title: Bioassay of pentachloronitrobenzene for possible carcinogenicity.
abstract: A bioassay of technical-grade pentachloronitrobenzene (PCNB) for possible carcinogenicity was conducted using Osborne-Mendel rats and B6C3F1 mice. PCNB 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 dietary concentrations of PCNB were, respectively, 10,064 and 5,417 ppm for male rats, 14,635 and 7,875 ppm for female rats, 5,213 and 2,606 ppm for male mice, and 8,187 and 4,093 ppm for female mice. After a 78-week period of compound administration, observation of the rats continued for an additional 33 to 35 weeks and observation of the mice continued for 14 or 15 additional weeks. For each species, 20 animals of each sex were placed on test as controls and fed only the basal diet. No rare or unusual tumors were observed during the histopathologic examinations and no statistically significant positive associations were demonstrated between chemical administration and the incidence of neoplasms in either sex of either species. It is concluded that under the conditions of this bioassay PCNB was not carcinogenic in either Osborne-Mendel rats or B6C3F1 mice.