IPCS INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
Health and Safety Guide No. 102
THALLIUM AND THALLIUM COMPOUNDS
HEALTH AND SAFETY GUIDE
UNITED NATIONS ENVIRONMENT PROGRAMME
INTERNATIONAL LABOUR ORGANISATION
WORLD HEALTH ORGANIZATION
WORLD HEALTH ORGANIZATION, GENEVA 1996
This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.
WHO Library Cataloguing in Publication Data
Thallium and thallium compounds: health and safety guide.
(Health and safety guide ; no. 102)
1.Thallium - toxicity I.Series
ISBN 92 4 151102 8 (NLM Classification: QV 618)
ISSN 0259-7268
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CONTENTS
1. PRODUCT IDENTITY AND USES
1.1. Identity
1.2. Physical and Chemical Properties
1.3. Analysis
1.4. Production and Uses
2. SUMMARY AND EVALUATION
2.1. Environmental transport, distribution and
transformation
2.2. Environmental levels and human exposure
2.3. Kinetics and metabolism in laboratory animals and humans
2.4. Effects on laboratory mammals and in vitro test
systems
2.5. Effects on humans
2.6. Human dose-response relationship
2.7. Effects on other organisms in the laboratory and field
3. CONCLUSIONS AND RECOMMENDATIONS
4. HUMAN HEALTH HAZARDS, PREVENTION AND PROTECTION, EMERGENCY ACTION
4.1. Human Health Hazards, Prevention and Protection, First
Aid
4.1.1. Advice to physicians
4.1.1.1 Signs and symptoms of exposure
4.1.1.2 First aid
4.1.1.3 Medical treatment
4.1.2. Health surveillance advice
4.1.3. Prevention and protection
4.1.3.1 General recommendations
4.1.3.2 Engineering control
4.1.3.4 Personal protective equipment and
hygienic measures
4.2. Explosion and fire hazards
4.3. Storage
4.4. Transport
4.5. Spillage
4.6. Disposal
5. HAZARDS FOR THE ENVIRONMENT AND THEIR PREVENTION
6. SUMMARY OF CHEMICAL SAFETY INFORMATION
7. CURRENT REGULATIONS, GUIDELINES, AND STANDARDS
7.1. Previous Evaluations by International Bodies
7.2. Exposure Limit Values
7.3. Specific Restrictions
7.4. Labelling, Packaging, and Transport
7.5. Waste Disposal
8. BIBLIOGRAPHY
INTRODUCTION
The Environmental Health Criteria (EHC) monographs produced by the
International Programme on Chemical Safety include an assessment of
the effects on the environment and on human health of exposure to a
chemical or combination of chemicals, or physical or biological
agents. They also provide guidelines for setting exposure limits.
The purpose of a Health and Safety Guide is to facilitate the
application of these guidelines in national chemical safety
programmes. The first three sections of a Health and Safety Guide
highlight the relevant technical information in the corresponding EHC.
Section 4 includes advice on preventive and protective measures and
emergency action; health workers should be thoroughly familiar with
the medical information to ensure that they can act efficiently in an
emergency. Within the Guide is a Summary of Chemical Safety
Information which should be readily available, and should be clearly
explained, to all who could come into contact with the chemical. The
section on regulatory information has been extracted from the legal
file of the International Register of Potentially Toxic Chemicals
(IRPTC) and from other United Nations sources.
The target readership includes occupational health services, those in
ministries, governmental agencies, industry, and trade unions who are
involved in the safe use of chemicals and the avoidance of
environmental health hazards, and those wanting more information on
this topic. An attempt has been made to use only terms that will be
familiar to the intended user. However, sections 1 and 2 inevitably
contain some technical terms. A bibliography has been included for
readers who require further background information.
Revision of the information in this Guide will take place in due
course, and the eventual aim is to use standardized terminology.
Comments on any difficulties encountered in using the Guide would be
very helpful and should be addressed to:
The Director
International Programme on Chemical Safety
World Health Organization
1211 Geneva 27
Switzerland
THE INFORMATION IN THIS GUIDE SHOULD BE CONSIDERED AS A STARTING
POINT TO A COMPREHENSIVE HEALTH AND SAFETY PROGRAMME
1. PRODUCT IDENTITY AND USES
1.1 Identity
The chemical names, chemical formula and CAS numbers of thallium
and of some thallium compounds are given in Table 1.
1.2 Physical and Chemical Properties
Thallium is a soft and malleable heavy metal with a bluish-white
colour. Its relative molecular mass is 204.283. Its most important
compound is the colourless odourless and tasteless thallium(I)
sulfate, previously used on a large scale as a rodenticide.
Monovalent (thallous) compounds behave like, and may be as, reactive
as, alkali metals, e.g., potassium, whereas the trivalent (thallic)
compounds are less basic, resembling aluminium.
Some physical properties are summarized in Table 1.
1.3 Analysis
Since concentrations of thallium in environmental samples are
normally very low, determination directly from the sample or from the
digestion solution usually lacks sufficient accuracy. Therefore,
preconcentration procedures are necessary. For the µg/kg range or
less, isotope dilution and inductively coupled plasma mass
spectrometry coupled with electrothermal vaporization or graphite
furnace atomic absorption spectrometry are used. Usually the limit of
detection for the latter is in the range of 0.6-20 µg/kg.
1.4 Production and Uses
Thallium is produced industrially only in small quantities (in
1987 and 1988 worldwide production was about 17 tonnes; in 1991
world-wide industrial consumption was 10 to 15 tonnes). However, each
year nearly 1000 tonnes of thallium are released into the environment,
mainly from mineral smelters, coal-burning power plants, brickworks
and cement plants.
