Adsorption coefficients, herbicide

Freundlich Soil Adsorption Coefficients. Control experiments indicated that all of the compounds were stable in the stock solutions, in the adsorption solutions, and in the soil during these studies. A preliminary adsorption run conducted to determine the time required for equilibration of the herbicides between water and soil indicated that ca. 3 hours shaking was adequate. 

Transport of the herbicides by vapor diffusion on moist soil was shown to be directly related to vapor pressure and inversely related to water solubility. Transport of the herbicides by leaching was shown to be inversely related to the Freundlich adsorption coefficient which in turn was directly related to the octanol/water partition coefficient and inversely related to water solubility (16). 

Tables 12.2 and 12.3. The effect of vertical variability is shown in Table 12.2, while the lateral spatial variability is shown in Table 12.3. The vertical and lateral spatial variabilities were defined on the basis of either the measured adsorption coefficient K), as generated from adsorption isotherms on soil profiles, or on adsorption coefficients on soil organic matter calculated as adsorption on organic carbon per unit weight of soil. We see that both vertical (Table 12.2) and lateral (Table 12.3) variability of soil affect the adsorption coefficients. A comparison between the bromide (conservative) and the two nonconservative herbicides distributions with depth after about 900mm of leaching is shown in Fig. 12.3. We see that, in the case of bromide, there is a continuous displacement of the center of mass with cumulative infiltration. In contrast, the bulk of the herbicide contaminant mass remains in the upper soil layer, with very little displacement.

The herbicidal action of fluoridone is strongly influenced by adsorption in the soil. According to Loh et al. (1979) a linear correlation exists between the adsorption coefficient (KJ of the soil, its organic substance content and the... 

A direct relationship between the organic matter content of the soil and the adsorption coefficient Ka having been established, a new coefficient Koc has been derived which is mainly independent of the properties of the soil. Xoc is defined as the ratio of the amount of herbicide adsorbed per unit weight of organic carbon in the soil to the concentration of the herbicide in solution at equilibrium ... 

This coefficient can be applied to all nonionic organic chemicals. Soil organic matter analysis has shown that approximately 58% is organic carbon,and a multiplication factor of 1.724 is therefore used to convert organic carbon to organic matter. Koc is an adsorption coefficient which describes the adsorption of a herbicide to soil based only on the properties of the molecule and therefore can be used to compare the relative amounts of adsorption of different herbicides. Table 7.1 gives some values reported... 

The adsorption coefficient Xqc provides a useful indication of the adsorption of a herbicide to soil and therefore enables an assessment of the proportion of herbicide remaining in the soil solution that is potentially mobile. 

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