Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
* lifetime residential history
* time spent outdoors in different age periods
* time spent in outdoor physical activities in each lifetime
residence.
To test the reliability of the retrospective assessment, a
test-retest design was chosen. The study included a convenience sample
of 168 non-smoking UC Berkeley college freshmen who had to be lifetime
California (USA) residents (San Francisco Bay Area or Los Angeles
Basin). It was shown that retrospective lifetime residential history
is highly reliable (Künzli et al., 1996). Using pollution monitor
data, averaged over lifetime across all respective residential
locations, may in fact improve the health effects assessment.,
compared with mere reliance on the ambient monitor data from the last
or actual residence only (Künzli et al., 1997a). Three retrospective
approaches to assess outdoor physical activity patterns have been
tested and two methods gave rather reliable overall estimates for time
spent in outdoor heavy or moderate activities, during summer. For the
activity table format (see Fig. 19), only 13% of the total variance
was attributed to reporting variability (test-retest). The
categorization into heavy and moderate activities based on published
data regarding energy expenditure (Ainsworth et al., 1993). Ambient
long-term mean daytime concentrations of ozone were weighted by the
duration and exertion level of the reported long-term average outdoor
physical activity. This "effective exposure", therefore, may be
considered a surrogate measure of ozone dose. Although the study had
some promising results regarding the feasibility of retrospectively
assessing exposure relevant surrogates over long periods of time,
validity of the time-activity data cannot be directly assessed.
Neither could the study answer the open question of whether
time-activity data may be needed in the assessment of long-term
effects of air pollution (Künzli et al., 1997a).
12.3.5 Combined exposure studies
The WHO, in a number of studies termed the Global Environmental
Monitoring System (GEMS), sponsored several studies of combustion
related air pollutants. GEMS, now renamed as the Air Management
Information System (AMIS), continues to coordinate the gathering of
data on levels of ambient air pollution in cities around the world.
GEMS also conducted a series of exposure studies to examine the
assumptions that fixed ambient monitoring accurately reflected
personal exposures. Studies were carried out in Toronto, Canada (WHO,
1982b); Beijing, China (WHO, 1985c); Zagreb, Croatia (WHO, 1982a); and
Bombay, India (WHO, 1984).
Through the GEMS, WHO and UNEP later formed the HEAL project. The
goal was to improve exposure monitoring internationally, using direct
measurements of human exposure with activity information, and provide
guidelines for techniques that could be used uniformly around the
world. Another goal was to increase the accuracy of risk assessment
studies with the goal of better protection of human health.
A study in Kenya was carried out to attempt to determine the risk
of acute respiratory infection by quantifying indoor air pollution
levels caused by home combustion sources (WHO, 1987). The study was
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