Thallium has a wide variety of industrial uses. Its use as a
depilatory for humans or as a rodenticide and insecticide has now been
prohibited or severely reduced. Thallium is now mainly used in the
electrical and electronic industries and in the production of special
glasses. Another important field of application is the use of
radioisotopes in medicine for scintigraphy and the diagnosis of
melanoma.
TABLE 1 PHYSICAL AND CHEMICAL PROPERTIES OF THALLIUM AND SOME SELECTED THALLIUM COMPOUNDSa
Name Chemical CAS registry Relative Specific Melting Boiling Colour Solubility in
formula number atomic/ gravity point point water
molecular (g/cm3) (°C) (°C) (g/litre)
mass
Thallium Tl 7440-28-0 204.38 11.85 303.5 1457 bluish-white, insoluble
metallic
Thallium(I) acetate TlC2H3O2 563-68-8 263.43 3.765 131 - silky white very
soluble
Thallium aluminium TlAl(SO4)2*12 52238-56-9 639.66 2.306 91 - colourless 117.8
sulfate H2O
Thallium(I) bromide TlBr 7789-40-0 284.29 7.557 480 815 pale yellow 0.5
(17.3°C) (25°C)
Thallium(I) carbonate Tl2CO3 29809-42-5 468.78 7.110 273 - white 40.3
(15.5°C)
Thallium(I) chloride TlCl 7791-12-0 239.84 7.004 430 720 white 2.9
(30°C) (15.5°C)
Thallium(III) TlCl3 13453-32-2 310.74 - 25 decomposes colourless, very
trichloride
hygroscopic soluble
TlCl3*4H2O 13453-33-3 382.80 - 37 100 (-H2O) colourless 862
Thallium ethylate TlOC2H5 20398-06-5 249.44 3.493 -3 130 colourless -
(20°C) (decomposes)
Thallium(I) fluoride TlF 7789-27-7 223.38 8.23 327 655 colourless 786
(4°C) (15°C)
TABLE 1 (Con't)
Name Chemical CAS registry Relative Specific Melting Boiling Colour Solubility in
formula number atomic/ gravity point point water
molecular (g/cm3) (°C) (°C) (g/litre)
mass
Thallium(III) TlF3 7783-57-5 261.38 8.36 550 - olive decomposes
trifluoride (25°C) (decomposes) green to TIOH
Thallium hydroxide TlOH 1310-83-4 221.39 - 139 - pale 259
(decomposes) yellow
Thallium(I) TlI 7790-30-9 331.29 7.29 440 (ß) 823 (ß) yellow 0.006
iodide (alpha) (20°C)
Thallium(I) TlNO3 10102-45-1 266.39 - 206 430 white 95.5
nitrate (alpha) (20°C)
Thallium (III) nitrate Tl(NO3)3*3H2O 13453-38-8 444.44 - 105-107 decomposes colourless
decomposes
trihydrate
Thallium(I) oxide Tl2O 1314-12-1 424.77 9.52 300 1080 (-O) black decomposes
(16°C) to TIOH
Thallium(III) oxide Tl2O3 1314-32-5 456.76 10.19 717 ± 5 875 (-O2) black insoluble
(22°C)
Thallium(I) sulfate Tl2SO4 7446-18-6 504.82 6.77 632 decomposes white 48.7
(20°C)
Thallium(I) sulfide Tl2S 1314-97-2 440.85 8.46 448.5 - - 0.2
(20°C)
a From: Stokinger (1987); Budavari (1989); Lide (1990)
2. SUMMARY AND EVALUATION
2.1 Environmental transport, distribution and transformation
Near point sources such as coal-fired power-generating stations,
some cement plants and metal smelting operations, the major source of
thallium in air is emission of fly ash. The results of one study
indicate that nearly all of the thallium in fly dust from a cement
plant was present as soluble thallium(I) chloride.
The fate of thallium added to soil (in deposited fly ash, for
example) depends largely on soil type. Retention will be greatest in
soils that contain large amounts of clay, organic matter and
iron/manganese oxides. Incorporation into stable complexes causes
enhanced thallium concentrations only in the upper levels of soils.
The uptake of thallium by vegetation increases as soil pH decreases.
In some strongly acid soils significant amounts of thallium can be
leached to local ground and surface water.
Most dissolved thallium in freshwater is expected to be in the
monovalent form. However, in strongly oxidized fresh water and most
seawater trivalent thallium may predominate. Thallium can be removed
from the water column and accumulate in sediment by various exchange,
complexation or precipitation reactions.
Although thallium can bioconcentrate, it is not likely to
biomagnify in aquatic or terrestrial food webs.
2.2 Environmental levels and human exposure
In areas not contaminated by thallium, concentrations in air are
usually < 1 ng/m3, those in water < 1 µg/litre, and those in water
sediments < 1 mg/kg. Mean concentrations in the earth's crust range
from 0.1 to 1.7 mg/kg, but very high concentrations are possible,
e.g., in coal up to 1000 mg/kg, and the rarely found minerals of
thallium consist of up to 60% of the element. Food of plant and
animal origin usually contains < 1 mg/kg dry weight and the human
average dietary intake of thallium appears to be less than 5 µg/day.
Uptake via the respiratory system is estimated to be < 0.005 µg
thallium/day.
There are only limited data about the actual thallium content of
workplace air. The most recent (1980s) concentrations of thallium
observed were < 22 µg thallium/m3 (in the production of a special
thallium alloy and in a thallium smelter). Average urinary
concentrations were determined to be in the range of 0.3-8 µg/litre
for cement workers and 0.3-10.5 µg/litre for foundry workers.
