ARSENIC CONTAMINATED GROUNDWATER IN BANGLADESH: A GEOSTATISTICAL AND EPIDEMIOLOGICAL FRAMEWORK FOR ESTIMATING HEALTH EFFECTS AND EVALUATING REMEDIES

During the past few decades, millions of wells have been installed in Bangladesh to provide pathogen-free groundwater for household use. These wells now supply practically the entire population with drinking water. Unfortunately, most of the groundwater is contaminated with arsenic: almost 50% of the wells produce water with arsenic concentrations in excess of 10 ppb, the World Health Organization’s acceptable limit, and 30% produce water with arsenic concentrations in excess of 50 ppb, the U.S. Environmental Protection Agency’s acceptable limit.

In this paper, we first model the geographic distribution of arsenic concentration in groundwater throughout Bangladesh. Using available field surveys, we combine geologic mapping with classical variogram analysis. Regional mapping of the geology and geomorphology of Bangladesh is shown to explain much of the large-scale ( > 10 km) spatial variability. Minimal spatial structure exists at scales less than 1 km, and a significant component of the small-scale spatial variability is explained by differences in well depths. We also estimate for each geologic region a depth trend in arsenic concentration—and typically find concentration decreasing with depth.

We combine the geographic distributions of arsenic concentration in regions with census data to estimate exposure distributions in each region. Then, we use epidemiological data from Taiwan and West Bengal to estimate dose-response functions for the health effects of certain types of arsenicosis and cancer, and we combine the dose-response functions with the exposure distributions to estimate the health effects due to groundwater arsenic. We predict that with long-term exposure to present concentrations of arsenic there will be prevalences of approximately 1,200,000 cases of hyperpigmentation, 600,000 cases of keratosis, and 150,000 cases of skin cancers, and an incidence of 3,000 fatalities per year for internal cancers of various types.

As a remedy, we consider the option of drilling deeper groundwater wells in selected regions of Bangladesh. We estimate that such a strategy could significantly reduce the health effects of drinking arsenic contaminated groundwater, provided that arsenic concentrations at deep wells remain low over time.