Limited Temporal Variability of Arsenic Concentrations in 20 Wells Monitored for 3 Years in Araihazar, Bangladesh

摘要

On the basis of 3 years of monitoring arsenic concentrations in 20 wells in a small area of Bangladesh, Cheng et al. (1) show that arsenic concentrations change very little in most wells and in all wells deeper than 10 m and draw conclusions from those trends. This comment accepts their data but widens the scope to discuss data and conclusions that are contrary to their view. Cheng et al. (1) state that their "most important conclusion... is that groundwater As concentrations typically do not vary over time." This conclusion is drawn in isolation from other available information and is potentially unsafe if extrapolated beyond their 20 wells or into the future. Three years of monitoring, while admirable and valuable, is too short a time for solid conclusions to be drawn. Without qualification, the implication to be drawn from their work by tube well owners, or their advisers, is that the arsenic concentration of well water will not change over time and, most importantly, that wells tested "safe" (i.e., below 10 or 50 μg L~(-1)) will remain safe. By omitting discussion of well-documented analyses that run counter to their conclusions, they risk exposing unsuspecting consumers of tube well water to dangerous concentrations of arsenic.