有机肥源抗生素在紫色土农田和果园中的迁移规律研究

Purple soil is the major land resource in the upper reaches of the Yangtze river, while the soil has a thin layer with low organic matter and poor aggregate structure but are rich in macropore preferential flow. The application of organic manure containing antibiotics to the farmland soil poses a potential threat to the ecological environment. However, the mechanisms and major influential factors of transport and fate of antibiotics in the purple soil are still unclear. In this study, three typical antibiotics (oxytetracycline, sulfamethazine and florfenicol) that have been frequently detected in manure-applied soils were selected as the target contaminants. Using soils of three different land-use types (dry land, vegetable land and orchard with chicken raising, respectively) for comparison, laboratory batch and column experiments and in-situ trials on field plots (equipped with self-made lysimeter system) will be conducted to examine the transport behavior of antibiotics in the soil. The effects of manure application on soil physicochemical and hydraulic properties, adsorption-desorption coefficients and degradation rate of antibiotics will be examined. Also, interactions between antibiotics and major factors of soil minerals, soil organic matter, dissolved organic matter and etc. that produce a significant influence on the transport of antibiotics will be studied. Finally, the path and dynamics of antibiotics of varying speciation (water soluble, colloidal and particulate bound) through surface runoff and leaching from field plots under natural rainfalls will be tested. This study will potentially provide an important scientific basis for the risk assessment of contamination caused by manure-induced antibiotics in the area of purple soil.

紫色土在长江上游低山丘陵区广泛分布，但土层浅薄、有机质含量低、团聚结构差、大孔隙优先流发育，因此，在土壤中施用含有抗生素的有机肥对生态环境构成潜在风险。目前，不同种类抗生素在紫色土中的迁移机制、环境归趋及主要影响因素尚不明确。本研究以检出频率较高的典型抗生素（土霉素、磺胺二甲基嘧啶和氟苯尼考）为对象，对比三种土地利用类型（旱地、菜地及林下养鸡模式下的果园）土壤，开展室内批量平衡与土柱实验、野外小区原位观测试验（结合自制的渗漏计监测采样系统）与模型模拟研究，查明有机肥施用对土壤孔隙结构与水力学参数、抗生素吸附-解吸特征常数和自然降解率的影响，阐明土壤矿物质、有机质组分、溶解性有机物等与抗生素的相互作用机理，揭示自然降雨条件下抗生素在紫色土中迁移的水文路径、形态（水溶态和颗粒结合态）、通量及其动态规律，并刻画其土壤结合残留特征，为该区域有机肥施用的抗生素污染风险评估提供重要科学依据。

畜禽粪便施肥是农田土壤中抗生素污染的主要来源。粪源基质中的胶体物质可与抗生素发生交互作用从而影响抗生素的淋溶迁移。然而目前，粪源基质和土壤水分运动影响下的抗生素迁移规律尚不明确，通过实验室内研究获取的机理也十分缺乏田间观测和验证。本研究以川中丘陵区典型石灰性紫色土为对象，探究不同种类粪源抗生素在土壤中的吸附-解吸、淋溶特性，以及在连续自然降雨事件下随土壤水文过程的迁移浓度、通量及其对降雨的动态响应规律。结果表明，猪粪和鸡粪中淋溶的溶解性有机物（DOM）含有丰富的类色氨酸成分，可增加土壤表面吸附位点，通过水土界面上的交互作用对弱吸附性抗生素（磺胺类、氟苯尼考）的吸附具有显著促进作用, 在饱和基质流条件下，可减少抗生素的淋溶迁移。田间观测表明，在蓄满产流机制下，连续强降雨可导致地表径流和地下渗流中的抗生素浓度都急剧增加，检出率>95%。降雨过程中，抗生素浓度对降雨强度有明显响应，浓度峰与雨强峰对应，而地下渗流的浓度峰存在时间滞后。磺胺类抗生素在地表径流和地下渗流中的平均浓度分别高达1.22 和4.07 μg/L，而在紫色土大孔隙流作用下，吸附性较强的喹诺酮类和四环素类抗生素也能在降雨初期的地下渗流中被检出。地下渗流是研究区紫色土中抗生素迁移的主要路径，其迁移总通量比地表径流高两个数量级。此外，粪肥处理下抗生素迁移浓度和通量显著高于对照，表明粪源基质对污染物具有辅助运移作用。降雨过程中pH和胶体浓度变化可引起抗生素形态及其与胶体结合作用的改变，是影响抗生素迁移的主要因子。相关分析表明，pH和胶体浓度与氟喹诺酮类抗生素呈显著负相关，与磺胺类抗生素、氟尼考和泰乐菌素呈显著正相关，而与四环素类抗生素无显著相关性。本研究为认识以紫色土为代表的优先流发育土壤中抗生素的迁移规律及对区域水环境污染风险评估提供了科学依据。