US EPA

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.

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.

The 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, and a PECO framework that outlines the evidence considered most pertinent to the assessment; and identification of key areas of scientific complexity.

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

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.