Antibiotic distribution, risk assessment, and microbial diversity in river water and sediment in Hong Kong

For the past fewer years, environment antibiotic residues have got more and more attention. The occurrence and distribution of eight common antibiotics, belonging to five classes, were determined in both water and sediment of eleven rivers of Hong Kong. The target antibiotics were found to be widely distributed. Sulfamethoxazole (n.d.-79.9 ng/L), sulfadimidine (n.d.-29.9 ng/L), and ofloxacin (n.d.-75.5 ng/L) were the dominant antibiotics in river water, with detection rates of 84.6, 76.9, and 69.2%, respectively. Tetracycline (n.d.-9.8 ng/g) was the dominant antibiotic in sediment, with a detection rate of 60%. The concentrations of all antibiotics in river water of Hong Kongwere lower than which in various rivers of Europe, North America and Australia, as well as the Pearl River Basin of China. All sediment sites exhibited significant bacterial diversity. Gammaproteobacteria (0.08-12.7%) and Flavobacteria (0.14-14.1%) were the dominant bacterial classes in all sediments. The bacterial compositions varied between sites; areas polluted with high levels of antibiotics had rich and highly diverse bacterial communities. The environmental risk assessment determined that the antibiotics in 73.1% of the samples posed ecological risks to algae, and two samples posed low risks to invertebrates. Ofloxacin was the main contributor of risk to aquatic organisms, while the antibiotics in 11.5% of the samples posed resistance selection risks.