This study was conducted to determine the significance of bromacil transport as a function of water and carbon content in soils and to explore the implications of neglecting sorption when making assessments of travel time of bromacil through the vadose zone. Equilibrium batch sorption tests were performed for loamy sand and sandy soil added with four different levels of powdered activated carbon (PAC) content (0, 0.01, 0.05, and 0.1%). Column experiments were also conducted at various water and carbon contents under steady-state flow conditions. The first set of column experiments was conducted in loamy sand containing 1.5% organic carbon under three different water contents (0.23, 0.32, and 0.41) to measure breakthrough curves (BTCs) of bromide and bromacil injected as a square pulse. In the second set of column experiments, BTCs of bromide and bromacil injected as a front were measured in saturated sandy columns at the four different PAC levels given above. Column breakthrough data were analyzed with both equilibrium and nonequilibrium (two-site) convection-dispersion equation (CDE) models to determine transport and sorption parameters under various water and carbon contents. Analysis with batch data indicated that neglect of the partition-related term in the calculation of solute velocity may lead to erroneous estimation of travel time of bromacil, i.e. an overestimation of the solute velocity by a factor of R. The column experiments showed that arrival time of the bromacil peak was larger than that of the bromide peak in soils, indicating that transport of bromacil was retarded relative to bromide in the observed conditions. Extent of bromacil retardation (R) increased with decreasing water content and increasing PAC content, supporting the importance of retardation in the estimation of travel time of bromacil even at small amounts of organic carbon for soils with lower water content.

译文

:这项研究的目的是确定溴麦草碱的运输作为土壤中水和碳含量的函数的重要性,并探讨在评估溴麦草碱通过渗流带的传播时间时忽略吸附的影响。对添加了四种不同水平的粉状活性炭(PAC)含量(0%,0.01%,0.05%和0.1%)的壤土和沙质土壤进行了平衡批吸附测试。在稳态流动条件下,还对各种水和碳含量进行了柱实验。第一组柱实验是在三种不同水含量(0.23、0.32和0.41)下,在含1.5%有机碳的质壤土砂中进行的,以测量以方脉冲形式注入的溴化物和苯甲嘧啶的穿透曲线(BTC)。在第二组色谱柱实验中,在上述四个不同的PAC浓度下,在饱和沙质色谱柱中测量了作为前沿注入的溴化物和溴苯甲酰胺的BTC。使用平衡和非平衡(两点)对流扩散方程(CDE)模型对色谱柱穿透数据进行了分析,以确定在各种水和碳含量下的迁移和吸附参数。使用批处理数据进行的分析表明,在溶质速度的计算中忽略与分区相关的项可能导致错误地估计了溴苯虫的传播时间,即溶质速度的高估了R倍。色谱柱实验表明,到达时间在土壤中,溴溴甲烷峰的“溴化物”峰大于溴化物峰的溴化物,表明在观察到的条件下,相对于溴化物,溴甲烷土的转运受阻。随着含水量的减少和PAC含量的增加,苯丙胺类药物的阻滞作用(R)的程度也增加,这支持了苯丙胺类药物的滞留在估算苯丙草胺的传播时间中的重要性,即使对于水分含量较低的土壤,即使有机碳含量较低也是如此。

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