Assessing RiskFeedback

The Toxicity Assessment uses data from published animal and human studies to identify adverse health effects that might be caused by exposure to the COPCs, as well as the dose at which harmful health effects may occur. For chemicals, harmful effects are broadly categorized as either pertaining to cancer or to noncarcinogenic effects. The adverse effect of primary concern for radionuclides is cancer. For most EPA risk assessments, the results of a chemical-specific toxicity assessment performed by EPA are incorporated into the risk assessment in the form of a cancer slope factor and/or chemical reference dose.

The Agency for Toxic Substances and Disease Registry (ATSDR – www.atsdr.cdc.gov) produces "toxicological profiles" for hazardous substances found at National Priorities List (NPL) sites. These hazardous substances are ranked based on frequency of occurrence at NPL sites, toxicity, and potential for human exposure. Toxicological profiles are developed from a priority list of 275 substances. ATSDR also prepares toxicological profiles for the Department of Defense (DOD) and the Department of Energy (DOE) on substances related to federal sites. So far, 289 toxicological profiles have been published or are under development as "finals" or "drafts for public comment"; 268 profiles were published as finals; 124 profiles have been updated. Currently, 15 profiles are being revised based on public comments received; 7 profiles are under development. These profiles cover more than 250 substances. These profiles can be found on ATSDR's website at www.atsdr.cdc.gov/toxpro2.html. Fact sheets that provide summaries of these hazardous substances are also available at www.atsdr.cdc.gov/toxfaq.html, or www.atsdr.cdc.gov/es/toxfaqs/es_toxfaqs.html.

The primary source of toxicity information for contaminants of concern (risk assessment information) is the Integrated Risk Information System (IRIS) prepared and maintained by EPA. IRIS is an electronic database containing information on human health effects that may result from exposure to various chemicals in the environment. 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, which can then lead to a risk management decision designed to protect public health.

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:

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

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. 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. IRIS also notes general findings from secondary literature sources, Agency for Toxic Substances and Disease Registry’s (ATSDR) toxicological profiles, and study titles and abstracts retrieved from searches of on-line toxicological databases, e.g., MEDLINE and TOXLINE. This recent health effects literature is contained in the "EPA Document and Review" sections for over 500 IRIS summaries. State accepted RfD/RfC and SF may differ from EPA – it is important to identify the lead agency and ensure proper inputs are used in risk assessments.

Traditionally, information and guidance related to exposure risk factors has been associated with adulthood or lifetime exposure rates. As scientific understanding of the risks associated with certain lifestages improves, such as the higher susceptibility of children to exposure risk factors, greater use can be made of data pertaining to age-based subpopulations. For the latest information on exposure risk factors to children, consult the EPA's New Cancer Guidelines for Children.

IRIS users may request information about the review methods and results from the IRIS Hotline at hotline.iris@epa.gov or call 202-566-1676.