Carcinogenic effects induced in Wistar rats by combined treatment with technical-grade dichlorodiphenyltrichloroethane and sodium phenobarbital.

A group of 38 female and 39 male outbred Wistar rats were treated with 500 ppm technical-grade dichlorodiphenyltrichloroethane (DDT) in the diet and 500 ppm sodium phenobarbital (PB) dissolved in drinking-water for lifespan. Twenty-three of 29 (79.3%) female and 13/28 (46.4%) male surviving animals developed primary tumours which were detected starting at 65 weeks of age. Most of the liver tumours were neoplastic nodules, but well-differentiated hepatocellular carcinomas were also found in 3 males and 5 females of the exposed animals. No liver-cell tumour was observed in 59 rats exposed to a diet containing 3% olive oil.