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September 1999 Introduction and Questions for Review

Introduction and Questions for Review for the Session:
Review of an Aggregate Exposure Assessment Tool

Presented by:
Carol Christensen
Elizabeth Doyle, Ph.D.
Francis B. Suhre, M.S.

United States Environmental Protection Agency
Office of Pesticide Programs
401 M St., S.W.
Washington, D.C. 20460

To the:

FIFRA Scientific Advisory Panel
September 1999


The Food Quality Protection Act of 1996 significantly changed the way EPA regulates pesticides. Among the regulatory changes is the requirement that when making a determination of safety for a pesticide, the Agency must consider aggregate exposure (i.e., exposure from residential, dietary and tap water sources) to the pesticide and the potential for cumulative toxicity from exposure to other substances that are toxic by a mechanism common with that of the pesticide. As part of its implementation of this regulatory requirement, the Agency has committed resources to developing policy documents and risk assessment models that will enable the Agency to estimate aggregate exposure and cumulative risk. EPA, USDA, and private organizations are participating in a co-operative agreement with Hampshire Research Institute (HRI) to develop a software package (LifeLineTM ) that will enable estimation of exposure and risk from multiple pathways and routes of exposure. HRI is a non-profit organization and the co-operative agreement stipulates that the LifeLineTM software (including all models, databases, and algorithms contained within) will be made available to the public at a nominal cost. EPA and USDA participation in this cooperative agreement should not be construed as an endorsement of the LifeLineTM model at the exclusion of all other models. EPA encourages all efforts to develop models for performing aggregate and cumulative risk assessments. All models used to estimate aggregate and cumulative risk in support of pesticide tolerances will be judged on their own merits based on risk assessment principles independently developed by the Agency and available to all interested parties.

The initial version of the LifeLineTM software estimates aggregate exposure to pesticides, and calculates distribution of dose rates for exposure periods ranging from one day to a lifetime. This background document presents a brief description of the conceptual basis of the initial version of the LifeLineTM software, and the modeling approaches employed by the software. Emphasis is placed on key scientific and technical issues in modeling aggregate exposure. The purpose of the session is to describe to the Scientific Advisory Panel the concepts and modeling approaches used by the LifeLineTM software to calculate aggregate exposure, and to solicit advice from the Panel at this stage of development of the software. Specifically, OPP would like the Panel to answer the following questions:


  1. The LifeLineTM Model combines information on daily activity and dietary patterns from well known surveys to evaluate daily exposures to an individual. And uses transition rules to specify how model input values are initially selected and when and how input values change over time.

    Does the panel agree that the use of multiple databases (with appropriate transition rules) is the only currently feasible approach to modeling aggregate exposures?

    Does the panel agree that aggregation of exposures requires a focus on demographic, spatial, and temporal factors affecting the exposed individual, rather than a combination of source-based exposure models?

    Does the panel view Microexposure Event Analysis with Monte Carlo techniques for incorporating probabilistic analysis as a viable foundation for a model of aggregate exposure?

  2. Does the Panel have any practical suggestions on how to interpret and report results of aggregate daily exposure estimates to individuals over their lifetime, e.g., to what extent should the exposure estimate be customized to fit the toxicology of each compound?

  3. Can the panel identify and/or prioritize key data gaps with respect to modeling aggregate exposure to pesticides?

  4. Can the Panel suggest additional surveys and/or data sources for use in the LifeLineTM model (or other models of this type)?
Scientific Advisory Panel: September 1999 Meeting

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