Human Exposure Pathways - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 505

Meteorological conditions, especially the intensity and frequency of wind, affect
both the emission and dispersion of particulate matter. The amount and distribution
of rainfall is also important, as rainfall directly affects the dust content of the air as
well as determining the soil moisture content, which is important for dust genera-
tion. Surface erosion by water may also be important in that the redistribution of the
fine-fraction of soil materials may affect subsequent wind erosion.
Chemical and physical properties of the soil affect the bioavailability of contam-
inants in soil particles for uptake in the lungs.
11.6.6 Influence of Human Behaviour
Important factors are occupancy on the contaminated site and time spent indoors
versus outdoors. Since human activity will vary considerably, normally, standard-
ised values are used in order to obtain conservative estimates of the exposure.
The type of activity on the site will also affect exposure, e.g., extensive gardening
work or sport activities may increase the concentrations of contaminated dust in the
air and also increase the inhalation rate.
11.6.7 Reliability and Limitations
As the specified dust concentrations in air are based on measurements, the values
should be of the correct order of magnitude. However, the dust concentration in air
varies with time over a large interval and is largely incident-steered, for example
dry windy conditions with high rates of dust generation, or wet, still conditions
with low rates of dust generation. Therefore, it is difficult to derive average dust
concentrations from measurements.
A further uncertainty is the fraction of respirable dust which is contaminated,
which depends on the dilution of dust from the contaminated area after suspen-
sion from the soil surface with other dust. Local conditions are important for this
parameter, particularly downstream of the site of dust generation to the place where
exposure takes place.
The concentration of contaminants in the respirable fraction of dust is an impor-
tant uncertainty in the model. This parameter has a direct effect on the calculated
exposure for contaminants, but there is relatively little information on the rela-
tionship between the contaminant concentration in the fine fraction of dust and
the contaminant concentration in the soil as a whole, or in different particle-size
fractions of the soil.
When no reference air concentration (RfC value) is available for a contaminant,
data on the oral toxicity of the contaminants may be extrapolated to the inhalation
pathway in some cases in order to assess the risks from the inhalation pathway. This
extrapolation gives rise to uncertainties associated with the differences in uptake,
metabolism and toxicity between the two exposure pathways. These uncertainties
have not been quantified, but may be important, particularly for contaminants which
have a direct effect on the function of the lungs.