Influence of livestock activities on residue antibiotic levels of rivers in Hong Kong.

Occurrence of 10 antibiotics in the Yuen Long (YLR), Kam Tin (KTR), and Shing Mun (SMR) rivers of Hong Kong and possible influence of livestock activities on the concentrations of antibiotics were investigated. Tetracycline (30-497 ng/L), sulfadiazine (2-80 ng/L), sulfamethoxazole (2-152 ng/L), ofloxacin (5-227 ng/L), and erythromycin (1-315 ng/L) were detected in all the three rivers; chlortetracycline (23-227 ng/L), oxytetracycline (7-104 ng/L), ciprofloxacin (12-68 ng/L), and roxithromycin (1-105 ng/L) were detected in YLR and KTR, whereas norfloxacin (3-34 ng/L) was detected in KTR only. Significant correlation between livestock population and antibiotic contamination was observed in YLR only, indicating the influences of other sources in KTR and SMR. Among the antibiotics, significant correlation was observed between tetracyclines and sulfonamides indicating the major influence of livestock farms, whereas tetracyclines/sulfonamides were negatively correlated with fluoroquinolones/macrolides implying the differential origin of the latter class of antibiotics. Water quality of KTR and YLR were highly influenced by the non-point source pollutions, while of SMR was relatively good. Particularly, Escherichia coli populations of the YLR and KTR were 3-4 logs higher than those of the SMR indicating the involvement of livestock farms and sewerages. Good correlation between tetracyclines (TCs)/sulfonamides (SAs) and number of livestock farms and a negative correlation between TCs/SAs and fluoroquinolones (FQs)/macrolides (MLs) could be used as an indicator to trace the possible source of pollution.