197605 

Technical Report 

NTP technical report on the toxicology and carcinogenesis studies of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (CAS no. 1746-01-6) in female harlan Sprague-Dawley rats (gavage studies) 

National Toxicology Program :: NTP 

2006 

National Toxicology Program 

Research Triangle Park, NC 

NTP TR 521; NIH Publication No. 06-4468 

Background
2,3,7,8-Tetrachlorobenzo-p-dioxin (TCDD) is one of a large family of hydrocarbons containing chlorine known as dioxins. Some dioxins or dioxin-like compounds are highly toxic and cause cancer, and usually contaminated sites contain many different varieties of these dioxin-like compounds. The National Toxicology Program conducted a
series of studies to try to gauge the relative toxicity of some of the more prevalent of these compounds both alone and in mixtures. This study evaluated the effects of TCDD on female rats for comparison with the potency of other chemicals in that family.
Methods
We exposed groups of 53 or 54 female rats by depositing solutions of TCDD dissolved in corn oil through tubes directly into their stomachs five days a week for two years. Daily doses of TCDD were 3, 10, 22, 46, or 100 nanograms (ng) per kilogram of body weight. Animals receiving corn oil alone served as the control group.
Tissues from more than 40 sites were examined for every animal.
Results
Exposure to TCDD caused a variety of diseases in several organs. Cancers of the liver, lung, mouth, and uterus were seen in female rats exposed to TCDD. A variety of other toxic lesions observed in exposed animals included hypertrophy, hyperplasia, fibrosis, and necrosis of the liver, hyperplasia of the oral mucosa, metaplasia of the lung, inflammation and atrophy of the pancreas, kidney nephropathy, cardiomyopathy of the heart, atrophy and hyperplasia of the adrenal gland, atrophy of the thymus, hyperplasia of the forestomach, hypertrophy of the thyroid gland, and inflammation of the mesentery.
Conclusions
We conclude that TCDD caused cancer and other toxic effects at several sites in female rats.