Assessing Cumulative Risk: The Critical Issue of Uncertainty Factors. E. A. Julien, L. M. Barraj, M. Kelley, J.R. Tomerlin, and B. J. Petersen, Novigen Sciences Washington DC
The Food Quality Protection Act of 1996 requires the EPA to assess potential "cumulative effects" from combined exposure to multiple pesticides if they act through a common mechanism of toxicity. In the absence of either direct data or validated models to predict risk from exposure to mixtures, cumulative risk assessments must rely on data from studies of individual pesticides, which typically vary with regard to test species, study duration, and effect measured. The present study investigated the consequences of using such toxicity data within the framework of three potential approaches for assessing cumulative risk- the Hazard Index (HI), Toxicity Equivalence Factor (TEF), and the Total Margin of Exposure (MOET) approaches. Health risk from dietary exposure to 9 organophosphorous pesticides was estimated and was found to be entirely dependent on whether the HI, TEF, or MOET approach was used. The 3 approaches were found to generate significantly different results because they differ in how they incorporate the Uncertainty Factors (UFs) associated with the individual pesticides included in the assessment. These findings indicate that an innovative, scientifically sound method for dealing with UFs must be developed if the available toxicity data are from studies of varying design. The present study examined potential methods to address the problem of UFs when assessing cumulative risk.
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