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粪源溶解性有机质对雷竹土壤中兽药迁移影响的试验与模型模拟

Experimental and Modeling Study on the Effects of Manure Dissolved Organic Matter on the Transport of Veterinary Antibiotics in Phyllostachys praecox Soil

  • 摘要: 粪肥往往含有多种兽药残留和大量溶解性有机质(dissolved organic matter,DOM),DOM会对兽药在施用粪肥土壤中迁移产生显著影响。然而,关于粪源DOM及其组分如何影响兽药迁移的试验与模型模拟研究仍较为缺乏。因此,以集约化经营雷竹园土壤为对象,通过土壤团聚体填装柱穿透试验与数值模型模拟,探究猪粪DOM及其亲水(hydrophilic fraction,HI)和疏水(hydrophobic fraction,HO)组分对4种典型兽药迁移行为的影响。结果表明:猪粪DOM及其HO组分主要通过与氟苯尼考形成水溶性复合物大幅提高其穿透率(升幅均大于20%),而HI组分则可能与氟苯尼考形成氢键进而共吸附于土壤颗粒,从而小幅降低其穿透率。猪粪DOM对磺胺二甲基嘧啶穿透的影响很小,其HI组分和HO组分仅在高浓度(100 mg/L)条件下使磺胺二甲基嘧啶穿透率分别稍有提高和降低(变幅均小于10%)。两区模型能较好地模拟兽药的非平衡迁移过程(决定系数:0.908~0.997,均方根误差:0.014~0.092),不同进水处理之间模型参数率定值的差异表明DOM及其组分是通过改变可动水区吸附位点分数和跨区质量交换系数影响兽药迁移。强吸附性兽药强力霉素和恩诺沙星在所有进水组成条件下均无法穿透土柱。该研究揭示了粪源DOM及其组分对兽药迁移的影响在机制上存在差异,为雷竹园土壤兽药淋溶风险评估及粪肥管理优化提供了科学依据。

     

    Abstract: Manure often contains various veterinary drug residues and a large amount of dissolved organic matter (DOM). Veterinary drugs can enter the soil through manure application, and then enter water bodies through runoff and leaching processes, thereby posing a potential risk to the ecosystem safety and human health. Moreover, DOM may significantly affect the transport of veterinary drugs in the soil. However, the impact of manure DOM and its components on the transport of veterinary drugs in soil is still insufficiently explored by both experimental and modeling means. Phyllostachys praecox plantations are widely distributed in southern China, and a large amount of manure is applied during the cultivation process. Therefore, this study focused on antibiotic transport in the soil of intensively managed Phyllostachys praecox plantation. Through transport experiments in repacked columns (5 cm in diameter and 10 cm in height) of soil aggregates under saturated condition and numerical model simulations, we investigated the effects of pig manure DOM and its hydrophilic (HI) and hydrophobic (HO) fractions on the transport of four typical veterinary drugs (doxycycline, sulfamethazine, enrofloxacin, and florfenicol). In all inflow treatments, sulfamethazine and florfenicol exhibited high recovery rates (≥58.4% and ≥60.9%, respectively) in outflows from soil columns, while enrofloxacin and doxycycline were not detected in all outflow samples. This finding implies higher potential for sulfamethazine and florfenicol to be leached into shallow groundwater upon rainfall and irrigation. The additions of pig manure DOM and its HO fraction were found to significantly increase the recovery rate of florfenicol (by more than 20%) mainly through forming water-soluble complexes. Contrastingly, the addition of HI fraction of pig manure DOM slightly reduced the recovery rate of florfenicol, possibly through binding with florfenicol via hydrogen bonding and subsequent co-adsorption onto soil particles. Pig manure DOM could hardly affect the transport of sulfamethazine, and only the additions of its HI and HO fractions at high concentration (100 mg L−1) led to a slight (by less than 10%) increase and decrease in the recovery rate of sulfamethazine, respectively. The performance of two-region model (TRM) (R2: 0.966−0.993; root mean square error: 0.019−0.039) was better than that of convection dispersion equation (R2: 0.951−0.992; root mean square error: 0.022−0.046) in simulating the breakthrough data of Br, which can be attributed to the good ability of TRM to describe the dominant role of macropores in conducting water in repacked columns of soil aggregates. TRM performed satisfactorily in simulating the non-equilibrium transport of veterinary antibiotics (R2: 0.908−0.997; root mean square error: 0.014−0.092). Differences in calibrated model parameters between inflow treatments suggest that DOM and it polarity fractions could change the transport of veterinary antibiotics by altering adsorption site fraction in mobile water region and inter-regional mass transfer coefficient. Strongly sorbing veterinary drugs doxycycline and enrofloxacin could not pass through the soil column under all inflow treatments. This study found the differences in mechanisms by which manure-derived DOM and its polarity fractions affect veterinary drug transport, providing a scientific basis for optimizing the selection of manure products to be applied in Phyllostachys praecox plantations, in order to minimize the risk of antibiotic pollution of local water bodies.

     

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