Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
Activity pattern data that may be useful in assessing exposure
can be divided into three categories:
* the distribution of time among activities, referred to in this
document as time allocation parameters
* the factors that influence the degree of media contamination in the
activities or locations of interest, referred to in this document
as microenvironmental parameters
* the intensity of contact while engaging in each activity.
5.2.1.1 Time allocation parameters
Time allocation parameters include the amount of time spent in a
given activity, the time of day, week and year of contact, and the
expected frequency with which the person or population engages in the
activity. The relevant spatial resolution for describing time-use
patterns, thus grouping activities for exposure assessment, depends
upon the characteristics of the pollutant, the media, the location and
the emission source(s).
The concept of microenvironment has been used to define an area
across which the concentration of an air pollutant is assumed to be
homogeneous (Duan, 1982). The most basic division of microenvironments
is whether a person is indoors or outdoors, although more refinement
is necessary for many exposure assessments. Time spent indoors is
especially important with regard to pollutants which depend on indoor
sources. Other typical microenvironments of interest in studying air
pollution are home, work or school, and modes of transportation.
Depending on the characteristics of the media and the pollutant,
a description of the actual activity may also be required to
understand exposure. General activity categories such as "socializing"
and "recreation" are less important than knowing whether the
participant is involved in specific activities that lead to contact
with environmental media in addition to or other than air. For
instance, swimming leads to water contact, and farming and gardening
lead to soil contact.
5.2.1.2 Microenvironment parameters
The distinction between people's activities and the pollutant
concentration in a microenvironment is not always clear. The use of
household appliances and consumer products that emit environmental
contaminants and/or influence pollutant fate and transport affect
microenvironmental concentrations. Thus, information on the
microenvironmental parameters, i.e., the factors affecting the
concentration in a given location, have also been included under the
rubric of time-activity data. Important microenvironmental parameters
for air pollution exposure assessment include building structure and
household characteristics (e.g., the type of heating and cooking fuel
used, the presence of parking garages and air conditioning units),
information on proximity to specific sources (e.g., heavy traffic,
cigarette smoking, cooking, solvent, pesticides), timing of emissions
for each source, indoor/outdoor air exchange rates and meteorological
and topographic factors.
5.2.1.3 Intensity of contact
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6/1/2007