Basic Information about the Integrated Risk Information System

On this page:

EPA’s mission is to protect human health and the environment. EPA’s IRIS Program supports this mission by identifying and characterizing the health hazards of chemicals found in the environment. Each IRIS assessment can cover a chemical, a group of related chemicals, or a complex mixture. IRIS assessments are an important source of toxicity information used by EPA, state and local health agencies, other federal agencies, and international health organizations.

The IRIS Program is located within EPA’s Center for Public Health and Environmental Assessment (CPHEA) in the Office of Research and Development (ORD). The placement of the IRIS Program in ORD is intentional. It ensures that IRIS can develop impartial toxicity information independent of its use by EPA’s program and regional offices to set national standards and clean up hazardous sites.

IRIS Toxicity Values

IRIS assessments provide the following toxicity values for health effects resulting from chronic exposure to chemicals.

More information on deriving RfD and RfC values can be found in EPA’s 2002 A Review of the Reference Dose and Reference Concentration Processes.

RfC An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty factors generally applied to reflect limitations of the data used. Generally used in EPA's noncancer health assessments. [Durations include acute, short-term, subchronic, and chronic and are defined individually in this glossary].: An estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark concentration, with uncertainty factors generally applied to reflect limitations of the data used.

RfDAn estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty factors generally applied to reflect limitations of the data used. Generally used in EPA's noncancer health assessments. [Durations include acute, short-term, subchronic, and chronic and are defined individually in this glossary].: An estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. It can be derived from a NOAEL, LOAEL, or benchmark dose, with uncertainty factors generally applied to reflect limitations of the data used.

More information on deriving cancer risk estimates can be found in EPA’s 2005 Guidelines for Carcinogen Risk Assessment.

Cancer descriptors characterize the chemical as:

  • Carcinogenic to Humans
  • Likely to Be Carcinogenic to Humans
  • Suggestive Evidence of Carcinogenic Potential
  • Inadequate Information to Assess Carcinogenic Potential
  • Not Likely to Be Carcinogenic to Humans

Oral slope factor An upper bound, approximating a 95% confidence limit, on the increased cancer risk from a lifetime oral exposure to an agent. This estimate, usually expressed in units of proportion (of a population) affected per mg/kg-day, is generally reserved for use in the low-dose region of the dose-response relationship, that is, for exposures corresponding to risks less than 1 in 100. (OSF) is an estimate of the increased cancer risk from oral exposure to a dose of 1 mg/kg-day for a lifetime. The OSF can be multiplied by an estimate of lifetime exposure (in mg/kg-day) to estimate the lifetime cancer risk.

Inhalation unit riskThe upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent at a concentration of 1 µg/L in water, or 1 µg/m³ in air. The interpretation of unit risk would be as follows: if unit risk = 2 × 10⁻⁶ per µg/L, 2 excess cancer cases (upper bound estimate) are expected to develop per 1,000,000 people if exposed daily for a lifetime to 1 µg of the chemical per liter of drinking water. (IUR) is an estimate of the increased cancer risk from inhalation exposure to a concentration of 1 µg/m3 for a lifetime. The IUR can be multiplied by an estimate of lifetime exposure (in µg/m3) to estimate the lifetime cancer risk.

What's the Role of IRIS Assessments in Risk Assessment?

Risk assessment is a four-step process described by the National Research Council (NRC) in 1983 as "the characterization of the potential adverse health effects of human exposures to environmental hazards." Characterizing risk involves integrating information on hazard, dose-response, and exposure.

Connection between IRIS, Risk Assessment, and Risk Management
Illustration of the first 2 steps of a human health risk assessment to risk management.
Click to enlarge: Connection Between IRIS and Risk Management

An IRIS assessment includes the first two steps of the risk assessment process:

  • Hazard Identification, which identifies credible health hazards associated with exposure to a chemical, and
  • Dose-Response Assessment, which characterizes the quantitative relationship between chemical exposure and each credible health hazard. These quantitative relationships are then used to derive toxicity values.

EPA’s program and regional offices identify human exposure pathways and estimate the amount of human exposure under different exposure scenarios (Exposure Assessment). Then they combine their exposure assessment with the hazard information and toxicity values from IRIS to characterize potential public health risks (Risk Characterization).

Guidelines & Tools

IRIS Glossary

IRIS's Glossary has been moved to the EPA shared terminology service database. Would you like to search the IRIS Glossary for a definition?

EPA follows Agency guidelines in developing IRIS assessments. Key guidelines, technical documents and a few popular tools used by the IRIS Program for developing assessments are listed below. Additional Agency guidelines, models and tools are available at the EPA Risk Assessment website.

EPA Guidelines Documents

Tools

EPA Guidelines Documents

EPA Cancer Guidelines

EPA Risk Assessment Guidelines

EPA Science Policy Council Guidelines

Other Guidelines Documents and Technical Panel Reports

References Cited in Older Assessment Documents but Superseded by More Recent Guidelines

Tools

Health and Environmental Research Online (HERO)

HERO is a searchable database of more than 1.6 million scientific studies and other references used to support the development of EPA assessments. Each HERO record provides detailed bibliographic information. Since 2010, all citations in new IRIS assessments are linked to entries in the HERO database.

Benchmark Dose Software (BMDS)

Benchmark dose (BMD) modeling is EPA’s preferred approach for deriving points of departure (PODs) used to develop toxicity values. Use of BMD modeling involves fitting a set of mathematical models to dose-response data from human and animal studies. EPA’s benchmark dose software (BMDS) was designed to facilitate the application of BMD methods in dose-response assessment.

IRIS Process for Developing Human Health Assessments

IRIS Process Diagram Illustrates the 7-Step Process for Developing IRIS Assessment
Click to enlarge: IRIS Process Figure

Step 1. Draft Development

Beginning an assessment, EPA’s Office of Research and Development (ORD) undertakes scoping and problem formulation to ensure that the product meets the scientific needs of the EPA program or regional office(s) requesting the assessment. These activities help focus the assessment by describing the routes of exposure, potential health effects, types of studies, and key science issues to be considered in the assessment. EPA ORD also develops an assessment protocol which presents the systematic review and dose-response methods being used to develop the draft assessment. EPA releases these preliminary assessment materials to obtain input from the scientific community and general public. A public science meeting may be held to obtain additional input.

For more detailed information on the methods used to develop a draft IRIS assessment, visit the “ORD Staff Handbook for Developing IRIS Assessments,” or “IRIS Handbook” webpage.

Step 2. Agency Review

Scientists in EPA’s program offices and regions review the draft assessment.

Step 3. Interagency Science Consultation

EPA ORD leads other federal agencies and departments in a review of the draft assessment.

Step 4. Public Comment and External Peer Review

After revising based on Agency and Interagency comments, a draft assessment and charge questions are released for public comment and peer review.

Step 5. Revise Assessment

The assessment is revised to address public comments and peer review recommendations, and a disposition of peer reviewer and public comments is developed.

Step 6. Final Agency Review/Interagency Science Discussion

The revised assessment is reviewed by EPA’s program offices and regions and other federal agencies and departments.

Step 7. Final Assessment

The final IRIS assessment is posted to the IRIS website.

Note: To learn more about the historical development of the IRIS Process, see the history of IRIS.

History of IRIS

 

IRIS

Contact Us about IRIS
Contact Us to ask a question, provide feedback, or report a problem.
Last updated on October 21, 2024