U.S. Environmental Protection Agency’s Integrated Risk Information System (IRIS): Toxicity Assessment of Chemicals
Updated September 12, 2022
U.S. Environmental Protection Agency’s Integrated Risk
Information System (IRIS): Toxicity Assessment of Chemicals
The U.S. Environmental Protection Agency (EPA)
EPA, this approach allows the agency to finalize an
established the Integrated Risk Information System (IRIS)
assessment more quickly. EPA’s selection of which
program in 1985 to consolidate human health toxicity
chemicals to assess has received scrutiny on occasion. For
assessments that the agency had prepared in order to
example, after some of EPA’s announcements of upcoming
implement various pollution control statutes (e.g., Clean Air
IRIS assessments, observers have raised questions about
Act and Clean Water Act). Specific incidents, such as the
whether the agency’s plans reflect an appropriate
1984 leak of methyl isocyanate from a Union Carbide
assessment of high priorities. In some instances, EPA has
facility in Bhopal, India, reinforced the need for a better
withdrawn an initiated assessment before it is completed
understanding of human health toxicity from exposure to
due to a change in priorities.
various chemicals. Over time, findings from IRIS
assessments have informed many different agency actions,
Assessment Process
including regulatory requirements that EPA has established
Since 2016, EPA has included a preamble in each IRIS
under various pollution control statutes. Given that these
assessment that summarizes the objectives and scope of the
actions may require regulated entities to incur significant
IRIS program, general principles and systematic procedures
compliance costs and determine the extent of health
used in developing assessments, and the overall
benefits, the process that EPA follows to conduct IRIS
development process and document structure. The preamble
assessments and the findings of such assessments have
is accompanied by the preface, which is chemical-specific
received considerable attention.
and describes procedures in the assessment that differ from
the general procedures described in the preamble. In the
EPA’s IRIS program is not authorized explicitly in statute,
preamble of each IRIS assessment since 2016, EPA
but multiple pollution control statutes include general
describes seven steps for developing IRIS assessments: (1)
research provisions intended for the agency to generate
draft development; (2) agency review; (3) interagency
information that may be useful in the implementation of
science consultation; (4) public comment, followed by
such statutes. Additionally, EPA continues to receive
external peer review; (5) assessment revision; (6) final
annual appropriations to its Science and Technology (S&T)
agency reviews and interagency science discussion; and (7)
account that largely funds its research efforts, including the
post final assessment.
IRIS program.
EPA staff preparing IRIS assessments may revisit prior
EPA maintains a public IRIS website that provides more
steps of the process based on input from program and
than 560 assessments on a range of chemicals. EPA
regional offices, other agencies, peer reviewers, or the
completed more than 80% of these assessments before
public. The process, from start to finish for assessments
1995. However, assessments completed more than 25 years
completed since 2013, has typically spanned at least five
ago may still be relevant if no new information is available
years, with the ethylene oxide carcinogenicity assessment
to warrant a revision of the existing assessment.
taking 17 years. EPA now states that it aims to complete an
assessment within three years.
Selection of Chemicals to Assess
EPA focuses on a select number of assessments at any
After selecting a chemical to assess and prior to developing
given time. EPA staff managing the IRIS program select
a draft assessment, EPA generally prepares a series of
chemicals for IRIS assessments through a prioritization
documents that detail how the agency plans to develop the
process, which involves soliciting internal input from EPA
draft. EPA practice is to issue each of these documents for
program and regional offices on which assessments may be
public comment, which may help to inform how the agency
useful and evaluating the extent to which resources and
performs the assessment. The first document that EPA
expertise are available to complete the assessments. EPA
prepares for an assessment is the scoping document, which
began issuing an IRIS Program Outlook in December 2018
describes the chemical being assessed, potential routes and
to provide periodic updates on the development of IRIS
durations of exposure to examine, considerations for
assessments.
susceptible populations and different life stages, and other
topics of interest. After receiving public comment for the
Assessments that examine multiple pathways of exposure
scoping document and finalizing it, EPA prepares a
(e.g., ingestion, inhalation, or direct contact) and potential
problem formulation that identifies the scientific issues that
associated health effects typically take many years to
the agency expects to address based on a preliminary
prepare. In some instances, EPA may decide to conduct an
literature search. Additionally, EPA generally identifies
assessment with a more narrow scope, focusing on a
protocols that the agency intends to use for the specific
specific pathway of exposure or health effect. According to
https://crsreports.congress.gov
U.S. Environmental Protection Agency’s Integrated Risk Information System (IRIS): Toxicity Assessment of Chemicals
assessment. The problem formulation and description of
multiple annual appropriations acts. For example, in the
protocols are published for public comment.
