Behaviors Of Norfloxacin In Soil And Its Ecotoxicity

Pharmaceutical antibiotics are widely used in human and veterinary medicine to treat and prevent infectious bacterial diseases. The pharmaceutical antibiotics are excreted in urine or faeces from the treated body, either unaltered or as metabolites, some of which are still bioactive. Entering into the environment, antibiotics are distributed in various environments through a number of physical and chemical processes, and then influenced the environmental progress. The effects of drugs on environment depend on the dose and form of antibiotics, which were decided by their behavior in environment. The behaviors of antibiotics are related to various environmental properties and pharmaceutical properties in environment. Copper, an industrial product and food additive, has been widely found in manure and sludge, and might finally enter into the agricultural environment. It can bond to some antibiotic molecules through some functional groups. Therefore, norfloxacin (Nor), a fluoroquinolone and most commonly used in animal industries worldwide, was selected in the present study to investigate the sorption and degradation behavior of norfloxacin in various soils, the effect of norfloxacin on soil enzymes, soil microbial community and wheat seedlings using HPLC, BIOLOG and PCR-DGGE. At the same time, the effect of copper on the behavior and ecotoxicity of norfloxacin were studied in the present study. The main results were presented as follows:Sorption experiments were studied by the batch equibibrium method and sorption of norfloxacin was different in different soils. With increasing of norfloxacin concentrations, sorption amount of norfloxacin increased in both the bulk soils and their SOM-removed soils, but the sorption capacity in SOM-removed soils was higher than that of their corresponding bulk soils, indicating that the process of norfloxacin sorption in soil was influenced by the soil properties including SOM. The sorption data in bulk soils and SOM-removed soils were fitted to Freundlich and Langmuir models. The correlation coefficients suggested that the experimental data fitted better to Freundlich equation than to Langmuir equation. Furthermore, the data from soil F and SOM-removed F could not be described by Langmuir equation. The norfloxacin sorption amount decreased in soil B and soil F, whereas it increased in soil R as solution pH increased. The maximum KD and KOC were achieved in soil R when the equilibrium solution pH was6. And the Nor sorption was also influenced by the exogenous Cu2+ions, which depended on the soil types and Cu2+concentrations. With increasing of Cu2+concentrations in solution, generally, sorption amount, KD and Koc for norfloxacin in soils increased and were up to a peak at100mg·L-1Cu2+, and then the sorption amount decreased regardless of norfloxacin levels.Results from the experiments with the degradation of norfloxacin suggested that with increasing of incubation time, the residue norfloxacin concentrations were decreased in all samples, while differences were found among soil types. The norfloxacin degradation data were fitted to the first dynamic equation, showing that the norfloxacin degradation was in the order of soil F> soil R> soil B.No significant differences in hydrogen peroxidase activity were found among soil samples treated with pollutants, however the activities of urease, phosphatase and sucrase were significantly influenced compared with the control. The effects of pollutants on activities of soil enzymes depended on the concentration of pollutant and exposure time, which also based on the soil types. The activities of soil enzymes were inhibited by adding copper, especially in the later incubation time. In Norl treatments, activities of soil phosphatase increased in every treatment in both soils except of the treatment exposure28-day in fluvo-aquic soil compared with respective control. After treating28-day, the activity of soil phosphatase was inhibited in fluvo-aquic soil, while it increased47%in black soil. The effects of cocontamination of norfloxacin and copper on soil enzymes were similar to the effect of norfloxacin alone, but the effect of cocontamination on soil enzymes was stronger and time-dependent.Biolog was employed to assess the effect of norfloxacin alone and cocotamination with copper on soil microbial functional community. With increasing of exposure time, the differences in average well colour development (AWCD) values were enlarged among treatments, and the AWCD value in28-day Nor10+Cu100treatment was significantly lower than that in any other treatment. Comparing diversity variation of soil microbial communities under different treatments revealed that the richness and evenness of microbial communities in norfloxacin alone treatments were different from that in co-contamination treatments. Higher percent of polymers was utilized by soil microbe in the whole incubation period compared with other substrates, and more amino acids, carbohydrates and carboxylic substrates were utilized in the soil treated with pollutant after14and28days.Cluster analyses also indicated that samples from different treatments could be distinguished from each other, and that exposure3-day treatments sorted into the same cluster, while28-day treatments distributed in different cluster.The polymerase chain reaction (PCR) based on16S rDNA, followed by denaturing gradient gel electrophoresis (DGGE), was used to describe the effect of norfloxacin alone and cocotamination with copper on soil microbial community. Microbial diversity in soil treated with pollutants changed with time. At28day, no significant changes were found in the number of bands in soil samples treated with norfloxacin alone. Diversity of microorganisms in soil obviously decreased under the stress of norfloxacin and copper compared to control, but the Nor10+Cu100were sorted into the same clusters. At56day, the number of bands increased in norfloxacin alone treatments and Nor10+Cu50compared to control.The number of bands in Nor10+Cu100was lower than that in control, while it was higher than that in the samples treated with Nor10+Cu100for28day. Comparison of the bacterial DGGE profiles among treatments revealed that the similarity of bacterial communities in the56-day treatments was significantly higher than that in the28-day treatments. The changes in microbial community function and composition in response to the pollutants could be attributed to increased tolerance of soil microbe to pollutants (norfloxacin, norfloxacin+copper) in soil system.The wheat seedlings growth and chlorophyll content were promoted by the treatment with norfloxacin at the rate of1.0mg·L-1, while they were significantly reduced at the rate of10mg·L-1compared with the control. The content of MDA was enhanced under norfloxacin stress and, was significantly higher in roots than in shoots. The activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD) and ascorbate peroxidase (APX) in wheat seedlings were changed by the treatment with norfloxacin. In shoots, compared with the control treatment, the activities of SOD and POD significantly increased, but the activities of CAT and APX significantly increased only at some norfloxacin concentration in shoots. In roots, the activities of SOD and POD obviously decreased, while the activity of APX remarkably increased by adding norfloxacin.