UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
RFC 2 I ";"p
' ULL' ° OSWER DIRECTIVE f 9285.7-16
OFFICE OF
SOLID WASTE AND EMERGENCY
RESPONSE
MEMORANDUM
SUBJECT: Use of IRIS Values in Superfund Risk^Assessment x-—\
FROM: William H. Farland, Director ^6OC**J//(3*Jbuu^
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At the same time, IRIS is not the only source of
toxicological 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 judgment and
consider all credible and relevant information available to it.
IMPLEMENTATION
As indicated in the preamble to the NCP, the Agency must
respond substantively to any comments raised during the public
comment period on the proposed plan that question the use of an
IRIS value; see 55 FR 8711 (March 8, 1990) . In responding to
such comments, Agency staff should keep in mind that the entry of
a value in IRIS is not a rulemaking. Thus, the entry of a value
on IRIS does not make the number legally binding (i.e., the value
is not entitled to conclusive weight) for the purposes of
Superfund risk assessments. When a toxicological value is
questioned in a comment on the proposed plan, a written
explanation for the value ultimately selected (whether it is the
IRIS value or another number) must be included in the
administrative record.
The weight to be given information from sources other than
IRIS will necessarily have to be determined on a case-by-case
basis. When presented with alternative toxicological information
that might be used in place of IRIS values, the Agency will
consider all credible and relevant information before it. The
evaluation of credible and relevant information should consider a
variety of factors in evaluating the hazards associated with
chemical exposure including: whether the study was designed
using approved protocols and whether it was conducted observing
good laboratory practices. In addition, the Agency wishes to
avoid duplicating work that was done in developing the IRIS
value. Thus, the work of the IRIS Workgroup may be a source of
1Such information may also be submitted by outside parties
earlier in the process, such as during the workplan development
phase of the baseline risk assessment. While EPA is not required
to respond at that time, timely evaluation of such information
can be more efficient than addressing issues only when they are
raised during the public comment period.
2For assistance in evaluating such information, regional
managers should contact the appropriate regional scientist and,
secondarily, the technical contacts listed in IRIS. For further
general information, contact the IRIS Risk Information Hotline at
(513) 569-7254.
December 21, 1993 Page 2
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information that will aid in explaining the Agency's rationale
that supports a toxicological value. Accordingly, while all
credible and relevant information must be considered, departing
from the IRIS value is generally discouraged where the
information submitted consists of data previously evaluated in
developing that value. In the event that the Agency determines
that an IRIS value should be replaced with another value, the
Toxics Integration Branch of the Office of Emergency and Remedial
Response will work with both the Office of Research and
Development and the Regions to promote the consistent use of
toxicological values for the Superfund program in all Regions.
Finally, those using values from IRIS are reminded that
toxicological values are subject to varying degrees of
uncertainty, for a variety of reasons, and that the existence of
such uncertainty should be taken into account in preparing site
specific risk analyses. Further guidance in this regard can be
found at section 7.6 of RAGS, and in the Deputy Administrator's
February 26, 1992 memorandum entitled "Guidance on Risk
Characterization for Risk Managers and Risk Assessors."
December 21, 1993 Page 3
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