Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
field would underestimate the amount of total dust collected when
final weights are obtained, which would in turn overestimate the
calculated mass concentration results. Because of water loss or gain,
changes in humidity may also significantly affect the before and after
weights of the samples. These potential sources of error must be
carefully controlled to make the results from preweighed wipe methods
reliable.
A specially designed preweighed wipe sampling method has been
developed to minimize the potential sources of error mentioned above.
This method, known as the Lioy-Weisel-Wainman (LWW) method, was
developed to quantitatively measure the toxicant concentration (mg/g)
and surface loading (mg/m 2 ) of dust on flat surfaces (Lioy et al.,
1993). The sampling device is not made from common materials and is at
this time only available from the research group that developed it.
8.2.2.2 Vacuum methods
Many researchers have collected samples from commercial household
vacuum cleaners, which are often referred to in the refereed
literature as research dust samplers. Some researchers state that they
sampled only the fine dust that settled to the bottom of the bag.
(Kaye et al., 1987; Moffat, 1989; Davies et al., 1990; Thornton et
al., 1990; Jensen, 1992). Other researchers modified their vacuum
cleaners to hold filters (Diemel et al., 1981; Watt et al., 1983).
A settled dust vacuum method, commonly called the DVM, is
constructed from conventional industrial hygiene sampling materials
that are likely to be available to researchers worldwide (Que Hee et
al., 1985). The sampler consists of a common personal air-monitoring
pump, usually operated at 2.5-3.0 litres/min. Sampling areas with this
method are typically 25 cm × 25 cm, and often take more than 5 min to
sample completely. A three-sided template is sometimes used on bare
floors to vacuum dust that has migrated to the walls. Sampling areas
are covered three times with overlapping passes in the horizontal and
vertical directions. Que Hee et al. (1985) state that the sampler was
designed to collect only small dust particles that would most likely
stick to a child's hands, not total lead on a surface. Therefore, the
amount of dust collected by this method from a given surface is
usually less than collected by other methods. This sampler has been
used in numerous studies in the USA and elsewhere, and its use has
provided considerable information linking lead in settled dust to lead
in children (e.g., Bornschein et al., 1985).
Researchers have also used laboratory rotary vane vacuum pumps
connected to the same three-piece filter cassettes as used with the
DVM described above, but with a much higher flow rate. The filter
cassette is often used openface or with a wide diameter nozzle so
sampling areas can be covered in fewer passes than required for the
DVM, thus reducing the time spent collecting samples (Solomon &
Hartford, 1976).
Prpic-Majic et al. (1992) described another vacuum pump sampling
method that used a prescreen at its nozzle entrance to prevent coarse
particles and small objects from being collected on the membrane
filter that served as the sampling surface. Total dust measurement was
obtained from the dust particles that reached the membrane filter.
There was no mention of potential loss of fine dust trapped in the
prescreen, especially after it was loaded with fibres and debris.
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