Promotion of mouse liver neoplasms by the organochlorine pesticides chlordane and heptachlor in comparison to dichlorodiphenyltrichloroethane.

The organochlorine pesticides chlordane and heptachlor were demonstrated to be liver neoplasm promoters in mice. Male B6C3F1 mice exposed to diethylnitrosamine (DEN) for 14 weeks followed by 25 weeks on control diet developed a 40% incidence of liver neoplasms whereas those given chlordane or heptachlor afterwards had approximately an 80% incidence of liver neoplasms, as did mice given DDT, a positive reference compound. Mice exposed to DEN also developed neoplasms of the forestomach and lung, but the incidences of these were not increased by chlordane, heptachlor or any other exposure. None of the chemicals given alone for the last 25 weeks of the study increased the incidence of liver neoplasms and none given before DEN produced a syncarcinogenic effect.