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Physical/Radiation -> Radionuclides

Flammable agents - 3rd degree

11.7 g/cu cm

Crystal structure: face-centered cubic to 1360 °C; density: 11.724 g/cu cm; body-centered cubic from 1360 to 1750 °C; density: 11.10 g/cu cm; enthalpy of fusion: 14 kJ/mol; thermal conductivity: 0.6 W/cm K at 25 °C; work function 3.49 eV

Relative density (water = 1): 11.7

11.72 @25 °C

Soft gray-white metal; cubic

Grayish-white, lustrous, radioactive, metal; somewhat ductile and malleable

Insoluble in water; soluble in hydrochloric acid, sulfuric acid, aqua regia; slightly soluble in nitric acid

Solubility in water at 20 °C: none

4788 °C

4788 °C

4500 °C @760 [mm Hg]

1750 °C

1750 °C

1750 °C

Vapor pressure: log(p/atm) = -28,780 (T/K)-1 + 5991 at 1757-1956 K

1 Pa at 2360 °C; 10 Pa at 2634 °C; 100 Pa at 2975 °C; 1 kPa at 3410 °C; 10 kPa at 3986 °C; 100 kPa at 4782 °C

Gray-white lustrous metal; [Merck Index]

Solid

GREY-WHITE METAL POWDER

This chemical does not meet GHS hazard criteria for 11.1% (2 of 18) of reports.

Danger

H272 (11.1%): May intensify fire; oxidizer [Danger Oxidizing liquids; Oxidizing solids]

P210, P220, P260, P261, P264, P264+P265, P270, P271, P280, P301+P317, P302+P352, P304+P340, P305+P351+P338, P319, P321, P330, P332+P317, P337+P317, P362+P364, P370+P378, P403+P233, P405, and P501 (click each P-code to see the statement)

Aggregated GHS information provided per 18 reports by companies from 4 notifications to the ECHA C&L Inventory. Each notification may be associated with multiple companies.

Chemical: Thorium

Hazard Traits - Carcinogenicity

Thorium: Does not have an individual approval but may be used as a component in a product covered by a group standard. It is not approved for use as a chemical in its own right.

The New Jersey Worker and Community Right to Know Act requires public and private employers to provide information about hazardous substances at their workplaces. (N.J.S.A. 34:5A-1 et. seq.)

Powdered thorium metal is often pyrophoric and should be carefully handled. When heated in air, thorium turnings ignite and burn brilliantly with white light.

... Some alloys may ignite spontaneously. The metal in massive form is not flammable. ... Dusts of thorium have very low ignition points and may ignite at room temperature.

The powdered metal ignites at 270 °C. ... There is no limiting oxygen pressure that will prevent thorium ignition, for ignition will occur in pure carbon dioxide.

... Powdered metal ignites when rubbed or crushed, or on pouring as a stream in air, owing to intergranular friction.

Fire hazard /is/ moderate in the form of dust, when exposed to heat or flame ...

Thorium is a naturally occurring, radioactive substance. In the environment, thorium exists in combination with other minerals, such as silica. Small amounts of thorium are present in all rocks, soil, water, plants, and animals. Soil contains an average of about 6 parts of thorium per million parts of soil (6 ppm). More than 99% of natural thorium exists in the form of thorium-232. It breaks down into two parts-a small part called "alpha" radiation and a large part called the decay product. The decay product is also not stable and continues to break down through a series of decay products until a stable product is formed. During these decay processes, radioactive substances are produced. These include radium and radon. These substances give off radiation, including alpha and beta particles, and gamma radiation. Some rocks in underground mines contain thorium in a more concentrated form. After these rocks are mined, thorium is usually concentrated and changed into thorium dioxide or other chemical forms. After most of the thorium is removed, the rocks are called "depleted" ore or tailings. Thorium is used to make ceramics, gas lantern mantles, and metals used in the aerospace industry and in nuclear reactions. Thorium can also be used as a fuel for generating nuclear energy.

