Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
measurements of toxicant levels in settled dust.
Roberts et al. (1991) documented total dust recoveries that
ranged from greater than 90% by weight on a smooth painted surface to
about 30% on a carpet. Chavalitnitikul & Levin (1984) compared several
types of wipe sampling methods. They conducted a laboratory wipe
sampling experiment with wipe materials on a smooth surface (Formica)
and a rough surface (plywood). The study examined different wipe
materials, such as Whatman filters, paper towels and adhesives --
paper labels, adhesive cloth and dermal adhesive. The researchers
determined that, on smooth surfaces, all techniques were comparable,
with about 85-90% recovery with carefully prescribed protocols. On
plywood, however, recoveries dropped to less than 43%. They also noted
that the Whatman filters fell apart on the rough surface. Other
sampling method characterization studies document similar differences
(US EPA, 1995a,b).
Three commonly cited methods used to sample lead in settled dust
(the DVM, BRM, and HUD methods) may collect very different amounts of
total dust from the same surface (Lanphear et al., 1995). Assuming
that a smooth hard surface is sampled, the difference in collection
efficiency between the DVM and the other two methods may be greater
than a factor of 10, with the DVM consistently collecting less dust
than the BRM and HUD methods. The latter two methods would probably
collect similar amounts of dust on a smooth hard surface.
Since contaminant loading is directly related to total dust
collected from the sampled surface, the DVM sampler will consistently
measure lower contaminant loading values on hard surfaces than the BRM
or HUD methods. This does not imply that a high collection efficiency
is better than a low efficiency. An argument in favour of the DVM's
low collection efficiency is that it measures the more biologically
active fraction of leaded dust available to a child (Que Hee et al.,
1985). However, results from the only study to use all three methods
side by side in children's homes suggest that the BRM and HUD methods
correlate slightly better with children's blood lead levels than the
DVM method (Lanphear et al., 1995). The same study showed that the BRM
collects much more dust from carpeted surfaces than the DVM or HUD
methods. The point to note is that lead loading measurements on the
same surface differ among sampling methods. Further research is needed
to determine the importance of collection efficiency for exposure
assessment studies.
As with contaminant loading, differences in collection efficiency
on different surface types and among sampling methods may affect
measurements of contaminant concentration. Differences in the relative
recovery of contaminant-containing dust and non-contaminant-containing
dust can result in different contaminant concentration measurements.
Theoretically, however, concentration measurements are likely to vary
less among methods than are loading measurements. Results from the
Lanphear study, which collected hundreds of side-by-side lead dust
samples with the DVM and BRM methods, are consistent with this theory.
Geometric mean lead levels and the corresponding standard deviations
suggest that, on average, side-by-side lead loading measurements
differ more between the two sampling methods than do the lead
concentration measurements (Lanphear et al., 1995).
8.4 Sampling strategies
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