FREQUENTLY ASKED QUESTIONS (FAQS) ABOUT
UPDATE OF STANDARD DEFAULT EXPOSURE FACTORS
(OSWER Directive 9285.6-03, dated February 6, 2014)
1. Why is EPA updating the default exposure factors for use in CERCLA risk assessment
equations?
The prior EPA default exposure values were issued in 1991 as OSWER Directive 9285.6-03 (EPA,
1991) and a few were updated or supplemented by subsequent Risk Assessment Guidance for
Superfund (RAGS). OSWER Directive 9285.6-03 stated, "As new data become available, either
for the factors themselves or for calculating RME [reasonable maximum exposure], this
guidance will be modified accordingly."
New data became available in September 2011, when EPA's National Center for Environmental
Assessment, Office of Research and Development (ORD/NCEA) issued a substantive update to its
exposure assessment recommendations, Exposure Factors Handbook-2011 Edition (EFH 2011).
EFH 2011 is an externally peer-reviewed document that summarizes relevant exposure
assessment data.
Following the publication of EFH 2011, EPA's regional risk assessors received inquiries from
other EPA program offices, states, the regulated community, and other interested parties
regarding the applicability of the ORD/NCEA's recommendations in EFH 2011 for use in human
health risk assessments. The OSWER Human Health Regional Risk Assessors Forum (OHHRRAF),
a workgroup consisting of human health risk assessors from EPA Regions and EPA Program
Offices, reviewed the recommendations in EFH 2011 in the context of the default exposure
factors used in the Superfund program and to derive Regional screening levels. As a result of a
consensus-driven process, the OHHRRAF identified several Superfund-specific default exposure
factors that warranted updating. OSWER Directive 9200.1-120 (Human Health Evaluation
Manual, Supplemental Guidance: Update of Standard Default Exposure Factors; dated February
6, 2014) incorporates and adopts the updates recommended by the OHHRRAF and updates
OSWER Directive 9285.6-03.
2. Why do some of the factors recommended in OSWER Directive 9200.1-120 differ from the
recommendations in the Exposure Factors Handbook-2011 Edition (EFH 2011)?
EFH 2011 is not a Superfund-specific document; rather, it provides a summary of the latest
developments in exposure science and provides recommendations for a broad range of EPA
programs. The OHHRRAF developed consensus recommendations based on the context, needs,
and existing health risk assessment policy/guidance for the Superfund Program, such as
ensuring that the recommended exposure factors are protective of the reasonable maximum
exposure (RME), consistent with the Comprehensive Environmental Response, Compensation,
and Liability Act, as amended (CERCLA) and the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP).
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FREQUENTLY ASKED QUESTIONS (FAQS) ABOUT
UPDATE OF STANDARD DEFAULT EXPOSURE FACTORS
(OSWER Directive 9285.6-03, dated February 6, 2014)
3. Why is the updated water ingestion rate for adults 2.5 L/day and for children 0.78 L/day,
instead of the values recommended in the Exposure Factors Handbook-2011 Edition?
The recommendation in EFH2011 is based on a 95th percentile value. OSWER Directive 9285.6-
03 selected the prior default values based upon a 90th percentile value. The OHHRRAF
consensus was to use the established percentile basis of exposure factors, where stated, to
maintain the historic mix of upper-bound and mid-range values as indicated in the original
Directive. Accordingly, the 90th percentile values were selected by OHHRRAF consensus for
water ingestion rate.
4. Why hasn't the average life expectancy (lifetime) been updated to 78 years as recommended
by the Exposure Factors Handbook-2011 Edition?
The OHHRRAF has been consulting with ORD/NCEA on the appropriateness of updating this
factor for purposes of calculating lifetime average daily dose. We currently understand that
ORD/NCEA is re-considering its recommendation as expressed in EFH2011. If this consultation
results in an ORD/NCEA recommendation to update this factor, additional documentation will
be provided.
5. Why is 26 years recommended as the residential exposure duration when the EFH2011
recommendation is 33 years?
The ORD/NCEA-recommended exposure duration (33 years) is based on a 95th percentile value.
As noted in the discussion on water ingestion, the OHHRRAF consensus was to use the
established percentile basis of exposure factors, where stated, to maintain the historic mix of
upper bound and mid-range values as indicated in the original Directive. The original basis for
the default value for residential exposure duration was a 90th percentile value. Accordingly, the
90th percentile value (26 years) was selected by OHHRRAF consensus for residential exposure
duration.
