Ferreira Julieta A, Martin-Neto Ladislau, Vaz Carlos M P, Regitano Jussara B
Instituto de Química de São Carlos, USP, Av. Trabalhador SãoCarlense, 400, 13560-970 São Carlos, SP, Brazil.
J Environ Qual. 2002 Sep-Oct;31(5):1665-70. doi: 10.2134/jeq2002.1665.
Soil sorption of most hydrophobic organic compounds (e.g., nonpolar pesticides) is directly related to soil organic matter (SOM) content. Humic substances are the major SOM components, containing carboxylic, phenolic, amine, quinone, and other functional groups, and specific structural configurations. In this paper, sorption interactions between imazaquin (2-[4,5-dydro-4-methyl-4-(1-methylethyl)-5-oxo-1H- imidazol-2-yl]-3-quinoline-carboxylic acid) herbicide (IM) and a humic acid (HA) extracted from a typical Brazilian Oxisol were studied with electron paramagnetic resonance (EPR) and Fourier-transform infrared (FTIR) spectroscopic techniques. A polarographic technique was used to quantify sorption. The IM amount sorbed on the HA was much higher than that on the whole soil within the pH range studied, emphasizing the prominent role played by SOM on IM sorption. Moreover, IM sorption increased as the soil-solution pH decreased. This enhancement in sorption was attributed to the hydrophobic affinity of the herbicide by the HA and to the electrostatic interaction between the protonated quinoline group of IM and the negative sites of the HA. Hydrophobic regions in the HA's interior at low pH (< 5.0) were recently demonstrated by an EPR detectable spin-label molecule. The FTIR and EPR spectroscopy and polarography data indicated weak interaction between IM and the soil and its HA, involving hydrogen bonding, proton transfer, and cation exchange (at low pH), and mainly hydrophobic interactions. However, no strong reaction mechanism, such as charge transfer, was involved. In addition, this research suggested that soil amendment with organic material might increase magnitude of IM sorption, consequently avoiding leaching and carryover problems usually found for mobile and persistent herbicides such as imazaquin.
大多数疏水性有机化合物（如非极性农药）在土壤中的吸附与土壤有机质（SOM）含量直接相关。腐殖物质是土壤有机质的主要成分，含有羧基、酚羟基、氨基、醌基和其他官能团以及特定的结构构型。本文采用电子顺磁共振（EPR）和傅里叶变换红外（FTIR）光谱技术，研究了咪唑喹啉（2-[4,5-二氢-4-甲基-4-(1-甲基乙基)-5-氧代-1H-咪唑-2-基]-3-喹啉羧酸）除草剂（IM）与从典型巴西氧化土中提取的腐殖酸（HA）之间的吸附相互作用。采用极谱技术对吸附进行定量分析。在所研究的pH范围内,IM在HA上的吸附量远高于在整个土壤上的吸附量，这突出了土壤有机质对IM吸附所起的重要作用。此外，IM的吸附量随着土壤溶液pH值的降低而增加。吸附作用的增强归因于除草剂与HA之间的疏水亲和力以及IM质子化喹啉基团与HA负电荷位点之间的静电相互作用。低pH值（<5.0）时，EPR可检测的自旋标记分子最近证实了HA内部存在疏水区域。FTIR、EPR光谱和极谱数据表明，IM与土壤及其HA之间存在弱相互作用，涉及氢键、质子转移和阳离子交换（在低pH值下），主要是疏水相互作用。然而，未涉及电荷转移等强烈的反应机制。此外，本研究表明，用有机材料改良土壤可能会增加IM的吸附量，从而避免通常在诸如咪唑喹啉等移动性和持久性除草剂中出现的淋溶和残留问题。
