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Modifications of BME Analysis 183

d[-]/dt, which takes into consideration exposure variations in space/time
as well as variabilities linked to the biological and physiological characteristics
of the individual. The output of the pollutokinetic model is a burden map
B for representative receptors (i.e., receptors sharing the same biological and
physiological characteristics). Burden provides a measure of the fraction of
the pollutant that reaches the target organs and tissues of a receptor and is
capable of affecting them.
• The burden map is then used in combination with an empirical burden-
response curve ^fil'] in order to obtain predictive maps of the exposure's
impact H on human health.
• The health effect H is, finally, substituted into a response-damage model
/[ •] to derive health damage indicators HDI (see, e.g., Eq. 9.4 above). Natu-
rally, each step of the approach above incorporates knowledge from a variety of
sources, including exposure monitoring, biologic monitoring, and health dam-
age surveillance. The example below is concerned with the human-exposure
assessment of ozone concentrations over eastern U.S.
EXAMPLE 9.13: The ozone burden maps of Figure 9.6 are produced from the
solution of a first-order pollutokinetic model (Christakos and Hristopulos, 1998;
see also Example 1.14, p. 18) and are associated with a class of representative
receptors. The pollutokinetic model provides the ozone burden on a receptor at
each space/time point p. This model is a function of an absorption rate, a re-
moval rate constant, and the ozone exposure maps of Figure 9.1. Studies have
shown that ozone burden and receptor response are correlated, and a knowl-
edge of ozone burden is prerequisite to an unambiguous evaluation of health
effects. Using the appropriate burden-response curve O-BR[~] and response-
damage model /[ • ], the burden map of Figure 9.6 leads to HDI maps for any
receptor that belongs to a specific cohort (i.e., a group of individuals with sim-
ilar time or activity profiles). Such is the health damage indicator map plotted
in Figure 1.6 on p. 8 (in which case the HDI expressed no. of representative
2
receptors affected/km ). While the burden maps represent the actual expo-
sure an individual representative receptor may receive in space/time, the HDI
maps offer an assessment of the absolute or relative impact of exposure on the
population as a whole. In other words, the HDI maps possess a social policy
dimension that burden maps do not.

Associations between environmental exposure
and health effect

Human-exposure analysis generally involves both physical and epidemiologic
variables, which means that techniques capable of integrating knowledge from
both the physical and epidemiologic sciences are needed. The application of
the random field model in human-exposure analysis involves some modeling
decisions. A common modeling decision is the spatiotemporal continuity of
the exposure and health-effect variables. While most environmental exposures