Previous - Next
DESIGNATIONS
CAS No.: 7440-28-0
Registry name: Thallium
Chemical name: Thallium
Synonyms, Trade names: Thallium
Chemical name (German): Thallium
Chemical name (French): Thallium
Appearance: very similar to lead: soft and ductile heavy metal; shiny white at fresh cuts turning blue-grey; (alpha-thallium has a hexagonal crystalline structure and is converted at temperatures above 232°C into beta-thallium with cubic structure)
BASIC CHEMICAL AND PHYSICAL DATA
Chemical symbol: Tl
Rel. atomic mass: 204.37 g
Density: 11.85 g/cm3
Boiling point: 1457°C
Melting point: 303°C
Vapour pressure: 0.013 Pa at 473°C
Solvolysis/solubility: in water: virtually insoluble (forming hydroxides in air saturated water); thallium sulphate: 48.7g/l insoluble in lyes, soluble in diluted nitric acid and alcohol
ORIGIN AND USE
Usage:
Together with sulphur and arsenic, thallium is used to produce
low-melting glass (around 150°C). Adding thallium to other
metals increases their resistance to deformation and corrosion.
The substance is used in the semiconductor industry in photocells
and as an activator for light-sensitive crystals. Thallium
sulphate (which used to be an important rat poison) is hardly
ever produced today because of its high toxicity.
Important thallium compounds:
- thallium sulphate (TI2SO4) - very toxic
- sodium thallide (NaTI);
- thallium(I) alkoxides.
Origin/derivation:
Thallium makes up approx. 10-4% of the Earth's crust
(61st position in element frequency table). It is found as an
accompanying metal in zinc, copper, iron and lead ores. All
thallium minerals such as lorandite, vrbite and crookesite are
extremely rare. Roasted pyrites used to produce cement may
contain considerable quantities of thallium (KEMPER, 1987).
Production:
Worldwide production < 100 t/a; the substance is
manufactured in the USA, Russia, Belgium and Germany (BREUER,
1981). According to ZARTNER-NYILAS et al. (1983), the worldwide
production of thallium and its compounds amounts to approximately
20 t/a.
Toxicity
| Humans: | LD 8-10 mg/kg | acc. ZARTNER-NYILAS et al., 1983 | |
| 220 µg/(kg·d) 1) | acc. ZARTNER-NYILAS et al., 1983 | ||
| 15.4 µg 2) | acc. ZARTNER-NYILAS et al., 1983 | ||
| Plants: | |||
| Various species | 20-30 mg/kg | Lower yield | BAFEF, 1987 |
| Young barley | 11-45 mg/kg | Lower yield | BAFEF, 1987 |
Notes:
1) Smallest toxic dose referenced to entire life
2) Tolerable daily thallium absorption from air, water, foodstuffs
Characteristic effects:
Humans/mammals: Thallium is assimilated by humans via the food chain, respiration and by skin resorption. It is distributed throughout the entire body through the bloodstream and mainly accumulates in the liver, kidneys, intestinal wall and muscle tissue. Additional accumulation takes place in the bones, skin, sweat glands, sebaceous glands, nails, hair and in the entire nervous system. Moreover, thallium passes through the placenta of pregnant women and can thus harm unborn children. The substance is excreted with urine and stool, as well as in small quantities via hair, sweat, tears, saliva and mother's milk (ZARTNER-NYILAS et al., 1983). Thallium and its compounds are very toxic. Symptoms are hair loss, cataracts, degeneration of the nerves, impaired vision, inhibited growth, neuralgia and psychosis. Accumulation takes place in the skin and hair.
Plants: Just like several other heavy metals, thallium is absorbed by plants via the roots and thus accumulates in the leaf tissue as well as in other parts of the plant. Phytotoxic effects may occur. The damage pattern, which involves chlorosis of the leaves as well as intercostal necrosis and/or necrosis around the edges, does however vary in terms of intensity and extent from plant to plant. The type/species-specific resistance is particularly apparent. Plants with a hard surface are usually subject to less damage than plants with soft, pilose surfaces (ZARTNER-NYILAS et al., 1983).
