Metal(loid)s in Rooftop Harvested Rainwater near Hazardous Waste and Toxic Release Sites

As global climate change exacerbates concerns of freshwater scarcity, specifically in arid/semi regions, rooftop rainwater harvesting has gained attention as a viable method to offset dependence on existing supplies. However, there is little information regarding the quality of harvested water and no monitoring programs. As part of a co-created citizen science (CS) program, harvested rainwater (HRW) was analyzed four times over one year. Collection times bracketed the two major precipitation periods in southwest USA: beginning and end of the North American summer monsoon and winter rains. Recruited CS were from rural and urban communities throughout Arizona that neighbor hazardous waste and/or designated toxic release sites. Dissolved aluminum (Al), arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) were selected for monitoring based on community input, nearby pollution sources, and potential exposures. CS participants received HRW quality feedback compared to federal/state water quality standards, e.g. US Department of Agriculture's (USDA) irrigation and livestock and Arizona Department of Environmental Quality's full- and partial-body contact standards. The highest concentrations observed were [Al] = 3,946, [As] = 32.5, [Cd] = 9.15, [Cu] = 296, [Pb] = 350, and [Zn] = 951,00 (μg L^-1). HRW samples received from community members neighboring an active mine and smelter site had significantly greater concentrations of Cd than samples received from the urban and other rural sites without an operating smelter. Arsenic concentrations from this site were also significantly greater than most others, the exception being a site with a legacy smelter. Exceedances of the USDA Cu and Zn irrigation standards were observed across all sites. Whether intended for irrigation, livestock drinking, or other purposes, participating CS are making informed decisions regarding how to use their rainwater. Findings will directly inform rainwater harvesting practitioners and regulatory authorities for future uses and contribute to possible health-based standards.