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.

Qiu R; Youkuangye 4 (4): 62-6 (1985). Uranium, radium and thorium biosorption review. Wastewater treatment, for radium and thorium and uranium removal. Adsorption: Wastewater treatment adsorption by microorganisms. ...

DHHS/ATSDR; Toxicological Profile for Thorium (1990) ATSDR/TP-90/25

/GUIDE 162: RADIOACTIVE MATERIALS (LOW TO MODERATE LEVEL RADIATION)/ Health: Radiation presents minimal risk to transport workers, emergency response personnel and the public during transportation accidents. Packaging durability increases as potential hazard of radioactive content increases. Undamaged packages are safe. Contents of damaged packages may cause higher external radiation exposure, or both external and internal radiation exposure if contents are released. Low radiation hazard when material is inside container. If material is released from package or bulk container, hazard will vary from low to moderate. Level of hazard will depend on the type and amount of radioactivity, the kind of material it is in, and/or the surfaces it is on. Some material may be released from packages during accidents of moderate severity but risks to people are not great. Released radioactive materials or contaminated objects usually will be visible if packaging fails. Some exclusive use shipments of bulk and packaged materials will not have "RADIOACTIVE" labels. Placards, markings and shipping papers provide identification. Some packages may have a "RADIOACTIVE" label and a second hazard label. The second hazard is usually greater than the radiation hazard; so follow this GUIDE as well as the response GUIDE for the second hazard class label. Some radioactive materials cannot be detected by commonly available instruments. Runoff from control of cargo fire may cause low-level pollution. /Thorium metal, pyrophoric/

/GUIDE 162: RADIOACTIVE MATERIALS (LOW TO MODERATE LEVEL RADIATION)/ Fire or Explosion: Some of these materials may burn, but most do not ignite readily. Uranium and Thorium metal cuttings may ignite spontaneously if exposed to air ... . Nitrates are oxidizers and may ignite other combustibles ... . /Thorium metal, pyrophoric/

/GUIDE 162: RADIOACTIVE MATERIALS (LOW TO MODERATE LEVEL RADIATION)/ Public Safety: CALL Emergency Response Telephone Number ... . Priorities for rescue, life-saving, first aid, fire control and other hazards are higher than the priority for measuring radiation levels. Radiation Authority must be notified of accident conditions. Radiation Authority is usually responsible for decisions about radiological consequences and closure of emergencies. As an immediate precautionary measure, isolate spill or leak area for at least 25 meters (75 feet) in all directions. Stay upwind. Keep unauthorized personnel away. Detain or isolate uninjured persons or equipment suspected to be contaminated; delay decontamination and cleanup until instructions are received from Radiation Authority. /Thorium metal, pyrophoric/

/GUIDE 162: RADIOACTIVE MATERIALS (LOW TO MODERATE LEVEL RADIATION)/ Protective Clothing: Positive pressure self-contained breathing apparatus (SCBA) and structural firefighters' protective clothing will provide adequate protection. /Thorium metal, pyrophoric/

For more DOT Emergency Guidelines (Complete) data for THORIUM, ELEMENTAL (8 total), please visit the HSDB record page.

Fresh air, rest.

Remove contaminated clothes. Rinse and then wash skin with water and soap. Use radiation detector to ensure no remaining contamination.

Rinse with plenty of water for several minutes (remove contact lenses if easily possible).

Rinse mouth.

Dry finely divided tantalum, thorium, titanium, zirconium metals, or titanium-nickel, zirconium-copper alloys are not normally shock-sensitive. However, if they are enclosed in glass bottles which break on impact, ignition will occur. Storage of these materials moist & in metal containers is recommended.

Evacuate danger area! Consult an expert! Personal protection: complete protective clothing including self-contained breathing apparatus. Sweep spilled substance into covered containers. Carefully collect remainder. Then store and dispose of according to local regulations.

