BIODEGRADATION, SORPTION, AND TRANSPORT OF 2,4-DICHLOROPHENOXYACETIC ACID IN SATURATED AND UNSATURATED SOILS

The fate of an organic contaminant in soil depends on many factors, in cluding sorption, biodegradation, and transport. The herbicide 2,4-dic hlorophenoxyacetic acid (2,4-D) was used as a model compound to illust rate the impact of these interacting factors on the fate of an organic contaminant. Batch and column experiments performed with a sandy loam soil mixture under saturated and unsaturated conditions were used to determine the effects of sorption and biodegradation on the fate and t ransport of 2,4-D. Sorption of 2,4-D was found to have a slight but si gnificant effect on transport of 2,4-D under saturated conditions (ret ardation factor, 1.8) and unsaturated conditions (retardation factor, 3.4). Biodegradation of 2,4-D was extensive under both batch and colum n conditions and was found to have a significant impact on 2,4-D trans port in column experiments. In batch experiments, complete mineralizat ion of 2,4-D (100 mg kg-1) occurred over a 4-day period following a 3- day lag phase under both saturated and unsaturated conditions. The bio degradation rate parameters calculated for batch experiments were foun d to be significantly different from those estimated for column experi ments.