Exposure Through Soil and Dust Ingestion - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 277

Rounding our figures, 100 mg/d was considered the best estimate of the
arithmetic mean soil ingestion for children under 7 years of age. Over the period
of study, the 95th percentile ingestion rates ranged from 217 to 449 mg/d with an
arithmetic mean of 236 mg/d for soil ingestion and 449 mg/d when both soil and
dust are considered. Rounding off, the recommended 95th percentile soil ingestion
rate for children is 400 mg/d based on soil and dust ingestion. In its revision of the
Child-specific Exposure Factors Handbook (US-EPA 2008 ), US EPA re-adjusted
their recommendations for values for daily soil, dust and soil/dust ingestion to
much lower ingestion values, see Table 6.4 . The revision relies on tracer studies and
one Biokinetic model comparison study. Ingestion values from tracer studies using
soil concentrations are interpreted as ingestion of soil outdoors and from soil used
indoors to support plant growth. Soil particles that have been tracked into the indoor
environment from outdoors are not included. Estimated ingestion values using dust
concentrations are used for the estimation of dust ingestion, including soil particles
tracked to the indoor environment. To derive the soil and dust ingestion values in
Table 6.4 , the US EPA assumes that the relative proportions of soil and dust ingested
are 45% soil and 55% dust, respectively.
US-EPA ( 2008 ) also provides an estimate for soil-pica (1,000 mg/d), which is
based on their definition (ingestion of high amounts of soil in the order of 1,000-
5,000 mg/d and the finding that in ingestion studies, the high-end of the intakes
exceed that quantity).
US-EPA ( 1997 ) recommends a CTE (Central Tendency Exposure) soil ingestion
value for adults of 50 mg/d, although they claim that this recommendation is highly
uncertain. Considering the uncertainties in the central estimate, a recommendation
for an upper percentile value would be inappropriate.
Zartarian et al. ( 2005 ) conducted an analysis of soil ingestion rates from
selected tracer studies to be used as input for the SHEDS-WOOD (Stochastic

Table 6.4 Recommended values for daily soil, dust and soil/dust ingestion by children) (US-EPA
2008 )

Soil a Dust b Soil + dust

Central
tendency
(mg/d)

Central
tendency
(mg/d)

Central
tendency
(mg/d) Upper percentile

Age group Soil-pica

(mg/d)

Geophagy
(mg/d)

6to<12
months

30 - - 30 60

100 c

1 to <6 years 50 1,000 50,000 60

100 c

6 to <21 years 50 1,000 50,000 60

-Norecommendation
a Includes soil and outdoor settled dust
b Includes indoor settled dust only
c Total soil and dust ingestion rate is 110 mg/d, rounded to one significant figure it is 100 mg/d