AN APPROACH FOR MODELING NONCANCER DOSE RESPONSES WITH AN EMPHASIS ONUNCERTAINTY

This paper presents an approach for characterizing the probability of adverse effects occurring in a population exposed to dose rates in exc ess of the Reference Dose (RFD). The approach uses a linear threshold (hockey stick) model of response and is based on the current system of uncertainty factors used in setting RfDs. The approach requires gener ally available toxicological estimates such as No-Observed-Adverse-Eff ect Levels (NOAELs) or Benchmark Doses and doses at which adverse effe cts are observed in 50% of the test animals (ED(50)s). In this approac h, Monte Carlo analysis is used to characterize the uncertainty in the dose response slope based on the range and magnitude of the key sourc es of uncertainty in setting protective doses. The method does not req uire information on the shape of the dose response curve for specific chemicals, but is amenable to the inclusion of such data. The approach is applied to four compounds to produce estimates of response rates f or dose rates greater than the RfD.