Effects of pig manure-derived dissolved organic matter on the transport of antibiotics in purple soils

The effects of pig manure-derived dissolved organic matter (DOM) on the sorption-desorption and leaching characteristics of florfenicol (FFC) and norfloxacin (NOR) in typical calcareous purple soils (sloping cropland and orchard) in the hilly areas of central Sichuan were studied, using batch equilibrium and packed soil column experiments. The results indicated that, FFC had weak adsorption capacity in purple soils (Kf = 0.34 and 0.85L/kg for the sloping cropland and the orchard soil, respectively), and negative desorption hysteresis was observed. When spiked simultaneously with pig manure DOM (50~200mg C/L), the adsorption of FFC increased significantly in both soils (Pf = 405.4 and 516.7L/kg for the sloping cropland soil and the orchard soil, respectively). In the presence of pig manure DOM, its adsorption increased a little in the cropland soil, while did not change in the orchard soil. According to the soil column breakthrough curves obtained under a simulated rainfall intensity of 20mm/h, FFC was highly mobile, and it leached out almost simultaneously with the water flow tracer Br- from the column of the cropland soil, which had an 11.03%~23.39% higher leaching capacity than that of the orchard soil. On the other hand, NOR did not penetrate, and 96.2%~98.6% of its residues were retained in 0~3cm topsoil. Being consistent with the results from the batch experiment, pig manure DOM delayed the breakthrough of FFC by 0.07~0.13 PV and increased its residues by 15.21%~25.96%, while such effect was not obvious for NOR. Based on FTIR and EEM fluorescence analysis, pig manure DOM was mainly composed of tyrosine and tryptophan, which were easy to form complex with FFC in the aqueous phase. Therefore, for the highly mobile antibiotics, manure-derived DOM may increase the retention of antibiotics in the soil through a co-adsorption mechanism; as for the hydrophobic antibiotics with strong adsorption, the effect is not significant. © 2020, Editorial Board of China Environmental Science. All right reserved.