Exposure Through Soil and Dust Ingestion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 280

Table 6.8 Statistical descriptors of the distributions for soil ingestion for adults obtained using
bootstrapping (mg/d)

Distribution of arithmetic
mean

Distribution of 95th
percentile Soil (outdoor and tracked-in)

Arithmetic mean 46 81

Standard Deviation 9 13

95.0% 60 104

the 75th percentile is used for adults to estimate the upper bound soil ingestion rate
(as proposed by Calabrese 2003 ) the values range between 37 and 120 mg/d with
an arithmetic mean of 65 mg/d. When these data are subjected to bootstrapping,
the distribution based on the arithmetic mean values is characterized by a mean
soil ingestion rate of 46 mg/d (95% = 60 mg/d). The distribution around the 95th

percentile has a mean value of 81 (95% 104 mg/d; Table 6.8 ).

So far, most soil ingestion values discussed were derived from tracer studies.
As mentioned in the introduction, tracer studies are just one of several possible
approaches to estimate soil ingestion rates. Estimates of soil ingestion can equally
well be derived from studies on hand-loading, provided sufficient details are avail-
able on micro activity patterns and transfer factors. The general equation used for
estimating non-dietary soil and dust ingestion via hand-to-mouth contact involves
the product of hand residue or soil loading, hand-to-mouth frequency, hand sur-
face area mouthed per event, the efficiency of hand-to-mouth transfer and exposure
duration. These parameters depend on the characteristics of the surfaces and con-
taminants involved and the activity the human being is involved in. All of them are
fraught with large variability. Van Holderbeke et al. ( 2008 ) calculated soil and dust
ingestion values based on data published on hand-loading by Holmes et al. ( 1999 )
for different target populations, e.g., day-care kids, children playing indoors, gar-
deners, archaeologists, et cetera. Estimated average dust ingestion rates for children
(1-4 years) playing inside for 10 h/day amount to 50 mg/d, which is compara-
ble to estimated dust ingestion values (45 mg/d) from tracer studies. Other dust
ingestion rates for indoor playing children range from 5 to 20 mg/d. However, the
age range considered was broad (3-13 years), and a higher ingestion rate is often
assumed for the younger children. The estimated soil ingestion for gardeners, utility
workers and archaeologists, assuming a working day of 8 hours, ranges from 20 to
55 mg/working day.
Although this methodology is suitable for calculating detailed time-dependent
soil ingestion rates (hourly ingestion rates), it should be kept in mind that the calcu-
lations are based on micro activity data mainly published in non-European literature.
More extensive data on, for example, time activity patterns for children in different
European countries may be required in order to obtain more accurate data for local
Risk Assessments. As well, age ranges are often broad and there still is a need for
more data on separate indoor and outdoor activities for children.
Van Holderbeke et al. ( 2008 ) used the Biokinetic model comparison
methodology based on the validation of exposure models for contaminants to

=