If material not on fire & not involved in fire: Contact the local, state, or Department Of Energy Radiological Response Team. Do not use water. Keep sparks, flames, & other sources of igintion away. Keep material out of water sources & sewers. Keep material dry. Do not attempt to sweep up dry material. /Thorium metal, pyrophoric/

Personnel protection: Keep upwind. Avoid breathing dusts, & fumes from burning material. ... Do not handle broken packages unless wearing appropriate personal protective equipment. Wash away any material which may have contacted the body with copious amounts of water or soap & water. /Thorium metal, pyrophoric/

Evacuation: Keep unnecessary people out of incident area until area declared safe by Radiological Response Team. /Thorium metal, pyrophoric/

To avoid risk of dust explosions in plants where thorium powder is mfr by pulverizing or grinding process, operations should be conducted in atmosphere of nitrogen or helium.

Thorium disintegrates with production of thoron ((220)radon), which is alpha emitter and presents radiation hazard. Good ventilation of areas where thorium is stored or handled is therefore essential.

273 men exposed to thorium and other rare earths between 1940 and 1973 at a monazite sand refinery were studied at Argonne National Laboratory from 1976 to 1980. In vivo measurements of body burden were made by counting gamma rays emitted by daughter products of retained thorium and by measuring exhaled thoron. Health status was ascertained through questionnaire, physical exam, and clinical lab tests. Measured body burden was found to be higher in those with a history of longer exposure. All parameters of the complete blood count were examined for evidence of an effect due to thorium. Comparisons of high and low body burden groups showed that only age and cigarette smoking had an effect on complete blood count parameters.

Treatment reversing the effects of irradiation is currently not possible. Anaesthetics and antiemetics are administered to counter the symptoms of exposure, as well as antibiotics for countering secondary infections due to the resulting immune system deficiency. (L1852)

Lungs and other internal organs can be penetrated by the alpha radiation produced by thorium. As a result, exposure to an aerosol of thorium can lead to increased risk of cancers of the lung, pancreas and blood. Exposure to thorium internally leads to increased risk of liver diseases. (L1094)

The substance can be absorbed into the body by inhalation.

Inhalation (L1094)

The ionizing radiation produced by thorium causes cellular damage that includes DNA breakage, accurate or inaccurate repair, apoptosis, gene mutations, chromosomal change, and genetic instability. This leads to loss of normal cell and tissue homeostasis, and development of malignancy. Ionizing radiation that does not directly damage DNA can produce reactive oxygen intermediates that directly affect the stability of p53, an important enzyme in cell-cycle regulation, and produce oxidative damage to individual bases in DNA and point mutations by mispairing during DNA replication. (L1837)

Cough.

Redness.

Exposure to high doses of ionizing radiation results in acute radiation syndrome, which can cause skin burns, hair loss, nausea, vomiting, dizziness, disorientation, low blood pressure, headache, fatigue, weakness, fever, birth defects, illness, infection, and death. (L1837, L1852)

Thorium-232 and its decay products

Group 1: Carcinogenic to humans

Volume 78: (2001) Ionizing Radiation, Part 2: Some Internally Deposited Radionuclides

2012

2009

1, carcinogenic to humans. (L135)

There is sufficient evidence in experimental animals for the carcinogenicity of mixed alpha-particle emitters (radium-224, radium-226, thorium-227, thorium-228, thorium-230, thorium-232, neptunium-237, plutonium-238, plutonium-239 (together with plutonium- 240), americium-241, curium-244, californium-249 and californium-252). /Radium, Plutonium, Americium, Curium, Californium/

