Dicofol, a synthetic organochlorine acaricide, was selected for bioassay by the National Cancer Institute because it is an alcohol analog of the known tumorigen DDT. Its widespread use on edible crops was also an important factor in its selection for testing.
A bioassay of technical-grade dicofol for possible carcinogenicity was conducted using Osborne-Mendel rats and B6C3F1 mice. Dicofol was administered in the feed, at either of two concentrations, to groups of 50 males and 50 females of each species. The high and low time-weighted average concentrations of dicofol were, respectively, 942 and 471 ppm for male rats, 760 and 380 ppm for female rats, 528 and 264 ppm for male mice, and 243 and 122 ppm for female mice. For each species, 20 animals of each sex were placed on test as controls. The period of compound administration was 78 weeks, followed by 34 weeks of observation in rats and 14 or 15 weeks in mice.
There was no statistically significant positive association between dietary concentration and mortality in either sex or species.
Hepatocellular carcinomas in dosed male mice were the only neoplasms that occurred in any dosed group of either species in statistically significant increased incidences when compared to controls. The Cochran-Armitage test as well as the Fischer exact test for both the high and low dose groups supported the association between compound administration and increased incidences of this tumor in the male mice. No increase in hepatocellular carcinomas was observed in dosed female mice.
Under the conditions of this bioassay, technical-grade dicofol was carcinogenic in male B6C3F1 mice, causing hepatocellular carcinomas. No evidence for carcinogenicity was obtained for this compound in Osborne-Mendel rats of either sex or in female B6C3F1 mice.