2.3 Kinetics and metabolism in laboratory animals and humans
Thallium is rapidly and well absorbed through the gastro-
intestinal and respiratory tracts and is also taken up through
the skin. It is rapidly distributed to all organs and passes the
placenta (as indicated by the rapid fetal uptake) and the blood-brain
barrier. Because of its rapid accumulation in cells, concentrations
of thallium in whole blood do not reflect the levels in tissues. In
acute poisoning of experimental animals or humans, initially high
concentrations of thallium appear in the kidney, low concentrations in
fat tissue and brain, and intermediate concentrations in the other
organs; later the thallium concentration of the brain also increases.
Elimination of thallium may occur through the gastrointestinal
tract (mainly by mechanisms independent of biliary excretion), kidney,
hair, skin, sweat and breast milk. Intestinal reabsorption (mainly
from the colon) may occur with a consequent decrease in total body
clearance. In rats, the main routes of thallium elimination are
gastrointestinal (about two thirds) and renal (about one third), in
rabbits the contribution of the two routes is about equal. Thallium
is also secreted in saliva.
As with many other substances, the excretion of thallium in
humans differs from that in laboratory animals, since the rate of
excretion is generally much lower in humans (rate constant
= 0.023-0.069 day-1) than in laboratory animals (average rate
constant = 0.18 day-1). Another major difference between humans and
animals is the relative contribution of the different routes of
excretion. In humans, renal excretion seems to be much more important
than in animals, although its relative contribution to the total body
clearance has not been definitively established, due principally to
the lack of sufficient human data. Moreover, exposure levels,
duration of exposure, impairment of excretory organ function,
potassium intake and concomitant treatment of acute poisoning may
considerably influence the results.
In one study renal excretion of thallium was reported to be about
73%, whereas that through the gastrointestinal tract was about 3.7% of
the daily excreted amount. Excretion through hair and skin, and sweat
has been estimated to be 19.5% and 3.7%, respectively.
The biological half-life of thallium in laboratory animals
generally ranges from 3 to 8 days; in humans it is about 10 days but
values up to 30 days have been reported.
No data on the biotransformation of thallium are available.
2.4 Effects on laboratory mammals and in vitro test systems
There are no striking species-specific differences in the
toxicity of thallium(I) salts. Usually an oral intake of 20 to 60 mg
thallium/kg body weight is lethal within one week. Guinea-pigs are
slightly more sensitive than other experimental animals. The water-
insoluble thallium(III) oxide shows a somewhat lower acute toxicity by
oral or parenteral administration than thallium(I) salts. Comparison
of acute toxicity data indicates a high degree of bioavailability from
all exposure routes. Most organs are affected, but the signs of
poisoning and the sequence in which they occur reveal some intra- and
interspecies variability.
The symptoms of acute intoxication generally follow the following
sequence: firstly anorexia, vomiting and depression, later diarrhoea,
skin changes (inflammation at body orifices, skin furuncles, hair
loss), and then dyspnoea and nervous disorders. Finally, respiratory
failure leads to death.
Symptoms of chronic intoxication are similar to those of acute
intoxication. Loss of hair regularly occurs.
Histological examination reveals necrosis or other cell damage.
Necrotic changes have been observed in the kidneys, liver, intestine,
heart and the nervous system. Swelling of mitochondria and loss of
cristae, dilatations of smooth endoplasmic reticulum, increased
numbers of autophagic vacuoles and lipofuscin granules, and loss of
microvilli have been observed in many cells. The thallium-induced
alterations of functional processes may arise from physical disruption
of the membranes of subcellular organelles. In the heart,
arrhythmogenic effects are restricted to the sinus node.
Thallium intoxication causes selective impairment of certain
behavioural elements, which are correlated with biochemical effects
(which indicate cellular damage) in certain regions of the brain.
Some neurological effects seem to be caused by direct action, e.g.
ataxia and tremor by cerebellar alterations or alterations in
endocrine activity through changes in the hypothalamus. The autonomic
nervous system, mainly the adrenergic, may be activated by thallium.
In peripheral nerves, thallium seems to interfere presynaptically,
with the spontaneous release of transmitter, by antagonizing these
calcium-dependent processes.
The exact mechanism of thallium toxicity is still unknown.
Several, perhaps interconnected, mechanisms have been postulated. An
important aspect of thallium intoxication is the significant increase
in lipid peroxidation and in the activity of the lysosomal enzyme
ß-galactosidase. The resulting deficiency of glutathione leads to the
accumulation of lipid peroxides in the brain and, presumably, finally
to lipofuscin granules. The mode of action of thallium seems to be
mainly due to a disturbance of the function of the mitochondria.
Sexual activity is usually reduced in chronically poisoned
animals, and gonadotoxic effects of thallium are evident in the male
reproductive system. In the testes of rats given 10 mg thallium/litre
in the drinking-water for 16 days, the Sertoli cells were most
sensitive, and desquamation of the spermatogenic epithelium led to
immature sperm cells in the semen. This could explain the decreased
survival rate of embryos or reduced life span of offspring after
sublethal thallium-poisoning of the fathers.
Teratogenic effects, growth inhibition and disturbances in the
development of bones were found to occur in chicken embryos after
injection of thallium into the egg, but such effects in mammals, even
at maternotoxic doses, are controversial. Although transplacental
transfer has been demonstrated, many strains of mice and rats show no
or only slight teratogenic effects.
Two microbiological mutagenicity tests in Salmonella typhimurium
were negative and in vivo tests on sister chromatid exchange were
controversial. However, single studies report chromosomal aberrations
or a significant increase of single-stranded DNA breaks.
