Hazard Summary

CAUTION: Unless otherwise noted, the quantitative information on these fact sheets are from "EPA Health Effects Notebook for Hazardous Air Pollutants-Draft", EPA-452/D-95-00, PB95-503579, December 1994." Please conduct a current literature search and check the appropriate current online database for the most recent quantitative information.

• No information is available on the acute (short-term) noncancer effects of the radionuclides in humans. Animal studies have reported inflammatory reactions in the nasal passages and kidney damage from acute inhalation exposure to uranium.
• Chronic (long-term) inhalation exposure to uranium and radon in humans has been linked to respiratory effects, such as chronic lung disease, while radium exposure has resulted in acute leukopenia, anemia, necrosis of the jaw, and other effects.
• The Reference Dose (RfD) for uranium (soluble salts) is 0.003 mg/kg/d.^a The U.S. Environmental Protection Agency (EPA) estimates that consumption of this dose or less over a lifetime would not likely result in the occurrence of chronic, noncancer effects.^b
• EPA has not established a Reference Concentration (RfC) for uranium, radium, or radon, and EPA has not established an RfD for radium or radon.
• Limited information is available on the reproductive or developmental effects of the radionuclides. Animal studies have reported fetal toxicity and degenerative changes in the testes from oral exposure to uranium.
• Cancer is the major effect of concern from the radionuclides. Radium, via oral exposure, is known to cause lung, bone, brain, and nasal passage tumors in humans, and radon, via inhalation exposure, causes lung cancer in humans. Uranium may cause lung cancer and tumors of the lymphatic and hematopoietic tissues. EPA has classified radium as a Group A, human carcinogen, and EPA has not classified radon or uranium for carcinogenicity.

^a Milligrams per kilogram per day is one way to measure the amount of the contaminant that is consumed in food.

^b The RfD is not a direct estimator of risk but rather a reference point to gauge the potential effects. Exceedance of the RfD does not imply that an adverse health effect would necessarily occur. As the amount and frequency of exposures exceeding the RfD increase, the probability of adverse health effects also increases.

Please Note: The main sources of information for this fact sheet are EPA's Integrated Risk Information System (IRIS), which contains information oral chronic toxicity and the RfD for uranium, and the Agency for Toxic Substances and Disease Registry's (ATSDR's) Toxicological Profiles for Uranium, Radium, and Radon.

Environmental/Occupational Exposure

• Uranium-238, a radioactive metal, is present in rocks, soil, and throughout the environment. Uranium-238 decays to form radium-226, which has a half-life of 1,600 years. Radium-226 then decays to form radon-222 gas, which has a half-life of 3.8 days. (1)
• Exposure to uranium can occur through the air, with an average daily intake estimated to be 0.0007 to 0.007 pCi/d.⁽¹⁾ Higher levels of exposure generally occur through food consumption, with average levels of 0.72 to 1.0 pCi/d, or through the drinking water, with average levels of 0.6 to 2.0 pCi/d. (3)
• Radium is found in soil, water, plants, and food at low concentrations. The greatest potential for human exposure to radium is through drinking water, where levels are usually less than 1 pCi/L but higher levels (>5 pCi/L) have been detected. (3)
• The major source of radon exposure is through inhalation, with background levels in ambient air ranging from 0.003 to 2.6 pCi/L. Higher levels of radon are frequently present in indoor locations, such as homes, schools, or office buildings. Indoor radon levels are usually about 1.5 pCi/L; however, higher levels (>200 pCi/L) have been measured in homes across the country. (4)
• People who work at factories that process uranium, work with phosphate fertilizers, or live near uranium mines have a greater chance of being exposed to higher levels of uranium, radium, and radon than the general population. (2)

Assessing Personal Exposure

• Uranium, radium, and radon can be measured in the urine, and there is a test to measure the total amount of radioactivity in the body. In addition, there is a test that measures the rate of elimination of radium and radon in exhaled breath. (2-4)

Health Hazard Information

Acute Effects:

• No information is available on the acute (short-term) effects of uranium, radium, or radon in humans. (2-4)
• Animal studies have reported inflammatory reactions in the nasal passages and kidney damage from acute inhalation exposure to uranium. (2)
• Acute animal tests, such as the LC50 and LD50 tests in rats, mice, and guinea pigs, have shown uranium to have low to moderate toxicity from inhalation exposure and high toxicity from oral exposure. (2)

Chronic Effects (Noncancer):

• Several studies have related inhalation exposure to uranium in humans with an increase in deaths from nonmalignant respiratory disease. One study reported kidney effects in humans following exposure to uranium, while several other studies have found no increased deaths in uranium workers due to kidney disease. (2)
• Animal studies have reported effects on the kidney from chronic inhalation and oral exposure to uranium. (2)
• EPA has not established an RfC for uranium (soluble salts or natural). (5,6)
• The RfD for uranium (soluble salts) is 0.003 mg/kg/d based on body weight loss and moderate nephrotoxicity in rabbits. (6)
• EPA has medium confidence in the study on which the RfD was based since it was well designed, but used a small number of experimental animals; medium confidence in the database because there are adequate studies on the effects of uranium in various species; and, consequently, medium confidence in the RfD. (6)
• Chronic exposure to radium in humans, by inhalation, has resulted in acute leukopenia, while oral exposure has resulted in anemia, necrosis of the jaw, abscess of the brain, and terminal bronchopneumonia. (3)
• Chronic exposure to radon in humans and animals via inhalation has resulted in respiratory effects (chronic lung disease, pneumonia, fibrosis of the lung), while animal studies have reported effects on the blood and a decrease in body weights. (4)
• EPA has not established an RfC or an RfD for radium or radon. (7,8)

