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

Authors: CHEN, SHUNTAO - Chinese Academy Of Sciences; Chee Sanford, Joanne; YANG, WENDY - University Of Illinois; SANFORD, ROBERT - University Of Illinois; CHEN, JIANQIU - China Pharmaceutical University; YAN, XIAOYUAN - Chinese Academy Of Sciences; SHAN, JUN - Chinese Academy Of Sciences

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2019
Publication Date: 12/10/2019
Citation: Chen, S., Chee-Sanford, J.C., Yang, W.H., Sanford, R.A., Chen, J., Yan, X., Shan, J. 2019. Effects of triclosan and triclocarban on denitrification and N2O emissions in paddy soil. Science of the Total Environment. 695:133782. https://doi.org/10.1016/j.scitotenv.2019.133782.
DOI: https://doi.org/10.1016/j.scitotenv.2019.133782

Interpretive Summary: Triclosan (TCS) and triclocarban (TCC) are two common antimicrobial compounds widely used globally in pharmaceuticals and personal care products. In agricultural systems, TCS and TCC enter soil via biosolids that are applied to crops as fertilizer. Little is known about the impact of TCS and TCC on natural soil microbial processes that are important for soil quality such as nitrogen cycling and environmental impacts such as the consequent emission of the potent greenhouse gas N2O. Here, rice paddy soil slurry experiments were used to track denitrification and N2O release rates using varying treatment levels of TCS and TCC, singly or in combination. Key microbial functional genes related to denitrification were also quantified. Our results showed that TCS and TCC exposure, either alone or jointly, significantly (p < 0.05) inhibited denitrification (7.0-36.7%) and N2O release rates (15.4-86.4%). The inhibitory effects of TCS and TCC exposure were mainly attributed to their negative net effects on bacteria and denitrification as suggested by the decrease in abundances of 16S rRNA-, narG, nirK and Clade I nosZ genes in the TCS and TCC treatments. Overall, our results indicated that the exposure of TCS and TCC in paddy soil might alter natural soil ecosystem processes by changing microbial community structure and function, but also suggests the role of bioactive compounds like antimicrobials present in agricultural soils as a factor in mitigating N2O release. The significance of this study demonstrated the effects of TCS and TCC on microbial denitrification, with farther reaching implications concerning the effect of antibiotic compound exposure on important soil microbial processes.

Technical Abstract: Triclosan (TCS) and triclocarban (TCC) are two common antimicrobial compounds that are widely used as ingredients in pharmaceuticals and personal care products. Increasingly, land application of biosolids as agricultural fertilizers result in the ubiquitous occurrence of TCS and TCC in soil. However, little is known about their effects on denitrification and the associated N2O release in rice paddy soils. Here, using a soil slurry experiment-based 15N tracer, effects of TCS and TCC exposure at various concentrations (applied alone and in combination) on denitrification and N2O release rates were investigated in a paddy soil, and functional genes related to denitrification were investigated by q-PCR to elucidate the microbial mechanisms of TCS and TCC’s effects. Our results showed that TCS and TCC exposure both singly or jointly significantly (p < 0.05) inhibited denitrification (7.0-36.7%) and N2O release rates (15.4-86.4%) except at a low concentration (0.01 mg kg-1) TCC treatment in which the denitrification rate 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 bacteria and denitrification as suggested by the decrease in abundances of 16S rRNA, narG, nirK and Clade I nosZ genes in the TCS and TCC treatments. Overall, our results indicated that the exposure of TCS and TCC in paddy soil might pose significant risks on the rice paddy ecosystem by altering denitrification and N2O release rates. The effects of TCS and TCC on the denitrification process should be taken into consideration when evaluating the environmental risk of TCS and TCC in the rice paddy field.