Reference dose (RfD): description and use in health risk assessments.

For many years the concept of the "acceptable daily intake" has served the toxicological and regulatory fields quite well. However, as approaches to assessing the health significance of exposures to noncarcinogenic substances receive greater scrutiny, some difficulties with this traditional approach have become more apparent. Consequently, the concept of the "reference dose" is introduced in order to avoid use of prejudicial terms (e.g., "safety" and "acceptable"), to promote greater consistency in the assessment of noncarcinogenic chemicals, and to maintain the functional separation between risk assessment and risk management.