CONCEPTUAL AND THEORETICAL ASPECTS OF HUMAN EXPOSURE AND DOSE ASSESSMENT

A formal, conceptual and mathematical framework for refining the chara cterization of human exposure and dose, resulting from contact with a toxicant, is introduced. The conceptual approach to the exposure chara cterization process leads to a mathematical description necessary for formalizing this process. Twelve steps are identified for guiding the information collection, management, and analysis needs for characteriz ation and estimation of exposure and dose. These steps are discussed i n terms of ten general principles for exposure and dose assessment tha t are related to: (1) The complicated character of exposure systems an d models, (2) the need for using appropriate metrics associated with t he exposure dynamics of individuals, populations and locations, (3) th e need to consider exposure as a sequence of coupled events and system s, (4) the need to treat exposure assessment as a dual prognostic and diagnostic problem and (5) as a dual phenomenological and mechanistic problem, (6) the fact that uncertainty in exposure characterization in cludes both irreducible and reducible components that have to be quant ified, (7) the need to specify probability distributions of exposures for individuals and populations, (8) the need for implementing state-o f-the-art computational data management methods for exposure related i nformation, (9) the need to formally and thoroughly evaluate exposure assessment modeling studies, and (10) the limitations in the exposure characterization process that affect the current practice of risk asse ssment. The theoretical approach described here represents an ''ideal' ' characterization model that will rarely, if ever, be fully implement ed in practice. However, this approach offers a consistent and general framework that can help identify specific needs for improvement in cu rrent measurements and estimation practices, and move exposure assessm ents closer to ''real'' exposure systems.