Occurrence of antibiotics in the aquatic environment of Jianghan Plain, central China.

The occurrence of 19 antibiotics (sulfonamide, fluoroquinolone, tetracycline and macrolide) was studied in surface water and groundwater samples collected from Shahu County of Jianghan Plain, central China, in autumn (dry season) and spring (wet season). In autumn, chlorotetracycline, doxycycline and enrofloxacin were the three antibiotics with the highest concentrations and high relevance ratios in all of the water samples. The concentration of chlorotetracycline was greatest in surface water at 122.3 n gL(-1) and was as high as 86.6 ng L(-1) in groundwater, which are among the highest values reported worldwide. In spring, tetracycline was found to be more than 100 ng L(-1) in groundwater and surface water, which also contained high concentrations of ofloxacin (135.1 ng L(-1)), norfloxacin (134.2 ng L(-1)) and erythromycin dehydrate (381.5 ng L(-1)). Most of the SMs were observed at higher detection frequencies in spring than in autumn, which can be ascribed to surface runoff by rain water during the wet season (spring). The average concentrations of compounds in the fluoroquinolone and tetracycline categories were far higher than those in the sulfonamide and macrolide categories, which had concentrations of less than 16 ng L(-1) in groundwater (except erythromycin dehydrate), while macrolides were found in all samples, except erythromycin dehydrate. The main antibiotics present in groundwater were also the dominant compounds found in surface water, with correlation coefficients of 0.93 and 0.97 in autumn and spring, respectively, indicating the potential contamination of groundwater by the infiltration of contaminated surface water.