Occurrences and regional distributions of 20 antibiotics in water bodies during groundwater recharge.

To develop a better understanding of the pollution conditions of antibiotics during the groundwater recharge process, a nation-wide survey was conducted across China for the first time. Overall, 15 recharge sites employing reclaimed water located in different humid, semi-humid and semi-arid regions were selected for analysis of the presence of the 20 most commonly used antibiotics, including tetracyclines (TCs), fluoroquinolones (FQNs), sulfonamides (SAs) and macrolides. All types of antibiotics were detected at concentrations of 212-4035 ng/L in reclaimed water and 19-1270 ng/L in groundwater. FQNs were the predominant antibiotics in reclaimed water samples (38%), followed by SAs (34%). In the SAs group, sulfamethoxazole (SMZ) and sulfamonomethoxine together with trimethoprim accounted for 78% of the total, while ofloxacin (OFL) and norfloxacin accounted for 90% of the FQNs, and doxycycline and oxytetracycline accounted for 82% of the TCs. The concentrations in groundwater were generally 1-2 orders of magnitude lower than in reclaimed water. The three most common antibiotics were OFL, erythromycin (ERY) and SMZ. Similar occurrences of different group antibiotics might be evidence of the influence of groundwater recharge by reclaimed water. FQNs were predominant in northern China, while SAs were predominant in the south. Ecotoxicological risk assessment showed that SMZ, ERY and OFL had the top three hazard quotient values, indicating they should receive preferential treatment before recharging. Overall, these results provide a theoretical basis for development of a recharge standard in China.