Sorption Behavior of Prochloraz in Different Soils

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Abstract
The sorption behavior of the imidazole fungicide prochloraz [PCZ; N-propyl-N-[2-(2,4,6-trichlorophenoxy)ethyl]imidazole-1-carboxamide] was studied in batch experiments with different soils. The soil organic matter content was found to control the amount sorbed by different soils. Kd values ranged from 56 ± 0 to 552 ± 10 (mean = 221 ± 5) and KOC values from 7273 ± 0 to 16250 ± 1300 (mean = 11829 ± 303). As calculated from a linear regression of Kd versus %OC, KOC was 12900 ± 1300. Additionally, the pH value of the soil had considerable influence on the sorption of the weakly basic PCZ (pKa = 3.8), giving rise to stronger sorption at lower pH. Kd values determined on pH-modified soils confirmed the pH dependency. Sorption isotherms on two soils were recorded, initial concentrations ranging from 0.09 to 5.71 mg L-1. The Freundlich isotherm was fitted to the values measured. The Freundlich exponents calculated were significantly smaller than unity, indicating nonlinear sorption. Sorption experiments with two metabolites of PCZ (PCZ-formylurea and PCZ-urea) revealed Kd values one-fourth to one-third those for PCZ on two soils. Keywords: Prochloraz; metabolites; soil; sorption; pH dependency