ENVIRONMENTAL BEHAVIOUR
Water:
Like other heavy metals, thallium accumulates in sediment.
Soil:
Very little is known to date about the persistence of
thallium in soil. Even thallium sulphate is washed out only to a
slight extent. The low thallium content in groundwater - even in
the immediate vicinity of emission sources - underlines that
soils are an important sink for thallium.
Food chain:
Certain plant species (e.g. curly kale) considerably accumulate
thallium from the soil. The accumulation proceeds in the food
chain.
ENVIRONMENTAL STANDARDS
| Medium/ acceptor |
Sector | Country/organ. | Status | Value | Cat. | Remarks | Source |
| Water: | Marine | USA | 0.01 mg/l (max.) |
Hazard threshold | EPA, 1973 | ||
| Marine | USA | 0.05 mg/l (max.) |
Minimal risk | EPA, 1973 | |||
| Soil: | D | G |
1 mg/kg |
KLOKE, 1980 | |||
| CH | G |
1 mg/kg |
VSBO | acc. LAU-BW, 1989 | |||
| Air: | D | L |
0.01 mg/m2d |
IW1 | 24 h1) | TA-Luft, 1986 | |
| Emiss. | D | L |
0.2 mg/m3 |
mass flow > 1 g/h | acc. TA Luft, 1986 | ||
| Workp | Aus | (L) |
0.1 mg/m3 |
Soluble compounds | acc. MERIAN, 1984 | ||
| Workp | B | (L) |
0.1 mg/m3 |
Soluble compounds | acc. MERIAN, 1984 | ||
| Workp | D | L |
0.1 mg/m3 |
MAK | Total dust | DFG, 1988 | |
| Workp | CH | (L) |
0.1 mg/m3 |
Soluble compounds | acc. MERIAN, 1984 | ||
| Workp | NL | (L) |
0.1 mg/m3 |
Soluble compounds | acc. MERIAN, 1984 | ||
| Workp | PL | (L) |
0.1 mg/m3 |
Soluble compounds | acc. MERIAN, 1984 | ||
| Workp | RO | (L) |
0.05 mg/m3 |
Short-time, soluble compounds | acc. MERIAN, 1984 | ||
| Workp | SF | (L) |
0.1 mg/m3 |
Soluble compounds | acc. MERIAN, 1984 | ||
| Workp | SU | (L) |
0.01 mg/m3 |
1967 | acc. ACGIH, 1982 | ||
| Workp | YU | (L) |
0.1 mg/m3 |
Soluble compounds | acc. MERIAN, 1984 | ||
| Plants: | D | G |
0.25 mg/kg |
acc. BAFEF, 1987 | |||
| Foodstuffs: | D | G |
0.25 mg/kg |
acc. BAFEF, 1987 |
Note:
1) Tl and its organic compounds within dust
sediments, stated as Tl
Comparison/reference values
| Medium/origin | Country | Value | Source |
| Water: | |||
| Rhine (km 865) | 0.5-2.5 µg/l | acc. ZARTNER-NYILAS et al., 1983 | |
| Soil: | |||
| Various soils (normal) | <0.5 mg/kg | ||
| Various soils (frequent) | 0.01-0.5 mg/kg | acc. KLOKE, 1980 | |
| Plants: | 0.01-0.5 mg/kg | ||
Assessment/comments
On the basis of the data available at present, the risk to the public from increased thallium exposure is slight. Local dust depositions from thallium-emitting industries (e.g. cement) have seldom given an indication of human health hazards. One case of remarkable thallium emissions from the cement industry is known in Germany. Animals and plants do however reveal regional damage. There is little information available on the chronic effects of thallium in humans as an environmental pollutant. Opinions differ on the subject of mutagenity, teratogenity and carcinogenity.