Improved groundwater geogenic arsenic hazard map for Cambodia

Abstract

Environmental context Groundwater arsenic is a major environmental risk to human health in many regions of the world, including Cambodia where groundwater is often used for drinking water. We present data for hitherto poorly sampled regions in Cambodia, notably around Tonle Sap and in the coastal provinces, and provide a geo-statistical model of arsenic in shallow groundwater for the whole country. Abstract Arsenic is a known environmental chemical hazard in shallow groundwaters of Cambodia and is increasingly recognised as a major problem for public health. Notwithstanding this, accurate arsenic data are not available for many wells in potentially arsenic-prone areas, particularly around the Tonle Sap Great Lake (TSL) and in the coastal provinces (CP). We present here new data for shallow groundwater (16–120-m depth) arsenic in the TSL and CP regions as well as an improved regression-kriging (RK) based groundwater arsenic hazard map for the whole country. High arsenic levels (up to 100μgL–1) were found in shallow groundwaters from the TSL and CP regions of Cambodia, but despite strong compositional similarities (near neutral, reducing, Na-Mg-Ca-HCO3 dominated) with high arsenic level groundwaters near the Mekong and Bassac rivers, groundwater arsenic levels in both the TSL and CP regions were most commonly low (interquartile range 0.09–1.2μgL–1). The RK geostatistical model was highly successful, accounting for over 50% of the observed variation in arsenic concentrations countrywide and represents a potentially useful tool for policymakers and those responsible and with the interest and authority to prepare arsenic mitigation and safe water supply plans.