Abstract
Because of water shortages, the Xiaodian area in northern China had a long history of sewage irrigation. To study the distribution of antibiotics in the vadose zone, a sewage sample and 5 soil profiles were collected and analyzed. Macrolides and Fluoroquinolones were the main antibiotics observed in the shallow vadose zone. The contents of antibiotics in the soil profile nearby the sewage irrigation area were 2-3 times greater than in the groundwater irrigation area, indicating that sewage irrigation has had a significant impact on the contents of antibiotics in the soil. The elevation of antibiotic contents during the wet season is likely related to the fluctuating water level within the shallow vadose zone. The distribution of antibiotics is influenced by the flow direction of irrigation water. Moreover, the possibility of introducing antibiotics into the soil of the shallow vadose via the lateral recharge of sewage in the Beizhang Drainage Canal can not be excluded. Approximately 50 % of Fluoroquinolones were reduced in the upper 50 cm of the soil zone and 70 % at 80 cm depth. Tetracyclines may have experienced significant lateral migration. Macrolides and Sulfonamides (SMs) have similar soil profile distributions, with a concentration decrease down to 20 cm depth.
Highlights
Four categories of antibiotics were analyzed by liquid chromatography coupled with tandem mass spectrometry as described in previous studies [1, 2]: (i) Sulfonamides (SMs): sulfapyridine (SPD), sulfathiazole (STZ), sulfamethoxazole (SMX), sulfamerazine (SMR), sulfamethazine (SMZ), sulfamethoxypyridazine (STP), sulfameter (SFM), sulfdiazine (SDZ); (ii) Fluoroquinolones (FQs): ofloxacin (OFL), lomefloxacin (LOM), ciprofloxacin (CIP), enrofloxacin (ENR), norfloxacin (NOR), sparfoxacin (SPA), gatifloxacin (GAT), fleroxacin (FLE), enoxacin (ENO); (iii) Macrolides (MLs): roxithromycin (RTM), clarithromycin (CTM), azithromycin (AZM), erythromycin (ERY); (iv) Tetracyclines (TCs): tetracycline (TC), oxytetracycline hydrochloride (OTC), chlorotetracycline hydrochloride (CTC), doxycycline hyclate (DOC)
The contents of antibiotics in the GS-1 to GS-4 boreholes and in GS-5 are significantly higher than observed in other areas [4], and can even exceed the Maximum Contaminant Level (MCL) value of 100 ng/g [5]
The elevation of antibiotic content within the vadose zone is likely a consequence of a rise in the water table during the wet season, when water level extends into the uppermost portions of the vadose zone sampled by the transect GS-1 to GS-4
Summary
China is an agricultural country, with agricultural irrigation accounting for more than 70% of total water use. The sources of irrigation water across China is quite complex. To make up for shortage of water, untreated sewage is used for irrigation purposes in northern China. This practice has a history of more than 40 years in Taiyuan City, but there are concerns that organic pollution from sewage irrigation could pose a threat to human health and ecological safety.
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