Metabolism of the herbicide methazole in cotton and beans, and fate of certain of its polar metabolites in rats

Abstract

METHAZOLE IN COTTON AND BEANS suggested that five of the minor fecal metabolites were a result of nonmetabolic breakdown of the robenidine which occurred during the extraction process. Chromatography in solvent system I of the radioactivity extracted from the feces with acidified ethanol revealed that all of the radioactivity remained near the origin, while chromatography in solvent system II resolved the radioactivity into ten radioactive spots, none of which was identified. Since more than 60% of the radioactivity found in feces was identified as unmetabolized robenidine, this suggests that robenidine was incompletely absorbed from the digestive tract and does not undergo extensive breakdown in the body of the animal.Tissues. In order to establish the relevance of the urinary metabolites to those occurring in tissues, the radioactivity in selected tissues was isolated by extraction and chromatographed in solvent system I. Benzene extracts of fat and skin, containing 93-95% of the total radioactivity in these tissues, revealed that robenidine was the only compound present. Ethanol extracts of liver, kidney, and muscle containing 87-97% of the total radioactivity in these tissues revealed the presence of p-chlorohippuric acid, p-chlorobenzoic acid, and robenidine as tissue residues. CONCLUSIONSince p-chlorobenzoic acid is excreted as p-chlorohippuric acid in dogs (Novello et al., 1926) and rabbits (Bray et al., 1952) and these compounds have been identified as urinary metabolites of robenidine, this evidence indicates that the scheme shown in Figure 1. represents a major route for the metabolism of robenidine in the rat. No 1amino-3-(p-chlorobenzylidineamino)guanidine, postulated to be a potential metabolite, was found.It is speculated that this aminoguanidine fragment may be a transient metabolite. It could be split by the rat to yield p-chlorobenzoic acid and 1,3-diaminoguanidine, as suggested from the mammalian metabolism of the related aldehyde derivatives of thiosemicarbazide (Williams, 1959). Since there is little literature on the known fate of guanidine in mammalian metabolism, no proposals can be made to suggest the possible fate of the aminoguanidine moiety.ACKNOWLEDGMENT We thank I. J. Morici of the American Cyanamid Company, Princeton, N. J., for conducting the acute toxicology tests. LITERATURE CITED

Aspects of the selective phytotoxicity of methazole. II. Behaviour in plants following root exposure

“…1972;Dorough. 1974: Dorough et at., 1973. This suggestion is supported by the inverse relationship between the amounts of parent compound and 'complexed" degradation products found in the four species in the present experiments (Fig.…”

Methazole Adsorption-Desorption in Soil

“…Following the equili bration period, each tube was centrifuged to remove par ticulates in solution having equivalent Stokes' radii > 0.02 /im (8000 rpm for 30 min). A 4-ml aliquot of the super natant liquid was removed and mixed with 10 ml of scin tillation liquid 3,4 , and 14 C was measured by scintillation spectrometry. The scintillation counts were corrected by the external standard ratio method, and radioactivity values were converted and expressed as nmol methazole in solution.…”

“…Methazole has been used for effective annual weed control in a variety of crops. Methazole is rapidly degraded in plants (4,9,10,16) and animals (4) to a number of products of which DCPMU is the major metabolite. In soil, methazole has also been shown to rapidly degrade principly to DCPMU with reported half-lives of from less than 4 days (10,19,20) to less than 44 days (2).…”

Reviews of Environmental Contamination and Toxicology

“…Opening of its imide ring was observed for procymidone (108) on cucumber leaves but only in trace amounts (Mikami et al 1984a). Methazole (112) underwent either opening of the 1,2,4-oxadiazoline-3,5-dione ring to the 3methyl-I-phenylurea derivative or decarboxylation to the 2-oxo-benzimidazole derivative, with greater amounts detected on the surface of cotton leaves (Dorough et al 1973). The latter degradate at least was considered to be formed by photoreaction because it was also detected in aqueous photolysis.…”