Human health risk assessment for ingestion exposure to groundwater contaminated by naturally occurring mixtures of toxic heavy metals in the Lao PDR.

This study constitutes the first systematic risk assessment in the Lao PDR of the safety of groundwater for consumption. Groundwater and hair samples were collected from seven Lao provinces to determine the quantitative health impact of heavy metals through ingestion exposure. Contamination levels for arsenic (As; 46.0 %) and barium (Ba; 16.2 %) exceeded World Health Organization (WHO) guidelines, especially in Mekong River floodplains. A USEPA assessment model for health risks from daily groundwater ingestion, with adjustments for local water consumption values, was applied to estimate the size of the population at risk for noncarcinogenic and carcinogenic health problems. As was the only element contributing to noncarcinogenic health risks in all contaminated areas. The populations of Bolikhamxai, Savannakhet, Saravane, Champasak, and Attapeu, moreover, were at risks of cancer. In addition to the As groundwater concentration factor, noncarcinogenic and carcinogenic risks were positively correlated with the average daily dose of As, exposure duration, and subject body weight. The level of As in hair correlated with groundwater consumption and average daily dose of As. 25.5 % of the population (n = 228) showed As levels in hair above the toxicity level.