Influence of the nature of soil organic matter on the sorption-desorption of 4-chlorophenol, 2,4-dichlorophenol and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D)

The sorption-desorption properties of three organic pollutants, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP) and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) on soil organic matter (SOM) were studied using kinetic and equilibrium measurements in aqueous suspensions. Chestnut wood, wheat straw, Kraft lignin, composted straw and a soil humic acid were chosen as sorbents to model different states of humification. Physico-chemical characterization using chemical fractionation, potentiometric titration and IR spectroscopy was done on all sorbents. The microbial biomass, sizes of total bacterial and fungal microflora and phenoloxidases activities were determined for the plant materials. The irreversibility of sorption was revealed by the desorption isotherms. Only a small proportion of 2, 4-D, which has little affinity for the fresh organic materials, was desorbed. Sorption of 2,4-DCP was strong on straw but was reversible to a large extent, indicating weaker interactions. By comparison, the sorption of 4-CP was significantly less reversible. Thus, the nature of SOM and the properties of the chemicals strongly influenced the extent of sorption and the type of interactions, and it controlled subsequent desorption and possible transformation of the sorbed species.