6. Why aren't age group defaults provided?
The purpose of OSWER Directive 9200.1-120 is to update and clarify the 1991 directive, which
did not include age-group-specific values. Users are directed to the Exposure Factors Handbook
-2011 Edition as a source for age-group-specific exposure factor values, as described in
Guidance on Selecting Age Groups for Monitoring and Assessing Childhood Exposures to
Environmental Contaminants (EPA, 2005).
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FREQUENTLY ASKED QUESTIONS (FAQS) ABOUT
UPDATE OF STANDARD DEFAULT EXPOSURE FACTORS
(OSWER Directive 9285.6-03, dated February 6, 2014)
7. Why are default factors for fish ingestion and homegrown produce ingestion no longer
provided?
Given the large geographic variability observed within these types of exposure values, the
OHHRRAF consensus is that fish ingestion and homegrown produce ingestion values for highly
exposed populations should be site specific. EFH 2011 also recommends site-specific analysis
for fish and produce consumption.
8. Will these updated exposure factors be considered in calculating Regional Screening Levels
(RSLs)? How does the update of these values affect the RSLs? When will the RSL tables be
updated? What should users do in the meantime?
The RSLs are updated biannually, and the next update is scheduled for May 2014. It is
anticipated that the next update of the RSL tables will incorporate the updated exposure
factors.
Users can use the RSL calculator to calculate updated RSLs for specific contaminants in the
interim. Based on preliminary analyses performed by the OHHRRAF, changes to the default
exposure factors will result in a slight increase to most of the medium-specific RSLs.
9. How should these updated exposure factors be weighed in Five Year Reviews ?
EPA, as required by statute and as a matter of policy, reviews the remedies at certain cleanup
sites every five years. To assess protectiveness of the respective remedy, the lead agency should
review and evaluate the current validity of all the exposure and risk parameters upon which the
original remedy selection decision was based (see Comprehensive Five-Year Review Guidance,
OSWER Directive 9355.7-03B-P, dated June 2001). Such protectiveness assessments should
consider the updated exposure factors recommended in Directive 9200.1-120.
Based on calculations performed by the OHHRRAF, updates to the default exposure factors are
generally expected to result in a slight decrease in calculated time-weighted exposures (and,
hence, risk estimates) for most chemicals. EPA recommends, however, that risk assessors
evaluate and verify impacts on risk estimates on a site-specific basis.
10. Why have inhalation rates been dropped from the default exposure factors?
Human health toxicity values currently derived by the EPA Integrated Risk Information System
(IRIS) for inhalation exposures (i.e., Reference Concentrations for non-cancer effects and
Inhalation Unit Risk values for cancer endpoints) are based upon exposure concentrations,
rather than intakes. The Risk Assessment Guidance for Superfund, Part F (EPA, 2009) was issued
to reflect this current practice. Users are encouraged to consult EFH 2011 to obtain inhalation
rate values as needed for alternative, site-specific approaches.
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FREQUENTLY ASKED QUESTIONS (FAQS) ABOUT
UPDATE OF STANDARD DEFAULT EXPOSURE FACTORS
(OSWER Directive 9285.6-03, dated February 6, 2014)
11. What if a current baseline risk assessment has been completed (or is nearing completion)
using the previous default exposure factors or exposure factors from EFH 2011 other than the
factors identified in this directive?
EPA recognizes that transitioning to the default exposure factors recommended in Directive
9200.1-120 will take time and that current risk assessments may have been developed using
factors other than those recommended here. In the near term, EPA recommends that this
discrepancy be addressed in the uncertainty section of the baseline risk assessment and the
impact on the risk characterization of the exposure factors used (versus using the exposure
factors in this Directive) be discussed.
It is the long-term expectation that baseline risk assessments will use the default exposure
factors in in Directive 9200.1-120.
12. How was the default exposure value calculated for surface area of a child? Are the listed
values correct for exposed surface area of a child and an adult worker?
For children, EPA used data in Table 7-8 of EFH 2011 to generate age-cohort-specific ratios. For
ages less than two years old, EPA used data from the nearest age.
In reviewing all surface area calculations in response to public inquiries, EPA identified that the
currently recommended value should have been listed as 2,373 cm2for a child and 3,527 cm2for
an adult worker. As a result Attachment 1 was updated with these corrections and two
corrections to citations.
Last updated February 24, 2015
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