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United States Department of Agriculture

Agricultural Research Service

Title: Measurements of Sorption-Desorption and Isotherm Analyses

Authors
item Clapp, Charles
item Hayes, Mhb - UNIVERSITY OF LIMERICK
item Mingelgrin, U - VOLCANI INSTITUTE ARO

Submitted to: Humic Substances and Chemical Contaminants
Publication Type: Book / Chapter
Publication Acceptance Date: December 11, 2000
Publication Date: N/A

Interpretive Summary: Sorption of chemical contaminants to organic molecules is feasible in soils and water. Such sorption in natural environments may influence the effectiveness and movement of these chemicals. The main fraction of organic matter is "humic substances." Soil humic acids were the strongest in complexing with the herbicide napropamide, water humic acids were weakest, and peat humic acids were intermediate. Napropamide also showed much stronger sorption to soil humic acids than two other herbicides, atrazine and alachlor. Our data show that complexation of herbicides and other organic monomers with soluble humic substances is strongly influenced by the chemistry of both humic substances and herbicides. We have summarized the theories and mechanisms by which synthetic and naturally- occurring macromolecules interact to form complexes in soil and water biosystems. Measurement techniques and methods are also presented to provide a basis for modeling the interactions. The results give environmental scientists, engineers, and consultants information about the occurrence and movement of herbicides and other chemical pollutants into the ground water under different farming systems.

Technical Abstract: Sorption-desorption are the two main processes that influence the behavior of organic chemicals in soil-water biosystems. The batch/slurry technique is widely used for studies of sorption from solution by solid phase sorbents. In the cases of water-soluble sorbents, equilibrium dialysis, gel chromatography, and continuous flow/stirred cell procedures provide appropriate data for calculating sorption isotherms. Desorption isotherms are obtained from data derived by batch/slurry and continuous flow/flow injection analysis methods. Observations of isotherm shapes, the relative ease of desorption, and isotherm analyses such as those based on the Langmuir equation and derivatives thereof, provide information about the extent and the mechanisms of sorption. However, for more specific interpretations of the nature of adsorbate/adsorbent interactions, it is important to utilize data from procedures such as calorimetry and spectroscopic analyses.

Last Modified: 10/23/2014