Application of the "filter model" to a risk assessment for vinyl chloride

The filter model was used to estimate thresholds for the induction of cancer from many dose-response sets for inhalation and ingestion exposure to vinyl chloride for rat and inhalation exposure for mouse. Estimates for a variety of end-point combinations were log-normally distributed over about 2 decades from about 1 to 100 ppm for inhalation exposure to rat and 0.1 to 30 ppm for mouse. When the data is transformed to "dose" (milligrams per kilogram body weight per day), the estimates for inhalation and ingestion exposure and also for rat and mouse are similar. Estimates for different experiments carried out for different durations of time (single exposure to 1 yr) are comparable. Since the threshold is an intrinsic property of the biological system, the estimate, even from a protocol for short exposure and less than lifetime observation, can be used directly in a risk assessment as the maximum safe dose.