Occurrence And Environmental Fate Of Selected Antibiotics In The Aquatic Environment Of The Pearl River Delta

Antibiotics are widely used for the treatment of bacterial diseases in humans, and some are applied to livestock and fish for disease prophylaxis and treatment or for growth promotion. But all kinds of drugs were misused seriously for lack of scientific direction, and as result, the residues of drugs can bring negative impact on human health and wildlife. There has been an increasing interest in the study of occurrence, fate and potential adverse effects of pharmaceuticals in the aquatic environment in recent years. However, there are few data in China, despite the large population, serious antibiotics misuse, and the still-low wastewater treatment rates in cities. The Pearl River Delta (PRD) locates in the subtropical region with distinct climate pattern and eco-system, different from temperate regions where most of previous studies took place. Therefore, it is of need to study the occurrence and environmental fate of antibiotics in the aquatic environment of this region.The results would show the source and environmental fate of antibiotics in the aquatic environment in the PRD. The data obtained in the present study may be useful in the evaluation of environmental risks of antibiotic residues in the aquatic environment of a subtropical region. On the whole, in this study we focused on:1. The methods for determination of selected antibiotics in the environment. A sensitive analytical method was developed for determining selected antibiotics (nine compounds including chloramphenicol, fluoroquinolone, sulfonamide, and macrolide groups) in water and sediment. Compounds in the water were enriched through solid phase extraction (SPE) with an Oasis HLB cartridge, for sediment samples, compounds were extracted using ultrasonic bath and clean up by SPE. The extracted antibiotics were analyzed using high-performance liquid chromatography-electrospray ionization tandem mass spectrometry with multiple reactions monitoring (MRM). Good recoveries rates and limits of quantification (LOQ) of target antibiotics in water and sediment were obtained.2. The occurrence and distribution of antibiotics in the aquatic environment in the PRD. The results showed that the concentrations of antibiotics were mainly below the limit of quantification (LOQ) in the marine water of Victoria Harbour. However, except for amoxicillin, all the target antibiotics were detected in the Pearl River during high (summer) and low (early spring) water seasons. The concentrations in early spring were about 2-15 times higher than that in summer with clearer diurnal variations. It was suggested that the antibiotics concentrations in the high water season was more affected by wastewater production cycles due to quick refreshing rate, while those in the low water season may be more sensitive to the water column dynamics controlled by tidal processes. Some of antibiotic concentrations in the Shenzhen River, especially the macrolides (range from 184 to 1343 ng/L) were much higher than other rivers, and even higher than the sewage treatment plant (STPs) in the developed countries. As the results, it has introduced the antibiotics contamination to the Shenzhen gulf with antibiotic concentrations from 10s to 100s ng/L levels were found.3. The occurrence and fate of antibiotics in STPs in the PRD. A total of five antibiotics, including two fluoroquinolones, two macrolides and one sulfonamide, were detected in the raw influents and effluents at the four selected STPs of the Pearl River Delta region, with concentrations ranged from 9 to 2050 ng/L. The removal of antibiotics in the four STPs was general incomplete. Fluoroquinolones were easily adsorbed to sludge during the treatment process with higher removal efficiency for effluents. The STPs with secondary or chemical enhanced treatment had higher removal rates for antibiotics in water. The daily consumption per person of the most frequently detected antibiotics in Guangzhou was higher than in Hong Kong.4. The sorption and environmental fate of four selected antibiotics were investigated in a FLUME system which was designed to model the subtropical riverine environment. Also a stand-still water/sediment environment was performed to compare with the FLUME environment. It suggested that the water velocity of 20 cm/s can disturb the sediment easily so that the main drugs sorbed onto the sediment. The results of vertical concentration profiles in the sediment at the end of the experiment showed that the main drugs were accumulated in the top layer (0-5 mm) and decreased with depth. However, certain concentrations were found under the top (5-10 mm) or even deeper (>10 mm). OFL showed a high tendency to adsorb onto sediment or solid particles. While the low Kd values of SMZ indicated that it was easily released from the sediment. According to Hollis' classification, OFL displayed a moderate persistence with DT₅₀ values in the sediment >22 d in the FLUME system while other three displayed impersistence.