Fenaminosulf, an aromatic diazo compound used exclusively as a fungicide, was selected for bioassay by the National Cancer Institute because of conflicting reports concerning its ability to induce hepatomas in rats.
A bioassay of formulated fenaminosulf for possible carcinogenicity was conducted using Fischer 344 rats and B6C3F1 mice. Fenaminosulf was administered in the feed, at either of two concentrations, to groups of 50 male and 50 female animals of each species. The time-weighted average high and low dietary concentrations of fenaminosulf were, respectively, 0.10 and 0.05 percent for rats, 0.19 and 0.10 percent for male mice, and 0.10 and 0.05 percent for female mice. After a 78-week period of compound administration, observation of the rats continued for up to an additional 31 weeks and observation of the mice continued for up to an additional 19 weeks.
Fifty male mice and 50 rats of each sex were placed on test as controls and fed only the basal diet. For female mice, 50 animals served as controls for the high dose group and 50 as controls for the low dose group.
For female rats there was no significant association between fenaminosulf dosage and mortality and, if the 21 male rats that died in the first two weeks of the bioassay were excluded from consideration, the same was true for male rats. For both male and female mice there was a significant positive association between dosage and mortality. In all groups of both species, however, adequate numbers of animals survived sufficiently long to be at risk from late-developing tumors.
No convincing, statistically significant positive associations were demonstrated between administration and the incidence of neoplasms in either sex of either species. An increased incidence of necrosis and mineralization of the tubular cells of the renal papilla occurred in treated rats and mice. These nonneoplastic lesions were not present in control animals of either species.
Under the conditions of this bioassay, dietary administration of formulated fenaminosulf was not carcinogenic in either Fischer 344 rats or B6C3F1 mice.