Exposure Through Soil and Dust Ingestion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 281

estimate soil and dust ingestion rates. Analysis of the available data suggest that
average soil/dust ingestion rates for children are not higher than 100 mg/d and may
well be lower, down to 50 mg/d. However, the data do not provide a better estimate
for a specific site than this more or less safe 100 mg/d, due to the uncertainties in soil
and dust contribution and the bioavailability in soil and dust. The data also do not
provide an estimate for the contribution of soil and dust, nor for the soil ingestion
rates for adults.
Another approach used by Van Holderbeke et al. ( 2008 ) is trying to establish
an empirical relation between contaminant concentrations in the environment and
Biomonitoring data. From their analysis Van Holderbeke et al. ( 2008 ) conclude
that typical soil ingestion rate values for children are below 50 mg/d, both for soil
and dust. The obtained dust and soil ingestion values range from 20 to 70 mg/d.
Insufficient data exist to estimate soil ingestion values for adults using this approach.
The majority of studies aims to estimate “normal” unintentional soil and dust
ingestion by children and adults. However, short-term or longer-term ingestion of
larger amounts of soil (g/day) can occur. Due to the limited data, it is difficult
to quantify pica ingestion rates. High-end estimates from tracer studies or survey
response information, however, can support the estimations.
6.2.4 Soil Ingestion Rates Recommended by International
Regulatory Bodies
The available studies are used by several international regulatory bodies to rec-
ommend or impose soil and dust ingestion rates for use in Human Health Risk
Assessments.
An overview of soil ingestion values recommended by international regulatory
bodies and ingestion values used in different exposure models (Swartjes 2002 ), is
given in Table 6.9 . The values used in exposure models are often at the high end
of the available ranges. This could be due to the fact that they are based on older
studies, but as well on the fact that these models are often screening models and
a high level of protection is envisaged. From the information available, it is not
always clear whether the values relate to soil ingestion or to soil and dust ingestion
combined. In most models, however, the value relates to soil ingestion, only.
6.2.5 Representativeness of Soil and Dust Ingestion Rates
The estimation of appropriate site-specific soil and dust ingestion rates remains dif-
ficult. Tracer element studies were mostly carried out over a relatively short time
period, thus estimated intake rates may not reflect long-term patterns. In this con-
text DEFRA ( 2006 ) comments “that current high-end exposures (derived from the
short two-week studies) overpredict typical longer-term exposure because they fail
to account for variability in the underlying data which when extrapolated to the
longer term leads to 'regression to the mean' ”.