Triclosan as a selective pressure on nitrifying microbial guilds: functional, genetic, and biogeochemical...

Triclosan (TCS), a widely used antimicrobial biocide, has raised significant concerns due to its environmental persistence and toxicity to aquatic organisms. TCS enters aquatic environments primarily through wastewater effluents, where it can disrupt critical steps of biogeochemical processes, such as nitrification, which is essential for maintaining nutrient balance in ecosystems. TCS inhibits ammonia monooxygenase (AMO) and nitrite oxidoreductase (NXR) activity and downregulates key nitrification gene expression including amoA and nxrB, thereby impairing nitrogen transformation pathways in aquatic ecosystems, and its effects are modulated by co-pollutants such as heavy metals and microplastics. This review outlines current evidence on the impact of TCS on nitrifying bacteria and associated shifts in microbial community structure integrating omics-based insights that reveal nitrification gene abundance and co-enrichment of TCS degraders and antibiotic resistance determinants. It emphasises the need for integrated research on the long-term effects of TCS on biogeochemical cycling and nitrification, and highlights implications for regulation and advanced green chemistry based wastewater management.