Integrating Social Vulnerability Index With Potential Upstream Iodine Effects on Downstream Community Water Systems

Abstract

Disinfection byproducts (DBPs) form when organic matter and other precursors such as iodine species react with chemical disinfectants during drinking water treatment. Iodinated-DBPs are particularly toxic but unmonitored and unregulated in the United States. Previous research established a discharge-intake flow index (DIFI) based on the relationship of possible upstream iodine discharges on downstream drinking water sources. Considering which community water systems (CWS) and their associated populations served can enhance understanding of potential effects from iodine discharges; therefore, DIFI values from 1,657 surface water-supplied CWSs were integrated with the Centers for Disease Control's Social Vulnerability Index (SVI) at census tract levels. Co-vulnerable systems were defined as those exceeding median values for both DIFI and SVI. The four SVI themes and overall SVI were analyzed. Co-vulnerable systems in the SVI 3 theme (racial/ethnic minority status) serve 39.3 million people across 364 CWSs—39% of the studied population served but only 22% of systems. Over 50% of co-vulnerable systems for SVI 3 were in Southern U.S. hydrologic regions (HUC03, 06, 08, 11, 12). Additionally, 121 CWSs serving 7.5 million people showed consistent co-vulnerability across all four SVI themes. Geographic clustering revealed concentrations in the South, Northeast, and Great Lakes regions, with some hydrologic regions showing >25% of systems as co-vulnerable. Incorporating social vulnerability data revealed distinct geographic patterns, with disproportionate potential effects on minority communities in the Southern U.S. These findings enable targeted prioritization of monitoring and regulatory efforts and address environmental justice concerns in drinking water quality management.