Leiva Jorge A, Nkedi-Kizza Peter, Morgan Kelly T, Kadyampakeni Davie M
Soil and Water Sciences Department, University of Florida, Institute of Food and Agricultural Sciences (UF-IFAS), Gainesville, United States of America.
UF-IFAS Southwest Florida Research and Education Center, Immokalee, United States of America.
PLoS One. 2017 Aug 24;12(8):e0183767. doi: 10.1371/journal.pone.0183767. eCollection 2017.
Imidacloprid (IMD) is a neonicotinoid pesticide soil-drenched to many crops to control piercing-sucking insects such as the Asian citrus psyllid (ACP). Neonicotinoids are persistent in the environment and transport analyses are helpful estimate leaching potential from soils that could result in groundwater pollution. The objective of this study was to analyze IMD breakthrough under saturated water flow in soil columns packed with three horizons (A, E, Bh) of Immokalee Fine Sand (IFS). Also, we used the dimensionless form of the convective-dispersive model (CD-Model) to compare the optimized transport parameters from each column experiment (retardation factor, R; fraction of instantaneous-to-total retardation, β; and mass transfer coefficient, ω) with the parameters obtained from sorption batch equilibria and sorption kinetics. The tracer (Cl-) breakthrough curves (BTCs) were symmetrical and properly described by the CD-Model. IMD BTCs from A, Bh, and multilayered [A+E+Bh] soil columns showed steep fronts and tailing that were well described by the one-site nonequilibrium (OSNE) model, which was an evidence of non-ideal transport due to IMD mass transfer into the soil organic matter. In general, IMD was weakly-sorbed in the A and Bh horizons (R values of 3.72 ± 0.04 and 3.08 ± 0.07, respectively), and almost no retardation was observed in the E horizon (R = 1.20 ± 0.02) due to its low organic matter content (0.3%). Using the HYDRUS-1D package, optimized parameters (R, β, ω) from the individual columns successfully simulated IMD transport in a multilayered column mimicking an IFS soil profile. These column studies and corresponding simulations agreed with previous findings from batch sorption equilibria and kinetics experiments, where IMD showed one-site kinetic mass transfer between soil surfaces and soil solution. Ideally, sandy soils should be maintained unsaturated by crop irrigation systems and rainfall monitoring during and after soil-drench application. The unsaturated soil will increase IMD retardation factors and residence time for plant uptake, lowering leaching potential from soil layers with low sorption capacity, such as the E horizon.
吡虫啉（IMD）是一种新烟碱类农药，通过土壤浇灌用于多种作物，以防治刺吸式口器害虫，如亚洲柑橘木虱（ACP）。新烟碱类农药在环境中具有持久性，进行迁移分析有助于评估土壤中的淋溶潜力，而这可能导致地下水污染。本研究的目的是分析在装有伊莫卡利细砂（IFS）三个土层（A、E、Bh）的土壤柱中，饱和水流条件下吡虫啉的穿透情况。此外，我们使用对流 - 弥散模型（CD模型）的无量纲形式，将每个柱实验得到的优化迁移参数（阻滞因子，R；瞬时阻滞与总阻滞的分数，β；以及传质系数，ω）与从吸附批次平衡和吸附动力学获得的参数进行比较。示踪剂（Cl - ）的穿透曲线（BTCs）是对称的，并且能被CD模型很好地描述。来自A、Bh和多层[A + E + Bh]土壤柱的吡虫啉BTCs显示出陡峭的前沿和拖尾现象，这可以被单站点非平衡（OSNE）模型很好地描述，这证明了由于吡虫啉向土壤有机质的传质导致的非理想迁移。总体而言，吡虫啉在A层和Bh层中吸附较弱（R值分别为3.72±0.04和3.08±0.07），而在E层中由于其低有机质含量（0.3%）几乎没有观察到阻滞现象（R = 1.20±0.02）。使用HYDRUS - 1D软件包，各个柱的优化参数（R、β、ω）成功模拟了在模拟IFS土壤剖面的多层柱中吡虫啉的迁移。这些柱实验研究和相应的模拟结果与先前批次吸附平衡和动力学实验的结果一致，在这些实验中吡虫啉在土壤表面和土壤溶液之间表现出单站点动力学传质。理想情况下，在土壤浇灌施用期间和之后，通过作物灌溉系统和降雨监测应使砂土保持不饱和状态。不饱和土壤将增加吡虫啉的阻滞因子和植物吸收的停留时间，降低来自低吸附能力土层（如E层）的淋溶潜力。
