Contents - Previous - Next


Thallium

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 232C 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: 1457C
Melting point: 303C
Vapour pressure: 0.013 Pa at 473C
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 150C). 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 g/(kgd) 1) acc. ZARTNER-NYILAS et al., 1983
15.4 g 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 g/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.


Contents - Previous - Next