CARCINOGENIC RISK ASSESSMENT - ETHYLENE DIBROMIDE

Ethylene dibromide has been shown to result in an increased incidence of gastric tumors in rats following intubation at 40 mg/kg/day. The U.S. Environmental Protection Agency (EPA) has used a one-hit carcinogenic model with parameters derived from this bioassay in rats to estimate the risk of cancer in humans arising from inhalation exposure to ethylene dibromide. The EPA estimated an almost 100% lifetime incidence of cancer to be expected in workers exposed to 0.4 ppm of ethylene dibromide at citrus fumigation centers. This communication reports a test of the validity of that prediction based on a comparison of the incidence of cancer predicted by the method used by the EPA with that observed in a group of 156 workers employed in the production of ethylene dibromide. The one-hit model, as used by the EPA, predicted a total of 85 tumors above the normal background incidence in this group of employees. A total of eight tumors has been observed. Therefore, use of this model to predict carcinogenic response in humans appears to result in highly exaggerated risk estimates. © 1979.