Stormwater alters the resistome of urban surface water, an impact that can be mitigated by green stormwater infrastructure†

Antibiotic resistance poses an escalating threat to global health, with environmental reservoirs being pivotal areas of concern, as well as opportunities for potential mitigation. Stormwater systems are an important type of environmental reservoir in the urban water cycle with a dearth of research related to impacts on antibiotic resistance. In particular, there has been limited research exploring the impact of diverse antibiotic resistance genes (ARGs) carried by stormwater from various land uses on surface water, nor has there been an examination of the role played by green stormwater infrastructure (GSI) in mitigating this impact. Therefore, this study sought to elucidate the variability of ARGs across diverse land uses and evaluate the efficacy of GSI in mitigating ARG dissemination. Five distinct stormwater samples—representing mixed, residential, urban, and GSI-treated effluents—were taken to assess variations in ARG resistomes based on land use types. The ARGs in stormwater collected from different land uses were found to be similar in composition and represent a similar level of diversity. A GSI system with a rock swale and bioretention cell connected in series, was also sampled to see how GSI impacted ARGs, and this GSI system did substantially alter the diversity of ARGs. Moreover, the bioretention cell was found to reduce ARG concentrations by 30%. This research also sought to assess the impact of all five stormwater samples on the resistome of surface water via lab-scale microcosm experiments. The urban and residential stormwater significantly (p < 0.05) altered the resistome of surface water, while the mixed-land use sample did not. This finding underscored stormwater's pivotal role in introducing distinct ARG resistome compositions into downstream waters, heightening the chances for development of antibiotic resistant bacteria. The effluent stormwater from the GSI system, however, had less of an impact on the resistome of surface water in the microcosm experiments in comparison to the influent (untreated) stormwater. In managing stormwater runoff through GSI systems, this study's findings highlight the potential of GSI designs and practices to limit the dissemination of diverse and abundant ARGs, safeguard public health, and contribute to sustainable stormwater management by minimizing the impact on downstream surface waters.