Long-term studies on the carcinogenicity of thallium are lacking.
2.5 Effects on humans
Since thallium salts are tasteless, odourless, colourless, highly
toxic, were easily obtainable in the past and still are in some
developing countries, thallium has often been used for suicide,
homicide and attempts at illegal abortion, causing acute thallium
poisoning. Indeed, thallium intoxication is considered one of the
most frequent causes, on a worldwide scale, of purposeful or
accidental human poisoning. Knowledge of chronic thallium
intoxication is limited to occupational exposure, to population groups
in contaminated areas and to cases of homicide involving multiple low
doses.
Symptoms of acute thallium toxicity depend on age, route of
administration and dose. Doses which have proved lethal vary between
6 and 40 mg/kg, being on average 10 to 15 mg/kg. Without therapy this
average dose usually results in death within 10 to 12 days, but death
occurring within 8-10 h has also been reported.
The triad of gastroenteritis, polyneuropathy and alopecia is
regarded as the classic syndrome of thallium poisoning, but in some
cases gastroenteritis and alopecia were not observed. Several other
signs and symptoms also occur, varying in order, extent and intensity.
Symptoms of thallium intoxication are often diffuse and initially
include anorexia, nausea, vomiting, metallic taste, salivation,
retrosternal and abdominal pain and occasionally gastrointestinal
haemorrhage (blood in faeces). Later, constipation is commonly seen
and may be resistant to treatment, thus interfering with antidotal
treatment.
After 2 to 5 days some of the typical thallium disorders slowly
develop, irrespective of the route of exposure. Effects on the
central and peripheral nervous system vary, but a consistent and
characteristic feature of thallium intoxication in humans is the
extreme sensitivity of the legs, followed by the "burning feet
syndrome" and paraesthesia. Involvement of the central nervous system
(CNS) is indicated by symptoms like hallucinations, lethargy,
delirium, convulsions and coma. Common circulatory symptoms are
hypertension, tachycardia and, in severe cases, cardiac failure. Loss
of head hair and sometimes body hair occurs after the second week of
poisoning; dystrophy of the nails is manifested by the appearance of
white lunular stripes (Mee's lines) 3 to 4 weeks after intoxication.
The black regions found in hair papillae are not caused by deposition
of pigments or thallium but are due to small amounts of air entering
the shaft.
In lethal cases the time until death occurs may vary from hours
to several weeks, but most commonly death occurs within 10 to 12 days.
Causes of death are mainly renal, CNS and cardiac failure.
In sublethal poisonings, recovery often requires months.
Sometimes neurological and mental disturbances as well as
electroencephalographic abnormalities and blindness can remain.
Additionally, intellectual functions seem to be adversely affected in
survivors.
In cases of chronic poisoning, symptoms are similar but in
general milder than in cases of acute intoxication. Sometimes
permanent blindness occurs. Complete recovery takes months and can be
interrupted by relapses.
In a well-investigated case of thallium emission around a cement
plant in Lengerich, Germany, thallium concentrations in the hair and
urine of exposed people did not correlate with certain features which
are known to be usually associated with chronic thallium poisoning,
but only with subjective neurological symptoms.
Postmortem examinations or biopsies following thallium poisoning
reveal damage of various organs. For example, after ingestion of
lethal doses, haemorrhages in the mucosa of the intestine, lung,
endocrine glands and heart, fatty infiltrations in liver and heart
tissue, and degenerative changes to glomeruli and renal tubules occur.
In the brain, fatty degeneration of ganglion cells, damage to axons
and disintegration of myelin sheaths can be observed.
Variations in blood pressure may be caused by direct effects of
thallium on the autonomic nervous system. Thallium intoxication
causes symmetric, mixed peripheral neuropathy. Distal nerves are
affected more than proximal nerves, and earlier but lesser degrees of
damage occur in nerves with shorter axons, e.g., cranial nerves.
Axons are swollen and contain vacuoles and distended mitochondria. In
lethal poisoning, severe damage of the vagus nerve, denervation of the
carotid sinus and lesions of the sympathetic ganglia have been
observed. In sublethal poisoning, affected nerves may undergo axonal
degeneration with no or only partial recovery within 2 years.
Retrobulbar neuritis and resulting visual disorders can develop
and persist for months after terminating treatment with thallium-
containing depilatories, and even optic atrophy may occur.
Limited data are available on the effects of thallium on human
reproduction. Menstrual cycle, libido and male potency may be
adversely affected. Effects on sperm are known to occur following
chronic intoxication. As in animal studies, transplacental transfer
occurs; this was seen following a thallium-induced abortion. However,
apart from a relatively low weight and alopecia of newborn babies,
fetal development was not affected in about 20 cases of thallium
intoxication during pregnancy.
No reports of any carcinogenic effects or data on immunological
effects of thallium are available. There is no adequate evidence of
genotoxic effects.
Therapies of thallium intoxication combine forced diuresis, use
of activated charcoal and prevention of re-absorption in the
colon by administration of Prussian blue, potassium ferric
hexacyanoferrate(II).
2.6 Human dose-response relationship
The mean urinary thallium concentration in unexposed populations
is 0.3 to 0.4 µg/litre. As thallium has a short biological half-life,
measured in days, and assuming steady-state conditions, this urinary
concentration can be taken as an indicator of total dose following
inhalation and dietary intake.
The mean urinary thallium concentration in a population sample
living near a thallium atmospheric emission source was 5.2 µg/litre.
