Navigating a Newly Posted IRIS Assessment

By Ashley Mayrianne Jones and Lou D’Amico, Ph.D.

Last week, EPA’s Integrated Risk Information System (IRIS) Program released the final assessment of trimethylbenzenes (TMBs). IRIS assessments provide health effects information and toxicity values for cancer and non-cancer health outcomes by using the best available scientific data.  Government and others combine IRIS toxicity values with exposure information to help characterize public health risks of chemical substances and use these assessments to support decisions designed to protect human health.

But you don’t need to wait until an assessment is finalized to learn more about the science that informs the Agency’s risk assessment and risk management decisions.

EPA is committed to transparency and providing information about its research and assessments. IRIS is no exception. Recently, EPA updated their web presence to help the general public find information faster and easier. As part of this update, EPA made significant changes to the IRIS website.

screenshot of the iris website

The online IRIS database contains crucial information from assessments on chemical substances that can be used to support hazard identification and dose-response assessment – two of the four steps in the human health risk assessment process.

So where to begin?  Well, the first place would be the IRIS Program home page at There, you’ll find links to general program materials (such as the IRIS multi-year agenda), a calendar of public meetings and workshops, and an  “About IRIS” page, which explains the IRIS process and program history. You can also sign up for the IRIS listserv using the form at the top of the home page. Even more ways to stay up-to-date on IRIS activities are described under “Staying Connected.”

The quickest option to search for a chemical is to enter the chemical name or CASRN (the CAS registry number – a unique identifier for chemical substances) in the “Search IRIS” box on the middle right of the home page. The “Assessments” link under the search bar on the home page allows for more advanced search options.  Using the link, you can browse chemicals alphabetically, by organ or system, and by current stage in the IRIS process. The quick check provides a convenient way of seeing what step of the IRIS process an ongoing chemical assessment is in.  Each chemical in the IRIS database has a chemical-specific webpage, with links to the toxicological reviews (if available), an IRIS summary of the findings, and key information on toxicity values and the organ systems that may be affected by exposure to a chemical.  Toxicological reviews can be lengthy documents though, and the IRIS summary provides a shorter description of the findings for a given chemical.

Anyone can browse the IRIS database or search for a specific chemical assessment, just like the newly added assessment for trimethylbenzenes (TMBs). TMB’s are a group of volatile hydrocarbons produced during petroleum refining and may be inhaled by exposure to vehicle emissions.  The IRIS assessment for TMBs actually contains information on three isomers: 1,2,3-TMB, 1,2,4-TMB, and 1,3,5-TMB, which all have specific chemical pages on the IRIS website.

scrren shot of the specific page within the IRIS website

Whether you’re interested in TMBs or any other chemical, a wealth of information is available on each chemical’s webpage.  The critical systems affected by a chemical are identified, along with toxicity values (like the reference dose and reference concentration for non-cancer effects) and are provided right on the main page.  For example, TMBs are associated with nervous, respiratory, and hematological system effects.  The carcinogenicity of a chemical is also described through a weight-of-evidence characterization, as well as quantitatively, if appropriate.  Each IRIS assessment provides authoritative, peer-reviewed information on a chemical’s toxicity.

A tremendous amount of work goes into completing the 7-step process to finalize a draft IRIS assessment. EPA releases a number of documents along the way, including past drafts of assessments, comments from interagency reviewers, and preliminary materials used early in assessment development.  Your gateway to all this information is through the “History” tab right on the main page for each chemical entry on the database.

IRIS assessments aren’t regulations, but they provide a critical part of the scientific information for decision-making to protect public health across EPA.  They’re also important resources for state environmental and public health agencies, and are widely used by the scientific community in the U.S and the world.

If you have any questions regarding the IRIS Program or the website, you can always contact us at the IRIS hotline at 202-566-1676 or

About the Authors: Ashley Mayrianne Jones is a student contractor and writer working with the science communication team in EPA’s Office of Research and Development.  Lou D’Amico is the Acting Communications Director for the National Center for Environmental Assessment, which houses the IRIS Program.

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