Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
6.6.1 Variability
Diverse sources of environmental contaminants lead to various
contaminated media (e.g., soil, dust, water, air, food), which in turn
result in a multitude of routes and pathways of human exposure. For a
given contaminant, the magnitude and relative contribution of each
exposure route and pathway may vary among geographic regions and over
time. In addition, differences in activities among individuals lead to
disparate rates of contact with contaminated media. In aggregate,
these factors result in varying levels of personal exposure to a
particular contaminant among the members of a population, i.e., a
distribution of exposures.
Exposure model inputs expressed as distributions can be used to
model inter-individual variability of exposures. Examples of
probabilistic human exposure models that explicitly consider
variability of exposure among individuals may be found in Finley et
al. (1994a) and MacIntosh et al. (1995, 1996). Variable parameters are
those that are stochastic with respect to the reference unit of the
assessment question (IAEA, 1989) and are described by probability
distributions that reflect their intrinsic randomness. Exposure
concentrations may vary between individuals owing to the influence of
personal activities (e.g., cigarette smoking contributions to indoor
respirable particulate levels). Such differences represent true
variability of factors that affect exposure among individuals and can
determine the relative position of an individual or type of individual
within the distribution of exposures for the population.
6.6.2 Uncertainty
http://www.inchem.org/documents/ehc/ehc/ehc214.htm
Page 105 of 284
6/1/2007