Ability of biosolids and a cationic surfactant to modify methidathion leaching. Modelling with pescol.

Packed columns were prepared with an agricultural soil to examine the ability of two organic soil modifiers, biosolid and the cationic surfactant tetradecyl trimethyl ammonium bromide (TDTMA), to alter the leaching of the insecticide methidathion. Ion chloride was used as a tracer of water flow and the mathematical model PESCOL was selected to predict the mobility of the insecticide. The biosolid addition (SB column) delayed the breakthrough curves for methidathion with respect to the non-amended soil (S) column. The cationic surfactant TDTMA, alone or combined with the biosolid (SS and SBS) and previously incorporated in the soil column, caused the highest retardation of this pesticide in the soil columns. Theoretical retardation factors (TRf) were similar to the experimental Rf values for the S and SB columns, and predicted the high retention observed in the SBS and SS columns. The simulation with PESCOL predicted the experimental results.