EVOLUTION OF SCIENCE-BASED UNCERTAINTY FACTORS IN NONCANCER RISK ASSESSMENT

The science behind the use of uncertainty factors has progressed consi derably. Increased knowledge of inter- and intraspecies sensitivity, m echanisms of action, and detailed evaluation of data bases can support the use of data-derived uncertainty factors, which ultimately results in a risk assessment with greater confidence. Papers that highlight a vailable data for each of several areas of uncertainty are discussed, indicating that choice of the appropriate factor requires scientific j udgement on a case-by-case basis. Case studies from EPA and Health Can ada risk values illustrate the use of data in chemical specific risk a ssessments to support the selection of uncertainty factors other than the default value of 10-fold. In the case studies, the types of data t hat have been used to support a change in the default value are explic itly reviewed, as well as why the data support a different uncertainty factor, how the uncertainty was reduced, and what assumptions have be en satisfied or replaced. Incorporation of all available scientific da ta into the risk assessment process fosters increased research and ult imately reduces uncertainty. The results of this review support the us e of data-derived uncertainty factors when appropriate scientific data are available. (C) 1996 Academic Press, Inc.