猪粪溶解性有机物对紫色土中抗生素迁移的影响

以川中丘陵区广泛分布的石灰性紫色土（坡耕地与果园土）为研究对象，通过批量平衡与填装土柱实验研究了猪粪溶解性有机物（DOM）对氟苯尼考（FFC）与诺氟沙星（NOR）在土壤中吸附-解吸和淋溶特性的影响.结果表明：FFC在紫色土中吸附较弱（K_f =0.34L/kg（坡耕地）和0.85L/kg（果园土））且存在解吸负迟滞现象.当它随猪粪DOM（50~200mg C/L）同时进入土壤时，FFC在两种土壤中的吸附都显著增加（P<0.05），而猪粪DOM（200mg C/L）预先与土壤发生作用的情况对FFC的吸附促进作用则明显减弱，表明两者对土壤吸附点位存在竞争的同时，猪粪DOM主要以共吸附机制促进FFC在土壤中的吸附；NOR吸附性很强（K_f =405.4L/kg（坡耕地）和516.7L/kg（果园土）），猪粪DOM也能促进NOR在坡耕地土壤中的吸附，而对果园土壤的影响不显著.在20mm/h模拟降雨强度下获得的土柱淋溶穿透曲线表明，FFC极易迁移，在坡耕地土柱中与水流示踪剂Br^-几乎同时穿透，其淋溶总量比果园高11.03%~23.39%；NOR未发生穿透，且96.2%~98.6%残留集中分布在0~3cm表层土壤中.与批量平衡实验结果一致，猪粪DOM使FFC穿透时间延迟0.07~0.13孔隙体积，土柱中残留量增加15.21%~25.96%，而对NOR的淋溶没有影响.FTIR与三维荧光光谱分析表明，猪粪DOM主要由酪氨酸和色氨酸组成，在水相中易与FFC形成复合物.综上，对于弱疏水型抗生素，粪源DOM可通过共吸附机制增加抗生素在土壤中的持留，从而减少其淋溶迁移，而对于强吸附性疏水型抗生素则影响不显著.

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 (K_f = 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 (P<0.05), while on the contrary, when pig manure DOM (200mg C/L) was introduced to the soils prior to FFC, the adsorption of FFC decreased. Despite the existence of competition for the adsorption sites, the results suggested that pig manure DOM promoted FFC's adsorption via a co-adsorption mechanism. NOR had a strong sorption capacity (K_f = 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.