Effects of biochar on adsorption-desorption of fluoroquinolones in purple soil

Effects of biochar application (at rates of 1 wt.% and 5 wt.%) and alternative dry-wet process of ageing (from May to November in field) on the sorption-desorption of three fluoroquinolones (ciprofloxacin, ofloxacin and enrofloxacin) were studied using a sloping cropland calcareous purple soil. The soil is abundantly distributed in the upper reaches of the Yangtze River. The absorption-desorption isotherms were fitted well by Freudlich equation, with all of the relevant coefficients being highly significant. The freshly-applied biochar decreased the adsorption of ciprofloxacin and ofloxacin to the soil, but enhanced that of enrofloxacin and such effect was positively correlated with the biochar application rate. Obvious increase in the content of dissolved organic matter in soil solutions was observed after addition of fresh biochar, which may play an important role in decreasing the adsorption of the antibiotics, but such increase was weakened after ageing. After ageing process, increased absorption of three antibiotics was observed in the soil amended with 1 wt.%biochar (P>0.05), while no difference was observed between the 5 wt.% biochar treatment and the control. Biochar addition also enhancedthe extent of desorption of ciprofloxacin and ofloxacin, but the aged biochar decreased the desorption of enrofloxacin. No apparent adsorption-desorption hysteresis was observed for all tested soils with different biochar treatments. © 2017, Editorial Board of China Environmental Science. All right reserved.