Agent Name

Thorium

CAS Number

7440-29-1

Formula

Th

Major Category

Physical/Radiation

Synonyms

Thorium-232; [HSDB]

Category

Radionuclides

Description

Gray-white lustrous metal; [Merck Index]

Sources/Uses

Thorium is a fairly abundant naturally-occurring element, about as common as lead and three times as common as uranium. Almost all of naturally-occurring thorium is Th-232. Th-230 and Th-228 are present in trace amounts and have half-lives of 75,400 and 1.9 years, respectively. Thorium is chiefly found in monazite sands. It is also found in the minerals thorite and thorianite. Used to make mantles for gas lanterns; Also used in crucibles, tungsten wire coating for electronic components, camera lenses, welding rods, and light bulb filaments; [Argonne]

Comments

"Thorium-232 and its decay products, administered intravenously as a colloidal dispersion of ThO2, are carcinogenic to humans." [IARC] Most Important Radionuclide: Thorium-232 Source: Monazite sand Half-Life: 14 billion years Effective Half-Life: 200 years Specific Activity: 0.00000011 Ci/g Decay Mode: Alpha GI Absorption: 0.02-0.05% Lung Clearance Half-Time: Years for oxides and hydroxides; Weeks for all other compounds; Critical Organ: Bone Internal Toxicity: Very High Annual Limit on Intake: 0.000001 mCi Average Radiation Energy (MeV): Alpha 4.0; Beta 0.012; Gamma 0.0013; [Argonne] Radiation Accidents (1945-2000): 3 incidents of "Meltings of Radioactive Materials"; [See Glossary for references.] See "Radiation, ionizing."

Restricted

No longer used in diagnostic radiology as a medical contrast agent (Thorotrast);

Reference Link

Thorium | Radiation Protection Program | US EPA

Exposure Assessment
Explanatory Notes

Water soluble compounds: chloride, fluoride, nitrate, and sulfate salts; Insoluble compounds: dioxide, carbonate, hydroxide, oxalate, and phosphate salts; [ATSDR ToxProfiles]

Reference Link

ATSDR - ToxFAQs - Thorium

Links to Other NLM Databases
Health Studies

Human Health Effects from Hazardous Substances Data Bank:

Toxicity Information

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Chemical Information

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Biomedical References

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Processes

Industrial Processes with risk of exposure: