UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
I WASHINGTON, D.C. 20460
OFFICE OF
SOLID WASTE AND
EMERGENCY
RESPONSE
December 5, 2003
OSWER Directive 9285.7-53
MEMORANDUM
SUBJECT: Human Health Toxicity Values in Superfund Risk Assessments
FROM: Michael B. Cook, Director/s/
Office of Superfund Remediation and Technology Innovation
TO: Superfund National Policy Managers, Regions 1-10
Purpose
This memorandum revises the hierarchy of human health toxicity values generally
recommended for use in risk assessments, originally presented in Risk Assessment Guidance for
Superfund Volume I, Part A, Human Health Evaluation Manual (RAGS) (OSWER 9285.7-02B,
EPA/540/1-89/009, December 1989).
(ht0://wvyw.epa.gov/supedlmd/prograins/risk/ragsa/index.htni)
It updates the hierarchy of human health toxicity values and provides guidance for the
sources of toxicity information that should generally be used in performing human health risk
assessments at Comprehensive Environmental Response Compensation and Liability Act
(CERCLA or "Superfund") sites. It does not address the situation where new toxicity
information is brought to the attention of the U.S. Environmental Protection Agency (EPA). It
also does not provide guidance or address toxicity or reference values for ecological risk.
This memorandum presents current Office of Solid Waste and Emergency Response
(OSWER) technical and policy recommendations regarding human health toxicity values in risk
assessments. EPA and state personnel may use and accept other technically sound approaches,
either on their own initiative, or at the suggestion of potentially responsible parties, or other
interested parties. Therefore, interested parties are free to raise questions and objections about
the substance of this memorandum and the appropriateness of the application of this document to
a particular situation. EPA will, and States should, consider whether the recommendations or
interpretations in this memorandum are appropriate in that situation. This memorandum does not
impose any requirements or obligations on EPA, States, or other federal ageaoies, or .the
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regulated community. The sources of authority and requirements in this matter are the relevant
statutes and regulations (e.g., CERCLA, Resource Conservation and Recovery Act). EPA
welcomes public comments on this memorandum at any time and may consider such comments
in future revisions of this memorandum.
Background
Superfund risk assessments are performed for a number of reasons, including to evaluate
whether action is warranted under CERCLA, to establish protective cleanup levels, and to
determine the residual risk posed by response actions. Generally, toxicity assessment is an
integral part of risk assessment. Volume I, Part A of RAGS provides guidance on how to
conduct the human health portion of the risk assessment. Chapter 7.4.1 presents a hierarchy of
human health toxicity values for use in risk assessments at Superfund sites. The hierarchy
presented in RAGS Part A is being updated to reflect that additional sources of peer reviewed
values have become available since 1989. In addition, the EPA Health Effects Assessment
Summary Tables (HEAST) document, which was identified as the second tier of data, has not
been updated since 1997. As a result, HEAST may not provide the most current source of
information on some contaminants.
This revised hierarchy recognizes that EPA should use the best science available on
which to base risk assessments. In general, if health assessment information is available in the
Integrated Risk Information System ["IRIS," http://www.epa.gov/iris/] for the contaminant under
evaluation, risk assessors normally need not search further for additional sources of information.
Since EPA's development and use of peer review in toxicity assessments, IRIS assessments have
undergone external peer review in accordance with Agency peer review guidance at the time of
the assessment. IRIS health assessments contain Agency consensus toxicity values. If such
information is not available in IRIS, risk assessors should consider other sources of available data
based on the hierarchy presented in this memorandum.
EPA recognizes that there may be other sources of toxicological information. As noted in
the December 1993 memorandum entitled "Use of IRIS Values in Superfund Risk Assessment"
(OSWER Directive 9285.7-16, December 21, 1993):
"...IRIS is not the only source of toxicology information, and in some cases more recent,
credible and relevant data may come to the Agency's attention. In particular,
toxicological information other than that in IRIS may be brought to the Agency by outside
parties. Such information should be considered along with the data in IRIS in selecting
toxicological values; ultimately, the Agency should evaluate risk based upon its best
scientific judgement and consider all credible and relevant information available to it."
This memorandum is intended to help regional risk assessors identify appropriate sources
of toxicological information as a means of streamlining decisions. It does not specifically
address the situation where additional scientific information is brought to the attention of EPA.
In those cases, EPA risk assessors and decision makers should consider the information as
appropriate on a case by case basis.
Revised Recommended Human Health Toxicity Value Hierarchy
This memorandum revises the recommended hierarchy of toxicological sources of
information which Regional risk assessors and managers should initially consider for site-
specific risk assessments. The revised recommended toxicity value hierarchy is as follows:
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Tier 1- EPA's IRIS
Tier 2- EPA's Provisional Peer Reviewed Toxicity Values (PPRTVs) - The Office of
Research and Development/National Center for Environmental Assessment/Superfund
Health Risk Technical Support Center (STSC) develops PPRTVs on a chemical specific
basis when requested by EPA's Superfund program.
