Risk Assessment Approaches for Dealing With Unusual Chemicals and Non-Standard Exposures

Abstract

It is estimated that there are approximately 70,000 chemicals used in commercial activities. Robust toxicological data, such as would be suitable for risk assessment, are available for only a small fraction of these chemicals. While this lack of toxicity data is being addressed by recent governmental efforts such as the REACH program in Europe, data development will take considerable time. In addition, there are chemicals not covered by these regulations (e.g., process chemicals) which may nonetheless be involved in accidental exposures. Likewise, unusual exposure pathways may be of concern that are not addressed by standard exposure assumptions. Risk assessors and regulators therefore need to be open to creative and flexible approaches for dealing with such situations. Two case examples are discussed which illustrate these potential challenges and identify some possible solutions. First, we consider the case of an industrial accident which resulted in community exposure to a chemical synthesis intermediate for which toxicity data were lacking. Using a Structure Activity Relationship approach, a surrogate chemical for which toxicity data were available was identified. This allowed for estimation of potential health risks for the affected community. In the second example, we consider an occupational scenario where workers received dermal exposures to chemicals present in newly synthesized polyurethane foams. Standard exposure assessment algorithms were not sufficient for evaluating this exposure. Situation-specific information was used to estimate the transfer of the chemicals from the foam surface/subsurface to the workers' skin with subsequent dermal absorption. While uncertainties were inherent in this exposure assessment approach, they were believed to be small relative to the overall margin of safety indicated in the final assessment. The results of this assessment were used to guide the design of a worker protection program. These two case examples illustrate some of the challenges practitioners of risk assessment face as risk assessment becomes ever more widely used. They also demonstrate the need to promote flexibility and creativity in the risk assessment process.