Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
in pollutant concentrations contacted. There is both between- and
within-individual variability in people's activities, which has
implications for the use of time-activity data in exposure assessment.
At one end of the spectrum are aspects of human activity patterns
that tend to be highly regular. For instance, many people tend to
follow daily routines with respect to how long they sleep and the time
they depart for work. In addition, because basic routines are fairly
uniform across individuals, diary data from several studies has shown
that the distribution of time reported in the microenvironments that
comprise the majority of the day (i.e., inside at home and inside at
work/school) exhibit relatively little variation from year to year
within a given study population or from place to place within the USA
(Robinson, 1985; Schwab et al., 1990).
The only large time-activity study done in conjunction with a
continuous monitoring device was the Denver/Washington, DC study of CO
exposures (Akland et al., 1985); this study yielded time-weighted
concentrations in specified microenvironments. Analyses of these
results suggest that variations in activities or locational attributes
(e.g., variations in source strength) that are finer than those
captured by these simple microenvironments explain much of the
variability in exposure. Although less variability in the
concentrations of some other air pollutants may be expected, these
results confirm the concerns raised above regarding the ability to
predict variations in exposure from the time allocation measures
typically collected in diary-type studies.
At the other end of the spectrum with respect to consistency in
activity patterns are aspects of human behaviour that influence the
intensity of contact with contaminated media. By their nature, these
activities are highly variable both across individuals and across time
for a given person. First, physical and demographic characteristics
influence the frequency and duration of activities. For instance, in
the case of dermal exposure it may be hypothesized that contamination
from lying on a surface (e.g., a lawn to which a weedkiller has
recently been applied) will be greater for a heavy person than a
lighter person. Similarly, a child's standing and sitting height, in
addition to crawling activities, mean that its breathing zone is much
closer to the floor than that of an adult, raising the possibility of
dust inhalation. Children also choose play locations that typical
monitoring studies might ignore, such as stairwells and corners.
5.4 Summary
Information on people's activity patterns can be used to identify
the determinants of measured exposures, predict unmeasured or
unmeasurable exposures, assess relationships between exposure and
health status, and identify high risk exposure situations that may be
amenable to public health actions. Some of the main activity patterns
important for assessing exposures by various media that were discussed
in this chapter are summarized in Table 16.
The relative cost of field sampling and laboratory analysis for
environmental and biological measurements highlights the potential
value of time-activity data. Assessments of long-term activity
patterns (e.g., lifetime) may only be feasible using time-activity
questionnaires. Various methods are used to collect information about
human activities, including diaries and questionnaires, mechanical
http://www.inchem.org/documents/ehc/ehc/ehc214.htm
Page 92 of 284
6/1/2007