The effects of triclosan on microbial communities in different sources of water and sediments

Triclosan is a widely used antimicrobial agent frequently detected in aquatic environments. Although its effects on environmental microorganisms have been extensively studied, findings often remain inconsistent due to variations in experimental setups and sediment characteristics. Comparative studies that assess microbial responses across different sediment types, however, are still scarce. Here, we employed a microcosm approach to assess triclosan-induced changes in microbial communities colonizing natural (pond and ditch) and OECD artificial sediments, aiming to compare microbial responses across sediment types and to identify environmental factors influencing triclosan effects. Natural sediments were collected from uncontaminated waterbodies, while artificial sediments were prepared following OECD guidelines and incubated for one month in pond and ditch sites, while natural sediments remained at their original locations. Following incubation, all sediments were exposed to triclosan (up to 1000 µg/L, resulting in a maximum sediment concentration of almost 1000 ng/g) under controlled laboratory conditions for seven days. Microbial community shifts were assessed using 16S rRNA gene sequencing. The results showed significant differences in microbial community composition between ditch and pond sediments, as well as within water bodies, between natural and OECD sediments. Following triclosan application, microbial communities in the sediment of the OECD ditch, natural ditch, and natural pond groups exhibited significant differences compared to the control treatment at the highest concentrations (380 ng/g, 643 ng/g, and 661 ng/g, respectively). Several bacterial families known for triclosan degradation or resistance increased in relative abundance. Redundancy analysis indicated that water nutrient concentrations and sediment organic matter content significantly influenced microbial responses to triclosan exposure. Nutrient-rich environments supported greater microbial complexity and resilience, while high organic matter likely reduced triclosan bioavailability through adsorption. Overall, this study underscores the importance of both sediment characteristics and overlying water conditions in modulating microbial sensitivity to emerging contaminants. Our findings highlight the need to account for environmental heterogeneity when designing experiments and conducting ecological risk assessments for chemical pollutants.