*Article* **Constructed Wetland Revealed E**ffi**cient Sulfamethoxazole Removal but Enhanced the Spread of Antibiotic Resistance Genes**

#### **Shuai Zhang 1, Yu-Xiang Lu 2, Jia-Jie Zhang 3, Shuai Liu 4, Hai-Liang Song 2,\* and Xiao-Li Yang 5,\***


Academic Editor: Derek J. McPhee

Received: 6 January 2020; Accepted: 11 February 2020; Published: 14 February 2020

**Abstract:** Constructed wetlands (CWs) could achieve high removal efficiency of antibiotics, but probably stimulate the spread of antibiotic resistance genes (ARGs). In this study, four CWs were established to treat synthetic wastewater containing sulfamethoxazole (SMX). SMX elimination efficiencies, SMX degradation mechanisms, dynamic fates of ARGs, and bacterial communities were evaluated during the treatment period (360 day). Throughout the whole study, the concentration of SMX in the effluent gradually increased (*p* < 0.05), but in general, the removal efficiency of SMX remained at a very high level (>98%). In addition, the concentration of SMX in the bottom layer was higher compared with that in the surface layer. The main byproducts of SMX degradation were found to be 4-amino benzene sulfinic acid, 3-amino-5-methylisoxazole, benzenethiol, and 3-hydroxybutan-1-aminium. Temporally speaking, an obvious increase of *sul* genes was observed, along with the increase of SMX concentration in the bottom and middle layers of CWs. Spatially speaking, the concentration of *sul* genes increased from the surface layer to the bottom layer.

**Keywords:** sulfamethoxazole; antibiotic resistance genes; *sul* genes; bacterial community; constructed wetlands
