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Hexachlorobenzene

DESIGNATIONS

CAS No.: 118-74-1
Registry name: Hexachlorobenzene
Chemical name: Hexachlorobenzene
Synonyms, Trade names:
HCB
Chemical name (German):
Hexachlorbenzol
Chemical name (French): Hexachlorobenzne
Appearance: colourless (technical: yellowish) crystals

BASIC CHEMICAL AND PHYSICAL DATA

Empirical formula: C6Cl6
Rel. molecular mass: 284.79 g
Density: 2.04 g/cm3 at 20C
Relative gas density: 9.84
Boiling point: 322-326C
Melting point: 229C
Vapour pressure: 1.1 x 10-3 Pa
Flash point: 242C
Solvolysis/solubility: in water 0.005 mg/l

in benzene 31.6 g/l, in fat 11.5 g/kg at 37C

Conversion factors: 1 ppm = 11.84 mg/m3

1 mg/m3 = 0.08 ppm

ORIGIN AND USE

Usage:
Hexachlorobenzene is a fungicide which has primarily been used as a seed protection agent to prevent bunt and for the treatment of soil. It is still used in many developing countries to fumigate grain. Nowadays, HCB is mainly used for fireproofing and as a plasticiser. It is an important base product in the synthesis of various chlorinated organic compounds. In addition, it is used as an additive in wood preservatives.

Origin/derivation:
There are no natural sources. HCB is produced by chlorinating low chlorinated benzenes. HCB forms the basis for the production of pentachlorophenol (PCP).

HCB may be a by-product of the industrial chlorination of hydrocarbons. It is released into the environment both as a result of the combustion of products containing chlorine (e.g. waste incineration) and due to the use of pesticides contaminated with HCB.

Production figures:
Approx. 10,000 t/a worldwide at the end of the Seventies;
EC (1978) approx. 8,000 t/a; D approx. 4,000 t/a (1974) and 2,600 t/a (1976).

Emission figures:
The values quoted are between 20% and 100% of the amount produced.

Toxicity

Mammals:
Rat LD50 >10,000 mg/kg, oral acc. DVGW, 1988
LD50 >6,800 mg/kg, dermal acc. RIPPEN, 1989
Rabbit LD50 2,600 mg/kg, oral acc. DVGW, 1988
Cat LD50 1,700 mg/kg, oral acc. DVGW, 1988
Aquatic organisms:
Fish LD50 >100 mg/kg acc. RIPPEN, 1989
Water flea (Daphnia magna) EC0 0.025 mg/l (24h, ability to float) acc. DVGW, 1988

Characteristic effects:

Humans/mammals: HCB is supposed to have carcinogenic potential. Mutagenic and teratogenic effects have not been established. There have been cases of skin disease in humans and of liver damage and neurotic symptoms in rats following chronic exposure. HCB is thoroughly resorbed from foodstuffs in the gastro-intestinal tract and slowly metabolised, accumulating in fatty tissue. As the fat depot is degraded, HCB is remobilised and may then be found in all organs.

ENVIRONMENTAL BEHAVIOUR

Water:
In water, HCB is readily adsorbed on suspended matter and thus accumulates in the sediment.

Soil:
HCB accumulates in soil and sewage sludge.

Degradation, decomposition products, half-life:

Estimated half-life (abiotic and biotic) > 1 year.
• No degradation in surface water.
• Half-life in soil roughly 2 years. 14% degradation (adsorbed) after 24 h exposure to strong, simulated sunlight.
• Photomineralisation observed at wavelengths > 230 nm (adsorbed).
• Thermal decomposition at 510-530C; mineralisation at 950C.
• Metabolites: 2,3,5-Trichlorophenol, tetrachlorobenzene and pentachlorobenzene

Food chain:
HCB accumulates in the fatty tissue of organisms.

ENVIRONMENTAL STANDARDS

Medium/ acceptor Sector Country/ organ. Status Value Cat. Remarks Source
Water: Drinkw A

(L)

0.01 g/l     acc. DVGW, 1988
Drinkw D

L

0.1 g/l     acc. DVGW, 1988
Drinkw EC

G

0.1 g/l     acc. DVGW, 1988
Drinkw WHO

G

0.01 g/l     acc. DVGW, 1988
Surface IAWR

G

0.1 g/l   Drinking water1) acc. DVGW, 1988
Surface IAWR

G

0.5 g/l   Drinking water2) acc. DVGW, 1988
Air: Workp D

L

15 g/dl BAT In plasma/ serum acc. DVGW, 1988
Workp SU

(L)

0.9 mg/m3   Skin resorption acc. KETTNER, 1979
Foodstuffs:    

 

 
       
Tea, spices   D

L

0.1 mg/kg     acc. DVGW, 1988
Vegetables, oilseed, coffee   D

L

0.05 mg/kg     acc. DVGW, 1988
Other vegetable foodstuffs   D

L

0.01 mg/kg     acc. DVGW, 1988

Notes:

1) Natural treatment methods
2) Chemophysical treatment methods

Usage is banned for example in the Federal Republic of Germany and Japan and restricted in countries such as Argentina (acc. CES, 1985).

Comparison/reference values

Medium/origin Country Value
Water:
Rhine (Koblenz, 1981) D 20 ppt (mean value)
Large lakes, Niagara River (1980) CDN 0.02-17 ppt (mean values: 0.04-0.06 ppt)
Mediterranean (1981)   0.7-3.2 ppt
Soil/sediment:
Soil CH 0.15-50 ppb
Sewage sludge CH 6-125 g/kg
Rhine   50-400 ppb
Large lakes (1980) CDN 0.02-320 ppb (n=71)
Mediterranean (1981)   <10-210 ppt
Air:
North Pacific   0.095-0.13 ng/m3 (mean value: 0.1 ng/m3)
North Pacific (precipitation)   <0.03 ng/l
Near dump with HCB storage   170 g/m3
Aquatic animals:
Oysters (contaminated areas)   0.63 g/kg
Eels (Rhine)   1-2 mg/kg
Trout (large lakes) CND 8-127 g/kg
Fish (North Sea, 1972)   0.2-97 g/kg
Humans:
Bone marrow   1.3-3.9 mg/kg
Fatty tissue   0.03-22 mg/kg

Note:
1) All data from RIPPEN, 1989.

Assessment/comments

HCB is one of the substances whose effects on the ecosystem have scarcely been researched. All HCB-emitting processes should therefore be subject to appropriately cautious assessment, both with regard to its use in pest control and in the chemical production of chlorine compounds for which HCB is an intermediate product.


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