Effects of antibiotic norfloxacin on the degradation and enantioselectivity of the herbicides in aquatic environment.

Antibiotics are currently extensively used in human medicine, animal farming, agriculture and aquaculture, and their residue has become a global environmental problem. However, the effects of antibiotic on other pollutants in aquatic environment are still poorly understood. In this study, the influences of norfloxacin on the residue, degradation and distribution of the herbicides (simazine, atrazine, terbuthylazine, acetochlor and metolachlor) and the enantioselectivity of acetochlor in sediment and water-sediment microcosm system were investigated. Sediment was spiked with norfloxacin and water was contaminated by herbicides to simulate environmental pollution. The amounts of herbicides in water and sediment samples were analyzed within 30 days of cultivation. The results showed that norfloxacin could significantly inhibit the dissipation, lengthen the half-lives and enhance the residues of herbicides in sediment. Take simazine as an example, its half-life significantly increased from 16.1 days to 19.3 days and its residual percentage grew from 24.2% to 30.4% when sediment was contaminated with 5 mg·kg-1 norfloxacin. However, only acetochlor degradation was significantly inhibited by norfloxacin in water-sediment microcosm and the distribution of the herbicides were not affected. Enantioselective degradation of acetochlor was observed both in control and norfloxacin-treated water-sediment system, with R-acetochlor preferential elimination, suggesting the co-existence of norfloxacin had very limited influence on the enantioselectivity. The findings indicated that co-contamination with norfloxacin could increase the persistence of herbicides in aquatic environment, thus increasing the environmental risks to aquatic organisms.