ANALYSIS OF SOIL-BOUND RESIDUES OF C-13-LABELED FUNGICIDE CYPRODINIL BY NMR-SPECTROSCOPY

C-13-NMR spectroscopy was applied to the evaluation of soil-bound resi dues of the fungicide cyprodinil (4-cyclopropyl-6-methyl-2-phenylamino pyrimidine). A mixture of the C-13- and C-14-labeled fungicide was use d to obtain structural information as well as information on the quant itative distribution in the various fractions. Bound residues were acc umulated by a 6-month incubation of the labeled compound with a clay l oamy soil. Depending on the concentration of [C-13]cyprodinil (500, 25 0, 80, and 3 mg/kg), binding ranged from 18% to 54% of the initial rad ioactivity. After methanol extraction of soil (10 g dry weight)treated with 500 mg/kg (5.0 mg) of the fungicide, the amount of unextracted b ound material was equivalent to 0.9 mg of C-13-labeled cyprodinil. Upo n fractionation, 0.21 mg of the bound fungicide was found in the dialy zed humic acid, 0.13 mg in fulvic acid (after extraction with CH2Cl2), and 0.24 mg in humin. The methylene chloride extract from fulvic acid mainly contained unchanged cyprodinil (0.21 mg) that was apparently s equestered in soil by physical forces. The humic acid fraction was dis solved in a 1% solution of NaOD and examined by C-13-NMR. The NMR spec trum of the material from the control sample exhibited all the charact eristic features of a typical humic acid. When the control humic acid was spiked with cyprodinil labeled uniformly with C-13 at the phenyl r ing, four additional signals at 121.9, 124.4, 131.8, and 143.4 ppm cou ld be distinguished in the NMR spectrum. However, when humic acid orig inated from the soil that was incubated with the phenyl-labeled fungic ide, only two strong NMR signals, at 122.5 and 131.8 ppm, and two less significant signals around 142 and 162 ppm were observed. The differe nce in the signal pattern indicated cleavage of the cyprodinil molecul e between the aromatic rings and independent binding of the phenyl and pyrimidyl moieties to humic acid.