Chemistry Reference
In-Depth Information
CHAPTER
41
Thallium
GEORGE KAZANTZIS
ABSTRACT
Exposure of the general population to thallium
may occur as a result of atmospheric pollution from
coal-burning power plants and from copper, lead,
and zinc smelters. Contamination of drinking water
may occur from smelting and refi ning operations
with these metals. Thallium intake in such polluted
areas may exceed the normal dietary intake in the
general population that has been estimated to be
<5
After rapid, almost total, absorption from the gas-
trointestinal tract, soluble thallium compounds are wide-
ly distributed in the body, the highest concentration being
accumulated initially in the kidneys. Excretion occurs
through both urine and feces, the disappearance of
thallium from the tissues following fi rst-order kinetics.
The biological half-time of
204
Tl in the rat has been cal-
culated at 3-4 days. In man, increased concentrations
of thallium may be found in urine and feces for several
weeks after absorption. Excretion also occurs through
hair, which in unexposed subjects has been shown to
contain the highest concentration of thallium in any
tissue. In the rat, 21 days after dosing by parenteral
or oral routes, up to 60% of the remaining body bur-
den was found in the hair. There are similarities be-
tween the ionic transport of thallium and of potassium
through cell membranes, but once intracellular, thal-
lium is less rapidly released than potassium.
Thallium has caused acute and often fatal poison-
ing as a result of unintentional, criminal, or suicidal
ingestion. Fatalities have also occurred after the now
obsolete therapeutic administration of thallium. Gas-
troenteritis, collapse, and later peripheral neuropathy
are the principal features in acute poisoning, but with
longer survival, alopecia becomes a characteristic fea-
ture after 2-3 weeks. In chronic poisoning, the main
features are vague ill health, paresthesias, and in some
cases loss of hair; this pattern is seen after low-level
occupational exposure. The widespread use of thal-
lium as a rodenticide has been responsible in some
countries for the death of domestic and wild animals
and their natural predators.
g/day, mostly from foodstuffs, which does not
constitute a threat to health. Where environmen-
tal monitoring shows thallium levels signifi cantly
above background, biomonitoring of the popula-
tion should be carried out, and where this reveals
evidence of excessive exposure, emissions should be
reduced.
µ
1 PHYSICAL AND CHEMICAL
PROPERTIES
Thallium (Tl): atomic weight, 204.4; atomic number,
81; density, 11.9; melting point, 303.5°C; boiling point,
1457°C; crystalline form blue-white metal, tetrago-
nal; oxidation states +1, +3. Compounds to be taken
up in this chapter are thallous sulfate, thallous nitrate,
and thallous acetate. Other common compounds are
thallium(I) oxide, thallium(III) oxide, thallous carbon-
ate, and thallous sulfi de.
Thallium shares group IIIa of the Periodic Table
with indium, gallium, aluminum, and boron. Thal-
lium metal forms a brownish black oxide on exposure
to air. Thallium is highly reactive, readily soluble in
acids, and forms monovalent thallous and trivalent
thallic salts, the latter being less stable (Lee, 1971).
