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)

established the Integrated Risk Information System (IRIS)

program in 1985 to consolidate human health toxicity

assessments that the agency had prepared in order to

implement various pollution control statutes (e.g., Clean Air

Act and Clean Water Act). Specific incidents, such as the

1984 leak of methyl isocyanate from a Union Carbide

facility in Bhopal, India, reinforced the need for a better

understanding of human health toxicity from exposure to

various chemicals. Over time, findings from IRIS

assessments have informed many different agency actions,

including regulatory requirements that EPA has established

under various pollution control statutes. Given that these

actions may require regulated entities to incur significant

compliance costs and determine the extent of health

benefits, the process that EPA follows to conduct IRIS

assessments and the findings of such assessments have

received considerable attention.

EPA’s IRIS program is not authorized explicitly in statute,

but multiple pollution control statutes include general

research provisions intended for the agency to generate

information that may be useful in the implementation of

such statutes. Additionally, EPA continues to receive

annual appropriations to its Science and Technology (S&T)

account that largely funds its research efforts, including the

IRIS program.

EPA maintains a public IRIS website that provides more

than 560 assessments on a range of chemicals. EPA

completed more than 80% of these assessments before

1995. However, assessments completed more than 25 years

ago may still be relevant if no new information is available

to warrant a revision of the existing assessment.

Selection of Chemicals to Assess

EPA focuses on a select number of assessments at any

given time. EPA staff managing the IRIS program select

chemicals for IRIS assessments through a prioritization

process, which involves soliciting internal input from EPA

program and regional offices on which assessments may be

useful and evaluating the extent to which resources and

expertise are available to complete the assessments. EPA

began issuing an IRIS Program Outlook in December 2018

to provide periodic updates on the development of IRIS

assessments.

Assessments that examine multiple pathways of exposure

(e.g., ingestion, inhalation, or direct contact) and potential

associated health effects typically take many years to

prepare. In some instances, EPA may decide to conduct an

assessment with a more narrow scope, focusing on a

specific pathway of exposure or health effect. According to

EPA, this approach allows the agency to finalize an

assessment more quickly. EPA’s selection of which

chemicals to assess has received scrutiny on occasion. For

example, after some of EPA’s announcements of upcoming

IRIS assessments, observers have raised questions about

whether the agency’s plans reflect an appropriate

assessment of high priorities. In some instances, EPA has

withdrawn an initiated assessment before it is completed

due to a change in priorities.

Assessment Process

Since 2016, EPA has included a preamble in each IRIS

assessment that summarizes the objectives and scope of the

IRIS program, general principles and systematic procedures

used in developing assessments, and the overall

development process and document structure. The preamble

is accompanied by the preface, which is chemical-specific

and describes procedures in the assessment that differ from

the general procedures described in the preamble. In the

preamble of each IRIS assessment since 2016, EPA

describes seven steps for developing IRIS assessments: (1)

draft development; (2) agency review; (3) interagency

science consultation; (4) public comment, followed by

external peer review; (5) assessment revision; (6) final

agency reviews and interagency science discussion; and (7)

post final assessment.

EPA staff preparing IRIS assessments may revisit prior

steps of the process based on input from program and

regional offices, other agencies, peer reviewers, or the

public. The process, from start to finish for assessments

completed since 2013, has typically spanned at least five

years, with the ethylene oxide carcinogenicity assessment

taking 17 years. EPA now states that it aims to complete an

assessment within three years.

After selecting a chemical to assess and prior to developing

a draft assessment, EPA generally prepares a series of

documents that detail how the agency plans to develop the

draft. EPA practice is to issue each of these documents for

public comment, which may help to inform how the agency

performs the assessment. The first document that EPA

prepares for an assessment is the scoping document, which

describes the chemical being assessed, potential routes and

durations of exposure to examine, considerations for

susceptible populations and different life stages, and other

topics of interest. After receiving public comment for the

scoping document and finalizing it, EPA prepares a

problem formulation that identifies the scientific issues that

the agency expects to address based on a preliminary

literature search. Additionally, EPA generally identifies

protocols that the agency intends to use for the specific

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U.S. Environmental Protection Agency’s Integrated Risk Information System (IRIS): Toxicity Assessment of Chemicals

assessment. The problem formulation and description of

protocols are published for public comment.

After the development of a draft IRIS assessment, the

agency’s IRIS staff generally seeks input on the draft from

EPA program and regional offices, other federal agencies,

external peer reviewers, and the public. Since 2014, EPA

has submitted draft IRIS assessments to the Chemical

Assessment Advisory Committee within its Science

Advisory Board for external peer review. Final IRIS

assessments generally include a list of authors, contributors,

intra- and inter-agency reviewers, and external peer

reviewers who contributed to the review of the assessment

at various stages of its development.

