| Antibiotics are widely used for prventing diseases including human diseases and animal diseases. Recently, antibiotics were overused seriously in China, and the society begins to concern about the contamination of antibiotics in the environment. The occurrence and fate of antibiotics residue in the environment are focused by scientists worldwide.In the recent decade, under the support of Chinese government, Nanning City is experiencing a rapid development and urbanization. Following the growth in population, large quantities of domestic wastewater were discharged into the Yongjiang River which is the sole receiving water body for treated and untreated wastewater in Nanning City. Therefore, antibiotics pollution in the Yongjiang River could be potentially widespread. The Yongjiang River is not only the "mother river" for Nanning City, but also the most important drinking water source of the city. However, to date, there has been no report on the occurrence of antibiotics in the Yongjiang River. This study investigated3groups of antibiotics including4macrolides,5sulfanilamides and trimethoprim in the water of the Yongjiang River, focusing on the contamination levels, distribution and ecological risks. This study will provide useful data for environmental protection, and it is meaningful to understand the ecological risks in the study area.The study area was divided into tributaries and a mainstream which includes3sections:upstream, midstream and downstream. The10selected antibiotics were detected in the mainstream and tributaries in different levels. The total concentration of10selected antibiotics in the mainstream and tributaries were in the range of10.2-120ng L-1and51.7-1834ng L-1, respectively. Generally, the residual concentrations in the tributaries were higher than those in the mainstream. The average antibiotic concentrations from different sections of the mainstream decreased in the following order:midstream (73.9ng L-1)>downstream (48.5ng L-1)> upstream (15.4ng L"1). Furthermore concentrations of most of the antibiotics were elevated along the section of the river in the urban area, highlighting the significant impact of high population density and human activities on the presence of antibiotics in the environment. A mass balance showed that tributaries discharge is one of the most important sources of antibiotics contamination in the mainstream.Sulfamethoxazole showed the highest concentration and detection rate. The concentration of Sulfamethoxazole in the mainstream and tributary was19.6ng L-1and190.5ng L-1, respectively, and the detection rate was up to100%, followed by Erythromycin and Sulfadiazine. These three antibiotics (Sulfamethoxazole, Erythromycin and Sulfadiazine) contributed to88%of the antibiotic contamination. The levels found in this study are lower than those reported in developed areas.The potential ecological risks of the detected antibiotics were assessed via using the risk quotients (RQs) approach. The results showed that Sulfamethoxazole and Erythromycin pose at least medium risk (RQ>0.1) to the relevant sensitive species (S. leopoliensis and P. subcapitata, respectively) in the mainstream. Sulfamethoxazole and Erythromycin posed high ecological risks in the midstream of the main river. On the contrary, the ecological risks posed by Sulfadiazine, Sulfamethazine, Trimethoprim and Azithromycin are not significant. Generally, antibiotics posed higher ecological risks in the tributaries than those in the mainstream. The RQ of Sulfamethoxazole in the Xinxu River (a tributary) was even up to49.5. Further, the ecological risks in the sediment (pore water) are much higher than those in both of the mainstream and the tributaries with the highest RQ value up to96. As a result, the ecological risks caused by antibiotics residue in the Yongjiang River can not be ignored. |
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