||Risk assessment on (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T), (2,4,5-trichlorophenoxy) propionic acid, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) /
Carcinogenic responses have been induced in mice and rats at low doses of TCDD. TCDD has been shown to be a cancer promoter. These results, together with the strongly suggestive evidence in epidemiology studies, constitute substantial evidence that TCDD is likely to be a human carcinogen. It appears that TCDD is a more potent carcinogen than aflatoxin B1 which is one of the most potent carcinogens known. The levels of TCDD (contained as an unavoidable contaminant of the 2,4,5-T) used in the 2,4,5-T studies apparently were too small to produce an observable response in those experiments. The lack of a statistically significant tumor incidence in most of the studies on the 2,4,5-T product may be attributed to the very low levels of TCDD in the product relative to the levels at which it produced carcinogenic effects in rats and mice, as well as to deficiencies of those studies. However, since TCDD is a carcinogen, any product containing TCDD, including 2,4,5-T and silvix, can be considered to pose a human carcinogenic hazard. Furthermore, a rat study on specially purified 2,4,5-T provides highly suggestive evidence that essentially pure 2,4,5-T may be a human carcinogen. Quantitative assessments have been calculated for the carcinogenic risk posed to humans.
Prepared for [the] Office of the General Counsel, U.S. Environmental Protection Agency. Prepared by [the] Office of Health and Environmental Assessment, Washington, D.C., Carcinogen Assessment Group. "PB 81-234825." Includes bibliographical references.