Other polychlorinated dibenzo para dioxins and dibenzo para dioxin could not be classified as to their carcinogenicity to humans for pcdfs the evaluation considered evidence from two large poisoning incidents involving rice oil contamination in japan and taiwan. Other polychlorinated dibenzo para dioxins and dibenzo para dioxin could not be classified as to their carcinogenicity to humans for pcdfs the evaluation considered evidence from two large poisoning incidents involving rice oil contamination in japan and taiwan. Iarc working group on the evaluation of carcinogenic risk to humans polychlorinated dibenzo para dioxins and polychlorinated dibenzofurans lyon fr international agency for research on cancer 1997 iarc monographs on the evaluation of carcinogenic risks to humans no 69. Summary of data reported and evaluation 51 exposure data polychlorinated dibenzo para dioxins pcdds are formed as inadvertent by products sometimes in combination with polychlorinated dibenzofurans pcdfs during the production of chlorophenols and chlorophenoxy herbicides and have been detected as contaminants in these products