13C-NMR spectroscopy was applied to the evaluation of soil-bound residues of the fungicide cyprodinil (4-cyclopropyl- 6-methyl-2-phenylaminopyrimidine). A mixture of the 13C- and 14C-labeled fungicide was used to obtain structural information as well as information on the quantitative distribution in the various fractions. Bound residues were accumulated by a 6-month incubation of the labeled compound with a clay loamy soil. Depending on the concentration of [13C]cyprodinil (500, 250, 80, and 3 mg/kg), binding ranged from 18% to 54% of the initial radioactivity. After methanol extraction of soil (10 g dry weight) treated with 500 mg/kg (5.0 mg) of the fungicide, the amount of unextracted bound material was equivalent to 0.9 mg of 13C-labeled cyprodinil. Upon fractionation, 0.21 mg of the bound fungicide was found in the dialyzed 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 sequestered in soil by physical forces. The humic acid fraction was dissolved in a 1% solution of NaOD and examined by 13C-NMR. The NMR spectrum of the material from the control sample exhibited all the characteristic features of a typical humic acid. When the control humic acid was spiked with cyprodinil labeled uniformly with 13C at the phenyl ring, four additional signals at 121.9, 124.4, 131.8, and 143.4 ppm could be distinguished in the NMR spectrum. However, when humic acid originated from the soil that was incubated with the phenyl-labeled fungicide, 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 difference in the signal pattern indicated cleavage of the cyprodinil molecule between the aromatic rings and independent binding of the phenyl and pyrimidyl moieties to humic acid.

The fungicide cyprodinil [4-cyclopropyl-6-methyl-2-(phenylamino)pyrimidine] labeled with 14 C 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.

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The effect of selected pesticides, monocrotophos, chlorpyrifos alone and in combination with mancozeb and carbendazim, respectively, was tested on nitrification and phosphatase activity in two groundnut (Arachis hypogeae L.) soils. The oxidation of ammonical nitrogen was significantly enhanced under the impact of selected pesticides alone and in combinations at 2.5 kg ha(-1) in black soil, and furthermore, increase in concentration of pesticides decreased the rate of nitrification, whereas in the case of red soil, the nitrification was increased up to 5.0 kg ha(-1) after 4 weeks, and then decline phase was started gradually from 6 to 8 weeks of incubation. The activity of phosphatase was increased in soils, which received the monocrotophos alone and in combination with mancozeb up to 2.5 and 5.0 kg ha(-1), whereas the application of chlorpyrifos singly and in combination with carbendazim at 2.5 kg ha(-1) profoundly increased the phosphatase activity after 20 days of incubation, in both soils. But higher concentrations of pesticides were either innocuous or inhibitory to the phosphatase activity.