Formation of soil-bound residues of cyprodinil and their plant uptake

The fungicide cyprodinil [4-cyclopropyl-6-methyl-2-(phenylamino)pyrimidine] labeled with C-14 in either the phenyl or the pyrimidyl ring was incubated with four different soils under various conditions to evaluate the formation of bound residues and their subsequent plant uptake. About 60% of the initially applied radioactivity was bound to nonsterile soils within 90-180 days, whereas negligible binding was observed under sterile and anaerobic conditions. More binding was observed at higher soil pH, cation exchange capacity, and organic carbon and nitrogen contents. When spring barley was grown in the methanol-extracted soil, the plant uptake of bound residues amounted to about 0.2% for the phenyl label and 1.2% for the pyrimidyl label. The difference indicated that the pyrimidyl moiety was detached from the cyprodinil molecule and taken up more readily.