Thursday, July 2, 2009

Case Studies in Environmental Medicine Uranium Toxicity: Who Is at Risk of Exposure to Uranium?

From the Centers for Disease Control (CDC) and ATSDR, comes this component of a Continuing Education program for health-care providers. It speaks to the inadequacies of past protective efforts but recognizes that there remain serious exposure risks because no fail-safe protections exist. Sections marked in red are my emphases.


Learning Objectives
Upon completion of this section, you will be able to identify the populations most heavily exposed to uranium and describe who is at risk for uranium exposure.

The occupations most heavily exposed to uranium are those employed in mining and milling operations, or in uranium enrichment and processing activities.

Communities living near Department of Energy (DOE) facilities and mining sites and those living in areas where naturally occurring uranium levels are elevated are most at risk for significant environmental exposure.

Past Occupational Exposures
In the past, uranium exposure has been associated mainly with mining and milling of the raw material, with workers engaged in uranium enrichment, and processing (DOE sites). In the 1980s, the United States stopped recycling and reprocessing uranium for antiproliferation purposes (other than for military fuel), increasing the need for mining and material production.

Past Para-occupational Exposures
In the past, industrial hygiene practices may not have been adequate to protect workers from bringing contamination home with them, resulting in possible exposures to family members. At DOE sites in the 1950s, in particular, workers often did not know the hazards they were working with due to the secrecy of the atomic weapon projects. While it is expected that workers became more aware of the industrial hazards after the end of World War II, industrial hygiene practices in general did not improve significantly until the mid-1970s.

In addition, some releases from DOE facilities during the 1950s and 1960s may have exposed nearby communities to elevated levels of radiation, including uranium.

Current Occupational Exposures
Very little mining or processing of uranium for the purpose of fuel or weapons development is currently underway. Occupational activities with potential for uranium exposure include workers
  • involved in using armor-piercing weapons,
  • decommissioning uranium-contaminated areas (e.g., handling wastes or debris suspected of containing uranium while decommissioning uranium contaminated areas),
  • processing nuclear fuel,
  • maintenance and/or repair activities at applicable U.S. government facilities,
  • mining or milling of uranium, silver, phosphorus, coal, etc.,
  • producing phosphate fertilizer,
  • operating power plants,
  • repairing, storing, transporting and using uranium weapons,
  • working with gyroscope, helicopter rotor counterbalances, or control surfaces of aircraft containing uranium metal weights, or
  • using uranium-containing glazes as artists, hobbyists, and glass workers.

Direct Domestic Exposures
As noted earlier, the most common non-occupational exposures are primarily a result of drinking water, eating food, and breathing air contaminated by naturally occurring uranium sources.
Communities located near contaminated sites may be exposed through accidental releases during remediation activities. Essentially no uranium is released from nuclear power plants because of the fuel assembly design and the chemical and physical nature of the uranium oxide fuel [ATSDR 2008b].

Background Exposures
Background exposures to uranium occur throughout the United States and the world because uranium is a naturally occurring element in the soil, water, and air. Average daily ingestion of uranium (both food and water) is estimated to be 3 micrograms (µg)/day in the United States. According to the Third National Report on Human Exposure to Environmental Chemicals, urine uranium levels were measured in a subsample of the National Health and Nutrition Examination Survey (NHANES) participants aged 6 years and older during 1999-2002.

The 95th percentile of urinary uranium concentrations was 0.034 µg/gram (gram) creatinine in the 1999-2000 survey years and 0.040 µg/g creatinine in the 2001-2002 survey years for the U.S. population aged 6 years and older [CDC 2009].

Key Points
Populations most heavily exposed to uranium are those employed in mining and milling operations, or in uranium enrichment and processing activities.

The most common nonoccupational exposures occur from exposure to naturally occurring uranium sources such as contaminated well water.

Communities located near mining sites or other potential sources of uranium contamination may also be at risk.

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