Bioassay of Fluometuron for Possible Carcinogenicity (CAS No. 2164-17-2).

Fluometuron is a phenylurea herbicide used in agriculture to control broad- leaved and grass weeds in cotton and sugarcane fields. The area of heaviest use is the Mississippi delta. Applications of low concentrations selectively kill weeds. A bioassay of the phenylurea herbicide fluometuron for possible carcinogenicity was conducted by administering the test chemical in feed to F344 rats and B6C3F1 mice. Groups of 50 rats of each sex were fed diets containing 125 or 250 ppm of fluometuron for 103 weeks, and groups of 50 mice of each sex were fed diets containing 500 or 1,000 ppm of fluometuron for 103 weeks. Matched controls consisted of groups of 50 untreated rats and 25 untreated mice of each sex. All surviving animals were killed at 103 to 105 weeks. Splenomegaly observed in rats in the subchronic studies influenced selection of the doses for the chronic study; however, no splenic effects were observed in the chronic study. Mean body weights of the dosed groups of male and female rats and mice were essentially the same as those of the corresponding control groups. Survival of dosed groups of rats and mice was similar to that of the corresponding control groups. Similarities between mean body weights and survival between dosed and control animals in thechronic study suggest that these animals could have tolerated higher doses. The only possible carcinogenic effects from compound administration were in male mice. Incidences of hepatocellular carcinomas or adenomas in male mice were dose related, and the incidence in the high-dose group was marginally higher than that in the corresponding matched controls or pooled controls from concurrent studies. Under the conditions of this bioassay, fluometuron was not carcinogenic for F344 rats or for female B6C3F1 mice. Equivocal results were obtained for male B6C3F1 mice which may have had an increased incidence of hepatocellular tumors. Because of the equivocal findings and because both rats and mice may have been able to tolerate higher doses, it is concluded that additional testing of fluometuron for carcinogenicity is warranted. Levels of Evidence of Carcinogenicity: Male Rats: Negative Female Rats: Negative Male Mice: Equivocal Female Mice: Negative Synonym: 1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl) urea