A clear dose-response relationship was found between urinary thallium
concentration and the prevalence of tiredness, weakness, sleep
disorders, headache, nervousness, paraesthesia, and muscle and joint
pain. A similar dose-response relationship was also reported when
thallium in hair was used as an indicator of exposure.
The Task Group considered that exposures causing urinary thallium
concentrations below 5 µg/litre are unlikely to cause adverse health
effects. In the range of 5-500 µg/litre the magnitude of risk and
severity of adverse effects are uncertain, while exposure giving
values over 500 µg/litre have been associated with clinical poisoning.
2.7 Effects on other organisms in the laboratory and field
Thallium affects all organisms, but species- and also strain-
specific differences are evident. Different inorganic thallium(I) and
thallium(III) compounds and organothallium compounds can show
different toxicities.
The most important effect of thallium on microorganisms seems to
be inhibition of nitrification by soil bacteria. Results of one study
suggest that microbial community structure is disturbed at soil
concentrations in the range of 1-10 mg/kg dry weight, but the form of
thallium used in this experiment was not identified.
Thallium is taken up by all plant parts, but principally by the
roots. After uptake into the cell, it is concentrated unevenly in the
cytosol, probably bound to a peptide. Thallium concentrations found
in plants depend on soil properties (especially pH, clay and organic
matter content), as well as on the developmental stage and on the part
of the plant. Thallium accumulates in chlorophyll-containing regions,
but to a lesser degree in thallium-resistant plants. Oxygen
production is reduced by thallium, presumably by direct action on
electron transfer in photosystem II. Interference with the pigments
is indicated by the occurrence of chlorosis. In addition, impaired
uptake of trace elements seems to be involved in the mechanism of
toxicity. Growth is also affected, roots reacting more sensitively
than leaves or stems. These effects have been reported at
concentrations as low as 1 mg thallium/kg of dry plant tissue, after
exposure to monovalent forms of thallium.
Most studies of effects on aquatic organisms have used soluble
monovalent thallium compounds. The lowest thallium concentration
reported to affect aquatic species is 8 µg/litre, which caused a
reduction in growth of aquatic plants. Invertebrates are often
affected at lower concentration than fish (96-h LC50 values are
2.2 mg thallium/litre for daphnids and 120 mg/litre for a freshwater
fish). The lowest LC50 value, reported after exposure for about 40
days, was 40 µg/litre for fish.
Many cases of thallium intoxication of wildlife have been caused
by its large scale application as a rodenticide. In seed-eating
animals and predators the CNS and/or the gastrointestinal tract are
most severely affected. These effects can also be observed in farm
animals. In addition, thallium causes a loss of dorsal feathers in
ducks, salivation from the nose and mouth of cattle, and reduced
growth in broilers, laying hens, sheep and steers.
3. CONCLUSIONS AND RECOMMENDATIONS
Thallium is currently produced and used industrially in only
small quantities. However, metal mixing and smelting operations, as
well as cement plants using thallium-containing pyrite, can release
significant amounts of thallium. Stack gases and wastewater should be
monitored and, if necessary, controlled. Measures should be taken to
reduce occupational exposure (e.g., protective clothing should be
worn, dust scattering should be avoided).
Environmental exposure to thallium does not pose a health threat
for the general population. The total intake has been estimated to be
less than 5 µg/day, the vast majority coming from food. Drinking-
water and air generally contribute only very small amounts of
thallium.
Exposures should be kept to levels that lead to urinary
concentrations of less than 5 µg/litre, which corresponds to a daily
oral intake of approximately 10 µg thallium.
Where thallium is still available for use as a rodenticide, the
potential for poisoning remains a significant concern. Thallium
should no longer be used for this purpose, particularly as less
hazardous methods of rodent control are available.
4. HUMAN HEALTH HAZARDS, PREVENTION AND PROTECTION, EMERGENCY ACTION
4.1 Human Health Hazards, Prevention and Protection, First Aid
Since all thallium compounds are toxic and since thallium is
rapidly absorbed through all exposed epithelia, it is essential that
the correct precautions should be observed during handling and use.
4.1.1 Advice to physicians
4.1.1.1 Signs and symptoms of exposure
In acute thallium poisoning the onset of symptoms is often
insidious, reaching a maximum in the second or third week after
exposure. The initial clinical features include a gradual development
of gastrointestinal disturbance (severe constipation), hyperaesthesia,
paraesthesia, hyperalgesia of the lower limbs (affecting especially
the soles of the foot), followed by motor weakness of the lower limbs
and foot drop. Encephalopathy and retrobulbar neuritis occur in
severe poisoning. At the end of the second week, the characteristic
symptom of hair loss appears. Development of psychiatric disturbances
ranging from hysterical behaviour to complete psychosis may be
observed. In severe poisoning the patient may die early of myocardial
failure.
4.1.1.2 First aid
Medical care and hospital treatment is necessary as soon as
possible. Contaminated skin should be flushed with water and washed
with soap and water. If the eyes are splashed with thallium-containing
liquids they should be flushed immediately with clean water for at
least 15 min. In the event of ingestion, vomiting should be induced in
conscious patients and followed by gastric aspiration and lavage.
Charcoal haemoperfusion has been shown to be successful if used within
48 h of thallium ingestion but this should be restricted to
intoxications with high doses of thallium.
4.1.1.3 Medical treatment
Forced diuresis (8-12 litres/day) may be used until the urinary
excretion rate is < 1 mg thallium/24 h (beware of heart failure due
to impairment of the pacemaker function of the heart and myocardial
contractility).
