Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
Choosing an appropriate sampling method is an important part of
designing a study to measure toxicants in house dust. However, it is
only part of designing a sampling strategy. The sampling method
specifies how to collect settled dust, whereas the sampling strategy
specifies the process of sampling. Several of the questions that need
to be answered when developing a sampling strategy are:
* What age group is targeted by the study?
* Which surfaces and substrates should be sampled?
* When and how should sampling take place?
* Should a composite sample be created?
* How will the samples be analysed?
As noted in the first section of this chapter, young children who
play on floors are likely to have higher exposure to settled dust than
adults. Children may be also routinely exposed to dust in areas of a
residence that adults do not contact. Different sampling strategies
may be appropriate for different age groups.
The potential effect of the surface type and substrate on dust
collection should be factored into the strategy because dust
collection efficiencies from different surface types can vary greatly.
For example, toxicant loading or concentration measurements may
correlate relatively well with biological measurements when dust is
collected on hard floors or on carpets. However, if the person's
relative exposure to dust from floors versus carpets differs from the
sampling method's relative collection efficiency on these surfaces,
the relationship between biological and settled dust measurements will
be different for each surface. Similar differences between a human's
exposure and a sampling method's collection efficiency may be found
between components within a room, such as between a windowsill and a
floor.
Another issue to note is that the sources of dust, its temporal
and spatial variability, and accessibility to humans, especially to
young children, may vary greatly from person to person, room to room
and house to house. However, little research has been done to examine
this variability across space and time. Interpretations of house dust
sample results may, therefore, be affected by this variation in
addition to the variation introduced by the choice of sampling method.
Short-term changes in a person's environment before sampling, possibly
influenced by sporadic house cleaning practices or by a person who has
just returned home from vacation, may offset the dust/biological
relationships owing to the timing of sample collection.
The toxicant levels in settled dust to which a person is exposed
may be thought of as a weighted average across the areas where the
person has dust contact, with weights roughly proportional to the time
a person spends in different areas. From a sampling perspective, the
average toxicant level to which a person is potentially exposed may be
estimated by collecting many individual samples of settled dust for
separate analysis and combining the results by calculating a weighted
average after analysis. Or, field composite samples can be collected
before laboratory analysis by collecting and physically combining two
or more settled dust samples from each of several areas in a dwelling.
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6/1/2007