Wastewater treatment plants (WWTPs) are a major point source of antibiotics and antimicrobial resistance in the aquatic environment. This study evaluated model predictions for ciprofloxacin (CIP), erythromycin, and sulfamethoxazole (SMX) concentrations, and the potential presence of their respective resistance within U.S. streams affected by WWTP discharges under varying instream flow conditions. We incorporate predicted no-effect concentrations (PNECs) for selection resistance into the previously developed De Facto Reuse Incidence Nations Consumable Supply model to identify potential antibiotic hotspots across the U.S. Our results suggest that under mean annual instream flow, more than one-third of sites (4629 out of 13,245) did not meet the antibiotic resistance (ABR) safety threshold for CIP. Under low instream flow conditions, dilution factors in 76.9% (n = 9885) of sites exceeded the ABR safety threshold for CIP, and ABR safety thresholds for two antibiotics were surpassed in 25.8% (n = 3323) of streams with available low flow data (n = 12,856). Despite considerable therapeutic use and the resulting presence of SMX in the effluent, the threat of SMX resistance is comparatively low due to a higher ABR threshold. We suggest that several streams across the U.S. are vulnerable to ABR development from compounds with relatively low PNECs, such as CIP, during average and low instream flow conditions.

There has been a growing concern about waterborne disease prevalence, especially in underserved communities. Stormwater best management practices (BMPs) can control surface runoff, and improve water quality by restoring the pre-development hydrologic cycle while providing social, economic, and health benefits. Although stormwater BMPs have been proven to effectively impact runoff quantity and quality, their effectiveness in waterborne disease reduction has not been investigated. In this study, we quantified for the first time the impact of BMPs on reducing waterborne diseases in underserved communities. We developed a geographic information system (GIS) – based framework to create multi-metric vulnerability indices identifying counties’ susceptibility to waterborne diseases considering environmental justice (race, ethnicity, and socioeconomic status) and at-risk age groups (under 5 and over 74) in Florida. The most vulnerable counties were then investigated for disease reduction by stormwater BMP implementation. Our findings indicated disproportionate occurrences of waterborne diseases in communities with higher minorities (Hispanics and Nonwhites), at-risk age groups, and low-income populations. Among evaluated BMPs, wetland basin, porous pavement, and retention pond were the most efficient in reducing cases of waterborne diseases with over 80% efficiency. Our findings demonstrate the need for stormwater BMPs that take socioeconomic status and racial diversity into account.

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