Kinetic study of adsorption and degradation of aniline, benzoic acid, phenol, and diuron in soil suspensions

Laboratory studies were conducted to investigate the effects of low temperature and accelerated soil-solution contact on soil adsorption of labile organic chemicals. The authors measured the kinetics of adsorption and degradation of 14C-aniline, 14C-benzoic acid, 14C-phenol, and 14C-diuron in the solution phase at 3 and 220C. In the initial stages of reactions, the adsorption of all four chemicals was instantaneous at both temperatures under accelerated soil and solution mixing. A steady state was observed after the onset of equilibrium for the adsorption reaction for all compounds within 10 to 30 min. Its length varied according to the expected order of susceptibility to microbial degradation, i.e., diuron > aniline > phenol ≥ benzoate. It was apparent that the steady-state period without or in combination with low temperature could be advantageously used to obtain adsorption measurements in microbially active systems. A mechanistic sorption-catalyzed degradation model was evaluated to uncouple mathematically these processes. The model described satisfactorily the disappearance of labile chemicals in soil suspensions. Numerical analysis allowed the concurrent determination of adsorption, desorption, and biodegradation rate coefficients