Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
(direction, velocity, and turbulence) and thermal properties
(stability) are the most important. A number of models are available
for estimation of ambient concentrations of pollutants. Most of them
are founded on the Gaussian air dispersion model, an introduction to
which may be found in Wilson & Spengler (1996). Two of the seminal
works in this field are Pasquill (1961) and Gifford & Hanna (1973).
Another area of air quality models focuses on determining the
sources of pollutants in outdoor air. As discussed in Chapter 2,
information on sources of exposure is important for evaluating
alternative strategies for managing risk. These models are commonly
used for apportioning concentrations of airborne particulate matter
among its various sources (e.g., coal-fired power plants,
gasoline-powered vehicles and diesel-powered vehicles). In such source
apportionment models, profiles of element concentrations in
particulate matter emitted from different sources are combined with
sophisticated statistical methods (e.g., principal component or factor
analysis) to estimate the relative abundance of particles from each
source type. Glover et al. (1991) and Daisey et al. (1986) provide a
good introduction to source apportionment models for particulate
matter, while Edgerton & Shah (1991) describe a source apportionment
model for VOCs.
Several approaches have been used to estimate expected indoor air
pollution concentrations (for reviews see Cooke, 1991; WHO, 1997b).
These include deterministic models based on a pollutant mass balance
around a particular indoor air volume; a variety of empirical
approaches based on statistical evaluation of test data and (usually)
a least squares regression analysis; or a combination of both
approaches, empirically fitting the parameters of a deterministic
model with values statistically derived from experimental measurements
(see Chapter 4). All three approaches have advantages and weaknesses.
The deterministic model provides more generality in its application,
but the results lack accuracy and precision. Deterministic models
include single- and multiple-compartment models. The empirical models,
when applied within the range of measured conditions for which they
were fitted, provide more accurate information. An example of an
empirical model for indoor concentrations of respirable particulate
matter may be found in Chapter 12. Often the compartment of the indoor
air mass balance models that is most difficult to represent is the
role of indoor surfaces as sources or sinks for contaminants. This is
an important field of inquiry with respect to inhalation exposures to
ozone and VOCs (Reiss et al., 1995).
6.4.2 Potable water
Exposure to contaminants in water may occur via the ingestion,
dermal absorption and inhalation routes. Ingestion of water primarily
occurs via two pathways: direct ingestion via drinking or cooking and
intrinsic water intake (i.e., the water intrinsic in foods prior to
preparation). It is important to consider both routes. Drinking-water
ingestion rates have also been shown to vary according to cultural
differences and can be an important source of uncertainty about
chemical exposure when extrapolating results of epidemiological
studies from one culture to another (e.g., Mushak & Crocetti, 1995).
Lognormal distributions of drinking-water ingestion rates for
individuals comprising various age groups in the USA (Table 18) are
available in the literature (Roseberry & Burmaster, 1992). Additional
information on drinking and cooking water as exposure media may be
found in Chapter 7.
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