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.
Highlights
In recent years, antibiotics have been extensively used as livestock food additives and to fight infections in animal husbandry [1,2]
antibiotic resistance genes (ARGs) could be spread through horizontal gene transfer (HGT) and vertical gene transfer (VGT), and in many cases, could be maintained in microbial populations, even without selection pressure from antibiotics [9,10,11]
The relative abundance of sul genes exhibited an increase, which tended to be stable among the treatment duration
Summary
Antibiotics have been extensively used as livestock food additives and to fight infections in animal husbandry [1,2]. The overuse of antibiotics results in their continuous release into the environment in China. ARGs have often been detected as part of antibiotic resistance super integrons. Even if antibiotic-resistant bacteria were damaged or killed, ARGs could still be released to the environment and transformed into other bacteria [14,15]. ARGs were regarded as fast-growing potential pollution because of the extensive application of antibiotics in the livestock industry [19,20,21]. Effective treatment processes for antibiotic removal could prevent the spread of ARGs
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