Integrated Risk Information System (IRIS) Database - Details The primary types of health assessments in IRIS are oral RfDs, inhalation RfCs and carcinogen assessments. Reference doses and concentrations are estimated human chemical exposures over a lifetime which are just below the expected threshold for adverse health effects. The carcinogen assessments include: a weight-of-evidence classification, oral and inhalation quantitative risk information, including slope factors, along with risk units calculated from those slope factors. A slope factor is the estimated lifetime cancer risk per unit of the chemical absorbed, assuming lifetime exposure. The health assessment information contained in IRIS, except as noted, has been reviewed and agreed upon by two interdisciplinary review groups of EPA scientists who have extensive experience in risk assessment. Thus, the information in IRIS represents an expert Agency concensus. This Agency-wide agreement on risk information is one of the most valuable aspects of IRIS. Chemicals are added to IRIS on a regular basis. Chemical file sections in the system will be updated as new information is made available to the two review groups. Because exposure assessment pertains to exposure at a particular place, IRIS cannot provide situational information on exposure. IRIS can be used with an exposure assessment to characterize the risk of chemical exposure. This risk characterization can be used to decide what must be done to protect human health. The database contains oral RfDs for 340 chemicals, inhalation RfC summaries for 25 chemicals, and carcinogen slope factors for 180 chemicals. The following information is quoted from the Introduction section of the IRIS database. INTRODUCTION TO IRIS OVERVIEW OF IRIS 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 health risk and U.S. EPA regulatory information on specific chemicals. IRIS was developed for EPA staff in response to a growing demand for consistent risk information on chemical substances for use in decision-making and regulatory activities. IRIS is designed for EPA staff, but is also accessible to state and local environmental health agencies. The information in IRIS is intended for EPA staff 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 numerical information in the following categories: -- Oral and inhalation reference doses (RfDs) for chronic noncarcinogenic health effects -- Oral and inhalation slope factors and unit risks for chronic exposures to carcinogens 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 and list of chemicals by CAS (Chemical Abstracts Service) number. -- Background documents describing the rationales and methods used in arriving at the results shown in the chemical files. -- Glossaries in which definitions are provided for the acronyms, abbreviations, and specialized risk assessment terms used in the chemical files and in the background documents. 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, p. 18). 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: 1. Hazard identification; 2. Dose-response assessment; 3. Exposure assessment; and 4. Risk characterizaton, 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 which 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, which 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's Reference Dose Work Group or Carcinogen Risk Assessment Verification Endeavor Work Group, respectively. These two work groups include high-level scientists from EPA's program offices and Office of Research and Development. Individual EPA offices have conducted comprehensive scientific reviews of the literature available on the particular chemical, and have performed the first two steps of risk assessment: hazard evaluation and dose-response assessment. These assessments have been summarized in the IRIS format and reviewed and revised by the appropriate Work Group. As new information becomes available, these Work Groups will reevaluate their work and revise IRIS files accordingly. For more information on these two Work Groups, contact the Risk Assessment Hotline in EPA's Environmental Criteria and Assessment Office, Cincinnati, OH (Telephone 513/569-7254 or FAX 513/569-7916). 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. Pricing: Current Edition $77.00 Sample File: Integrated Risk Information System (IRIS) (19-page Sample Extract) 53,820 bytes. IRIS0316 1,3,5-Trinitrobenzene; CASRN 99-35-4 (10-page, 10/01/97-revision file) 26,450 bytes. 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