November 10, 2020
U.S. Environmental Protection Agency’s Integrated Risk
Information System (IRIS): Toxicity Assessment of Chemicals
The U.S. Environmental Protection Agency (EPA)
conduct an assessment with a more narrow scope, focusing
established the Integrated Risk Information System (IRIS)
on a specific pathway of exposure or health effect. This
program in 1985 to consolidate human health toxicity
approach allows the agency to finalize an assessment more
assessments that the agency had prepared in order to
quickly. EPA’s selection of which chemicals to assess has
implement various pollution control statutes (e.g., Clean Air
received scrutiny on occasion. For example, after some of
Act and Clean Water Act). Specific incidents, such as the
EPA’s announcements of upcoming IRIS assessments,
1984 leak of methyl isocyanate from a Union Carbide
observers have raised questions about whether the agency’s
facility in Bhopal, India, reinforced the need for a better
plans reflect an appropriate assessment of high priorities.
understanding of human health toxicity from exposure to
various chemicals. Over time, findings from IRIS
Assessment Process
assessments have informed many different agency actions,
Since 2016, EPA has included a preamble in each IRIS
including regulatory requirements that EPA has established
assessment that summarizes the objectives and scope of the
under various pollution control statutes. Given that these
IRIS program, general principles and systematic procedures
actions may require regulated entities to incur significant
used in developing assessments, and the overall
compliance costs and determine the extent of health
development process and document structure. The preamble
benefits, the process that EPA follows to conduct IRIS
is accompanied by the preface, which is chemical-specific
assessments and the findings of such assessments have
and describes procedures in the assessment that differ from
received considerable attention.
the general procedures described in the preamble.
EPA’s IRIS program is not authorized explicitly in statute,
In the preamble of each IRIS assessment since 2016, EPA
but multiple pollution control statutes include general
describes seven steps for developing IRIS assessments:
research provisions intended for the agency to generate
information that may be useful in the implementation of
Step 1. Draft development;
such statutes. Additionally, EPA continues to receive
Step 2. Agency review;
annual appropriations to its Science and Technology
account that largely funds its research efforts, including the
Step 3. Interagency science consultation;
IRIS program.
Step 4. Public comment, followed by external peer
EPA maintains a public IRIS website that provides more
review;
than 560 assessments on a range of chemicals. EPA
Step 5. Assessment revision;
completed more than 80% of these assessments before
1995. However, assessments completed more than 25 years
Step 6. Final agency reviews and interagency science
ago may still be relevant if no new information is available
discussion; and
to warrant a revision of the existing assessment.
Step 7. Post final assessment.
Selection of Chemicals to Assess
EPA staff preparing IRIS assessments may revisit prior
EPA staff managing the IRIS program select chemicals for
steps of the process based on input from program and
IRIS assessments through a prioritization process. This
regional offices, other agencies, peer reviewers, or the
involves soliciting internal input from EPA program and
public. The process, from start to finish for assessments
regional offices on which assessments may be useful and
completed since 2013, has typically spanned at least five
evaluating the extent to which resources and expertise are
years, with the ethylene oxide carcinogenicity assessment
available to complete the assessments. Changes in these and
taking 17 years. EPA now states that it aims to complete an
other factors may also lead EPA to withdraw an initiated
assessment within three years.
assessment before it is completed. EPA began issuing an
IRIS Program Outlook in December 2018 to provide
After selecting a chemical to assess and prior to developing
periodic updates on the development of IRIS assessments.
a draft assessment, EPA generally prepares a series of
documents that detail how the agency plans to develop the
Given limited resources and many chemicals to assess, EPA
draft. EPA practice is to issue each of these documents for
has decided to focus on a select number of assessments at
public comment, which may help to inform how the agency
any given time. Assessments that examine multiple
performs the assessment. The first document that EPA
pathways of exposure (e.g., ingestion, inhalation, or direct
prepares for an assessment is the scoping document, which
contact) and potential health effects typically take many
describes the chemical being assessed, potential routes and
years to prepare. In some instances, EPA may decide to
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U.S. Environmental Protection Agency’s Integrated Risk Information System (IRIS): Toxicity Assessment of Chemicals
durations of exposure to examine, considerations for
Congressional Action
susceptible populations and different life stages, and other
Congress has included language focused on improving the
topics of interest. After receiving public comment for the
IRIS program in explanatory statements accompanying
scoping document and finalizing it, EPA prepares a
multiple annual appropriations acts. For example, in the
problem formulation that identifies the scientific issues that
FY2001 appropriations process, Congress requested that
the agency expects to address based on a preliminary
EPA conduct “needs assessments” to determine the
literature search. Additionally, EPA generally identifies
appropriate pace for completing IRIS assessments.
