Pesticides, organic, adsorption onto

Colenut and Thorburn [51,52] have also described the procedure using gas stripping of the aqueous sample followed by adsorption onto active carbon from which surface they are taken up in an organic solvent for gas chromatographic analysis. They optimized conditions for the determination of parts per billion of pesticides and polychlorinated biphenyls. 

Studies involving the adsorption of organic substances onto solid phases have largely centered around organic pesticides because of the environmental significance of these toxic substances. The extent of adsorption of Bromacil onto freshwater... 

The organochlorine pesticides are considered persistent chemicals. Degradation is quite slow when compared with other pesticides, and bioaccumulation, particularly in aquatic ecosystems, is well documented. Their mobility in soil depends on the composition of the soil the presence of organic matter favors the adsorption of these chemicals onto the soil particles, whereas adsorption is poor in sandy soils. Once adsorbed, they do not readily desorb. These compounds induce significant abnormalities in the endocrine balance of sensitive animal and bird species, in addition to their adverse impact on humans, and their use is appropriately banned in most areas. 

Solid-phase microextraction (SPME) is a technique that was first reported by Louch et al. in 1991 (35). This is a sample preparation technique that has been applied to trace analysis methods such as the analysis of flavor components, residual solvents, pesticides, leaching packaging components, or any other volatile organic compounds. It is limited to gas chromatography methods because the sample must be desorbed by thermal means. A fused silica fiber that was previously coated with a liquid polymer film is exposed to an aqueous sample. After adsorption of the analyte onto the coated fiber is allowed to come to equilibrium, the fiber is withdrawn from the sample and placed directly into the heated injection port of a gas chromatograph. The heat causes desorption of the analyte and other components from the fiber and the mixture is quantitatively or qualitatively analyzed by GC. This preparation technique allows for selective and solventless GC injections. Selectivity and time to equilibration can be altered by changing the characteristics of the film coat. 

The extent to which an organic compound partitions out of water onto soil is determined by physical-chemical properties of both the soil and the compound. The soil s organic matter content is the single best characteristic for estimating the amount of soil adsorption of pesticides and other organic molecules. The partition, or sorption, coefficient of the organic molecule Koc (equal to ATp/SOM) is rather independent of soil type. This suggests that SOM is the principal soil component responsible for pesticide sorption and that the role of SOM is similar in different soils. 

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