Retention of coumaric acid by soil and its colloidal components

In this study of the behavior of coumaric acid added to soil, the disappearance of the acid was found to be due to adsorption plus microbial degradation, and was influenced by the concentration and contact time. Adsorption experiments set up with soils varying widely in their chemical and physical properties, showed that the Freundlich isotherm fits the data quite well and that among the different soil factors, only the pH was closely and negatively correlated with coumaric acid adsorption. Approximately at pH > 7 no adsorption occurred, perhaps due to the repulsion between the negatively charged soil colloids and the dissociated acidic groups of coumaric acid. Adsorption experiments carried out with different adsorbents showed that the hydroxy-Fe compound was the most effective in retaining coumaric acid, followed by humic acid, illite, kaolinite and vermiculite, in this order.