Reproductive/Developmental Effects:

• Limited evidence from epidemiological studies suggests that uranium or radon exposure may result in a decreased ratio of live male to female births in humans. (2,4)
• Animal studies have not reported adverse reproductive effects from inhalation exposure to uranium, while fetal toxicity, reduced offsprings, and degenerative changes in the testes were noted from oral exposure in animals. (2)
• No information is available on the developmental or reproductive effects of radium in humans or animals. (3)

Cancer Risk:

• Radium and radon are potent human carcinogens. Radium, via oral exposure, is known to cause lung, bone, brain, and nasal passage tumors. Radon, via inhalation exposure, causes lung cancer. (2-4)
• Smokers exposed to radon are at greater risk for lung cancer (approximately 10 to 20 times) than are nonsmokers similarly exposed. (1)
• Studies in uranium miners have shown an increase in lung cancer and tumors of the lymphatic and hematopoietic tissues from inhalation exposure. However, it is not known whether the cancer risk is from uranium itself, or from radon or other confounding factors. (2)
• EPA has classified radium as a Group A, human carcinogen. (3)
• EPA has not classified radon or uranium for carcinogenicity. (2,4)

Physical Properties

• Natural uranium is a silver-colored radioactive metal that contains three forms (isotopes) of uranium: uranium-234, uranium-235, and uranium-238. The amount of uranium-238 in natural uranium is more than 99 percent, but the uranium-235, present at 0.72 percent in natural uranium, is the most radioactive. (2)
• The chemical symbol for uranium is U, and it has an atomic weight of 238.03 g/mol. (2)
• Radium is a naturally occuring silvery-white radioactive metal formed when uranium decays in the environment. (3)
• The chemical symbol for radium is Ra, and it has an atomic weight of 226.03 g/mol. (3)
• Radon is a colorless, odorless, tasteless, radioactive gas that is formed from the radioactive decay of uranium. (1,4)
• The chemical symbol for radon is Rn, and it has an atomic weight of 222 g/mol. (4)

Uses

• Uranium is used in nuclear power plants and nuclear weapons. Very small amounts are used in the manufacture of some ceramics, lightbulbs, photographic chemicals, and household products. (2)
• Radium is used as a radiation source for treating neoplastic diseases, as a radon source, in radiography of metals, and as a neutron source for research. (3)
• Radon is used for treating malignant tumors and for experimental studies. (4)

Conversion Factors: For uranium: 1 µg = 0.72 pCi.

Health Data from Inhalation Exposure from Uranium

See notes on following page.
ACGIH TLV--American Conference of Governmental and Industrial Hygienists' threshold limit value expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effects.
LC₅₀ (Lethal Concentration₅₀)--A calculated concentration of a chemical in air to which exposure for a specific length of time is expected to cause death in 50% of a defined experimental animal population.
NIOSH REL--National Institute of Occupational Safety and Health's recommended exposure limit; NIOSH-recommended exposure limit for an 8- or 10-h time-weighted-average exposure and/or ceiling.
OSHA PEL--Occupational Safety and Health Administration's permissible exposure limit expressed as a time-weighted average; the concentration of a substance to which most workers can be exposed without adverse effect averaged over a normal 8-h workday or a 40-h workweek.

^a Health numbers are toxicological numbers from animal testing or risk assessment values developed by EPA.
^b Regulatory numbers are values that have been incorporated in Government regulations, while advisory numbers are nonregulatory values provided by the Government or other groups as advice.

Health Data from Inhalation Exposure from Radon

NCRP--National Council of Radiation Protection.

^a Health numbers are toxicological numbers from animal testing or risk assessment values developed by EPA.
^b Regulatory numbers are values that have been incorporated in Government regulations, while advisory numbers are nonregulatory values provided by the Government or other groups as advice.

References

1. Agency for Toxic Substances and Disease Registry (ATSDR). Case Studies in Environmental Medicine. Radon Toxicity. U.S. Public Health Service, U.S. Department of Health and Human Services, Altanta, GA. 1992.
2. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Uranium (Draft). U.S. Public Health Service, U.S. Department of Health and Human Services, Altanta, GA. 1989.
3. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Radium (Draft). U.S. Public Health Service, U.S. Department of Health and Human Services, Altanta, GA. 1989.
4. Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Radon (Draft). U.S. Public Health Service, U.S. Department of Health and Human Services, Altanta, GA. 1990.
5. U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Uranium, Natural. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1993.
6. U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Uranium, Soluble Salts. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1993.
7. U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Radium 226, 228. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1993.
8. U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Radon 222. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1993.

1. * A picocurie (pCi) is a unit of measurement for radionuclides that measures the number of disintegrations per second.