Uranium, natural

CASRN 7440-61-1

IRIS Assessment Plan for Uranium (Scoping and Problem Formulation Materials)

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In January 2018, EPA released the IRIS Assessment Plan for Uranium (Oral Reference Dose) (Scoping and Problem Formulation Materials). An IRIS Assessment Plan (IAP) communicates to the public the plan for assessing each individual chemical and includes summary information on the IRIS Program’s scoping and initial problem formulation; objectives and specific aims for the assessment; the PECO (Populations, Exposures, Comparators, and Outcomes) criteria that outlines the evidence considered most pertinent to the assessment; and identification of key areas of scientific complexity. The PECO provides the framework for developing literature search strategies and inclusion/exclusion criteria, particularly with respect to evidence stream (i.e., human, animal, mechanistic), exposure measures and outcome measures.


U.S. EPA. IRIS Assessment Plan for Uranium (Scoping and Problem Formulation Materials). U.S. Environmental Protection Agency, Washington, DC, EPA/635/R-17/787, 2018.

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Uranium is a naturally occurring radioactive element which in nature is a mixture of three isotopes: 234U, 235U, and 238U. The most common isotope, 238U, makes up a majority natural uranium. Uranium is enriched by processes that remove and concentrate 235U, with the remaining uranium being termed "depleted." Enriched uranium is used in nuclear reactor fuel and in nuclear weapons; it is not a subject of this assessment. Due to its physical properties, depleted uranium is used as a counterbalance in aircraft applications, for shielding against ionizing radiation, and both in military armor and in armor penetrating munitions.

Environmental exposures to uranium include ingestion of soil, foods, surface water, or groundwater including ingestion of locally grown or foraged food. Uranium is naturally present in many soils with higher concentrations found in the western United States. Uranium mining, milling, and processing operations can release this element into the environment leading to elevated levels of uranium in affected soils and dusts. The general population is primarily exposed to uranium through intake of food and drinking water.


Date Description
01-Jan 2018EPA released the IRIS Assessment Plan (IAP) for Uranium (Oral Reference Dose). EPA also identified an incorrect docket number associated with the IAP in the Federal Register Notice. EPA is working to correct this, and will issue a corrected notice shortly. [Federal Register Notice Jan 31, 2018]
02-Feb 2018EPA posted a correction to the docket number for public comments on the draft IAP. [Federal Register Notice Feb 16, 2018]
03-Mar 2018EPA hosted an IRIS Public Science Meeting (Webinar Only) to discuss this chemical on March 22, 2018.
04-Apr 2019EPA suspended the assessment in fiscal year 2019. It may be restarted as Agency priorities change.
05-Jun 2021This assessments was unsuspended and included in the June 2021 IRIS Program Outlook as a chemical back under development.

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