Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
measurement programmes. The challenge is to develop exposure databases
and models that allow maximum extrapolation from minimum measurements
or costs. Such models need to reflect the structures of the physical
environments and human activities of interest in exposure assessment.
In addition to the essentially physical (deterministic) exposure
models, physical-stochastic (probabilistic) and statistical
(regression) models are used. The former type is particularly useful
for population exposure distribution assessments, the latter requires
less supporting information but cannot be used for extrapolation
outside of the study population. Exposure models are discussed in
detail in Chapter 6.
3.5.2.3 Questionnaires as an indirect approach to assessing exposure
Questionnaires typically provide qualitative, often
retrospective, information. They may be used to categorize respondents
into two or more groups with respect to potential exposure (e.g.,
exposed or unexposed, high exposure or low exposure) and are commonly
used for this purpose in epidemiological studies. As noted earlier,
questionnaires may also be used to aid in interpretation of personal
and environmental monitoring results. A priori knowledge of the
determinants of the exposure of interest is required to develop
effective questionnaires relevant to exposure assessment (e.g., high
formaldehyde exposure for workers in a certain industry, or high
carbon monoxide and lead exposure for traffic policemen, bus drivers
and road toll collectors). Most often the information necessary to
develop questionnaires is obtained from previous studies that utilized
environmental measurements, models or biological monitoring to measure
exposure. In many cases, basic socio-demographic questionnaire data
may provide extremely valuable information as they might be strong
surrogates of exposure. It has long been known that rates of disease
differ in social strata. In addition, it is readily apparent in many
countries that the physical characteristics of one's residential
environment are linked to income level. For lead exposure, differences
in exposure among groups defined by income and social status have been
demonstrated. Phoon et al. (1990) have shown that diet and job
category were the most important predictors of blood lead levels among
men in Singapore. In the USA, elevated blood lead levels have been
linked to children who live in older, inner-city housing, particularly
properties in poor repair (MMWR, 1997). Homes in these areas are more
likely to have been painted with leaded paints (pre-1950) and have
higher concentrations of lead in soil owing to deposition of emissions
from leaded gasoline prior to the 1970s. Haan et al. (1987) found an
increased risk of death among people living in a poverty area in the
USA as compared to an adjacent non-poverty area, even after adjusting
for differences in smoking, race, baseline health status, access to
medical care, employment status, marital status, depression, sleep
patterns and body mass index. These results suggest that sociophysical
aspects of the environment, such as increased exposure to contaminants
from poorer housing, may be important contributors to the association
between socio-economic status and excess death rates.
3.6 Summary
A good study design is the most important element of any exposure
assessment. It includes the purpose and objectives of the
investigation as well as relevant methods for sampling, measurements,
statistical analyses, and quality assurance. Methods for
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