A very effective oral antidote is Prussian Blue, potassium ferric
hexacyanoferrate(II), an inorganic pigment which is not absorbed by
the gut. Potassium ions in the molecule are exchanged for thallium
ions. Thus, absorption in the intestine is prevented and the thallium-
loaded molecule is excreted with the faeces. This therapy results in
faecal elimination greatly exceeding urinary elimination.
Two 10 g doses of Prussian Blue should be given daily (preferably
intraduodenally in 100 mg 15% mannitol as a laxative) until urinary
thallium excretion is < 0.5 mg/24 h. Daily defecation is necessary.
4.1.2 Health surveillance advice
People suffering from renal or hepatic disease, anaemia, blood
dyscrasias, hypertension, alcoholism, chronic infections or endocrine
gland dysfunction should be excluded from working with thallium.
The urinary thallium concentration of people exposed
occupationally should be determined periodically in a programme of
biological monitoring. The intervals between monitoring should depend
on the degree of exposure. Periodic examinations should pay
particular attention to the typical effects of thallium, e.g., kidney
and eye function, the presence of pain in the limbs and hair loss.
4.1.3 Prevention and protection
Recommendations for the protection of employees in industrial
plants using thallium fall under three headings:
4.1.3.1 General recommendations
Access to rooms in which thallium is used should be restricted to
a limited number of employees. Employees should be repeatedly
informed about risk and industrial hygiene, as applies to employees
working with radioisotopes. They should be instructed to report any
unusual health symptoms. Employees should be encouraged to eat
potassium-rich food, e.g., bananas.
4.1.3.2 Engineering control
Dust scattering should be avoided and handling of thallium should
be carried out under a hood. Dust should be controlled within the
recommended threshold limit value of 0.1 mg/m3. Floors and tables
should be wet-mopped. Dust samplers should be installed for the
determination of thallium concentrations in the air.
4.1.3.4 Personal protective equipment and hygienic measures
Employees should be required to use protective workclothes,
including gloves. The complete set of personal work clothes should be
kept separate from normal clothes. They should be washed at least
once a week. Clothes should be changed before eating, drinking or
smoking, which should all be prohibited at the working place. Washing
and showering facilities should be provided and their use encouraged.
Individual respirators should be worn in all operations producing dust
or fumes.
4.2 Explosion and Fire Hazards
Finely dispersed thallium particles can form explosive mixtures
in air. However, thallium compounds do not present an explosion risk,
nor are they flammable. Only thallium(III) nitrate trihydrate
(Tl(NO3)3.3H2O) is classified as a fire supporting agent and so
contact with flammable compounds should be avoided.
4.3 Storage
All products should be stored in secure buildings, kept dry and
out of the reach of children and animals, and separated from food,
drinks and animal feed.
Thallium should be stored in a fireproof location, separate from
strong oxidants, strong acids, fluorine and oxygen, and kept under
vasoline oil.
4.4 Transport
For transport unbreakable packaging should be used or breakable
packaging should be put into unbreakable containers. Transporters
should comply with national and international requirements regarding
the transport of hazardous materials.
4.5 Spillage
The danger area should be evacuated and an expert be consulted.
The spilled substance should be swept up and placed into containers.
Extra personal protection is required, i.e. complete protective
clothing including a self-contained breathing apparatus.
4.6 Disposal
Thallium(III) oxide can be precipitated with sodium hydroxide
from aqueous solutions of thallium compounds.
5. HAZARDS FOR THE ENVIRONMENT AND THEIR PREVENTION
Thallium is not used on a large scale in industry, but emissions
can pollute the environment around mineral smelters, coal-burning
power plants, brickworks and cement plants using thallium-enriched
pyrite. The emissions can be reduced by the use of raw material with
low concentrations of thallium and by the exclusion of enrichment
procedures. Waste slags should be marked and sealed to avoid leaching
into soil and pollution from dust. The discharge of thallium from
tailing ponds and emissions into the atmosphere should be reduced by
adequate procedures.
Since thallium is incorporated into stable humus complexes, it
remains for a long time in the upper layer of the soil. In regions
with contaminated agricultural or garden soil, the thallium
concentrations in the upper layer should be reduced by deep ploughing
or by the addition of uncontaminated soil.
Thallium is toxic to aquatic organisms but effects are likely to
be limited to sites adjacent to point sources. Although it can
bioconcentrate, thallium is unlikely to biomagnify in aquatic or
terrestrial food webs.
The use of thallium as a rodenticide has resulted in poisoning of
non-target organisms, including foxes, badgers, martens, partridges,
pheasants and eagles. Poisoning of domestic animals, such as dogs,
cats, ducks and pigeons, has also been widely reported. Less
hazardous methods or rodent control should be used.
6. SUMMARY OF CHEMICAL SAFETY INFORMATION
This summary should be easily available to all health workers
concerned with, and users of, thallium. It should be displayed at, or
near, entrances to areas where there is potential exposure to thallium
and on processing equipment and containers. The summary should be
translated into the appropriate language(s). All persons potentially
exposed to the chemical should also have the instructions in the
summary clearly explained.
Space is available for insertion of the National Occupational
Exposure Limit, the address and telephone number of the National
Poison Control Centre, and local trade names.
SUMMARY OF CHEMICAL SAFETY INFORMATION
PHYSICAL PROPERTIES THALLIUM METAL THALLOUS OTHER CHARACTERISTICS
SULFATE
Relative atomic/molecular mass 204.4 504.8 Thallium
Melting point (°C) 304 632 Soft malleable heavy metal with bluish-white colour; reacts with
halogens at room temperature; incompatible with strong acids,
Boiling point (°C) 1457 decomposes strong oxidants and oxygen; forms toxic compounds on contact with
moisture; finely dispersed thallium particles can form explosive
Water solubility (g/litre at 20°C) insoluble 48.7 mixtures in air; thallium may be absorbed into the body by
inhalation, through the skin or by ingestion; dust formation can lead
Relative density (water = 1) 11.9 6.77 to harmful concentration of airborne particles.
