Contributions to ecological chemistry CXII balance of conversion of buturon‐¹⁴C in wheat under outdoor conditions¹

Abstract

The urea herbicide buturon (N-[p-chlorophenyl]-N'-methyl-N'-isobutinyl-urea), 14C-labeled, was sprayed on winter wheat as an aqueous formulation (2.98 kg/ha) under outdoor conditions. Upon harvest (three months after application), a total of 49.2% of the applied radiocarbon was recovered: 2.0% in the plants, 46.9% in the soil, and 0.3% in the leaching water (depth greater than 50 cm); less than 0.1% was in the grains (0.464 ppm). Only about half of the radioactivity present in plants could be recovered under mild extraction conditions; about half of this was unchanged buturon. In straw and husk extracts, the following metabolites were identified by gaschromatography/mass spectrometry:N-(p-chlorophenyl)-N-methyl-O-methyl-carbamate (metabolite I), N-phenyl-N'-formyl-urea (metabolite II), two unstable metabolites giving (p-chlorophenyl)-isocyanate upon purification (metabolites III and IV), N-(p-chlorophenyl)-N'-methyl-N'-isobutenylol-urea (metabolite V), p-chloroformanilide (metabolite VI) and biologically bound p-chloroaniline (metabolite VII). In the root and basal stem extract, the following metabolites were identified by gas chromatography/mass spectrometry: N-(p-chlorophenyl)-O-methyl-carbamate (metabolite VIII) and N-(p-chlorophenyl)-N'-methyl-urea (metabolite IX).

Application of14C-Labeled Herbicides in Lysimeter Studies

“…Calculated on the basis of the specific activity of the ap plied compound, the concentrations of methabenzthiazuron were 16 mg/kg in straw, 1.4 mg/kg in the chaff, and 0.07 mg/kg in the grains on a dry-weight basis (Table 4). The untreated rye that followed contained only one-tenth as much residual 14 C in comparison to the methabenzthiazurontreated spring wheat.…”

“…As summarized in Table 3, 85% of the radioactivity applied as [benzene ring-U- 14 C] methabenzthiazuron and about 74% of the 14 C applied as [3 -14 C] metamitron could be accounted for after one growing season. Only 2 and 0.8% of the applied radioactivity was found in the treated plants, while 83 and 73%, respectively, were recovered from the soil, predominantly in the upper 5 cm (Figure 2).…”

“…Therefore, in experiments with 14 Root uptake is greatly influenced by experimental con ditions (Table 7). When [ethylene-14 C 2 ] isocarbamide was applied either to the lysimeter soil (20) or to potting soil in a greenhouse (19), using the same soil, the concentra tion of the active substance, relative to the surface area of the experimental unit, was identical in both experiments.…”

“…Tracer techniques using 14 was chosen as a reference soil ( Generally, fertilization, soil management, and additional plant protection were conducted in accordance with good agricultural practice and were standardized throughout the experiments (9,20,22).…”

Non-extractable pesticide residues in soils and plants

“…Table 5 gives some examples of the occurrence of non-extractable residues in plants, derived from different classes of chemicals (ref s. [3][4][5][6]8,[22][23][24][25][42][43][44]. As in the case of non-extractable residues in soil, the chlorinated hydrocarbons form the lowest portion of non-extractable residues and higher percentages are formed from phenols and nitrogen-containing compounds.…”