Exposure Through Soil and Dust Ingestion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 276

to do this the raw data records from the original studies are required, data that
are often not available. Equally, age dependency of the contribution of soil and
dust and of ingestion rates can play a role and is often not considered in these
studies.
In the survey response methodology , responses to survey questions regarding soil
and dust ingestion, e.g., soil and dust ingestion behaviour, frequency and quantity,
are analysed (US-EPA 2008 ). In these studies, children or children's caretakers
are surveyed. Different data collection methodologies can be used, e.g., on the
basis of personal interviews or mailed questionnaires. Each collection methodology
has specific limitations, which results in either positive or negative response bias.
Respondents' perception of a correct answer, question wording difficulties, lack of
understanding of definitions and terms used, language and dialect differences, etc
can cause bias (US-EPA 2008 ).
According to the lead isotope ratio methodology , lead isotope ratios in children's
urine or blood, water, food, and house dust are measured and compared to infer
sources of lead exposure that may include dust or other environmental exposures
(US-EPA 2008 ).
Another approach that might be used to derive soil and dust ingestion rate val-
ues is the use of empirical relations between contaminant levels in the environment
and Biomonitoring data . In this approach, the slope between the biomarker and the
concentration in soil or dust is used to calculate the ingestion rate. As this approach
is based on statistical regression analysis and not on mechanistic processes, regres-
sions that account for as many variables as possible (e.g., dust, soil, food, air, age,
socio-economic factors) are preferred, so as to obtain a slope which is optimally
related to soil or dust ingestion.
6.2.3 Soil and Dust Ingestion Rates for Children and Adults
Most authors derive soil ingestion rates from a selection of tracer studies. However,
as mentioned above, also other methodologies can be applied to estimate the amount
of soil and dust ingested by children.
Until recently, the US EPA recommended soil ingestion values for children
from age 1-7 years on the basis of some key studies, i.e., studies with a superior
experimental design or with a particular attribute needed for the recommenda-
tions (US-EPA 2006 ). The arithmetic mean ingestion rates ranged from 38 mg/d
to 193 mg/d with a weighted average of 90 mg/d for soil ingestion and 106 mg/d
when it was considered that a portion of the soil ingested comes from dust. These
estimates are based on weighted averages using aluminium and silicon as tracers.
Also for US EPA these tracer elements were considered the most reliable, based
on a review of the current literature. Results obtained using titanium as a tracer
were not considered. The reason for this is that in some children's diet titanium is
present in large quantities and titanium dioxide pigment in paints may provide an
additional source of titanium exposure through the ingestion of paint chips or dust
(Davis et al. 1990 ).