Internalized radionuclides that emit alpha-particles are carcinogenic to humans (Group 1). In making this overall evaluation, the Working Group took into consideration the following: Alpha-particles emitted by radionuclides, irrespective of their source, produce the same pattern of secondary ionizations and the same pattern of localized damage to biological molecules, including DNA. These effects, observed in vitro, include DNA doublestrand breaks, chromosomal aberrations, gene mutations and cell transformation. All radionuclides that emit alpha-particles and that have been adequately studied, including radon-222 and its decay products, have been shown to cause cancer in humans and in experimental animals. Alpha-particles emitted by radionuclides, irrespective of their source, have been shown to cause chromosomal aberrations in circulating lymphocytes and gene mutations in humans in vivo. The evidence from studies in humans and experimental animals suggests that similar doses to the same tissues - for example lung cells or bone surfaces - from alpha- particles emitted during the decay of different radionuclides produce the same types of non-neoplastic effects and cancers. /Internalized alpha-emitters/

Industrial exposures to thorium occur during the refining of monazite sand, the handling of various thorium salts, the fabrication of thorium ingots, the handling thorium salts in various industrial uses, the casting and machining of thorium alloy parts, and the production of glazed tiles. In addition, there is potential for exposure through fumes from welding with thoriated-tungsten electrodes and from fires and explosions caused by thorium metal powder. ... Measurement of the radioactive gas, thoron (220Rn), a daughter product of Th, in exhaled air provides another measure of past thorium exposure

PRINCIPAL HAZARDS FROM THORIUM IN INDUSTRY ARE INHALATION OF THORIUM DUST & OF THORON GAS & ITS DECAY PRODUCTS, & EXPOSURE TO EXTERNAL BETA & GAMMA RADIATION. INHALATION HAZARD IS GREATEST IN DUSTY OPERATIONS SUCH AS GRINDING OF METALS, CERAMICS, HANDLING OF THORIUM POWDER, & CONTAMINATION FROM THORIUM FIRES.

Persons in charge of vessels or facilities are required to notify the National Response Center (NRC) immediately, when there is a release of this designated hazardous substance, in an amount equal to or greater than its reportable quantity of 100 curie or 3.7X10+12 becquerel. The toll free number of the NRC is (800) 424-8802. The rule for determining when notification is required is stated in 40 CFR 302.4 (section IV. D.3.b). /Thorium-226/

Persons in charge of vessels or facilities are required to notify the National Response Center (NRC) immediately, when there is a release of this designated hazardous substance, in an amount equal to or greater than its reportable quantity of 1 curie or 3.7X10+10 becquerel. The toll free number of the NRC is (800) 424-8802. The rule for determining when notification is required is stated in 40 CFR 302.4 (section IV. D.3.b). /Thorium-227/

Persons in charge of vessels or facilities are required to notify the National Response Center (NRC) immediately, when there is a release of this designated hazardous substance, in an amount equal to or greater than its reportable quantity of 0.01 curie or 3.7X10+8 becquerel. The toll free number of the NRC is (800) 424-8802. The rule for determining when notification is required is stated in 40 CFR 302.4 (section IV. D.3.b). /Thorium-228/

Persons in charge of vessels or facilities are required to notify the National Response Center (NRC) immediately, when there is a release of this designated hazardous substance, in an amount equal to or greater than its reportable quantity of 0.001 curie or 3.7X10+7 becquerel. The toll free number of the NRC is (800) 424-8802. The rule for determining when notification is required is stated in 40 CFR 302.4 (section IV. D.3.b). /Thorium-229/

For more CERCLA Reportable Quantities (Complete) data for THORIUM, ELEMENTAL (8 total), please visit the HSDB record page.

Exposure to thorium can occur following inhalation, ingestion, or dermal exposure. Once in the body thorium accumulates mainly in the liver, spleen, lymph nodes, lungs, and bone. Transferrin plays a major role in the transport and cellular uptake of thorium. Thorium may combine with oxygen to form thorotrast (thorium dioxide), a colloid which may affect protein uptake. Thorium and thorotrast are excreted mainly in the faeces. (L1838)

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]

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

Mining [Category: Industry]

Because the thorium atom density is higher in thorium metal than in any thorium compound, metal is the preferred form of thorium where the highest nuclear reactivity or highest density is wanted.

