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Introduction to IRIS
OVERVIEW
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:
-- Alphabetical list of the chemical files in IRIS, SEARCHable by
name and CASRN (Chemical Abstracts Service Registry Number).
-- Background documents and references that describe the rationales
and methods used to develop the values and associated information
in the chemical files.
-- A discussion of the limitations to the use of information in IRIS.
-- A GLOSSARY of scientific terms used in the chemical files and in
the background documents, and 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 parts of 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 Risk Information Hotline in EPA's National Center for Environmental
Assessment, Cincinnati, OH (Telephone 513-569-7254 or FAX 513-569-7159 or email
RIH.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.
Last updated: 20 February 1998
URL: http:/www.epa.gov/iris/INTRO.HTM
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