Department Water Resources and Drinking Water

Naturally occurring arsenic in groundwater affects millions of people worldwide. We created a global prediction map of groundwater arsenic exceeding 10 micrograms per liter using a random forest machine-learning model based on 11 geospatial environmental parameters and more than 50,000 aggregated data points of measured groundwater arsenic concentration. Our global prediction map includes known arsenic-affected areas and previously undocumented areas of concern. By combining the global arsenic prediction model with household groundwater-usage statistics, we estimate that 94 million to 220 million people are potentially exposed to high arsenic concentrations in groundwater, the vast majority (94%) being in Asia. Because groundwater is increasingly used to support growing populations and buffer against water scarcity due to changing climate, this work is important to raise awareness, identify areas for safe wells, and help prioritize testing.

Human endeavours into deep space exploration and the prospects of establishing colonies on nearby planets would invariably involve components of bioregenerative life support for food production, cabin atmosphere renewal, and waste recycling. Growing plants and their microbiomes in porous media under different gravitational fields may present new challenges due to effects of liquid distribution on gaseous exchange with roots and microorganisms. We provide the first direct evidence that capillary driven liquid reconfiguration in porous media under reduced gravity conditions reduces oxygen diffusion pathways and enhances anoxic conditions within bacterial hotspots. Parabolic flight experiments using model porous media inoculated with aerobic and facultative anaerobic bacteria reveal the systematic enhancement of anoxic conditions during the reduced gravity periods in the presence but not in the absence of bacterial activity. The promotion of anoxic conditions under reduced gravity may lead to higher nitrous oxide and methane emissions relative to Earth conditions, on the other hand, anoxic conditions could be beneficial for perchlorate bioremediation of Martian soil. The results highlight changes in soil bacterial microhabitats under reduced gravity and the challenges of managing bioregenerative life support systems in space.

It has been reported that persistent cyanide pollution occurs in artisanal small-scale gold mining (ASGM) catchment areas in Burkina Faso. In the present study, logistic regression (LR) and Regression Kriging (RK) methods were applied to predict cyanide pollution hazard at the catchment level as well as to determine the most vulnerable areas to prioritize for restoration of degraded ecosystems. Soil samples were collected from two ASGM sites in Burkina Faso: the northern Zougnazagmiline site and the southern Galgouli site. Free cyanide (FCN) concentration in each sample was measured and the use of the LR and RK methods identified the relationships between pollution sources and pathways. However, RK was able to identify more areas with a high cyanide hazard than LR. Nevertheless, the two methods reveal that the cyanidation zones and catchments outlets within the two catchments are where the highest risk of cyanide pollution occurs, with probabilities of 0.8 and 1 in Zougnazagmiline and Galgouli, respectively.