As fuel in nuclear reactors, as source of fissionable uranium-233. In manufacture of incandescent gas-light mantles, welding electrodes, ceramics. As hardener in Mg alloys; for filament coatings in incandescent lamps and vacuum tubes; as chemical catalyst.

Nuclear fuel (thorium-232 is converted to uranium-233 on neutron bombardment after several decay steps), sun lamps, photoelectric cells, target in X-ray tubes, alloys.

The purest specimens often contain several tenths of a percent of the oxide.

The crude alloy contains 4.1-7.0% Zn.

Over a ton of thorium is produced annually, approximately half of which is devoted to the production of gas mantles.

Principal nonenergy applications were in Welsbach incandescent gaslight mantles, as a hardener in thorium-magnesium alloys in thoriated tungsten electrodes, and in dispersion hardening, refractories, electronics, and chemical catalytic uses.

... The route to thorium metal is ... reaction of the oxide or a halide with metals, electrolysis in molten salts, or thermal decomposition of a halide. The principal reactions that have led to production processes are: ... 1) Electrolysis of fused salts: KThF5 in NaCl; ThF4 in NaCl - KCl; ThCl4 in NaCl - KCl. 2) Reduction with reactive metals: ThO2 with Ca; ThCl4 with Mg; ThF4 with Ca. 3) Thermal dissociation of ThI4. ... The following four production methods have been tested on a full scale: (1) reduction of fluorides and chlorides; (2) reduction of ThO2; (3) thermal decomposition of ThI4; and (4) fused salt electrolysis.

It can be obtained by reducing thorium oxide with calcium, by electrolysis of anhydrous thorium chloride in fused mixture of sodium and potassium chlorides, by calcium redn of thorium tetrachloride mixed with anhydrous zinc chloride, and by redn of thorium tetrachloride with alkali metal.

(1) Reduction of thorium dioxide with calcium, (2) fused salt electrolysis of the double fluoride ThF4.KF. The product of both processes is thorium powder, fabricated into the metal by powder metallurgy techniques. Hot surface decomposition of the iodide produces crystal bar thorium.

To make small samples of ultrapure thorium metal, the van Arkel de Bor process has been used. Lower purity thorium metal and a small amount of iodine or of thorium iodide are confined in moderately heated evacuated vessel. Thorium iodide vapors pass to a very hot surface, eg, a tungsten filament, where they decompose and deposit the metal. The iodine vapors recycle to the lower purity thorium and then react forming fresh metal iodide, and the cycle continues.

For more Methods of Manufacturing (Complete) data for THORIUM, ELEMENTAL (7 total), please visit the HSDB record page.

Powder, unsintered bars, sintered bars, sheets.

-200 mesh, 99.8% pure grade in airtight glass under argon.

Thorium: ACTIVE

The principal production stages are the concentration of thorium minerals, extraction of thorium from them, purification, and conversion to the metal or desired compounds, usually ThO2.

Monazite is the most common and commercially important thorium bearing mineral. ... Monazite sand is separated from other sands by physical or mechanical means following dredging operations. ... The metallurgical extraction of monazite sand concentrates for producing lighting mantle-grade thorium consists of digestion with hot, fuming sulfuric acid for several hours. The resulting mass is diluted with water which dissolves thorium, ... . Neutralization of liquor precipitates thorium phosphate ... . Instead of selective precipitation, the impure concentrate may be further treated by a liq-liq extraction process to yield reactor grade thorium.

(1985) Thorium product used and produced by the domestic industry came from imports, industry and government stocks

Source: Monazite, thorite. It is about as abundant as lead.

Domestic mine production of thorium-bearing monazite ceased at the end of 1994 as world demand for ores containing naturally occurring radioactive thorium declined.