United States
Environmental Protection Agency
Region II!
Philadelphia, PA 19107
EPA/903-K-95-003
December 1995
Region III
Technical Guidance Manual
Risk Assessment
Assessing Dermal Exposure from Soil
EPA Contact: Jennifer Hubbard
EPA
Region III
Hazardous Waste Management Division
Office of Superfund Programs
December 1995
Dermal absorption from soil is one of the routes of exposure that may be addressed during risk assessment at
Superfund sites. One factor necessary to estimate dose, and therefore risk, via this route is the absorption factor of
a chemical from soil. This document is intended to provide default assumptions for this factor in the assessment of
dermal soil exposure.
ASSESSING DERMAL
EXISTING GUIDANCE
CONTACT WITH SOIL;
Risk Assessment Guidance for Superfund. Volume I.
Human Health Evaluation Manual (Part A) ("RAGS";
EPA, 1989) presents an equation used to estimate
exposure from dermal contact with soil:
AD = CS x CF x SA x AF x ABS x EF x ED
BWxAT
Where:
AD = Absorbed dose (mg/kg/day)
CS = Chemical concentration in soil (mg/kg)
CF = Conversion factor (10"" kg/mg)
SA = Skin surface area available for contact
(cm2/event)
AF = Soil-to-skin adherence factor (mg/cm2)
ABS = Absorption factor (unitiess)
EF = Exposure frequency (events/year)
ED = Exposure duration (years)
BW = Body weight (kg)
AT = Averaging time (period over which exposure
is averaged-days)
(RAGS, Exhibit 6-15)
RAGS then states: "Absorption factors (ABS) are used
to reflect the desorption of the chemical from soil and
the absorption of the chemical across the skin and into
the bloodstream. Consult the open literature for
information on chemical-specific absorption factors. In
the absence of chemical-specific information, use
conservative assumptions to estimate ABS.' The use of
conservative assumptions is appropriate when
determining Reasonable Maximum Exposure (RME),
and reflects EPA's policy that protection of human
health should be ensured.
Assessment of dermal exposure is important for a
complete risk assessment This document summarizes
chemical-specific and general (for classes of
compounds) absorption factors that have been found in
the limited database available. The factors were
compiled from existing national guidance and peer-
reviewed scientific literature. It is recommended that
these numbers be used as defaults for the ABS
parameter when calculating RME soil exposure in the
absence of chemical-specific, site-specific information.
These defaults are presented in order to facilitate
performance of risk assessments by compiling these
factors in one place, and to promote consistency in risk
assessment
POLYCHLORINATED BIPHENYLS (PCBs)
A review of studies assessing the dermal absorption of
3,3',4,4'-tetrachlorobiphenyl (TCB) from soil appeared
in EPA, 1992. The range of absorption was reported to
be 0.6% to 6%. Region III recommends accepting the
6% value as a conservative assumption of ABS for
polychlorinated biphenyls, in keeping with RAGS.
EPA Report Collection
Information Resource Center
US EPA Region 3
Philadelphia, PA 19107
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CHLORINATED DIOXINS
A review of studies assessing the dermal absorption of
2,3,7,8-tetrachlorodibenzo-p_-dioxin (TCDD) from soil
appeared in EPA, 1992. The range of absorption was
reported to be 0.1% to 3%. Region III recommends
accepting the 3% value as a conservative assumption
of ABS for chlorinated dioxins, in keeping with RAGS.
CADMIUM
A review of studies assessing the dermal absorption of
cadmium from soil appeared in EPA, 1992. The range
of absorption was reported to be 0.1% to 1%. Region
III recommends accepting the 1% value as a
conservative assumption of ABS for cadmium, in
keeping with RAGS.
ARSENIC
In vivo studies from Wester et al. 1993a, report 3.2% for
a dose of 0.6 ug/cm2. Region III recommends
accepting this as a default ABS for arsenic.
OTHER METALS
Suggested ABS factors based on the pharmacokinetic
properties of chemicals appeared in Ryan et at. 1987.
The proposed range for dermal absorption of
inorganics from soil was 0.1% to 1%. This was also
consistent with a review of the studies for cadmium, an
inorganic, as assessed in EPA, 1992. Region III
recommends accepting the 1% value as a conservative
assumption of ABS for inorganics, in keeping with
RAGS.
VOLATILE ORGANIC COMPOUNDS
Volatile organics are especially difficult to assess,
because most studies to date have involved occluding
the skin, which may give artificially high ABS values,
since these compounds would also be expected to
volatilize from the skin. Suggested ABS factors based
on the pharmacokinetic properties of chemicals
appeared in Ryan etal. 1987. The proposed range for
dermal absorption of volatile organics from soil was
10% to 25%. However, experimental data show even
lower ABS values for volatile organics. For volatile
organics such as benzene (vapor pressure
approximately 95.2 mm Hg), Region III recommends
accepting the 0.05% value based on Skowronski etal.
1988, and Franz, 1984. This would include chemicals
such as 1,1-dichloroethane 1,1,1-trichloroethane, and
other volatiles with vapor pressure similar to or greater
than that of benzene. For volatiles such "as
ethylbenzene, tetrachloroethene, toluene, and xylenes,
which have vapor pressures lower than that of benzene
(and less volatilization from the skin may occur), a
default ABS of 3% is recommended.