CAS No. 7440-28-0 7446-18-6
Thallous sulfate
White crystals; decomposes on heating emitting very toxic fumes
of thallium and sulfur oxides; not combustible, not explosive; may be
absorbed into the body by inhalation of its aerosol, through the skin
and by ingestion.
SUMMARY OF CHEMICALS SAFETY INFORMATION (continued)
HAZARD/SYMPTOM PREVENTION AND PROTECTION FIRST AID
GENERAL: Short-term exposure may result Prevent any spillage dispersion of dust; avoid
in effects on the nervous system and in inhalation of dust or skin contact; pregnant
death; effects may be delayed; long-term women should avoid exposure
exposure may cause hair loss and have
effects on vision, the liver, lungs,
nervous system and kidneys; may cause
birth defects, specifically skeletal
deformation, low birth weight, and
premature birth; danger of cumulative
effects
INHALATION: Nausea, vomiting, loss of Apply ventilation, local exhaust or breathing Remove victim to fresh air and keep warm;
hair, abdominal colic, pain in legs and protection if breathing has stopped, apply artificial
chest, nervousness, irritability respiration; obtain medical attention
immediately
SKIN: May be absorbed, resulting in the Avoid skin contact; wear clean, impervious Remove contaminated clothes and shoes
same symptoms as following inhalation clothing, gloves and shoes immediately; rinse and then wash skin with
plenty of water and soap; obtain medical
attention immediately
EYES: May be absorbed; redness, pain, Wear safety goggles or eye protection First rinse with plenty of water for at
blurred vision (after exposure to thallium least 15 min. (remove contact lenses if
sulfate) possible), then obtain medical attention
INGESTION: Abdominal pain, constipation, Do not eat, drink, chew, or smoke during work; Rinse mouth; in conscious patients vomiting
diarrhoea, headache, nausea, vomiting, do not keep food in areas with potential can be induced (e.g. by giving two glasses
loss of vision, loss of hair, nervousness, exposure; change clothes before eating, of milk); subsequently give a slurry of
irritability, tremor, delirium, drinking or smoking activated charcoal in water to drink;
convulsions, paralysis, coma (in the case obtain medical attention
of thallous sulfate)
SUMMARY OF CHEMICALS SAFETY INFORMATION (continued)
HAZARD/SYMPTOM PREVENTION AND PROTECTION FIRST AID
ENVIRONMENT: May be hazardous to aquatic Contamination of water, soil and atmosphere
and terrestrial organisms and to the soil should be avoided by proper methods of
microflora storage, transport, and waste disposal
SPILLAGE STORAGE FIRE AND EXPLOSION
Evacuate the area and consult an expert; Store away from foodstuffs and separate from Thallium
sweep up spilled substance and place into strong oxidants, strong acids, fluorine and Combustible, explosive, when in contact
containers; remove to safe place (extra oxygen; keep under vasoline oil in a dry, with fire or flame; finely dispersed
personal protection required: complete fire-proof and well-labelled room particles form explosive mixtures in air;
protective clothing including NO open flames prevent deposition of dust;
self-contained breathing apparatus) use in closed system with dust
explosion-proof electrical equipment and
lighting; extinguish fires with foam,
carbon dioxide, water spray, or powder;
provision to contain effluent from fire
extinguishing
Thallous sulfate
Not combustible or explosive; avoid contact
with hot surfaces; in case of fire
extinguish with water in large amounts,
foam, carbon dioxide, or powder; provision
to contain effluent from fire extinguishing
SUMMARY OF CHEMICALS SAFETY INFORMATION (continued)
WASTE DISPOSAL NATIONAL INFORMATION
Dilute thallium solutions may be buried in National occupational exposure limit:
an approved dump or landfill where there
is no risk of contamination of surface or
groundwater; when possible, thallium
should be recovered and returned to the
suppliers; comply with any local
legislation regarding disposal of toxic
wastes National Poison Control Centre:
7. CURRENT REGULATIONS, GUIDELINES, AND STANDARDS
Most of the information given in this section has been extracted
from the International Register of Potentially Toxic Chemicals (IRPTC)
legal file. A full reference to the original national document from
which the information was extracted can be obtained from IRPTC.
The reader should be aware that regulatory decisions about
chemicals, taken in a certain country, can only be fully understood in
the framework of the legislation of that country. Furthermore, the
regulations and guidelines of all countries are subject to change and
should always be verified with appropriate regulatory authorities
before application.
7.1 Previous Evaluations by International Bodies
A Poisons Information Monograph for thallium has been issued
(IPCS, 1992).
On the basis of an acute oral LD50 of 11 mg/kg, thallium sulfate
has been classified in the WHO Recommended Classification of Pesticides
by Hazard as "highly hazardous" (Class Ib).
International Chemical Safety Cards have been issued for thallium
metal (no. 77) and for thallous sulfate (no. 336) (CEC/IPCS, 1990,
1991).
7.2 Exposure Limit Values
Some exposure limit values are given in the Current Regulations,
Guidelines and Standards table
7.3 Specific restrictions
In the Czech Republic the presence of thallium or its compounds
in cosmetics is prohibited. In the European Economic Community
countries, no detectable quantities of thallium may be contained in
colouring matter authorized for use in foodstuffs intended for human
consumption.
The use of thallium as a rodenticide has been prohibited in many
countries.
