Behavior of Bromacil and Napropamide in Soils: I. Adsorption and Degradation

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Abstract
The adsorption and degradation of napropamide [2‐(α‐naphthoxy)‐N,‐N‐diethyl propionamide] and bromacil (5‐bromo‐3‐sec‐butyl‐6‐methyluracil) was studied in a number of Israeli soils with various properties. The adsorption of napropamide by soils was moderate, with Kd (adsorption coefficients) values ranging from 0.27 to 2.96 mL/g. Bromacil was adsorbed only slightly with Kd values of 0.03 to 0.39 mL/g. Adsorption was only slightly correlated with the soil clay content but was highly correlated with soil organic matter content, giving KOC (the adsorption per unit weight of organic carbon) values of 34 and 336 mL/g organic carbon for bromacil and napropamide, respectively. Use of the aqueous solubility of the compounds to predict adsorption gave values with considerable error in comparison with those measured, but by using the octanol/water partition coefficient (KOW) predictions were improved considerably. Degradation was studied at several moisture contents, temperatures, and initial concentrations. For the soils studied temperature and moisture content affected degradation more than did soil type or initial concentration. Degradation fit first‐order kinetics, with half lives of 17 to 1,643 d for napropamide and 14 to 1,494 d for bromacil.