Tier 3- Other Toxicity Values - Tier 3 includes additional EPA and non-EPA sources of
toxicity information. Priority should be given to those sources of information that are the
most current, the basis for which is transparent and publicly available, and which have
been peer reviewed.
IRIS remains in the first tier of the recommended hierarchy as the generally preferred
source of human health toxicity values. IRIS generally contains reference doses (RfDs),
reference concentrations (RfCs), cancer slope factors, drinking water unit risk values, and
inhalation unit risk values that have gone through a peer review and EPA consensus review
process. IRIS normally represents the official Agency scientific position regarding the toxicity of
the chemicals based on the data available at the time of the review.
The second tier is EPA's PPRTVs. Generally, PPRTVs are derived for one of two
reasons. First, the STSC is conducting a batch wise review of the toxicity values in HEAST
(now a Tier 3 source). As such reviews are completed, those toxicity values will be removed
from HEAST, and any new toxicity value developed in such a review will be a PPRTV and
placed in the PPRTV database. Second, Regional Superfund Offices may request a PPRTV for
contaminants lacking a relevant IRIS value. The STSC uses the same methodologies to derive
PPRTVs for both.
The third tier includes other sources of information. Priority should be given to sources
that provide toxicity information based, on similar methods and procedures as those used for Tier
I and Tier II, contain values which are peer reviewed, are available to the public, and are
transparent about the methods and processes used to develop the values. Consultation with the
STSC or headquarters program office is recommended regarding the use of the Tier 3 values for
Superfund response decisions when the contaminant appears to be a risk driver for the site. In
general, draft toxicity assessments are not appropriate for use until they have been through peer
review, the peer review comments have been addressed in a revised draft, and the revised draft is
publicly available.
Additional sources may be identified for Tier 3. Toxicity values that fall within the third
tier in the hierarchy include, but need not be limited to, the following sources.
• The California Environmental Protection Agency (Cal EPA) toxicity values are peer
reviewed and address both cancer and non-cancer effects. Cal EPA toxicity values are
available on the Cal EPA internet website at
http.7/www. oehha. ca. go v/risk/chemicalDB//index. asp.
• The Agency for Toxic Substances and Disease Registry (ATSDR) Minimal Risk Levels
(MRLs) are estimates of the daily human exposure to a hazardous substance that is likely
to be without appreciable risk of adverse non-cancer health effects over a specified
duration of exposure. The ATSDR MRLs are peer reviewed and are available at
http://www.atsdr.cdc.aov/nirls.html on the ATSDR website.
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• HEAST toxicity values are Tier 3 values. As noted above, the STSC is conducting a
batch wise review of HEAST toxicity values. The toxicity values remaining in HEAST
are considered Tier 3 values. The radionuclides HEAST toxicity values are available at
http://www.epa.gov/radiatioiVheast/. The HEAST values on chemical contaminants are
not currently available on an EPA internet site. They may be obtained by contacting a
Superfund risk assessor.
Neither IRIS nor the PPRTV database contains radionuclide slope factors. Because
EPA's Office of Radiation and Indoor Air (ORIA) obtains peer review on the radionuclide slope
factors contained in Table 4 of HEAST (which are available on EPA/ORIA's internet website at
http://www.epa.gov/radiatton/heast/dowiiload.htm). routine consultation with STSC is generally
not necessary on these values even when they may be a risk driver on a Superfund site. These
radionuclide slope factors have been adopted by EPA in its Preliminary Remediation Goals for
Radionuclide Calculator and are available on EPA's internet website at:
htIp://epa-prgs. ornl.gov/radionuciides/ and the Soil Screening Guidance for Radionuclide
documents, which are available at: http://w\\^v.epa.gov/superfi.md/resources/radiation/radssg,
Implementation
This memorandum provides a revised recommended hierarchy of human health toxicity
values for Superfund sites and represents a revision of Chapter 7 of RAGS, Volume I, Part A.
Superfund risk assessors should look to this hierarchy when evaluating risk for CERCLA
response actions. Additional sources of toxicity values, which are not specifically referenced in
this recommended hierarchy, can be considered.
Additional Information
Questions regarding this guidance or its use and implementation on a particular site
should be directed to an EPA Regional Superfund risk assessor or lexicologist. Questions of a
more general nature relating to this guidance should be directed to Mr. Dave Crawford of my
staff at (703) 603-8891, Crawford.Davefgtepa. gov.
cc: Nancy Riveland, Superfund Lead Region Coordinator, USEPA Region 9
NARPM Co-Chairs
Joanna Gibson, OSRTI Documents Coordinator
OSRTI Center Directors and Senior Process Managers
Jim Woolford, FFRRO
Debbie Dietrich, OEPPR
Robert Springer, OSW
Cliff Rothenstein, OUST
Linda Garczynski, OBCR
Sandra Connors, FFEO
Susan Bromm, OSRE
Peter Preuss, NCEA
Charles Openchowski, OGC
John Michaud, OGC
David Kling, FFEO
Stephen Luftig, Senior Advisor to OSWER Assistant Administrator
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