), indicating persistent faecal contamination. Monsoon rainfall was associated with a consistent increase in faecal/anthropogenic indicators and ARGs, reaching 1 to 3 orders of magnitude higher relative abundance compared to pre-monsoon conditions. Post-monsoon, ARG levels in water generally declined toward pre-monsoon levels, whereas sediment-associated ARG signals remained elevated post- compared to pre-monsoon, indicating persistence in depositional reservoirs. Although heavy metal concentrations frequently reached ranges previously linked to co-selection, they showed no significant correlations with ARG abundances, identifying faecal pollution as the dominant driver of seasonal resistance dynamics. No consistent increases in ARGs or faecal markers were detected downstream of wastewater treatment plants, supporting widespread non-point source inputs. Overall, monsoon events act as major amplifiers of antibiotic resistance in severely impacted urban rivers by mobilising faecal contamination and counteracting dilution. Mitigation should prioritise reducing unmanaged sewage and solid waste inputs, particularly before and during monsoon periods.
Bagra et al. (Mon,) studied this question.