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Thorium Dioxide Toxicity

Identification and Uses :
CAS Number :1314-20-1
Thorium Dioxide is a heavy, white, crystalline (sand-like) powder.
It is used in :
-in nuclear fuels,
-as a catalyst,
-in electrodes for arc welding.
Toxicology :
Thorium Dioxide emits alpha particles which can be breathed in and swallowed.
I-Acute Health Effects :
Exposure can reduce the ability of the bone marrow to make white blood cells.
II-Chronic Health Effects :
A-Carcinogenesis :
Thorium Dioxide is a carcinogen in humans. It has been shown to cause angiosarcoma, liver and kidney tumors, lymphoma and other tumors of the blood system, and tumors at the site of application.
B-Reproductive Hazard :
Thorium Dioxide has not been tested for its ability to affect reproduction.
Because Thorium Dioxide gives off very dangerous radiation, it has the potential for causing reproductive damage in humans.
C-Other Long-Term Effects :
Overexposure can occur with no acute symptoms.
Low repeated exposures may scar the lungs.
After exposure, some Thorium Dioxide is retained in the bones, lymph system, lungs and other body organs for many years.
Exposure may damage the liver and kidneys.
Medical Surveillance :
I-Clinical :
Any evaluation should include a careful history of past and present symptoms with a physical examination.
II-Laboratory :
Before beginning employment and at regular times after that, the following are recommended:
-White blood cell count.
-Lung function test.
-Consider periodic chest x-ray for persons with potentially high or repeated lower exposure.
If symptoms develop or overexposure is suspected, the following may be useful :
-Liver and kidney function tests.
Medical tests that look for damage already done are not a substitute for controlling exposure.
Ways of Reducing Exposure :
I-Enclose operations and use local exhaust ventilation at the site of chemical release. If local exhaust ventilation or enclosure is not used, respirators should be worn.
II-A regulated, marked area should be established where Thorium Dioxide is handled, used, or stored.
III-All processes involving Thorium Dioxide should be mechanized, enclosed or automated.
IV-When working with small quantities of Thorium Dioxide, use in a glove box.
V-Wear protective work clothing.
VI-Wash thoroughly immediately after exposure to Thorium Dioxide and at the end of the workshift.
VII-Post hazard and warning information in the work area. In addition, as part of an ongoing education and training effort, communicate all information on the health and safety hazards of Thorium Dioxide to potentially exposed workers.
Workplace Controls and Practices :
Unless a less toxic chemical can be substituted for a hazardous substance, engineering controls are the most effective way of reducing exposure.
The best protection is to enclose operations and/or provide local exhaust ventilation at the site of radiation release. Isolating operations can also reduce exposure. Using respirators or protective equipment is less effective than the controls mentioned above, but is sometimes necessary.
In evaluating the controls present in your workplace, consider:
-how hazardous the substance is,
-how much of the substance is released into the workplace and
-whether harmful skin or eye contact could occur. Special controls should be in place for highly toxic chemicals or when significant skin, eye, or breathing exposures are possible.
I-Additional Recommended Controls :
A-Automatically transfer Thorium Dioxide from drums or other storage containers to process containers.
B-Specific engineering controls and personnel monitoring are required according to local legislation.
II-Work practices :
Good work practices can help to reduce hazardous exposures. The following work practices are recommended:
A-Workers whose clothing has been contaminated by Thorium Dioxide should change into clean clothing promptly.
B-Do not take contaminated work clothes home. Family members could be exposed.
C-Contaminated work clothes should be laundered by individuals who have been informed of the hazards of exposure to Thorium Dioxide.
D-If there is the possibility of skin exposure, emergency shower facilities should be provided.
E-On skin contact with Thorium Dioxide, immediately wash or shower to remove the chemical. At the end of the workshift, wash any areas of the body that may have contacted Thorium Dioxide, whether or not known skin contact has occurred.
F-Do not eat, smoke, or drink where Thorium Dioxide is handled, processed, or stored, since the chemical can be swallowed. Wash hands carefully before eating or smoking.
G-Employees exposed to ionizing radiation should be provided with personal monitoring equipment such as film badges or pocket dosimeters.
H-Use damp methods to control dust. Test for trace levels of radioactivity after clean-up.
Personal Protective Equipment :
Workplace controls are better than personal protective equipment.
However, for some jobs (such as outside work, confined space entry, jobs done only once in a while, or jobs done while workplace controls are being installed), personal protective equipment may be appropriate
The following recommendations are only guidelines and may not apply to every situation.
I-Clothing :
A-Avoid skin contact with Thorium Dioxide. Wear protective gloves and clothing. Safety equipment suppliers/manufacturers can provide recommendations on the most protective glove/clothing material for your operation.
B-All protective clothing (suits, gloves, footwear, headgear) should be clean, available each day, and put on before work
II-Eye Protection :
-Wear dust-proof goggles and face shield when working with powders or dust, unless full facepiece respiratory protection is worn.
III-Respiratory Protection :
Improper use of respirators is dangerous :
Such equipment should only be used if the employer has a written program that takes into account workplace conditions, requirements for worker training, respirator fit testing and
medical exams.
Engineering controls must be effective to ensure that exposure to Thorium Dioxide does not occur.
At any exposure level, use an approved supplied-air respirator with a full facepiece or use an approved self-contained breathing apparatus with a full facepiece operated in pressure-demand or other positive pressure mode.
First Aid :
I-Eye Contact :
Immediately flush with large amounts of water for at least 15 minutes, occasionally lifting upper and lower lids.
II-Skin Contact :
Quickly remove contaminated clothing. Immediately wash contaminated skin with soap and large amounts of water
III-Breathing :
Remove the person from exposure.
Begin rescue breathing if breathing has stopped and CPR if heart action has stopped.
Transfer promptly to a medical facility.
Workplace Exposure Limits :
Exposure to radioactive materials is regulated by local legislation.
Thorium Dioxide is a carcinogen in humans. There may be no safe level of exposure to a carcinogen, so all contact should be reduced to the lowest possible level.
References :
1-Occupational Medicine,Carl Zenz, last edition.
2-Clinical Environmental Health and Toxic Exposures, Sullivan & Krieger; last edition.
3-Sax's Dangerous Properties of Industrial Materials, Lewis C., last edition.
4-Toxicologie Industrielle et Intoxications Professionnelles, Lauwerys R.R. last edition.
5-Chemical Hazards of the Workplace, Proctor & Hughes, 4th edition

Out Bound Links

Edouard Bastarache M.D.
Occupational & Environmental Medicine
Author of "Substitutions for Raw Ceramic Materials"
Tracy, Québec, CANADA


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