Metabolism of14C-Pronamide in the Soil and in Lettuce (Lactuca sativa) under Field Conditions

Abstract

Metabolism of14C-pronamide [N-(1,1-dimethylpropynyl)-3,5-dichlorobenzamide, carbonyl-14C] was studied in silt loam soil (located in Louvain-la-Neuve, Belgium) and in lettuce (Lactuca sativaL., ‘Appia′, Clause3) from a crop planted in soil that had been treated before planting. During the experiment, most of the14C remained in the 0- to 6-cm soil layer. The percentage of14C-pronamide degraded to14CO2during the experiment was less than 10%. The soil-extractable14C was made up of pronamide and its first ketone metabolite [N-(1,1-dimethylacetonyl)-3,5-dichlorobenzamide]. About 30% of the pronamide present in the soil was bound to the soil. The bound residue, i.e., the14C that could not be extracted by acetone, at lettuce harvest was about 80% of the14C contained in the soil at that time; 3,5-dichlorobenzoic acid was the main component of the bound residue. The harvested lettuce also contained pronamide, the ketone, and 3,5-dichlorobenzoic acid. Similar kinetics of metabolism were observed with lettuces grown on loamy sand soil (located in St. Kathelijne-Waver, Belgium). However, pronamide was not bound to this type of soil.