Elucidating the impact of common stormwater pollutants on antibiotic resistance: the role of heavy metals, nutrients, and salts†

Antibiotic resistance poses a significant global health threat, and the urban water cycle presents an opportunity to augment or limit the spread of antibiotic resistance. In particular, stormwater runoff has recently been revealed as a key conduit for antibiotic-resistant bacteria (ARB). The specific role of stormwater pollutants, however, on antibiotic resistance has not been isolated. Understanding the impact of specific pollutants common to stormwater could help optimize design and operation of stormwater systems for management of antibiotic resistance. The objective of this research was to establish the potential contributions of common stormwater pollutants to antibiotic resistance proliferation. Lab-scale stormwater microcosms were amended with either heavy metals, nutrients, or salts, and then ARB and antibiotic resistance gene (ARG) concentrations were quantified over a seven-day period. The microcosm experiments revealed that heavy metals (5–1000 μg L⁻¹) on average significantly increased (p < 0.05) ARGs and ARB concentrations 0.30 log and 0.96 log, respectively, and the effects were dependent on the concentration of the metal. Total bacterial counts increased by 174% in nutrient-amended microcosms, while ARG levels remained statistically unchanged (p > 0.05). Salts, a common pollutant in colder climates, exhibited no impact. Moving forward, targeted interventions focusing on heavy metal removal, alongside careful stormwater treatment design, could offer promising avenues for addressing antibiotic resistance dissemination in urban environments.