Uranium, natural

CASRN 7440-61-1 | DTXSID1042522

Protocol for the Uranium IRIS Assessment (Oral) (Preliminary Assessment Materials)

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EPA announced the release of the Protocol for the Uranium IRIS Assessment (Oral) (Preliminary Assessment Materials) for a 30-day public comment period as announced in a February 14, 2024 Federal Register Notice. The deadline for comments is March 15, 2024.


In February 2024, EPA released the Protocol for the Uranium IRIS Assessment (Oral) (Preliminary Assessment Materials) for a 30-day public review and comment period. As part of developing a draft IRIS assessment, EPA presents a protocol that describes the methodology for how the assessment will be conducted, including systematic review and dose-response. These could include strategies for literature searches, criteria for study inclusion or exclusion, considerations for evaluating study methods, information management for extracting data, approaches for synthesis within and across lines of evidence, and methods for derivation of toxicity values.


U.S. EPA. Protocol for the Uranium IRIS Assessment (Oral) (Preliminary Assessment Materials). U.S. Environmental Protection Agency, Washington, DC, EPA/635/R-24/013, 2024.

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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 2018 EPA released the IRIS Assessment Plan (IAP) for Uranium (Oral Reference Dose). [Federal Register Notice Jan 31, 2018]
03- Mar 2018 EPA hosted a public science meeting on March 22, 2018 to discuss preliminary assessment materials for uranium.
04- Apr 2019 EPA suspended the assessment in fiscal year 2019. It may be restarted as Agency priorities change.
05- Jun 2021 The assessment was unsuspended and announced in the June 2021 Outlook.
06- Feb 2024 EPA released the Protocol for the Uranium IRIS Assessment (Preliminary Assessment Materials). The deadline for comments is March 15, 2024. [Federal Register Notice Feb 14 2024]


The IRIS Program will use the protocol to develop the draft assessment.

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This download(s) is distributed solely for the purpose of pre-dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by EPA. It does not represent and should not be construed to represent any Agency determination or policy.

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Comments on the assessment may be submitted and reviewed using the Docket ID EPA-HQ-ORD-2017-0747

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