Sorption and Degradation of Aldicarb and its Oxidation Products in a Soil‐water Flow System as a Function of pH and Temperature

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Abstract
The sorption and degradation of aldicarb [2‐methyl‐2‐(methylthio) propionaldehyde O‐(methylcarbamoyl)oxime], aldicarb sulfoxide [2‐methyl‐2‐(methylsulfinyl)propionaldehyde O‐(methylcarbamoyl)oxime], and aldicarb sulfone [2‐methyl‐2‐(methylsulfonyl)propionaldehyde O‐(methylcarbamoyl) oxime] in a sandy loam soil were determined under varying pH and temperature conditions. The experiments were performed using a soil‐column methodology, which allows a steady state water flow and nonsteady state addition of pesticide. The edition curve (concentration vs. time) was interpreted using analytical solutions to the convection‐dispersion equation that included linear sorption and pseudo‐first‐order degradation. The sorption of the three species changes slightly with pH over the range studied (pH 5–8).The degradation varies with pH, but not in the same manner as found in aqueous solution studies. Sorption decreases as the temperature is increased from 15 to 35°C. Degradation is also temperature dependent in this range and for aldicarb sulfone can be represented by a linear Arrhenius plot from which activation energies can be derived. There is good agreement between the calculated activation energy for aldicarb sulfone and that obtained in aqueous solution studies. The results of this study have provided information about the thermodynamics of the aldicarb system and have demonstrated the usefulness of the soil‐column flow method as a good laboratory model for chemical transport and transformation in soil.