[Effect of Manure Application on the Adsorption of Antibiotics to Soil].

Sulfonamide antibiotics and florfenicol(FFC) are commonly used antibiotics in Zhejiang Province. They have weak adsorption on soil and are easy to migrate, with high environmental risks. In recent years, most of the studies on the potential risk of fecal-derived antibiotics to farmland soil were conducted by adding manure under laboratory conditions; therefore, it is impossible to assess the risk of antibiotic pollution under natural fertilization. Therefore, batch balance experiments were conducted to explore the effects of different soil types and manure types on the adsorption of antibiotics in the soil, in which five types of dryland farmland soils[Lin'an(LA), Jiashan(JS), Longyou(LY), Kaihua(KH), and Jinhua(JH)]in Zhejiang Province that have been used with different fertilizers(chicken manure, pig manure, and chemical fertilizer) for a long time were chosen, and four types of commonly used antibiotics[sulfadiazine(SD), sulfamethazine(SMT), sulfamethoxazole(SMZ), and FFC]were selected. The results showed that the adsorption of the four antibiotics in the experimental soil was weak, and the adsorption capacity decreased in the order of:SMT(1.44-13.23 mg1-(1/n)·L1/n·kg-1)>SMZ(0.73-6.05 mg1-(1/n)·L1/n·kg-1)>SD(0.16-5.57 mg1-(1/n)·L1/n·kg-1)>FFC(0.27-3.81 mg1-(1/n)·L1/n·kg-1). The Freundlich model was superior to the linear model in fitting the isotherm adsorption of SD, SMT, and FFC, in which SD and FFC belonged to "S" type adsorption, and SMT belonged to "L" type adsorption. For SMZ, the fitting effect of the linear model was better than that of the Freundlich model. The contents of total organic carbon(TOC) and dissolved organic carbon(DOC) could better predict the adsorption capacity of the four antibiotics(r=0.548-0.808), and the values of cation exchange capacity(CEC) and electrical conductivity(EC) could better predict the adsorption capacity of SMT and FFC(r=0.758-0.841). Compared with the application of chemical fertilizer, manure application increased the values of TOC, DOC, CEC, and EC in acidic and neutral soils, which was conducive to the adsorption of antibiotics on the soil. Meanwhile, manure application also increased pH in acidic and neutral soils, which was not conducive to the adsorption of antibiotics on the soil. In addition, manure application reduced the values of TOC, DOC, CEC, EC, and pH in alkaline soils. The lower pH was conducive to antibiotic adsorption on the soil, whereas the lower content of the other four was not conducive to antibiotic adsorption on the soil. For the acidic soil with low fertility, the application of manure increased soil fertility and thus increased the adsorption of antibiotics on the soil, such as the LA soil with chicken manure, the LY(1) soil with pig manure, and the JH soil with chicken manure and pig manure. However, for the acidic and neutral soils with high fertility, the application of manure had significantly increased soil pH and thus reduced the adsorption of antibiotics on the soil, such as the JS soil with chicken manure and pig manure and the LY(2) soil with chicken manure. For calcareous soil with high fertility and pH(such as KH soil), the adsorption profiles of the four types of antibiotics on the soil showed diversity after the application of manure:the adsorption capacity of SD increased significantly after the application of chicken manure and pig manure, whereas the adsorption capacity of SMT and SMZ decreased significantly, and the adsorption capacity of FFC declined significantly after the application of chicken manure. Therefore, manure application according to soil fertility could effectively control the environmental risk of fecal antibiotics.