Exposure factors: How to characterize the data?
Öberg, T., Filipsson M, Bergbäck B.
Posterpresentation vid the Annual
Meeting of the Society for Risk Analysis, San Antonio, Texas, 9-12 december
2007
Abstract
The exposure to chemicals is, apart from level of contamination and release,
controlled by human behavior, physiological characteristics and environmental
factors. The quantifiable statistics used to describe this information are
called exposure factors, and are instrumental for any risk assessment. Evaluated
data on exposure factors are often accessed from the literature or compilations
such as the Exposure Factors Handbook from the U.S. EPA. However, these factors
may differ between countries and regions, and we have recently collected and
evaluated a similar range of country-specific data from Sweden. Our compilation
includes the population age distribution, moving patterns, body weights, skin
surface areas, activity patterns, dietary intakes and home produced items,
drinking water consumption and private wells, residential building
characteristics, and soil parameters. One problem that we faced in this study
was the choice on how to best describe and present the available data. Some
examples from previous compilations are arithmetic means, standard deviations,
percentiles, and specific parametric distributions. We have in earlier work
highlighted the uncertainty in choosing distributions, and the overconfidence
that is conveyed in assigning single numbers or specific distributions. In the
present study, we have instead chosen to estimate and present both parameters (mean,
standard deviation, kurtosis, and skewness) and multiple percentiles (1-99%)
with uncertainty ranges (95% confidence intervals). These uncertainty
estimations were performed by resampling (bootstrapping) from the primary data.
This tabulated compilation can serve as a basis for estimating exposure with
several different approaches; deterministic, intervals, Monte Carlo-simulations,
or probability bounds analysis. In this poster we will exemplify and discuss how
the compilation and presentation of data on exposure factors affect the
methodological choices and outcome of an exposure assessment.
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