Sertraline inhibits top-down forces (predation) in microbial food web and promotes nitrification in sediment.

Sertraline is a widely used antidepressant that becomes an aquatic pollutant through metabolic excretion and improper disposal. Determining the impact of sertraline on benthic microbial ecosystems is important for the transformation of river biogenic elements. However, the molecular initiating event induced by sertraline is more readily observed at higher levels, such as the individual or population level of larger organisms, and the effect is not pronounced in benthic organisms, which are directly involved in nitrogen transformation. Therefore, this study used DNA metabarcoding to analyze the effect of sertraline on the microbial ecosystem and material cycles in river sediment through the lens of a microbial food web. The presence of sertraline in the river sediment enhanced the mineralization capacity of nitrogen and increased the accumulation of nitrate in the sediment. Sertraline affected the structure of the microbial food web by stimulating different successions of bacteria and eukaryotes. A structural equation model revealed that sertraline affected the microbial food web model through top-down forces (predation) by reducing the trophic transfer efficiency from metazoans to protozoans. This effect resulted in decreases in the trophic transfer efficiency from protozoans to bacteria and increases in nitrogen mineralization capacity. This was followed by a gradual increase in the nitrification reaction under the action of nitrifying bacteria, increasing the threat to the ecological health of rivers. The results show that sertraline affects the material cycle of river ecosystems and emphasizes that the assessment of the ecological risks of sertraline needs to be considered from the perspective of the material cycle of ecosystems.