Sorption behavior of prochloraz in different soils

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. K-d values ranged f rom 56 +/- 0 to 552 +/- 10 (mean = 221 +/- 5) and K-OC values from 7273 +/- 0 to 16250 +/- 1300 (mean = 11829 +/- 303). As calculated from a linear re gression of K-d versus % OC, K-OC was 12900 +/- 1300. Additionally, the pH value of the soil had considerable influence on the sorption of the weakly basic PCZ (pK(a) = 3.8), giving rise to stronger sorption at lower pH. K-d values determined on pH-modified soils confirmed the pH dependency. Sorptio n 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 meas ured. The Freundlich exponents calculated were significantly smaller than u nity, indicating nonlinear sorption. Sorption experiments with two metaboli tes of PCZ (PCZ-formylurea and PCZ-urea) revealed K-d values one-fourth to one-third those for PCZ on two soils.