Exposure Through Soil and Dust Ingestion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 264

external soil, but only 50% of house dust. In addition to being more mobile, fine
particles adhere more effectively to the skin, thus increasing the potential for expo-
sure. Furthermore, the degrading or ageing processes that are effective at removal
of contaminants outside do not operate or they operate at reduced efficiency indoors
compared to outdoors, because they are protected from sunlight, rain, temperature
extremes, and microbial action (Egeghy et al. 2007 ). Contaminant concentrations in
house dust are often higher than in exterior soil. This could be due to enrichment in
the finer fractions and lack of removal processes. Another explanation may be the
possible presence of indoor sources of contaminants, which can contribute signifi-
cantly to overall concentrations in house dust. Given the importance of tracked-in
soil on indoor contaminant concentrations, exposure to soil-derived dust should be
included in Risk Assessment in regard to contaminated sites.

6.1.3 Calculating Exposure Through Ingestion of Soil and Dust

Exposure to contaminants via ingestion of house dust and soil can be calculated
according to the following equations,

IR soil/dust ∗ F soil ∗ RBA soil ∗ C soil
BW

D soil ingestion = (6.1)

IR soil/dust ∗ (1 F soil ) ∗ RBA dust ∗ C dust

BW

−

D dust ingestion = (6.2)

where

kg bw -1 d -1 )

D soil ingestion - exposure through soil ingestion (mg · ·

d -1 )
IR soil/dust - combined ingestion rate of soil and dust (kg/d -1 )
RBA soil - relative oral bioavailability in the human body for contaminants in
soil (-)
RBA dust - relative oral bioavailability in the human body for contaminants in
dust (-)
F oral_soil - fraction of soil and dust ingestion which is soil (-)
C soil - contaminant concentration in soil (mg

kg bw -1 D dust ingestion - exposure through dust ingestion (mg · ·

kg dw -1 )
C dust - contaminant concentration in dust (mg

·

kg dw -1 )

·

BW - body weight (kg)

The derivation of soil and dust ingestion rates is discussed in detail in this
chapter. If, depending on the studies used, a separate estimate is available for the soil
ingestion rate and for the dust ingestion rate, these values can replace the product of
IR ∗ F .
Relative oral bioavailability in the human body of contaminants from soil allow
transformation of the exposure from soil and dust to an exposure that can be com-
pared to the Toxicological reference value or that can be summed up as exposure
from other oral exposure pathways.