Exposure factors in risk assessment
Filipsson, M., Bergbäck, B., Öberg, T.
Report 5802
Swedish Environmental Protection Agency, 2008.
 

Abstract
Exposure is defined as the contact between a chemical, physical or biological agent and the outer boundary of an organism. Human exposure to chemicals in the environment is controlled not only by the occurrence of the pollutant, but also by behavior, physiological characteristics and different external factors. The quantifiable statistics used to describe this information are called exposure factors.

The U.S. Exposure Factors Handbook is perhaps the most complete compilation of such data, but similar attempts have also been made in Europe. However, human behavior, physiological characteristics and environmental factors differ between countries. It is therefore of value to also compile country-specific data for Sweden. A compilation could contribute towards the standardization of risk assessments.

The exposure factors presented here cover the above mentioned areas and a substantial portion of them are similar to those covered by the international compilations. The selection and presentation is, however, to a large extent determined by the availability of data. In practice this means that for some factors we lack data on variability (natural variation) and uncertainty. These limitations in the available data are particularly pronounced with regard to the consumption of tap water and homegrown vegetables, and time-use patterns.

However, there is a substantial amount of data available for physiological characteristics like body weight and skin surface area as well as for the general food consumption. These exposure factors have been characterized by statistical parameters like the mean, standard deviation, kurtosis, and skewness. Estimated uncertainty intervals are also given for these parameters. Percentiles are useful alternatives to present variability and these estimates are also presented together with the accompanying uncertainty intervals.

Other exposure factors that are included in this report are; the age distribution of the population, moving patterns, residential building characteristics, contact with soil and dust, and soil properties. Apart from the tabulated values, references are also given to the primary data sources to facilitate for anyone interested to make more in-depth evaluations.

The data collected is compared to the parameter settings suggested in the draft version of the Swedish exposure model for estimating guideline values. This comparison shows that the values selected sometimes correspond to a central or best estimate, often a conservative estimate, and sometimes a very conservative estimate. It is not possible from this comparison to draw firm conclusions regarding the impact on the final risk assessment or risk management decisions.

The authors hope that this compilation of data on exposure factors will facilitate and accelerate the transition to risk assessment methods that permit evaluation and quantitative estimates of variability and uncertainty.

A Swedish version of this report is available for download as a PDF file (1320 kb)