Dynamics of chloroacetanilide herbicides in various types of mesocosm wetlands

Constructed wetlands (CWs) for pesticide mitigation from agricultural runoff became widespread in the last decade. However, comparison of different types of CWs at one location is missing. Therefore, site by site comparison of three different types (subsurface flow, surface flow and floating hydroponic root mat) of CWs treating four chloroacetanilide herbicides (acetochlor, s-metolachlor, metazachlor, dimethachlor) were carried out. All three planted systems are effective in removing the four herbicides with removal efficiency >92% after 9days. The metabolites ethane sulfonic acids (ESA) and oxanilic acids (OA) of the four herbicides peaked at 9days in the surface flow CWs with soil, but all the metabolites didn't peaked in the subsurface flow with gravel systems and the floating hydroponic root mat system after 21days. All the detected metabolites account about 20% of the mother compounds. There is no noticeable metabolites accumulation in the control system (no plants and no substrate), which indicate no microbial degradation taken place. Plant accumulation and soil adsorption are negligible for the removal of the four herbicides, which are <0.6%. In conclude, plants can enhance the removal of chloroacetanilide herbicides in all the CWs, and the floating hydroponic root mat is the most cost-efficient alternatives for chloroacetanilide herbicides removal due to the absence of substrate.