What is IRIS?

Introduction

The Integrated Risk Information System (IRIS), prepared and maintained by the U.S. Environmental Protection Agency (U.S. EPA), is an electronic data base containing information on human health effects that may result from exposure to various chemicals in the environment. IRIS was initially developed for EPA staff in response to a growing demand for consistent information on chemical substances for use in risk assessments, decision-making and regulatory activities. The information in IRIS is intended for those without extensive training in toxicology, but with some knowledge of health sciences.

The heart of the IRIS system is its collection of computer files covering individual chemicals. These chemical files contain descriptive and quantitative information in the following categories:

Oral reference doses and inhalation reference concentrations (RfDs and RfCs, respectively) for chronic noncarcinogenic health effects. Hazard identification, oral slope factors, and oral and inhalation unit risks for carcinogenic effects.

To aid users in accessing and understanding the data in the IRIS chemical files, the following supportive documentation is provided:

IRIS Background documents. A discussion of the limitations of IRIS information. An IRIS glossary of scientific terms, and a A definition of acronyms and abbreviations used.

Risk Assessment and Risk Management

The information in IRIS is intended for use in protecting public health through risk assessment and risk management. These two processes are briefly explained below.

Risk assessment has been defined as "the characterization of the potential adverse health effects of human exposures to environmental hazards" (NRC,1983). In a risk assessment, the extent to which a group of people has been or may be exposed to a certain chemical is determined, and the extent of exposure is then considered in relation to the kind and degree of hazard posed by the chemical, thereby permitting an estimate to be made of the present or potential health risk to the group of people involved.

Risk assessment information is used in the risk management process in deciding how to protect public health. Examples of risk management actions include deciding how much of a chemical a company may discharge into a river; deciding which substances may be stored at a hazardous waste disposal facility; deciding to what extent a hazardous waste site must be cleaned up; setting permit levels for discharge, storage, or transport; establishing levels for air emissions; and determining allowable levels of contamination in drinking water.

Essentially, risk assessment provides INFORMATION on the health risk, and risk management is the ACTION taken based on that information.

A complete risk assessment consists of the following four steps:

Hazard identification; Dose-response assessment; Exposure assessment; and Risk characterization,

with risk characterization being the transitional step to risk management.

The following discussion of the four steps of risk assessment was excerpted from "Principles of Risk Assessment: A Nontechnical Review":

Hazard identification involves gathering and evaluating data on the types of health injury or disease that may be produced by a chemical and on the conditions of exposure under which injury or disease is produced. It may also involve characterization of the behavior of a chemical within the body and the interactions it undergoes with organs, cells, or even partsof cells. Data of the latter types may be of value in answering the ultimate question of whether the forms of toxicity known to be produced by a substance in one population group or in experimental settings are also likely to be produced in humans. Hazard identification is not risk assessment; we are simply determining whether it is scientifically correct to infer that toxic effects observed in one setting will occur in other settings (e.g., whether substances found to be carcinogenic or teratogenic in experimental animals are likely to have the same results in humans).

Dose-response assessment involves describing the quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease. Data are derived from animal studies or, less frequently, from studies in exposed human populations. There may be many different dose-response relationships for a substance if it produces different toxic effects under different conditions of exposure. The risks of a substance cannot be ascertained with any degree of confidence unless dose-response relations are quantified, even if the substance is known to be toxic.

Exposure assessment involves describing the nature and size of the population exposed to a substance and the magnitude and duration of their exposure. The evaluation could concern past or current exposures, or exposures anticipated in the future.

Risk characterization generally involves the integration of the data and analysis of the first three components of the risk assessment process (hazard identification, dose-response assessment, and exposure assessment) to determine the likelihood that humans will experience any of the various forms of toxicity associated with a substance. (In cases where exposure data are not available, hypothetical risk can be characterized by the integration of hazard identification and dose-response evaluation data alone.) A framework to define the significance of the risk is developed, and all of the assumptions, uncertainties, and scientific judgments of the preceding three steps are presented.

The Role of IRIS in Risk Assessment / Risk Management

IRIS is a tool that provides hazard identification and dose-response assessment information, but does not provide situational information on individual instances of exposure. Combined with specific exposure information, the data in IRIS can be used for characterization of the public health risks of a given chemical in a given situation, that can then lead to a risk management decision designed to protect public health.

The information contained in Section I (Chronic Health Hazard Assessment for Noncarcinogenic Effects) and Section II (Carcinogenicity Assessment for Lifetime Exposure) of the chemical files represents a consensus opinion of EPA health scientists representing the Program Offices and the Office of Research and Development. From 1985 to 1995, the consensus bodies were referred to as the RfD/RfC Work Group and the Carcinogen Risk Assessment Verification Endeavor Work Group, or CRAVE. The consensus process involves interpreting the scientific literature applicable to health effects of a chemical, and using established methodologies to develop values for oral reference dose, inhalation reference concentration, carcinogenic slope factor and unit risk. The products of this work, summarized in IRIS and elaborated in chemical-specific support documents, have been subject to EPA's peer review policy since its issuance in 1994. As new scientific information becomes available, EPA will review it, as appropriate, and revise IRIS files accordingly.

For more information on the process for developing information for IRIS,contact the IRIS Hotline in EPA's National Center for Environmental Assessment, contractor facilities, Greenbelt, MD (Telephone 301-345-2870 or FAX 301-345-2876 or email Hotline.IRIS@epamail.epa.gov).

References

NRC (National Research Council). 1983. Risk Assessment in the Federal Government: Managing the Process. National Academy Press, Washington, DC.

U.S. EPA. 1985. Principles of Risk Assessment: A nontechnical review. Prepared for a risk assessment workshop. Easton, MD, March 17-18.

U.S. EPA. 1994. Peer Review and Peer Involvement at the US Environmental Protection Agency.