[Seasonal variation of distribution and removal of high-risk tetracycline resistance genes in constructed wetland.]

Livestock wastewater is an important reservoir of antibiotic resistance genes (ARGs), with high environmental risks. We investigated the seasonal variations of distribution and removal of swine wastewater originated high-risk tetracycline resistance genes (TRGs) in horizontal subsurface flow constructed wetlands. The effects of exogenous addition of tetracycline (TC) and copper ion (Cu2+) on the abundance of TRGs in effluent with single and combined pollution of antibiotic and heavy metal were studied. The results showed that all the three high-risk TRGs (tetM, tetO and tetW) were detected in swine wastewater. Wetlands could effectively reduce the ARGs, with the absolute abundance of TRGs in effluent being decreased by 1.1-2.4 and 1.7-2.9 orders of magnitude in summer and winter compared with the influent, respectively. The abundance of TRGs in wetland soils showed the characte-ristics that the outflow side was lower than the inflow side, the non-rhizosphere area was lower than the rhizosphere area, and lower in winter than in summer. In summer and winter, single and combined pollution of TC and Cu2+ in swine wastewater would increase the abundance of TRGs in effluent compared with that in the control. The constructed wetland is suitable for controlling the environmental diffusion of ARGs in livestock wastewater.