Snowmaking Infrastructure: A Selective Barrier or Potential Vector for Antibiotic Residues and Resistance Determinants in Mountain Catchments

Snowmaking systems are increasingly used to serve winter tourism in mountain regions, yet their role in the environmental dissemination of antimicrobial resistance (AMR) remains poorly understood. Here, we investigated how snowmaking infrastructure affects the transport, retention and reduction of antibiotic residues, antibiotic resistance genes (ARGs) and phenotypically resistant bacteria along two interconnected water chains feeding technical snow production in mountain catchments. Over two winter seasons (2023/24 and 2024/25), we quantified a panel of clinically relevant antibiotics, ARGs and resistance phenotypes in wastewater effluent, intake water, reservoirs, technical snow, aged snow, meltwater and receiving streams; culturable bacteria, resistance phenotypes and ARGs were additionally assessed in reservoir sediments and snow cannon filter material. Wastewater and intake water exhibited the highest antibiotic loads and ARG richness, dominated by fluoroquinolones, macrolides and β-lactam resistance determinants. Reservoirs accumulated substantial amounts of antibiotics but their reduction occurred further along the snowmaking chain. Fresh technical snow still contained multiple antibiotics and ARGs, and harbored resistant Enterobacteriaceae, indicating that snowmaking systems can redistribute AMR determinants into the snowpack. Aged snow, meltwater and receiving streams showed nearly complete loss of antibiotic residues and reduced ARG richness, due to processes of snow transformation and downstream transport. By integrating chemical, molecular and phenotypic data with the technical layout of the infrastructure, we identify specific components as AMR retention hotspots and clarify where barrier functions are most effective. Our findings demonstrate that snowmaking infrastructure can both concentrate and distribute antibiotic residues and resistance determinants in mountain catchments, highlighting the need to consider snowmaking systems in environmental AMR risk assessments and One Health frameworks.