CURRENT REGULATIONS, GUIDELINES AND STANDARDS
Exposure Limit Values
Medium Specification Country Exposure limit description Value Effective date
AIR Occupational Argentina Maximum permissible concentration (MAC)
- Time-weighted average (TWA) 0.1 mg/m3 1991
Canada Threshold limit value (TLV)
- Time-weighted average (TWA) 0.1 mg/m3 1991
Germany Maximum worksite concentration (MAK)
- Time-weighted average (TWA) 0.1 mg/m3
- Short-term exposure limit (STEL) (30 min) 1.0 mg/m3 1992
Mexico Maximum limit (MXL)
- Time-weighted average (TWA) 0.1 mg/m3 1991
United Kingdom Occupational exposure standard (OES)
- Time-weighted average (TWA) 0.1 mg/m3 1992
USA (ACGIH) Threshold limit value (TLV)
- Time-weighted average (TWA) 0.1 mg/m3 1991
WATER surface Russian Maximum allowable concentration (MAC) 0.0001 mg/litre 1990
Federation
7.4 Labelling, Packaging and Transport
The United Nations Committee of Experts on the Transport of
Dangerous Goods and the International Maritime Organization classify
thallium compounds as poisonous substances (Hazard Class 6.1) and,
with regard to packing, as substances presenting medium danger
(Packing Group II).
European Economic Community legislation requires labelling as a
very toxic substance, using the symbol T+ and the following pictogram:
The following label statements are required for thallium
R 26/28 Very toxic by inhalation and if swallowed
R 33 Danger of cumulative effects
S 2 Keep out of reach of children
S 13 Keep away from food, drink and animal feeding stuffs
S 28 After contact with skin, wash immediately with plenty of
soap and water
S 45 In case of accident or if you feel unwell, seek medical
advice immediately (show label where possible)
For thallium sulfate the following label statements are required:
R 28 Very toxic if swallowed
R 38 Irritating to skin
R 48/25 Toxic: danger of serious damage to health by prolonged
exposure if swallowed
S 13 Keep away from food, drink and animal feeding stuffs
S 36/37 Wear suitable protective clothing and gloves
S 45 In case of accident or if you feel unwell, seek medical
advice immediately (show the label where possible)
7.5 Waste Disposal
When possible, thallium should be recovered and returned to the
suppliers. Dilute thallium solutions may be buried in an approved
dump or landfill where there is no risk of contamination of surface or
groundwater. Local legislation regarding disposal of toxic wastes
must be complied with.
8. BIBLIOGRAPHY
Aderjan R, von Clarmann M, Daldrup T, Geldmacher-von Mallinckrodt M,
van Heijst ANP, Machbert G, Schütz H, & Stöppler (in Press) [Thallium
- clinical toxicological analysis after acute intoxications.
Communications of the Senate Committee on clinical and toxicological
analysis.] German Research Council (in German).
ATSDR (1992) Toxicological profile for thallium. Atlanta, Georgia,
Agency for Toxic Substances and Disease Registry, pp. 1-90
(ATSDR/TP-91/26).
Barlow SM & Sullivan FM (1982) Reproductive hazards of industrial
chemicals. An evalution of animal and human data. Chapter 41: Thallium
and its compounds. New York, Academic Press 530-537.
Bowen HJM (1979) Environmental chemistry of the elements. New York,
London, Academic Press.
Cavanagh JB (1979) Metallic toxicity and the nervous system. In: Smith
WT & Cavanagh JB ed. Recent advances in neuropathology. Edinburgh,
Churchill Livingstone, pp. 247-275.
CEC/IPCS (1990) International Chemical Safety Card 77: Thallium
metal. Luxemburg, Commission of the European Communities.
CEC/IPCS (1991) International Chemical Safety Card 336: Thallous
sulfate. Luxembourg, Commission of the European Communities.
DFG (German Research Council) (1990) [Maximal concentrations at the
work place and biological tolerance values of chemicals in the work
area.] Weinheim, Verlag Chemie (in German).
IPCS (1992) Poisons information monograph: Thallium. Geneva, World
Health Organization (IPCS/INTOX/PIM/525).
Kemper FH & Bertram HP (1991) Thallium. In: Merian E ed. Metals and
their compounds in the environment. Weinheim, Verlag Chemie,
1227-1241.
LIS (Land Institute of Protection against Emissions) (1980)
[Environmental burden by thallium. Investigations in the neighbourhood
of the Dyckerhoff-cement plant AG in Lengerich and other thallium-
emitting plants in the country NW.] Bonn, Bonner Universitätsdruckerei
(in German).
Oehme FW ed. Toxicity of heavy metals in the environment. New York,
Marcel Dekker Inc, vol. 1.
Schoer J (1984) Thallium. In: Hutzinger O ed. The handbook of
environmental chemistry. Volume 3: Anthropogenic compounds, Part C.
Berlin, Springer Verlag, 143-214.
Sessions HK & Goren S (1947) Report of investigation of health hazards
in connection with the industrial handling of thallium. US Navy Med
Bull, 47: 545-550.
Smith IC & Carson BL (1977) Trace metals in the environment. Volume 1:
Thallium. Ann Arbor, Ann Arbor Science. Publishers.
US EPA (US Environmental Protection Agency) (1980) Ambient water
quality criteria for thallium. Springfield, Virginia, US
Department of Commerce, National Technical Information Service
(EPA 440/5-80-074).
Zitko V (1975) Chemistry, applications, toxicity, and pollution
potential of thallium. Department of Environment, Fisheries and Marine
Services, Research and Development Directorate (Technical Report
No. 518).