Human Exposure Pathways - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 497

dilution will be substantial due to changing weather conditions. There may also be
correlations between the parameters, for example hot dry periods give dryer soils
with larger releases and often lower wind speeds. There may also be a correlation
with the risk of exposure as people are more likely to stay outdoors during such
periods.
Despite these limitations the models are likely to overpredict exposure in most
situations if conservative data on soil moisture and wind speeds are used. The
available models are therefore judged to be fit for the purposes of identifying when
inhalation of outdoor air may be an important exposure pathway, i.e., in first tier
Risk Assessment.
11.5.7 Verification and Validation
The models used for atmospheric dilution are all, to some extent, based on empir-
ical data and can be expected to give reasonable approximations for the situations
they are derived for, generally dispersion over relatively flat surfaces. The mod-
els are simplifications of more complex dispersion models that have been tested
and validated. However, when extrapolating to more complex situations (e.g., for-
est or built-up areas) their ability to predict dilution will be more limited. In cases
when this exposure pathway is judged to be critical, actual measurements of air
concentrations can be made in site-specific Risk Assessments. However, as actual
concentrations may vary considerably depending on the meteorological conditions,
measurements over extended periods may be needed.
Measurements of outdoor air samples may also be a part of a general Risk
Assessment for sites with volatile contaminants. A comparison of measurements
in soil pore air, indoor air and outdoor air is recommended to get a better picture of
the origin of the air contamination and for assessing the risks.
11.6 Exposure Through Inhalation of Dust
This exposure pathway relates to the inhalation of dust originating from contami-
nated soils. Dust inhalation can occur both indoors and outdoors, and both adults
and children may be exposed. Exposure through ingestion of dust is described in
Bierkens et al. ( Chapter 6 of this topic).
The exposure pathway through inhalation of dust considers long-term exposure
levels, when dust arises principally from wind action on the soil surface. Short-
term events with increased dust concentrations in air, for example when soils are
mechanically disturbed during digging, are not considered in this chapter, though
they may need to be considered when evaluating short-term or acute health risks.
There is a large amount of evidence that the contaminant concentration in dust
is related to the total exposure to contaminants, see for example Thornton et al.
( 1990 ). Some, but not all, of the exposure to contaminated dusts is via the inhalation
pathway.