Cáceres-Jensen L, Gan J, Báez M, Fuentes R, Escudey M
Dep. de Química de los Materiales, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile.
J Environ Qual. 2009 May 20;38(4):1449-57. doi: 10.2134/jeq2008.0146. Print 2009 Jul-Aug.
Glyphosate (N-phosphonometylglycine) is widely used due to its broad spectrum of activity and nonselective mode of action. In Chile it is the most used herbicide, but its adsorption behavior in the abundant and widespread variable charge soils is not well understood. In this study, three volcanic ash-derived soils were selected, including Andisols (Nueva Braunau and Diguillin) and Ultisols (Collipulli), to evaluate the adsorption kinetics, equilibrium isotherms, and the effect of pH in glyphosate adsorption. The influence of glyphosate on soil phosphorus retention was also studied. Glyphosate was rapidly and strongly adsorbed on the selected soils, and adsorption isotherms were well described by the Freundlich relationship with strong nonlinearity (n(fads) < 0.5). The n(fads) values were consistently higher than n(fdes) values, suggesting strong hysteresis. Adsorption (K(ads)) increased strongly when pH decreased. The presence of glyphosate (3200 mug mL(-1)) changed the adsorption behavior of phosphate at its maximum adsorption capacity. Andisol soils without the addition of glyphosate had similar mean K(ads) values for Nueva Braunau (5.68) and Diguillin (7.38). Collipulli had a mean K(ads) value of 31.58. During the successive desorption steps, glyphosate at the highest level increased K(ads) values for phosphate in the Andisol soils but had little effect in the Ultisol soil. This different behavior was probably due to the irreversible occupation of some adsorption sites by glyphosate in the Ultisol soil attributed to the dominant Kaolinite mineral. Results from this study suggest that in the two types of volcanic soils, different mechanisms are involved in glyphosate and phosphate adsorption and that long-term use of glyphosate may impose different effects on the retention and availability of phosphorus. Volcanic ash-derived soils have a particular environmental behavior in relation to the retention of organic contaminants, representing an environmental substrate that may become highly polluted over time due to intensive agronomic uses.
草甘膦（N-膦酰基甲基甘氨酸）因其广泛的活性谱和非选择性作用模式而被广泛使用。在智利，它是使用最广泛的除草剂，但在大量分布且电荷可变的土壤中，其吸附行为尚未得到充分了解。在本研究中，选择了三种火山灰衍生土壤，包括安第斯土（新布劳瑙和迪吉林）和老成土（科利普利），以评估草甘膦的吸附动力学、平衡等温线以及pH对草甘膦吸附的影响。还研究了草甘膦对土壤磷保留的影响。草甘膦在所选土壤上迅速且强烈地被吸附，吸附等温线通过具有强非线性（n(fads) < 0.5）的弗伦德利希关系得到很好的描述。n(fads)值始终高于n(fdes)值，表明存在强滞后现象。当pH降低时，吸附（K(ads)）强烈增加。草甘膦（3200 μg mL(-1)）的存在改变了磷酸盐在其最大吸附容量时的吸附行为。未添加草甘膦的安第斯土中，新布劳瑙（5.68）和迪吉林（7.38）的平均K(ads)值相似。科利普利的平均K(ads)值为31.58。在连续的解吸步骤中，最高水平的草甘膦增加了安第斯土中磷酸盐的K(ads)值，但对老成土的影响很小。这种不同的行为可能是由于老成土中占主导的高岭石矿物导致草甘膦不可逆地占据了一些吸附位点。本研究结果表明，在这两种火山土壤中，草甘膦和磷酸盐吸附涉及不同机制，长期使用草甘膦可能对磷的保留和有效性产生不同影响。火山灰衍生土壤在有机污染物保留方面具有特殊的环境行为，代表了一种环境基质，由于密集的农艺用途，随着时间的推移可能会受到高度污染。
