Influence of Organic Cosolvents on the Sorption Kinetics of Hydrophobic Organic Chemicals

A quantitative examination of the kinetics of sorption of hydrophobic organic chemicals by soils from mixed solvents reveals that the reverse sorption rate constant (k₂) increases log-linearly with increasing volume fraction of organic cosolvent (f_c). This relationship was expected, based on the existence of a log-log inverse relationship between k₂and the equilibrium sorption constant (K_p), and a log-linear inverse relationship between K_pand f_c. These results are interpreted in terms of a conceptual model wherein sorption kinetics is controlled by diffusion of sorbate within the matrix of sorbent organic matter. Decreased polarity of the mixed solvent, caused by the addition of a cosolvent, appears to influence the conformation of the polymeric organic matter and, hence, the rate of sorbate diffusion.