Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
In addition to time allocation measures and microenvironmental
parameters, information on the intensity of contact is needed to
assess exposure. Here the focus is on micro-level activities that
affect the rate of contact with the contaminated media while the
person is in a certain microenvironment (e.g., outdoors at home) and
performing a specific activity (e.g., cleaning). The potential for
dermal contact depends upon the surface area of exposed skin, thus
clothing type and fabric consistency as well as the size of the
person, whether the individual is sitting, crawling, kneeling or using
their hands on the contaminated surface, or otherwise handling the
contaminant. In addition, exposure for the given event depends upon
the duration and frequency of each contact between the exposed skin
and the contaminated media; e.g., 50 1-min contacts between the
person's hand and the floor while cleaning. As described in Chapter 7,
dietary factors, including the type of foods that are consumed and the
amount consumed per time period of interest, are the most obvious.
Concern also has been raised about the potential for contamination of
foods from contact with surfaces during storage, preparation and
consumption (Berry, 1992, Freeman et al., 1997). Hand-mouth and
object-mouth contact, although difficult to measure, may be one of the
most important routes of exposure to contaminants such as pesticides
and lead that reside in house dust, especially in children (Charney et
al., 1980; Rabinowitz & Bellinger, 1988; Davies et al., 1990). For
pollutants for which inhalation is the primary route of exposure, the
intensity of contact is influenced by one's level of exertion (often
referred to as "activity level"). Breathing rate or heart rate is
needed to predict dose (the amount of contaminant that enters the
body), thereby producing a more accurate estimate of the resulting
health effects.
Finally, depending on the purpose of the exposure assessment, the
required temporal resolution of the time-activity data may vary
substantially. Whereas short-term time-activity patterns may be
important for acute exposures, long-term average time-activity
patterns may be more relevant in other circumstances. If long-term
exposure is of major interest, e.g., over years or lifetime,
residential history is an important information to assign respective
ambient monitor data for the entire period of interest (Künzli et al.,
1996).
5.2.2 Surrogates of time-activity patterns
For many exposures surrogates of time-activity patterns may be
developed on the basis of generalizations about the activities of
people at a particular time, who live in a specific geographic
location or who share a specific set of living conditions. Usually the
most important time-activity surrogate is age group. Some activities
that are useful for predicting exposure to air pollutants, such as
distance and timing of travel or duration of work and its locations,
also show systematic differences in their frequency and duration by
demographic characteristics. For instance, Schwab et al. (1990)
documents how time in the kitchen, which influences exposure to
combustion products, is greater among women in the USA than among men,
even after adjusting for whether the woman works outside the home;
likewise, men spend more time in transit, regardless of their age or
employment status. It is likely that the frequency of contact with a
wide variety of toxins differs across groups defined by gender and
age, owing to traditional divisions of labour in many cultures.
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