Arsenic in private drinking water supplies: human health risk based on underlying geology

Abstract

Background Revised regulations governing the quality of private drinking water supplies (PWS) were introduced in 2008 as EU Directives, and transposed into UK Regulations in 2009, but there is a lack of coordinated information on the geographical distribution of known hazards such as those related to arsenic (As) and underlying geology. Aim To explore a methodology for risk assessment of exposure to As in drinking water based on the underlying geology and exceedances of the permissible limit. Methods Households in Cornwall with a PWS were identified from a register and a subset was selected to represent areas of different underlying geology. Approximately 500 residents were invited to provide tap and borehole water samples and information on water use. Water samples were analysed for As and other chemical parameters by ICP-MS and ion chromatography. The geological classification of the bedrock was complex in the study area with a need to simplify the categorisation in order characterise exposure in relation to geology. The British Geological Survey simplified this to 8 categories for practical analysis. Results In the first phase of the study covering east Cornwall in 2011, 258 PWS were sampled. Out of the 8 simplified geologies, Mineralisation areas and Gramscatho were more likely to have higher levels of As than others. A possible risk variation by geology category was found, but statistical significance was only borderline. Households found to have water supplies with exceedances for As or other hazards were advised about re-testing and interventions such as water treatment. Conclusions Potential exposure of a proportion of the Cornwall population to As was identified. In relation to risk related to underlying geology, there is an indication that some geologies are more likely to have higher levels of arsenic than others. Results of further analyses in a wider sampling area will estimate the potential influence of geology on the exposure of the population.