The gel filtration method of Hummel and Dreyer (1962) has been used for the study of binding of herbicides by water‐soluble organic substances extracted from soil with distilled water. Evidence is offered for the binding of bromacil (5‐bromo‐3‐sec‐butyl‐6‐methyluracil), diuron [3‐(3,4‐dichlorophenyl)‐1,1,dimethylurea], chlorotoluron [3‐(3‐chloro‐4‐methylphenyl)‐1,1‐dimethylurea], simazine (2‐chloro‐4,6‐bis‐ethylamino‐s‐triazine), glyphosate [N‐(phosphonomethyl) glycine], and diquat (1,1‐ethylene‐2,2‐bipyridylium ion) by water soluble soil organic materials (WSSOM). Infrared and gel filtration data showed that the WSSOM consist of compounds with molecular masses in the range of 700 to 5000 daltons and resemble very closely the fulvic acids present in soil and surface waters. The amount of herbicide bound by WSSOM was determined from the elution diagram of the herbicide‐WSSOM complex. The results of this study point to the significance of WSSOM in relation to the fate and behavior of pesticides and pollutants in soil and water. The binding of these chemicals by WSSOM may figure important in the assessment of their mobility and transport in the environment.
Sorption of bromacil (5‐bromo‐3‐sec‐butyl‐6‐methyluracil), chlortoluron [3‐(3‐chloro‐4‐methylphenyl),1,1‐dimethylurea], and diuron [3‐(3,4‐dichlorophenyl)1,1‐dimethylurea] by soils containing contrasting organic carbon (OC) content was studied. The sorptive capacity of the soils was assessed at 4 and 25°C by the batch equilibrium procedure over a broad range of aqueous phase herbicide concentrations. The herbicides showed the following order of increasing tendency to be sorbed: diuron > chlortoluron > bromacil. Sorption constants (Kf) were from 50‐ to 120‐fold higher for the organic soil than for the loamy sand soil, reflecting sorption dependence on soil OC. This variation in Kf was reduced to less than twofold variation in Koc by normalizing sorption to OC. Although sorption was higher at 4 than at 25°C, the difference was only minor at this temperature range. The isosteric heats of sorption (δHs) were relatively small and exothermic, suggesting the involvement of entropy driven mechanism. Water solubility (S) and octanol‐water partition coefficient (Kow) of the herbicides were determined and used to derive equations for estimating Koc with r2 ≥0.989. The practical utility of these correlations is that they allow reasonable estimates of Koc from more easily determined molecular parameters.
The gel filtration method of Hummel and Dreyer has been used for the study of binding of bromacil (5‐bromo‐3‐sec‐butyl‐6‐methy‐luracil), diuron [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea], chlortoluron [3‐(3‐chloro‐4‐methylphenyl)‐1,1‐dimethylurea], simazine (2‐ chloro‐4,6‐bis‐ethylamino‐s‐triazine), glyphosate [N‐(phosphonomethyl) glycine], and diquat (1,1‐ethylene‐2,2‐bipyridylium ion) by humic acid. The chromatographic method was found germane for the study of the ionic, as well as the nonionic herbicides. The results expressed as the number of moles of herbicide complexed per unit weight humic acid indicated the utility and reliability of the procedure for the quantitative evaluation of binding. Valid quantitative data on the interaction of herbicides with humic acid would be indispensable for the assessment of these chemicals mobility and transport in soil and water environments.
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