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In a two-generation reproduction study, rats were fed dietary levels of 0, 20, 100, and 500 ppm of 2,4 dichlorophenyl-p-nitrophenyl ether (TOK) (1.8 to 1.1 mg/kg/ day, 9.2 to 5.2 mg/kg/day, and 46 to 26 mg/kg/day, respectively). The survival of the offspring was not affected at the 0 and 20 ppm dietary levels. At the 100 ppm dietary level the survival of the offspring to weaning was reduced and at the 500 ppm dietary level no offspring survived the neonatal period in the two breedings of the first generation. In further studies rats were dosed during pregnancy either by stomach tube or by adding TOK to the diet. The reduction in the number of surviving litters was caused by poorly developed lungs in the exposed groups. Technical TOK had the same effect as 99% pure TOK. Furthermore, 2,7-dichlorodibenzodioxin, which may be a contaminant of TOK, does not affect the maturation process of the lungs when given at a dose of 0.04 mg/kg/day on days 7 to 15 of gestation.

Male and female Sherman strain rats were fed polychlorinated biphenyls Aroclor 1260 and Aroclor 1254 at 0, 20, 100, 500 and 1,000 ppm in their diet. Rats received the dietary levels for eight months. Light microscopic changes consisted of hypertrophy of the liver cells, inclusions in the cytoplasm, brown pigment in Kupffer cells, lipid accumulation, and, at the higher dietary levels, adenofibrosis. Ultrastructural changes of the livers of exposed animals consisted of an increase in smooth endoplasmic reticulum and atypical mitochondria. Lipid vacuoles were occasionally surrounded by concentric membranes. The epithelial component of adenofibrosis consisted of goblet cells and cells that resembled the epithelium which lines the bile ducts. In general, the effect of Aroclor 1254 on the liver was more pronounced than that of Aroclor 1260.

Adult male rats were fed different dosage levels of DDT, dieldrin, or combination of the two. After eight weeks, hexobarbital sleeping time was determined in some of these rats. Livers of the other rats were examined with the light microscope and electron microscope. Hexobarbital sleeping time was significantly reduced in all treated rats compared to that of controls, but no difference was found between the various treated groups. Liver weights of all treated groups were significantly higher than those of the controls, and livers of rats fed the combination of DDT and dieldrin weighed significantly more than those rats given DDT or dieldrin alone. Morphological changes, including an increase in smooth endoplasmic reticulum and atypical mitochondria, were observed in all treated groups and were more pronounced in rats given both DDT and dieldrin.