Carcinogenesis of hexachlorobenzene in mice

Hexachlorobenzene (HCB) is a fungicide and a by‐product in the manufacture of many chlorinated solvents and pesticides. In Turkey, between 1955 and 1959 HCB was the causative agent of an epidemic of toxic porphyria, which involved more than 3,000 people, predominantly children. HCB was studied in long‐term experiments for carcinogenicity in mice. Outbred Swiss mice were given HCB in the diet at dose levels of 50, 100 and 200 parts per million (ppm), for 101–120 weeks. Survival rates in females and males of group HCB 200 were markedly affected by deaths due to toxic manifestations of HCB. All survivors were killed at 120 weeks. Exposure to HCB resulted in an increased incidence of liver‐cell tumors in groups HCB 100 and HCB 200. No liver‐cell tumors were observed in the controls and in the group fed HCB 50. The incidence of mouse lympho‐mas was 35% in controls and 11% in HCB 200. The decrease reflects probably the shortest life‐span of HCB‐treated animals. The incidence of lung tumors was higher in controls than in the treated groups, but the multiplicity (nodule/mouse) was approximately the same in all groups. In a separate experiment 30 female and 30 male mice were administered 300 ppm HCB in the diet for only 15 weeks. Most of the males died early. The survival rate at 110 weeks of age was 10% and comparable to that of controls. Two mice in the HCB 300 group developed liver‐cell tumors. The proportion of tumor‐bearing animals and the incidence of lymphomas, lung adenomas and other tumor types in HCB 300 mice were similar to those reported in control animals. The present results indicate the carcinogenicity effect of HCB in mice.