Introduction

Uranium exposures are limited on the basis of both its chemical and radiological toxicities. In occupational settings, the Occupational Safety and Health Act regulates the limits of worker exposures based on the solubility of the uranium compound. The Department of Energy (DOE) has issued regulations applicable to its facilities that limit environmental discharges and worker exposure to uranium isotopes [DOE 2000, 2009]. The Nuclear Regulatory Commission (NRC) has also established standards and provisions for non-DOE environmental discharges and worker exposure to uranium isotopes [NRC 2009].

In addition, EPA has established standards for uranium concentrations in drinking water [EPA 2006a].

Workplace Standards

OSHA established the permissible exposure level (PEL) for airborne insoluble uranium in the workplace as 0.25 milligram (mg)/cubic meter (m³) time weighted average (TWA). A TWA is the “average” exposure in any 8-hour work shift of a 40-hour work week. The PEL is the TWA concentration to which it is believed that nearly all workers may be repeatedly exposed, day after day, without adverse effect. Put another way, an employee's exposure to a given substance in any 8-hour work shift of a 40-hour work week, shall not exceed the 8-hour TWA limit given for that substance. This current limit was set based upon early animal study results [Voegtlin and Hodge 1953]. For more information on the OSHA PEL for insoluble uranium, please visit either OSHA's TABLE Z-1 Limits for Air Contaminants-1910.1000 TABLE Z-1 [OSHA 2006] or Safety and Health Topics Uranium (as U), Insoluble compounds [OSHA 2004].

Uranium is primarily an alpha-emitter. Workers exposed to various alpha-emitting uranium compounds protect themselves by wearing anti-contamination clothing, eye protection, and respirators when appropriate. These protective barriers are designed to eliminate external alpha radiation exposure, for such barriers easily block alpha radiation.

The OSHA PEL for airborne soluble uranium is 0.05 mg/m³. This is lower because soluble uranium compounds are absorbed to a greater extent by the body. For the same exposure, soluble uranium compounds are more likely to cause chemical effects than insoluble uranium. For more information on the OSHA PEL for soluble uranium , please visit either OSHA's TABLE Z-1 Limits for Air Contaminants-1910.1000 TABLE Z-1 [OSHA 2006] or Safety and Health Topics Uranium (as U), Insoluble compounds [OSHA 2004].

The NRC and DOE limit external radiation exposure to 5 REM per year. This is applicable to all sources combined, less background. The REM (Roentgen Equivalent Man) is the unit of dose actually absorbed taking biological effects into account. Both NRC and DOE have adopted internal exposure limits termed annual limits on intake (ALIs). The ALIs for inhalation or ingestion of uranium-238 are 10 microcurie/year for ingestion and 0.04-1 microcurie/year for inhalation of soluble and insoluble forms. For more information on the NRC and DOE ALIs, please visit NRC's Appendix B to Part 20-Annual Limits on Intake (ALIs) and Derived Air Concentrations (DACs) of Radionuclides for Occupational Exposure; Effluent Concentrations; Concentrations for Release to Sewerage [NRC 2009].

Environmental Standards

EPA has established a maximum contaminant level (MCL) for uranium of 30 micrograms per liter (µg/L) in drinking water. The MCL is the maximum permissible level of a contaminant in water that is delivered to any user of a public water system. EPA finalized this MCL for uranium of 30 µg/L in December 2000. Before this time, EPA did not have a limit specific to uranium in drinking water and instead regulated uranium content through gross alpha and gross beta limits. EPA's rule became effective in 2003. For more information on the EPA MCL, please visit either EPA's Radionuclides in Drinking Water [EPA 2006a] or Radiation Protection-Uranium [EPA 2009b].

EPA established the Reportable Quantity Accidental Release standard, which requires that accidental uranium waste releases containing 0.1 curies of radioactivity be cleaned up.

In addition, EPA issued two standards for controlling uranium mill tailing hazards in 1983 and amended these in 1993. For more information on these standards, please see EPA's Laws We Can Use Summary [EPA 2009a].

They provide for the clean-up and disposal of mill tailings at abandoned sites and at licensed sites after operations cease. They require disposal and cleanup that will limit radium concentration in soil and radon emissions (decay products of uranium), protect groundwater, and prevent misuse.

Progress Check