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Arsenic

DESIGNATIONS

CAS No.: 7440-38-2
Registry name: Arsenic
Chemical name: Arsenic
Synonyms, Trade names:
Grey arsenic, metallic arsenic
Chemical name (German):
Arsen
Chemical name (French): Arsenic
Appearance: bright silver-grey metal, brittle and of average hardness;
other modifications: yellow (unstable), black

BASIC CHEMICAL AND PHYSICAL DATA

Chemical symbol: As
Rel. atomic mass: 74.92 g
Density: 5.72 g/cm3
Boiling point: 613░C (subl.)
Melting point: 817░C (at 3.7 MPa)
Vapour pressure: 0 Pa
Solvolysis/solubility: in water: very low

BASIC DATA ON SELECTED COMPOUNDS

CAS No: 1327-53-3 7784-42-1
Chemical name: Arsenic trioxide Arsine
Synonyms, Trade names: White arsenic  
Chemical name (German): Arsentrioxid, Wei▀arsenik, Arsenik Arsin, Arsenwasserstoff
Chemical name (French): Arsenic Arsine, hydrure d'arsenic
Appearance: white powder or small white pieces, odourless colourless gas with garlic-like odour
Empirical formula: As2O3 AsH3
Rel. molecular mass: 197.82 g 77.95 g
Density: 3.7-3.87 g/cm3 3.48 g/l
Relative gas density:   2.7
Boiling point:   -55░C
Melting point: 200░C (subl.) -117░C
Solvolysis/solubility: in water: 18 g/l in water: 20 vol.%
Conversion factors: 1 ppm = 0.12 mg/m3

1 mg/m3 = 8.22 ppm

1 ppm = 0.31 mg/m3

1 mg/m3 = 3.24 ppm

ORIGIN AND USE

Usage:
The demand for metallic arsenic is limited. Arsenic is used in nonferrous alloys (e.g. to enhance the temper of lead-alloys) and highly pure arsenic is needed to produce GaAs- and InAs-semiconductors.
With the introduction of antibiotics, pharmaceutical products containing arsenic have become less important. Moreover, arsenic compounds have been used as pesticides (prohibited in Germany) and in the production of pigments.

Origin/derivation:
Arsenic is an element. The average arsenic content of the earth's crust has been estimated at 5 x 10-4 %. It is mainly obtained from complex ores. France, the former USSR, Sweden and Mexico are the main arsenic producing countries.

Production figures:
Arsenic production in tons of As2O3 content per year (1978)

France 7280
USSR 7640
Sweden 6706
Mexico 6263
World 40283

(figures taken from ULLMANN 1985)

Toxicity

Humans: LDLo 1 mg/kg, oral (arsenic trioxide) acc. Koch 1989
TCLo 0.5 ppm, inhalation (arsine) acc. Koch 1989
LD 50 mg/m3, inhalation (arsine) acc. Koch 1989
Mammals:    
Rat LD50 4.5 mg/kg, oral ( arsenic trioxide) acc. Koch 1989
Mouse LD50 43 mg/kg, oral ( arsenic trioxide) acc. Koch 1989
Rabbit LDLo 4.5 mg/kg, oral ( arsenic trioxide) acc. Koch 1989
Aquatic organisms:    
Fish LC50 10-100 mg/l (96h), arsenic trioxide acc. Koch 1989

Characteristic effects:

Humans/mammals: Pure arsenic is not toxic, but contaminations of technical arsenic (e.g. with As2O3) have to be considered. Acute poisoning mostly occurs by ingestion and inhalation of inorganic trivalent compounds such as As2O3. Symptoms are strong gastrointestinal disturbances, cramps and circulatory collapse. Airborne dusts often result in irritation of exposed skin and mucous membranes. Chronic poisoning can be caused by the intake of food and water with arsenicals or by inhalation of airborne dusts during long-term occupational exposure. Symptoms may appear even after many years of latency. Chronic poisoning results in damage to bone marrow, blood, liver, respiratory tract and central nervous system.

Acute poisoning with arsine results in retarded but rapid hemolytic anemia.

ENVIRONMENTAL BEHAVIOUR

In aquatic systems, arsenic mainly exists in the form of arsenides and arsenates. In sediments and soils, arsenates are readily absorbed at iron or aluminium hydroxides thus reducing their percolative abilities and speed as well as their availability for biological systems. In aquatic phases, arsenic forms insoluble precipitates with a number of compounds (Ca,S,Ba,Al,Fe) resulting in the elimination of arsenic compounds from the water. In microorganisms, plants and animals, methylation and reduction of arsenic compounds take place. Thus, a number of chemophysically and biologically stable arsenic compounds are produced [KOCH 1989].

Half-life:
The average biological half-life is about 60 days (rats/rabbits) due to the accumulation of arsenic in the erythrocytes. For humans, half-life is shorter because of a fast excretion of arsenic [KOCH 1989].

ENVIRONMENTAL STANDARDS

Medium/ acceptor

Sector

Country/ organ.

Status

Value

Cat.

Remarks

Source

Air: Emiss. D

L

0.2 mg/m3   mass flow > 5 g/h2) acc. TA Luft, 1986
Workp D

L

0.1 mg/m3 TRK oxides, acids and their salts acc. AUER Technikum 1988
Workp D

L

0.2 mg/m3 MAK arsine acc. AUER Technikum 1988
Workp USA

(L)

1) TWA oxides acc. AUER Technikum 1988
Workp USA

(L)

0.2 mg/m3 TWA arsine acc. AUER Technikum 1988
Workp SU

(L)

0.3 mg/m3   oxides acc. AUER Technikum 1988
Workp SU

(L)

0.3 mg/m3   arsine acc. AUER Technikum 1988

1) suspected human carcinogens
2) dustlike As and its compounds, stated as As

ASSESSMENT/COMMENTS

The toxicity of arsenic compounds differs significantly. Anorganic compounds are generally more toxic than organic ones. Some arsenic compounds are even carcinogenic. It is particularly significant as a workplace poison.


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