PARENT SESSION
PM4 - Complex Mixtures
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P250) Applicability of Toxic Equivalency Factors (TEFs) For Risk Assessment of Complex Mixtures.
Reese, Erica*,1, Harris, Benjamin2, Dimitriou-Christidis, Petros1, Autenrieth, Robin1, Donnelly, Kirby1, McDonald, Thomas1, Safe, Stephen1, 1 Texas A&M University, College Station, Texas, USA2 Environmental Resources Management, Katy, Texas, USA
ABSTRACT- Complex environmental problems can readily be framed in a risk based assessment approach for either ecological or human health applications. Risk assessment is a valuable tool limited by the uncertainty associated with necessary assumptions in the process. Chemical toxicity is determined largely on a single compound exposure, but environmental exposures are frequently to multiple compounds. Polycyclic aromatic hydrocarbons (PAHs) represent a class of chemical mixtures to which humans are regularly exposed and are linked to adverse health effects. The overall goal of this research was to provide improvements in the science of risk assessment of complex mixtures and to identify the areas of risk assessment that need to be further researched. The primary objective of this research was to reduce the uncertainty in the toxicity assessment of a complex mixture of PAHs. A user-friendly criterion was developed for generating toxic equivalency factors (TEFs) for PAHs that have little or no toxicity data available. This criterion was also used to develop TEFs for the alkylated versions of the parent PAHs. A secondary objective was to identify the sensitive parameters in the assessment. Identification of these parameters is used to categorize modifications that are necessary in current software/model equations and to provide a means to better design sampling regimes. The importance of chemical structure and substitutions to parent structures revealed instances of increased toxicity due to numbers and positions of substitutions on the parent compound. Consequently, the proposed TEFs increased risk estimates two to four orders or magnitude from the initial assessments that did not include toxicity values for uncharacterized but identified substituted PAHs. Risk assessments that ignore a toxicity contribution of substituted PAHs can easily result in an underestimation of exposure consequences. Structure based TEF estimates provide a rational approach for estimating toxicity contributions by identified but uncharacterized compounds.
Key words: Risk Assessment, Polycyclic Aromatic Hydrocarbons(PAHs), Toxic Equivalency Factors (TEFs), Complex Mixtures