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Fate and transport of viruses, bacteria and antimicrobial resistance associated with wet wipes and microplastics through wastewater treatment to coastal waters
Summary
Researchers found that tiny plastic particles and wet wipes flowing through wastewater treatment plants can carry viruses like norovirus and antibiotic-resistant bacteria, with wet wipes holding onto more germs than plastic beads. While treatment plants remove most of this contamination before water reaches the coast, sewage overflow events (when storms cause untreated sewage to spill directly into waterways) can release higher germ-carrying plastic and wipe debris into the ocean, making better overflow management important for protecting swimmers and coastal water quality.
Microplastics (MPs) in wastewater are increasingly recognised as potential vectors for pathogens and antimicrobial resistance (AMR), yet their role across treatment remains poorly understood. This study tracked viral, bacterial, and AMR associations with MPs from hospital wastewater through to coastal receiving waters, including simulated combined sewer overflow (CSO) events, using quantitative real-time PCR, and shotgun metagenomics. MP concentrations found naturally in the wastewater matrix, declined from 467 to 33 particles L⁻¹ during WWTP passage, achieving 93% removal. Norovirus (GI and GII) and bacteria colonised beads and wet wipes throughout, with wet wipes retaining higher viral and AMR loads than plastic beads, likely due to structural complexity. Sequential sampling across treatment stages showed a reduction in norovirus and bacterial loads by ∼1 log, yet pathogens remained detectable on beads and wet wipes in final effluent. NoV GI predominated, while NoV GII concentrations and the class I integron-integrase (intI1) gene varied by treatment stage and sample type. Metagenomics showed enrichment of potentially pathogenic genera (Aeromonas, Pseudomonas, Flavobacterium) in bead and wet wipe biofilms, and network analysis identified associations between Aeromonas and clinically relevant beta-lactam resistance genes (OXA, CTX). Shifts at the activated sludge stage indicated bead and wet wipe associated communities in effluent reflect treatment microbiota rather than influent sources. Environmental MP concentrations are below those required to deliver an infectious viral dose, suggesting MP-mediated transmission is unlikely under normal conditions. However, during CSO events, beads and wet wipes retained high viral loads and may act as pathogen transport vectors. These findings highlight CSO management as a priority for reducing MP-associated pathogen risks in receiving waters.