An Alternative Method for Estimating Age-Adjusted Intake Factors. K. E. Linton, ERM-Southwest, 16300 Katy Freeway, Suite 300, Houston, Texas 77094-1611; and M. T. Morandi, University of Texas School of Public Health, P.O. Box 20186, Houston, TX 77225
Exposure estimates throughout a lifetime are impacted by age-dependent intake factors. The traditional approach in regulatory guidance to account for age-related effects consists of using age-adjusted intake factors which produce a weighted average intake. This is accomplished by using factors for a child for the first years of exposure and adult factors for the remainder of the exposure period. However, this approach results in an underestimate of intake when used for evaluation of risk for noncancer endpoints. In addition, it can be shown that this approach produces the counterintuitive result that intake estimates are inversely related to exposure duration. The currently proposed approach for addressing this issue in regulatory guidance is to evaluate noncancer endpoints based on exposures only during the 6 years of childhood, excluding exposures experienced during adulthood. The rationale for this revised methodology is that childhood exposures represent the majority of the lifelong intake and that children are assumed to be a more sensitive population subgroup. The method presented here allows the use of age-adjusted intake factors which would account for childhood exposures continuing into adulthood for both cancer and noncancer evaluations. As a first step, this method averages intake for each age category separately and removes cumulative averaging time from the risk equation. This eliminates the two major limitations to the traditional approach described above. Further, to more accurately address the impact of age on intake estimates, the age-adjusted intake equation can be broken down into smaller incremental age-group categories rather than assuming that the exposure factors remain constant during the first six years of life and also during the remaining years of the exposure period. Finally, Monte Carlo simulation can be incorporated into the age-adjusted intake estimates using the approach proposed by Harrington et al. (1995). This study will present age-adjusted intake factors using this alternative approach.