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This paper explores the adequacy of using currently available exposure assessment models for indoor air inhalation exposures in the context of the uncertainty that exists in both the dose-response assessment and the exposure assessment. A tiered system is proposed for implementing exposure assessments. Each tier involves additional research, but also would lead to reductions in uncertainty. The authors discuss a possible comprehensive research program that will permit the building of well-validated models for indoor air inhalation exposures among classes of chemicals, building types, and exposure scenarios. The authors believe that until such a research program is undertaken, modeling of exposures (and therefore risks) using the current, unvalidated modeling approaches provides little more than worst-case estimates that are useful primarily for making screening decisions about risks.
Evaluating the human health risk resulting from chemical exposure has two primary scientific com1-Jponents: (1) the dose-response curve for the health effect of concern and (2) the exposure.(1,2,3) Viewed in a traditional industrial hygiene perspective, the essence of risk assessment and management lies in the comparison of the human exposure to any particular toxicant with the exposure limit for that material. This paper discusses issues related to risk assessment and indoor modeling. To establish a common ground and aid the reader in understanding what may be new nomenclature, a short list of conceptual definitions used in this paper is presented below:
(1) Risk-the probability that a specific untoward health effect may occur as a result of a specified exposure to a toxic compound.
(2) Acceptable risk-a level of risk that is considered low enough to be deemed insignificant or de minimis. For example, an incremental lifetime risk of cancer from a chemical product that is less than 1 in 100 000 is considered insignificant in the context of California's product labeling law, known as Proposition 65.* 1 2 * (4) Other laws and regulatory limits may have differing de minimis risk levels. Most often, risks of various health effects are evaluated using the classical concept of toxicity thresholds.
(3) Upper bound estimate of risk-a level of risk that is usually assumed by a risk assessor in the absence of detailed information about the toxicity of the compound or its exposure. If one is totally ignorant of a compound's...