Kah M, Brown C D
Central Science Laboratory, Sand Hutton, York YO41 1LZ, UK.
Chemosphere. 2007 Jul;68(7):1335-43. doi: 10.1016/j.chemosphere.2007.01.024. Epub 2007 Feb 22.
Adsorption of six pesticides (2,4-D, dicamba, fluroxypyr, fluazifop-P, metsulfuron-methyl and flupyrsulfuron-methyl) in nine contrasting soils was measured using two techniques: (i) a classical batch method and (ii) a centrifugation method that allowed the measurement of adsorption at a realistic soil to solution ratio after one and seven days. Although the batch method gived significantly higher values of Kd than the centrifugation method for the more strongly sorbed molecules in the more sorptive soils, it tended to give lower adsorption coefficients compared to the centrifugation method when adsorption was lower. Discrepancies between the two methods were probably mainly due to the vigorous shaking applied in the batch technique that artificially enhances the availability of adsorption sites. This implies that shortly after application, more pesticide may be present in the soil solution and thus be available for degradation, plant uptake or leaching than will be predicted from adsorption coefficient determined using the batch method. Adsorption significantly increased between one and seven days and the extractability of total residues decreased with time. The increase in adsorption was not directly related to the level of adsorption although it was more important in soils containing more organic carbon (p=0.022). These results confirm the importance of time-dependent processes and the necessity to include them in risk assessment procedures. The centrifugation technique is a useful method to measure adsorption of pesticides at realistic soil moisture contents and seems to be an adequate technique to characterise the fraction of pesticide that is available for leaching at a given time after application.
采用两种技术测定了六种农药（2,4-滴、麦草畏、氟草烟、精稳杀得、甲磺隆和甲基二磺隆）在九种不同土壤中的吸附情况：（i）经典批量法；（ii）离心法，该方法能够在1天和7天后以实际的土液比测定吸附情况。尽管对于吸附性更强的土壤中吸附性更强的分子，批量法得出的分配系数（Kd）值比离心法显著更高，但在吸附较低时，与离心法相比，批量法得出的吸附系数往往更低。两种方法之间的差异可能主要是由于批量技术中剧烈的振荡人为地增加了吸附位点的可用性。这意味着在施药后不久，土壤溶液中可能存在更多的农药，因此与使用批量法测定的吸附系数预测的相比，可用于降解、植物吸收或淋溶的农药更多。在1天到7天之间吸附显著增加，总残留的可提取性随时间下降。吸附的增加与吸附水平没有直接关系，尽管在含有更多有机碳的土壤中吸附增加更为显著（p = 0.022）。这些结果证实了时间依赖性过程的重要性以及将其纳入风险评估程序的必要性。离心技术是一种在实际土壤湿度条件下测量农药吸附的有用方法，似乎是一种表征施药后给定时间可用于淋溶的农药部分的合适技术。
