standard and 28.3 percent above the WHO guidelines. The distribution of arsenic levels in the tube wells is more or less similar pattern in all three districts of the study region. The dependency on groundwater is higher in areas where the availability of surface water is low. There exists an inverse relationship between arsenic level and water availability index. The arsenicosis prevalence rate for all three districts is less than 1 percent. Conclusions The preliminary analysis of the arsenic levels of the tube wells demonstrates that the farm households locating in the downstream are more exposed to arsenic problem than those in the upstream of the command area. This is mainly due to higher dependency on groundwater. Three alternative strategies to reduce arsenic level may be suggested, viz. improving the performance of surface irrigation, making less dependency on groundwater and adaptation of arsenic removal strategy.