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Rare Earth Compounds Toxicity


Occurrence and Chemical
Properties :


 

The term rare earths usually refers to
the lanthanum series (atomic numbers 57 to 71) with yttrium (39),
also called the lanthanons (39, 57 to 71).


They are found together in various
combinations in many ores :


-monazite,

-xenotime,

-gadolinite,

-samarskite,

-fergusonite,

-apatite,

-euxenite,

-bastnaesite,

 

mainly in the following countries
:


-Norway,

-Sweden,

-USA,

-Australia,

-India,

-Canada,

-Brazil.

 

They have similar molecular structures,
this makes separation of them difficult.


All are relatively soft metals,
malleable, with a bright silver luster, altough some oxidize
readily in air.


The most common is cerium and it is more
abundant than lead or copper.


 

Industrial Processes and
Uses :


 

The rare earths are the subject of much
research and new uses will be found.


 

Cerium is used in :

-optical glass,

-electrodes,

-printing,

-dyeing,

-ceramics,

-fireworks,

-metallurgical alloys,

-mildew-proofing (textile
industry),


-tracer bullets,

-carbon arc rods,

-etc.

 

Praseodymium is used :

-to color glass,

-to make arc cores for lights in theater
projection machines, searchlights, and other intense lighting
situations.


-to make alloys like most rare
earths.


 

Neodymium COLOR="#004080"> is a source of promethium.

It is used :

-to make purple glass,

-in doping glass lasers,

-in carbon arc rods.

 

Promethium COLOR="#004080"> is used in luminescent dials.

 

Samarium is used :

-in making infra-red absorbing
glass,


-as a dopant for lasers,

-as a neutron absorber in nuclear
reactors,


-as a constituent of television
phosphors.


 

Terbium COLOR="#004080"> is used as a solid-state and laser dopant.

 

Erbium is used :

-in metallurgy,

-nuclear research,

-to color glass and porcelain.

 

Thullium COLOR="#004080"> has 16 important isotopes. Isotope 170 is used in
small portable radiation units.


 

Ytterbium COLOR="#004080"> is another rare earth that is used in :

-lasers,

-alloys,

-and as an x-ray source for portable
irradiation devices.


Ytterbium 169 emits gamma rays and is
used in radiography of small castings and other small
materials.


 

Yttrium is used :

-in optical glasses,

-in ceramics,

-in color TV tubes,

-in alloys to increase their
strenght


 

Europium COLOR="#004080"> can be used to detect chrome in contaminated
water


Uses in Medicine :

 

Many rare earths were and/or are used as
diagnostic and therapeutic tools.


 

Rare Earth Analysis
:


 

With the exception of cerium, atomic
absorption spectrophotometry is the method of choice for rare
earth quantitative determination.


 

Biologic effects
:


 

I-Absorption :

The rare earth metals are not absorbed
from the skin, are poorly absorbed from the gastrointestinal
tract, and are slowly absorbed from the lungs or on
injection.


On absorption, scandium and the rare
earth metals tend to collect in the liver and the skeleton. There
is a transition to more bone with the rare earths of higher atomic
number. After deposition in the skeleton it may take years before
removal is completed.


Starvation lessened the
excretion.


 

II-Clinical Findings :

 

A-General :

Headache and nausea from dust and fumes
from using cored light carbons containing lanthanum has been
reported.


 

B-Lungs :

 






1-Acute exposure :

If in great enough quantity, the rare
earth compounds can produce, on inhalation, acute chemical
irritation pneumonitis, and bronchitis.


 

2-Chronic exposure :

More than 20 cases of occupational
pneumoconiosis have been reported, mainly in photoengravers and
projectionists, from chronic inhalation of rare earth oxide fumes
from carbon arc lamps.


Cerium, lanthanum, and neodymium are the
major oxides in the fumes; but samarium, terbium, ytterbium,and
lutenium have also been removed from fibrotic pneumoconiosis
nodules. In some of these cases abnormal levels of rare earths
were demonstrated in the nails suggesting absorption from the
lungs.


 

C-Skin :

Terbium chloride has been noted to be an
irritant to the intact skin.


Gadolinium and samarium chlorides
produced ulcers on abraded skin.


Lutetium and europium chlorides caused
extensive scarring on abraded skin, and, along with dysprosium,
holmium, and erbium, produced nodules from intradermal
injections.


 

D-Eyes :

The chloride of each of the rare earths
caused ocular irritation in the form of transient conjunctivitis.
In addition, terbium chloride produced corneal damage.


The lanthanons can produce opacity to
the abraded cornea.


 

Diagnostic Methods :

 

There are no signs or symptoms
pathognomonic of toxicity from lanthanons.A history of exposure
would be necessary in making the diagnosis.


 

A-Chest X-Ray :

 

1-Acute Exposure :

A chest x-ray after massive acute
inhalation might show signs of oedema or pneumonitis.


 

2-Chronic Exposure :

Chronic inhalation can produce a diffuse
nodular pattern on chest x-ray from the birotic nodules composed
of rare earths. The pulmonary function test might show a
restrictive pattern.


Energy dispersive x-ray fluorescence of
bronchoalveolar lavage fluids can establish or confirm
occupational exposure of workers to rare earths.


 

B-Urinary Excretion :

Excretion of the rare earth metals in
the urine is a small part of the total excretion by the body but
could be measured accurately. No standards of urinary level have
been established, because it is not yet known if there is a
correlation between the urinary level and either the exposure or
the fecal excretion.


 

C-Fecal Excretion :

Ingestion estimates have usually been
based on measurements of the rare earths in the feces.


Fecal excretion of lanthanons is
measurable. The level of excretion varies greatly with the route
of exposure and the solubility of the lanthanon.


No indices of toxicity based on fecal
excretion have been established, but fecal levels do afford an
inconvenient method of monitoring exposure.


 

 

Treatment :

 

Some lanthanons delay healing, cause
irritation and ulcers on abraded skin, and form nodules
intradermally. Extra care should be used in cleaning wounds
contaminated with a lanthanon.


If lanthanon toxicity is suspected, the
patient should be removed from further exposure.


There is no specific therapy, and
treatment of any findings that are believed to be related to the
lanthanon exposure, such as acute chemical pneumonitis, hematuria
or leukopenia, are treated in the usual manner.


 

 

Exposure Limit :

 

The VEMP in Quebec for yttrium is
1mg/m3.


 

Exposure Control
:


 

Incidental ingestion is considered
harmless.


Skin contact should be avoided,
especially with rare earths of the terbium and ytterbium
groups.


Employees with skin cuts, abrasion,
dermatitis, conjunctivitis, corneal injuries, or keratoconus need
protection that will prevent contamination of the skin lesion or
the eye by any rare earth.


Employees with lung disease, decreased
pulmonary function, or x-ray evidence of fine lung opacities
(pneumoconiosis) need special consideration to avoid rare earth
dusts or fumes.


Consideration should be given to
avoiding exposure to rare earths for employees with increased
blood coagulation time or leukopenia.


Heated rare earths give off toxic fumes
that should be controlled.


 

 

 

 

References :

 

1-Occupational Medicine, Carl Zenz,
last edition.


2-Sax's Dangerous Properties of
Industrial Materials, Lewis C., last edition.


3-Toxicologie Industrielle et
Intoxications Professionnelles, Lauwerys R.R.,last
edition.


4-INRS, Exposition aux
poussières de terres rares, Peltier A., 1986


 


 

Related Information

Links

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.

By Edouard Bastarache


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