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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.





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

Low repeated exposures may scar the

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


Medical Surveillance


I-Clinical :


Any evaluation should include a careful
history of past and present symptoms with a physical


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


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


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


Workplace Controls and
Practices :


Unless a less toxic chemical can be
substituted for a hazardous substance,
COLOR="#004080">engineering controls COLOR="#004080"> 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


B-Specific engineering controls and
personnel monitoring are required according to local


II-Work practices :


Good work practices can help to reduce
hazardous exposures. The following work practices are


A-Workers whose clothing has been
contaminated by Thorium Dioxide should change into clean clothing


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


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


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


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


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

5-Chemical Hazards of the Workplace,
Proctor & Hughes, 4th edition

By Edouard Bastarache

Related Information


Typecodes Article by Edouard Bastarache
Edouard Bastarache is a well known doctor that has written many articles on the subject of toxicity of ceramic materials and books on technical aspects of ceramics. He writes in both English and French.

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