protocols that the agency intends to use for the specific
assessment. The problem formulation and description of
As part of the FY2018, FY2019, and FY2020
protocols are published for public comment.
appropriations processes, the House and Senate Committees
on Appropriations have directed EPA to maintain funding
After the development of a draft IRIS assessment, the
for IRIS at FY2017 levels. The committees also have urged
agency’s IRIS staff generally seeks input on the draft from
expedited completion of an IRIS handbook and directed the
EPA program and regional offices, other federal agencies,
agency to provide an opportunity for public comment on
external peer reviewers, and the public. Since 2014, EPA
the IRIS handbook before formally adopting it for use. The
has submitted draft IRIS assessments to the Chemical
IRIS handbook is intended to provide standard operating
Assessment Advisory Committee within its Science
procedures for completing an IRIS assessment. To date,
Advisory Board for external peer review. Final IRIS
EPA has not issued an IRIS handbook.
assessments generally include a list of authors, contributors,
intra- and inter-agency reviewers, and external peer
Legislation in the 116th Congress
reviewers who contributed to the review of the assessment
H.R. 89 would amend Section 7 of the Environmental
at various stages of its development.
Research, Development, and Demonstration Act of 1978
(42 U.S.C. 4364) to decentralize IRIS assessment activities
After EPA posts a final assessment, the Information Quality
from EPA’s Office of Research and Development to the
Act (44 U.S.C. 3516 note) provides a mechanism for
agency’s program and regional offices. H.R. 89 would also
interested persons to request that EPA correct parts of the
establish a hazard identification and dose-response steering
assessment that do not meet the agency’s own Information
committee within EPA to coordinate relevant assessments.
Quality Guidelines. EPA has received requests for
These assessments would be subject to certain scientific
corrections to certain IRIS assessments. Generally, the
standards. Other bills would require EPA to take certain
agency has found that these requests reiterate concerns
actions based on findings of an IRIS assessment. H.R. 1165
expressed and already considered earlier in the process. If
and S. 451 would require EPA to consider findings of an
EPA relies on the findings of a final IRIS assessment in
IRIS assessment in relevant rulemaking and evaluate
rulemaking, that assessment becomes part of the
potential adverse effects from industrial sources of a
rulemaking record, which is subject to public comment
chemical recently evaluated under IRIS. S. 2980 would
upon the proposal of the rule. Upon promulgation of a rule,
require EPA to promulgate effluent limitations and
the Administrative Procedure Act (5 U.S.C. 500 et seq.) and
pretreatment standards under the Clean Water Act (33
various environmental pollution control statutes provide the
U.S.C. 1251 et seq.) for per- and polyfluoroalkyl substances
opportunity for judicial review of the rule, including the
(PFAS) that have a specific draft toxicity value under the
rulemaking record.
IRIS program. H.R. 4447 and H.R. 5842 would authorize
EPA to award grants to eligible communities to participate
Use of Toxicity Information to Evaluate Risk
in decisions that relate to an actual or potential release of a
EPA may use the findings of IRIS assessments to inform
covered hazardous air pollutant, which includes any
various agency actions, including
chemical classified as carcinogenic by an IRIS assessment.
the registration of pesticides under the Federal
Concluding Observations
Insecticide, Fungicide, and Rodenticide Act;
In December 2018, EPA’s IRIS program office announced
its selection of 13 chemical assessments to prepare. The
the establishment of National Emission Standards for
office also announced its plans to discontinue or suspend
Hazardous Air Pollutants under the Clean Air Act;
certain ongoing assessments not identified as priorities.
Given limited resources to assess chemicals, EPA must
the establishment of Effluent Guidelines and Human
choose specific assessments to complete over others. In
Health Ambient Water Quality Criteria under the Clean
some cases, prioritizing certain assessments may delay the
Water Act;
dissemination of assessment findings that may help to
inform specific agency actions. Many past IRIS
the establishment of a maximum contaminant level
assessments have gained near-consensus approval, but
under the Safe Drinking Water Act; and
others have led to disagreement among stakeholders. As a
result, stakeholders are expected to continue their scrutiny
the selection of screening levels and cleanup standards
of the program.
in the federal remediation of contaminated sites under
the Comprehensive Environmental Response, Liability,
Jerry H. Yen, Analyst in Environmental Policy
and Compensation Act.
IF11680
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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 1 · NEW