ABSTRACT
Karst aquifers are highly susceptible to contamination because compounds in water from the land surface are able to enter aquifers directly through sinkholes and travel rapidly through conduits. To investigate the occurrence and profiles of antibiotics in the typical karst river system in Kaiyang, southwest China, 34 aqueous samples were collected periodically to delineate seasonal trends in antibiotic levels. Thirty-five antibiotics, including nine sulfonamides, four tetracyclines, five macrolides, 16 quinolones and chloramphenicol, were analysed via solid phase extraction combined with ultra-performance liquid chromatography-tandem mass spectrometry. A total of 25 antibiotics were detected with the highest detection frequency reaching 94.1%, indicating the ubiquity of antibiotics in the study area. The total concentration of antibiotics ranged from 0.37 to 508.6â¯ng/L, with the dominating proportion including macrolides and quinolones based on the distribution profiles and seasonal variation. Due to the natural attenuation, the total concentration of antibiotics gradually decreased with the flow direction in the southern part of the river. The total concentrations of antibiotics in the mainstream were significantly higher in the dry season than in the rainy seasons. However, the distribution profiles were susceptible to anthropogenic activities, such as the leakage of septic tank wastewater. The dendrogram and heatmap revealed that three clusters of sample sites represented tributaries and the upstream areas, the downstream areas, and the potential pollutant source, and three clusters of antibiotics represented different concentration patterns. The high ecological risks of tetracycline, erythromycin and ciprofloxacin for algae and ofloxacin for plants were determined. These findings contributed to the establishment of a database for future monitoring and control of antibiotics in karst areas.
ABSTRACT
Antibiotics are widely used, and there is a serious concern about its adverse impacts on the environment and human health. To our knowledge, prior to this work, there was no evidence of the potential presence of antibiotics in groundwater in China, despite populous speculations. This study reported the detection of 35 target antibiotics of 6 groups (chloramphenicois, lincosamides, marcrolides, quinolones, sulfonamides, and tetracyclines), in shallow groundwater samples collected in northern and southwestern China. Thirty-four of thirty-five target antibiotics were detected in the groundwater samples; 73 of 74 monitoring wells contained at least one antibiotic; and at least two antibiotics were detected in 72 of the 74 wells. Ofloxacin (1199.7 ng/L), lincomycin (860.7 ng/L), and norfloxacin (441.9 ng/L) as well as antibiotics with the highest detection frequency such as sulfapyridine (70%), norfloxacin (69%), and lincomycin (64%) were detected at elevated concentrations. The highest detection frequency and concentration of lincosamides were observed in those groundwater samples, but no clear distribution patterns were observed for the six antibiotic groups. Moreover, shallow groundwater in southwestern China seemed to contain most antibiotics, likely due to the high antibiotics discharge and frequent exchange of groundwater with surface matrices. The findings from this work suggest that groundwater in China has been widely contaminated by antibiotics, and presumably other pharmaceutical compounds that have not been investigated to date.
