Chemistry Reference
In-Depth Information
CHAPTER
44
Tungsten
GEORGE KAZANTZIS AND PER LEFFLER
ABSTRACT
of the metal in the few nonindustrially exposed sub-
jects studied. The sparse data on the biological effects
of tungsten have been previously reviewed by Brown-
ing (1969) and Stokinger (1981), and the chemistry and
uses of tungsten have been reviewed by Rieck (1967)
and Rose (1994). Industrial, medical, and military uses
of tungsten have been expanding rapidly, as has the
potential for the spread of tungsten to the environment
(Leggett, 1997).
Almost one half of an ingested dose of tungsten is
in the form of a soluble salt, and one third of a depos-
ited inhaled aerosol of tungstic oxide was rapidly ab-
sorbed in those animal models that have been studied.
Most of the absorbed tungsten was rapidly excreted
in the urine. The small amount of tungsten retained
was transferred in part from plasma to red blood cells
and distributed mainly to spleen, kidney, and bone.
Approximately 3 months after ingestion and 6 months
after inhalation, the largest proportion of the body bur-
den of tungsten was found in bone, although this was
only a very small part of the administered dose.
The metabolism of tungsten is related to that of
molybdenum, which it closely resembles in chemical
properties.
Little is known about the toxicity of tungsten com-
pounds, although the LD
50
of soluble salts in the rat is
relatively high. After occupational exposure to tung-
sten carbide dust by inhalation, cases of pulmonary
fi brosis have been reported, but this “hard-metal dis-
ease” as it is often called is more likely to be caused by
cobalt, with which tungsten carbide is fused. Recent
studies have shown a risk of cancer induction after
exposure to heavy metal tungsten alloys that requires
further investigation. A reliable biokinetic model for
tungsten in humans is required.
Apart from occupational sources, small quantities
of tungsten are present in food and water; trace quan-
tities, related to industrial emissions, have been found
in the general atmosphere. Tungsten is also present
in trace amounts in human serum and in urine and
feces, elimination approximately balancing the intake
1 PHYSICAL AND CHEMICAL PROPERTIES
Tungsten (W): atomic weight, 183.9; atomic number,
74; melting point, 3410°C; boiling point, 5660°C; spe-
cifi c gravity, 19.3; oxidation states, +2, +3, +4, +5, +6;
crystalline form, grey-black, cubic.
Tungsten, known also as wolfram, is a transitional
element that belongs to group VIb of the periodic sys-
tem, together with molybdenum and chromium. Tung-
sten is not oxidized in air at ordinary temperatures
and is highly resistant to acids. Its chemical properties
resemble those of molybdenum. Among the more com-
mon compounds are the canary yellow trioxide, tung-
stic acid, sodium tungstate, ammonium paratungstate,
and tungsten carbide.
2 METHODS AND PROBLEMS
OF ANALYSIS
Environmental samples can be analyzed for tung-
sten by atomic absorption spectrophotometry (AAS)
with a detection limit of 3
µ
g/mL. The addition of
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