FY2001 appropriations process, Congress requested that
EPA conduct “needs assessments” to determine the
After the development of a draft IRIS assessment, the
appropriate pace for completing IRIS assessments. Also,
agency’s IRIS staff generally seeks input on the draft from
certain Members have requested GAO and EPA’s Office of
EPA program and regional offices, other federal agencies,
Inspector General examine aspects of EPA’s IRIS program
external peer reviewers, and the public. Since 2014, EPA
to provide recommendations for improving the program.
has submitted draft IRIS assessments to the Chemical
Assessment Advisory Committee within its Science
As part of the FY2018, FY2019, and FY2020
Advisory Board for external peer review. Final IRIS
appropriations processes, the House and Senate Committees
assessments generally include a list of authors, contributors,
on Appropriations directed EPA to maintain funding for
intra- and inter-agency reviewers, and external peer
IRIS at FY2017 levels. The committees also urged
reviewers who contributed to the review of the assessment
expedited completion of an IRIS handbook and directed the
at various stages of its development.
agency to provide an opportunity for public comment on
the IRIS handbook before formally adopting it for use. The
After EPA posts a final assessment, the Information Quality
IRIS handbook is intended to provide standard operating
Act (44 U.S.C. 3516 note) provides a mechanism for
procedures for completing an IRIS assessment. Upon
interested persons to request that EPA correct parts of the
preparing a draft IRIS handbook, EPA requested the
assessment that do not meet the agency’s own Information
National Academies of Science, Engineering, and Medicine
Quality Guidelines. EPA has received requests for
(NASEM) to review the procedures and considerations
corrections to certain IRIS assessments. Generally, the
outlined in the handbook for completing an IRIS
agency has found that these requests reiterate concerns
assessment. NASEM completed its review in November
expressed and already considered earlier in the process. If
2021, and EPA anticipates issuing a final IRIS handbook by
EPA relies on the findings of a final IRIS assessment in
2023. For FY2022 appropriations, the House and Senate
rulemaking, that assessment becomes part of the
Committees on Appropriations directed EPA to “continue
rulemaking record, which is subject to public comment
the IRIS program within the Office of Research and
upon the proposal of the rule. Upon promulgation of a rule,
Development and to utilize the IRIS program to support the
the Administrative Procedure Act (5 U.S.C. 500 et seq.) and
Agency’s mission to protect human health and the
various environmental pollution control statutes provide the
environment.”
opportunity for judicial review of the rule, including the
rulemaking record.
Legislation in the 117th Congress
In the 117th Congress, one bill focuses on making changes
In January 2021, the U.S. Government Accountability
to the administrative aspects of completing an IRIS
Office (GAO) found that EPA has not produced timely
assessment. H.R. 62 would amend Section 7 of the
assessments. GAO also noted that EPA has not identified
Environmental Research, Development, and Demonstration
the resources needed by the IRIS program to meet user
Act of 1978 (42 U.S.C. 4364) to decentralize IRIS
needs for chemical assessments.
assessment activities from EPA’s Office of Research and
Development to the agency’s program and regional offices.
Use of Toxicity Information to Evaluate Risk
H.R. 62 would also establish a hazard identification and
EPA may use the findings of IRIS assessments to inform
dose-response steering committee within EPA to coordinate
various agency actions, including
relevant assessments. These assessments would be subject
to certain scientific standards.
the registration of pesticides under the Federal
Insecticide, Fungicide, and Rodenticide Act;
Concluding Observations
In December 2018, EPA’s IRIS program office announced
the establishment of National Emission Standards for
its selection of 13 chemical assessments to prepare. The
Hazardous Air Pollutants under the Clean Air Act;
office also announced its plans to discontinue or suspend
certain ongoing assessments not identified as priorities.
the establishment of Effluent Guidelines and Human
Given limited resources to assess chemicals, EPA must
Health Ambient Water Quality Criteria under the Clean
choose specific assessments to complete over others. In
Water Act;
some cases, prioritizing certain assessments may delay the
dissemination of assessment findings that may help to
the establishment of a maximum contaminant level
inform specific agency actions. In June 2021, EPA
under the Safe Drinking Water Act; and
announced it would reinitiate the development of four
chemical assessments that had been previously suspended.
the selection of screening levels and cleanup standards
Many past IRIS assessments have gained near-consensus
in the federal remediation of contaminated sites under
approval, but others have led to disagreement among
the Comprehensive Environmental Response, Liability,
stakeholders. As a result, stakeholders are expected to
and Compensation Act.
continue their scrutiny of the program.
Congressional Action
Jerry H. Yen, Analyst in Environmental Policy
Congress has included language focused on improving the
IRIS program in explanatory statements accompanying
IF11680
https://crsreports.congress.gov
U.S. Environmental Protection Agency’s Integrated Risk Information System (IRIS): Toxicity Assessment of Chemicals
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https://crsreports.congress.gov | IF11680 · VERSION 2 · UPDATED