These numbers only apply to non-occluded skin, which
would be the scenario expected for most environmental
exposures. If, however, the skin is occluded for any
reason, higher ABS values (up to 100%) should be
used.
PENTACHLOROPHENOL
In vivo studies from Wester et al. 1993b, report
24.4% for a dose of 0.7 ug/cm2 in soil. Region III
recommends accepting this as a default ABS for
pentachlorophenol.
OTHER SEMIVOLATILE ORGANIC COMPOUNDS
Suggested ABS factors based on the pharmacokinetic
properties of chemicals appeared in Ryan et al. 1987.
The proposed range for dermal absorption of
semivolatile organics from soil was 1% to 10%. The
reported absorption of topically applied pure
benzo[a]pyrene in studies in EPA, 1992, ranged from
1% to 13%. Kao et al, 1985, reported approximately 3%
for absorption of topically applied pure benzo[a]pyrene
by in vitro human skin. The absorption from soil would
be expected to be lower and indicates that the range in
Ryan et al. 1987, may be conservative with respect to
this particular compound but not necessarily
unreasonable. Region III recommends accepting the
10% value as a conservative assumption of ABS for
semivolatile organics, in keeping with RAGS.
PESTICIDES
Suggested ABS factors based on the pharmacokinetic
properties of chemicals appeared in Ryan et al. 1987.
The proposed range for dermal absorption of pesticides
from soil was 1% to 10%. The reported absorption of
topically applied pesticides and herbicides in acetone
to in vitro human skin was reported to be within this
range for lindane, aldrin, dieldrin, malathion, parathion,
and 2,4-D in Feldmann and Maibach, 1974. DDT
absorption from soil in monkey and human skin was
reported to range from 1.04 to 3.3% in EPA, 1992.
These studies indicate that the range in Ryan et al.
1987, may be conservative but not necessarily
unreasonable. Region III recommends accepting the
10% value as a conservative assumption of ABS for
pesticides, in keeping with RAGS.
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APPLICATIONS OF THIS GUIDANCE
This document represents a summary of best
professional judgment at this time. It is not intended to
be a detailed technical analysis of dermal exposure
experimentation. As a summary of best professional
judgment and default parameters, the recommendations
herein may be superseded by newer, chemical-specific
and route-specific studies, or by site-specific studies of
acceptable quality.
These factors apply to absorption from soil or sediment
Dermal absorption of chemicals from water is discussed
in RAGS and EPA, 1992.
It should be noted that when estimating absorbed
doses for chemicals, dose-response parameters such
as Reference Doses (RfDs) and Cancer Slope Factors
(CSFs) should be adjusted accordingly, where possible
and appropriate, as per RAGS Appendix A.
SUMMARY
Dermal absorption from soil is one of the routes of
exposure that may be addressed during risk
assessment at Superfund sites. One factor necessary
to estimate dose, and therefore risk, via this route is the
absorption factor of a chemical from soil. This
document recommends default assumptions for this
factor in the assessment of dermal soil exposure, based
on the limited available information and best
professional judgment.
REFERENCES
EPA, 1989. Risk Assessment Guidance for Superfund,
Volume I, Human Health Evaluation Manual (Part
A). Office of Emergency and Remedial Response,
December, 1989. EPA/540/1-89/002.
Kao, J.K., F.K. Patterson, and J. Hall, 1985. Skin
penetration and metabolism of topically applied
chemicals in six mammalian species, including
man: An in vitro study with benzo[a]pyrene and
testosterone. Toxicol. Appl. Pharmacol. 81:502-
518.
Ryan, EA, E.T. Hawkins, et al. 1987. Assessing Risk
from Dermal Exposure at Hazardous Waste Sites.
In Bennett, G. and J. Bennett, eds. Superfund '87:
Proceedings of the Eighth National Conference;
November 16-18; Washington, D.C. The Hazardous
Materials Control Research Institute, pp. 166-168.
Skowronski, GA, R.M. Turkall, and M.S. Abdel-
Rahman. 1988. Soil adsorption alters
bioavailability of benzene in dermally exposed male
rats. Am. Ind. Hyg. Assoc. J. 49(10):506-511.
Wester, R.C., H.I. Maibach, etal. 1993a. In vivo and jn
vitro percutaneous absorption and skin
decontamination of arsenic from water and soil.
Fundamental and Applied Toxicology. Vol. 20. No.
3, pp. 338-340.
Wester, R.C., H.I. Maibach, etal. 1993b. Percutaneous
absorption of pentachlorophenol from soil.
Fundamental and Applied Toxicology. Vol. 20, No.
1, pp. 68-71.
For additional information, call (215) 597-1309.
Approved by:
Thomas C. Voltagrfio
Hazardous Waste Maria
tor
ment Division
EPA, 1992. Dermal Exposure Assessment: Principles
and Applications. Interim Report Office of Health
and Environmental Assessment January, 1992.
EPA/600/8-91/011/B.
Feldmann, R.J. and H.I. Maibach, 1974. Percutaneous
penetration of some pesticides and herbicides in
man. Toxicol. Appl. Pharmacol. 28:126-132.
Franz, T.J., 1984. Percutaneous absorption of
benzene. Adv. Modern Environ. Toxicol. Vol. 6.
Applied Toxicology of Petroleum Hydrocarbons.
Princeton Scientific Publishers, Inc., Princeton, N.J.
pp. 61-70.
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