After EPA posts a final assessment, the Information Quality

Act (44 U.S.C. 3516 note) provides a mechanism for

interested persons to request that EPA correct parts of the

assessment that do not meet the agency’s own Information

Quality Guidelines. EPA has received requests for

corrections to certain IRIS assessments. Generally, the

agency has found that these requests reiterate concerns

expressed and already considered earlier in the process. If

EPA relies on the findings of a final IRIS assessment in

rulemaking, that assessment becomes part of the

rulemaking record, which is subject to public comment

upon the proposal of the rule. Upon promulgation of a rule,

the Administrative Procedure Act (5 U.S.C. 500 et seq.) and

various environmental pollution control statutes provide the

opportunity for judicial review of the rule, including the

rulemaking record.

In January 2021, the U.S. Government Accountability

Office (GAO) found that EPA has not produced timely

assessments. GAO also noted that EPA has not identified

the resources needed by the IRIS program to meet user

needs for chemical assessments.

Use of Toxicity Information to Evaluate Risk

EPA may use the findings of IRIS assessments to inform

various agency actions, including

 the registration of pesticides under the Federal

Insecticide, Fungicide, and Rodenticide Act;

 the establishment of National Emission Standards for

Hazardous Air Pollutants under the Clean Air Act;

 the establishment of Effluent Guidelines and Human

Health Ambient Water Quality Criteria under the Clean

Water Act;

 the establishment of a maximum contaminant level

under the Safe Drinking Water Act; and

 the selection of screening levels and cleanup standards

in the federal remediation of contaminated sites under

the Comprehensive Environmental Response, Liability,

and Compensation Act.

Congressional Action

Congress has included language focused on improving the

IRIS program in explanatory statements accompanying

multiple annual appropriations acts. For example, in the

FY2001 appropriations process, Congress requested that

EPA conduct “needs assessments” to determine the

appropriate pace for completing IRIS assessments. Also,

certain Members have requested GAO and EPA’s Office of

Inspector General examine aspects of EPA’s IRIS program

to provide recommendations for improving the program.

As part of the FY2018, FY2019, and FY2020

appropriations processes, the House and Senate Committees

on Appropriations directed EPA to maintain funding for

IRIS at FY2017 levels. The committees also urged

expedited completion of an IRIS handbook and directed the

agency to provide an opportunity for public comment on

the IRIS handbook before formally adopting it for use. The

IRIS handbook is intended to provide standard operating

procedures for completing an IRIS assessment. Upon

preparing a draft IRIS handbook, EPA requested the

National Academies of Science, Engineering, and Medicine

(NASEM) to review the procedures and considerations

outlined in the handbook for completing an IRIS

assessment. NASEM completed its review in November

2021, and EPA anticipates issuing a final IRIS handbook by

2023. For FY2022 appropriations, the House and Senate

Committees on Appropriations directed EPA to “continue

the IRIS program within the Office of Research and

Development and to utilize the IRIS program to support the

Agency’s mission to protect human health and the

environment.”

Legislation in the 117th Congress

In the 117th Congress, one bill focuses on making changes

to the administrative aspects of completing an IRIS

assessment. H.R. 62 would amend Section 7 of the

Environmental Research, Development, and Demonstration

Act of 1978 (42 U.S.C. 4364) to decentralize IRIS

assessment activities from EPA’s Office of Research and

Development to the agency’s program and regional offices.

H.R. 62 would also establish a hazard identification and

dose-response steering committee within EPA to coordinate

relevant assessments. These assessments would be subject

to certain scientific standards.

Concluding Observations

In December 2018, EPA’s IRIS program office announced

its selection of 13 chemical assessments to prepare. The

office also announced its plans to discontinue or suspend

certain ongoing assessments not identified as priorities.

Given limited resources to assess chemicals, EPA must

choose specific assessments to complete over others. In

some cases, prioritizing certain assessments may delay the

dissemination of assessment findings that may help to

inform specific agency actions. In June 2021, EPA

announced it would reinitiate the development of four

chemical assessments that had been previously suspended.

Many past IRIS assessments have gained near-consensus

approval, but others have led to disagreement among

stakeholders. As a result, stakeholders are expected to

continue their scrutiny of the program.

Jerry H. Yen, Analyst in Environmental Policy

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U.S. Environmental Protection Agency’s Integrated Risk Information System (IRIS): Toxicity Assessment of Chemicals

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