Regions and populations at risk
Areas predicted to have high arsenic concentrations in groundwater exist on all continents, with most being located in Central, South, and Southeast Asia; parts of Africa; and North and South America. Known areas of groundwater arsenic contamination are generally well captured by the global arsenic prediction map, for example, parts of the western United States, central Mexico, Argentina, the Pannonian Basin, Inner Mongolia, the Indus Valley, the Ganges-Brahmaputra delta, and the Mekong River and Red River deltas. Areas of increased arsenic hazard where little concentration data exist include parts of Central Asia, particularly Kazakhstan, Mongolia, and Uzbekistan; the Sahel region; and broad areas of the Arctic and sub-Arctic. Of these, the Central Asian hazard areas are better constrained, as evidenced by higher probabilities.
Probability threshold values of 0.57 from the sensitivity-specificity comparison and 0.72 from the positive predictive value (PPV)–negative predictive value (NPV) comparison were found using the full dataset (combined training and test datasets) of arsenic concentrations. The proportions of high modeled arsenic hazard by continent associated with each of these probabilities are shown in Fig. 3. Global maps of the potentially affected population in the risk areas, as determined by these two thresholds, are shown in Fig. 4. As described in the methods, these maps were then used to estimate the population potentially affected by drinking groundwater with arsenic concentrations exceeding 10 μg/liter.