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this range are appropriate for the assessment of exposure to soil contaminants via
house dusts.
11.6.3.4 Fraction of Dust Which is Respirable
The dust concentration in air which is specified in the first approach is usually based
on measurements of particle concentrations in air. Measurements are often made of
the concentration of the particle fraction PM10, i.e., particles with the same aero-
dynamic properties as a sphere with diameter up to 10
m. The PM10 fraction is
a measure of particles that can pass into the lungs. In some cases, a finer fraction,
PM2.5 is also measured. This fraction is equivalent to the fine particles which can
reach the alveoli. The PM2.5 fraction is usually about 50-90% of the PM10 fraction,
with a mean of 73% (Putaud et al. 2003 ).
In the Dutch CSOIL model, the retention of particles reaching the lungs is
assumed to be 75% for both adults and children (Brand et al. 2007 ; Van den Berg
1991 / 1994 / 1995 ), which is equivalent to the fraction of PM2.5 particles in the PM10
size fraction. Contaminants present in PM10 particles may also have adverse effects,
even if they do not reach the alveoli.
μ
11.6.3.5 Contamination in Dust
Contamination levels are usually higher in fine particles than in soil in average.
However, these relationships vary depending on soil type and the origin of the con-
tamination (Bright et al. 2006 ). Normally, soil investigations are not performed on
extremely fine particles in the soils. Young et al. ( 2001 ) measured lead concentra-
tions in soils and dust (PM10) and found that the concentration in the PM10 fraction
was up to 8 times higher than in the soil on average. This is consistent with mea-
surement of fine particle materials found on samples from Swedish wood treatment
plants and glass works. In the Swedish model an enrichment factor of 5 is used
for calculating the generic soil guidelines. In the German UMS model an enrich-
ment factor of 4 is used for inorganic contaminants and a factor of 8 for organic
contaminants (UMS 1997 ).
11.6.4 Inhaled Volume
Assessments of the risk from exposure through inhalation of contaminated soil parti-
cles is usually based on estimates of the volume of air inhaled over a longer period of
time. The volume of air inhaled varies with physical characteristics, such as gender,
age, body size and fitness as well as on work rate and activity level. The inhalation
rate shows large short-term variations, depending on activity levels. The assumed
volume of air inhaled over a longer period of time takes into account the short term
variations.
The volume of air which is inhaled per day is assumed to be 20 m 3 /d for adults
in a number of Risk Assessment models, e.g., the Dutch model (CSOIL), and the
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