Mitigating the impacts of arsenic on human health and rice yield in Bangladesh

Abstract

Naturally-occurring groundwater arsenic can threaten human health and food security. In Bangladesh, >50 million people are estimated to have chronically consumed water with arsenic above the World Health Organization (WHO) guideline of 10 μg/L, which can contribute to cancer, cardiovascular disease, and reproductive and developmental effects. Studies relating arsenic exposure to health impacts generally estimate dose based on participants' primary household wells. Using a mass-balance for arsenic and water, we estimate that participants in Araihazar, Bangladesh obtain 37±8% of their water from primary household wells and 31±14% from other wells, and we thus recommend the inclusion of other wells in dose estimation. Concentrations of arsenic in well water are spatially variable, enabling many exposed households to switch to nearby lower-arsenic wells in response to area-wide well testing. Following well testing and education in Araihazar, arsenic exposure declined and remained lowered for at least eight years. Participants with arsenic-unsafe wells were 6.8 times more likely to switch wells over the first two years and 1.4-1.8 times more likely to switch wells over the ensuing decade. Rice comprises more than 70% of calories consumed in Bangladesh, and rice yield is negatively impacted by the buildup of arsenic in soil from irrigation with high-arsenic water. We investigated the effect of soil arsenic on yield using a controlled study design where we exchanged the top 15 cm of soil between high-arsenic and low-arsenic plots. Differences in yield were negatively correlated to differences in soil arsenic between adjacent soil replacement and control plots, suggesting that boro rice yield countrywide may be diminished by 7-26% due to arsenic in soil. Soil testing and removal of high-arsenic soil may enable farmers to mitigate the impacts of arsenic on rice. Twelve measurements made with the ITS Econo-Quick field kit could be used to estimate whether soil arsenic was above or below a 30 mg/kg intervention threshold with 80-90% accuracy. A soil inversion, where deep low-arsenic soil was exchanged with surface high-arsenic soil, decreased soil arsenic, organic carbon, nitrogen, and phosphorus concentrations by about 40% in the top 20 cm of soil and improved rice yield by 15-30%.