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DESIGNATIONS
CAS No.: 118-74-1
Registry name: Hexachlorobenzene
Chemical name: Hexachlorobenzene
Synonyms, Trade names: HCB
Chemical name (German): Hexachlorbenzol
Chemical name (French): Hexachlorobenzène
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 20°C |
| Relative gas density: | 9.84 |
| Boiling point: | 322-326°C |
| Melting point: | 229°C |
| Vapour pressure: | 1.1 x 10-3 Pa |
| Flash point: | 242°C |
| Solvolysis/solubility: | in water 0.005 mg/l in benzene 31.6 g/l, in fat 11.5 g/kg at 37°C |
| 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 510-530°C; mineralisation at 950°C.
• 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 µg/l | acc. DVGW, 1988 | ||
| Drinkw | D | L |
0.1 µg/l | acc. DVGW, 1988 | |||
| Drinkw | EC | G |
0.1 µg/l | acc. DVGW, 1988 | |||
| Drinkw | WHO | G |
0.01 µg/l | acc. DVGW, 1988 | |||
| Surface | IAWR | G |
0.1 µg/l | Drinking water1) | acc. DVGW, 1988 | ||
| Surface | IAWR | G |
0.5 µg/l | Drinking water2) | acc. DVGW, 1988 | ||
| Air: | Workp | D | L |
15 µg/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 µg/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 µg/m3 | |
| Aquatic animals: | ||
| Oysters (contaminated areas) | 0.63 µg/kg | |
| Eels (Rhine) | 1-2 mg/kg | |
| Trout (large lakes) | CND | 8-127 µg/kg |
| Fish (North Sea, 1972) | 0.2-97 µg/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.