Effects of triclosan and triclocarban on denitrification and N2O emissions in paddy soil

Triclosan (TCS) and triclocarban (TCC) are two common antimicrobial compounds, which are widely used as ingredients in pharmaceuticals and personal care products. They occur ubiquitously in soil due to biosolid application as agricultural fertilizers, but their influence on microbially mediated soil biogeochemical processes is poorly understood. We tested the effects of varying concentrations of TCS and TCC applied both individually and together on denitrification and N2O emissions in paddy soil. We also quantified denitrification functional gene abundances by q-PCR to elucidate the microbial mechanisms of TCS and TCC's effects. Our results showed that TCS and TCC exposure both individually and together significantly (p < 0.05) inhibited denitrification (7.0-36.7%) and N2O emissions (15.4-86.4%) except for the 0.01 mg kg(-1) TCC treatment in which denitrification was slightly but significantly (p < 0.05) stimulated. The inhibitory effects of TCS and TCC exposure were mainly attributed to their negative net effects on denitrifying bacteria as suggested by the decrease in abundances of 16S rRNA, narG, nirK and clade I nosZ genes in the TCS and TCC treatments. Overall, we found that TCS and TCC exposure in paddy soil could substantially alter nitrogen cycling in rice paddy ecosystems by inhibiting denitrification and N2O emissions. These effects should be taken into consideration when evaluating the environmental impacts of TCS and TCC. (c) 2019 Elsevier B.V. All rights reserved.