Carcinogenic bioassay of the herbicide, 2,4,5-trichlorophenoxyethanol (TCPE) with different 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) content in Swiss mice.

The carcinogenic effect of a herbicide trichlorophenoxyethanol (TCPE) was investigated. The substance always contains 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) as a trace contaminant. Outbred Swiss-H/Riop mice were treated for 1 year with different doses of the various admixtures of the two compounds and those of dioxin alone to determine whether their carcinogenic effects are dose-dependent. Observation time after TCPE treatment was 1 and 2 years. The maximum tolerable dose of TCPE (70 mg/kg) with a dioxin concentration of 7.10(-6) mg/kg doubled the number of liver tumours as compared to the controls. The occurrence of liver tumours decreased at the administration of lower doses of the two compounds. No change in tumour frequency could be detected when the level of dioxin as a trace contaminant was raised, either (10 ppm). According to our preliminary results, dioxin has a more toxic than carcinogenic effect. The use of TCPE as a herbicide in accordance with the proper factory regulations and the consumption of products treated with it does not seem to bear a carcinogenic risk for the consumer.