Interactions between antibiotic resistance and arsenic metabolizing genes in geogenic contaminated groundwater: Consequence for arsenic migration

Geogenic contaminants and emerging contaminants co-occur frequently in disturbed aquifer environments, complicating the evolution of geogenic contaminated groundwater and resultant health risk posed to human beings. The development of antimicrobial resistance (AMR) was found to affect critical microbial activities responsible for arsenic (As) mobilization, yet the underlying processes and mechanism remain undervalued from limited field investigation. By virtue of joint field campaign, molecular biological analysis, and hydrogeochemical modeling, this research provides novel insights into influence of cross-resistance between As and antibiotics on As biotransformation and enrichment in groundwater. Our basin-scale hydrogeological investigation reveals that lithological characteristics of Quaternary formations and associated regional groundwater flow regime led to gradual co-increase of antibiotic and As concentrations from recharge area to discharge area. While antibiotic resistance genes (ARGs) in groundwater exhibited spotty distribution pattern in the recharge area, they tended to accumulate in the discharge area. Consequently, microbially-mediated Fe(III)-oxide reduction was inhibited in groundwater subject to high-level antibiotics, whereas microbial SO42- reduction was sustained under high-antibiotic environmental stress. Moreover, cross-resistance was likely to develop after the accumulation of ARGs, thereby enhancing As biotransformation and re-migration. Hence, primary mechanism underlying As enrichment probably shifted from microbial dissolution of Fe(III) oxides to ARGs-driven As bio-migration in antibiotic-affected aquifers. These findings highlight the underestimated impact of AMR on evolution of geogenic As-contaminated groundwater in areas with significant antibiotic pollution. This research additionally warrants a careful re-assessment of in-situ groundwater remediation approaches in disturbed aquifer environments.