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Metabolism of TOK Herbicide in the Dairy Cow

Pesticide Residue Laboratory, Department of Entomology, Cornell University, Ithaca, New York

ABSTRACT

The herbicide 2,4-dichloro-4'-nitrodiphenyl ether (TOK) is selective for weed control in alfalfa, corn, and other crops. The possibility of residues in forage rations for cattle prompted this study of the fate of TOK in a lactating dairy cow.

No residues of TOK were found in the milk, urine, or feces of a cowT fed 5 ppm of the herbicide in its feed. It readily disappeared in the presence of fresh rumen fluid in vitro as determined by electron affinity gas chromatography. A metabolite was rapidly produced in the rumen fluid which had a retention time identical with that of the nitro reduction product of TOK, 2,4-dichloro-4'-aminodiphenyl ether (amino-TOK). This metabolite was absent in the chromatograms of milk, urine, and feces.

Experimental Procedure

A Holstein cow was catheterized and fed pure, recrystallized TOK at the 5-ppm level (based on a daily ration of 26.2 kg) for four days. The compound in absolute ethyl alcohol was mixed with the grain.