Rainwater Harvesting: Prevalence of Metal(loid)s in Arizona Communities Adjacent to Toxic Release Sites

Abstract

As global warming exacerbates concerns of water scarcity, specifically in arid regions, rooftop rainwater harvesting has gained attention as a viable method by which dependence on existing water supplies may be offset. Project Harvest (PH), a co-created citizen science project organized at the University of Arizona in partnership with the Sonora Environmental Research Institute (SERI) completed analysis of citizen-collected samples to investigate the quality (with respect to inorganic, organic, or microbiological contaminants) of harvested rainwater as well as the quality of the soil and plants irrigated with harvested rainwater. Citizen scientists were recruited from rural and urban communities in Arizona, neighboring hazardous waste and toxic release sites. Communities include: Dewey-Humboldt, Globe/Miami, Hayden/Winkelman, and Tucson, each of which submitted water samples four times per year at the beginning and end of the winter rains (December 2017 – February 2018) and the North American monsoon season (July 2018 – September 2018), Monitoring of selected metal(loid)s of concern; aluminum (Al), arsenic (As), Cadmium (Cd), Copper (Cu), Lead (Pb), and Zinc (Zn), selected based on nearby sources of pollution, system type, and a literature review of the six elements. All but Zn had higher pervasiveness in harvested rainwater samples for the monsoon collection periods relative to winter rain samples. Peak concentrations of Al, As, Cd, Cu, Pb, and Zn were: 3,946 μg L-1, 32.5 μg L-1, 9.15 μg L-1, 296 μg L-1, 350 μg L-1, and 951,271 μg L-1, respectively. PH informs participants on their water quality based on intended uses for the roof-harvested rainwater; relying on various non-potable federal and state water quality standards and recommendations. The United States Department of Agriculture’s recommended maximum trace element concentration for irrigation and livestock drinking waters as well as the full- and partial-body contact water standards set by the Arizona Department of Environmental Quality were used to determine usability of harvested rainwater. Median metal(loid) concentrations in harvested rainwater samples decreased in the order of Zn > Al > Cu > Pb > As > Cd for Dewey-Humboldt and Tucson, while concentrations for Globe/Miami and Hayden-Winkelman decreased in the order of Zn > Al > Cu > As > Pb > Cd. Globe-Miami had the highest median concentrations for Al, Hayden-Winkelman had the highest median concentrations for As, Cd, Cu, and Pb, and Tucson had the highest median concentrations of Zn. Findings from this study will inform rainwater harvesting practitioners and regulatory authorities.