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DESIGNATIONS
CAS No.: 71-43-2
Registry name: Benzene
Chemical name: Benzene
Synonyms,Tradenames: Benzol, bicarburate of hydrogen, carbon oil, coal naphtha, cyclohexatriene, mineral naphtha, motor benzol, phene, phenyl hydride
Chemical name (German): Benzol, Benzen
Chemical name (French): Benzčne
Appearance: colourless, highly volatile liquid with aromatic odour
BASIC CHEMICAL AND PHYSICAL DATA
| Empirical formula: | C6H6 |
| Rel. molecular mass: | 78.12 g |
| Density: | 0.879 g/cm3 |
| Relative gas density: | 2.7 |
| Boiling point: | 80.1°C |
| Melting point: | 5.5°C |
| Vapour pressure: | 102 hPa |
| Flash point: | -11°C |
| Ignition temperature: | 555°C |
| Solvolysis/solubility: | in water: 1.79 g/l (25°C) soluble in fats miscible with acetone, ether, alcohol, chloroform |
| Conversions factors: | 1 ppm = 3.26 mg/m3 at 20°C 1 mg/m3 = 0.31 ppm |
ORIGIN AND USE
Usage:
In the chemical industry pure benzene forms the most important
basis for aromatic intermediate products as well as for the group
of cycloaliphatic compounds. Plastics, synthetic rubber, dyes,
paints, varnishes, resins, detergent raw materials and pesticides
are all produced on the basis of benzene.
Origin/derivation:
Benzene is found in small quantities and at low concentrations in
nature. It is a component part of crude oil (max. 0.4 g/l).
Benzene is produced and processed on a large scale as pure
benzene. It is normally obtained from crude oil. Standard grade
petrol contains between 12 and 16 g/l, premium petrol up to 24
g/l of benzene. Emission sources apart from motor vehicles are
coking plants, furnaces, refineries and the chemical industry in
addition to the storage and distribution of petrol.
Production figures:
The estimated figures for overall worldwide annual production
vary. They are estimated at more than 15 million tons of pure
benzene and some 10 million tons in fuels. Production of pure
benzene:
| D (1983): | 1.34 mio t | EC (1978/79): | 4.4 mio t |
| F (1983) | 1.37 mio t | USA (1983) | 4.28 mio t |
| Japan (1983) | 1.75 mio t | USSR (1977) | 1.54 mio t |
Emission figures (estimated):
Worldwide 100,000-1,000,000 t/a; USA into atmosphere
110,000-224,000 t/a (of which 40,000-80,000 t/a from fuels);
USA into surface/groundwater 3-14 t/a;
D 55,000-70,000 t/a (of which 50,000-60,000 t/a
from fuels)
Toxicity
| Humans: | TLC0 0.68 mg/l, inhalation 1) |
| Mammals: | |
| Rat (male) | LD50 3.8-6.5 g/kg, oral |
| Rat (male) | LD50 17.6 g/kg, dermal |
| Rat (male) | LC50 18 mg/l, inhalation (4 h) |
| Rat (female) | LD50 6.2-7.2 g/kg, oral |
| Rat (female) | LD50 19.4 g/kg, dermal |
| Rat (female) | LC50 23 mg/l, inhalation (4 h) |
| Insects: | |
| Weevil | LC50 210 mg/l |
| Aquatic organisms: | |
| Golden orfe | LC0 31 +/- 25 mg/l (96 h) (ringtest, 11 laboratories) |
| Goldfish | LC0 36 mg/l (24 h) |
| Trout | LC50 22 mg/l (96 h) |
| Herring | EC0 <0.8 mg/l (reproduction) |
| Water flea (Daphnia magna) | LC50 200 mg/l (48 h) |
| Water flea (Daphnia magna) | LC50 15 mg/l (96 h) |
| Blue algae | EC0 >1400 mg/l (inhibition of cell reproduction) |
| Green algae | EC0 >1400 mg/l (inhibition of cell reproduction) |
| Green algae | EC50 310-460 mg/l (reduced photosynthesis) |
| Marine algae | EC0 approx. 1400 mg/l (reduced productivity) |
| Other organisms: | |
| Earthworm | LC50 100-1000 µg/cm2 (48 h) |
Note: 1) All data as per RIPPEN, 1989
Characteristic effects:
Humans/mammals: The inhalation of benzene vapours may
affect the central nervous system depending on the concentration
and the duration of exposure. The symptoms of acute poisoning are
dizziness, headaches, nausea, drowsiness and disturbance of
consciousness with states of agitation and spasms, finally
resulting in loss of consciousness and paralysis of the
respiratory centre. Liquid benzene irritates the skin and mucous
membranes and may be resorbed through the skin.
Chronic exposure causes damage to bone marrow. Benzene is a blood toxin: chromosomal changes in blood corpuscles of workers subjected to exposure and in blood corpuscles and bone cells of rats subjected to exposure have been found.
Proven carcinogenity in humans; carcinogenic tumours in rats and mice;
Plants: High atmospheric concentrations (>50 mg/m3, 30 min.) have a lethal effect. In water used for watering plants, small benzene concentrations stimulate plant growth and root formation. On the other hand, high concentrations close to the saturated solution inhibit growth.
Note: A detailed list of the investigations performed to establish the characteristic effects of benzene can be found in OAK RIDGE NATIONAL LABORATORY, 1987 and BUA, 1988.
ENVIRONMENTAL BEHAVIOUR
Water:
Benzene is highly volatile: evaporation half-life 2.7-5 hours
(4.8 h in 1m deep body of water at 25°C).
Air:
Benzene is a moderate source of smog. It readily reacts with
OH radicals, whose concentration governs the dwell time in the
atmosphere (between several hours and several days). Wash-out
effects merely result in short-term extraction from the
atmosphere since benzene readily evaporates again from the
surface of water or soil.
Soil:
Benzene is highly volatile and thus considerable losses from
the topsoil into the atmosphere take place. In deeper soil
layers, the substance is relatively mobile. Thus, elution into
groundwater may result. Benzene accumulates in sewage sludge.
Degradation, decomposition products, half-life:
Degradation in the atmosphere primarily takes place by
indirect phototransformation; no photolysis at wavelengths
>290nm. In the troposphere the half-life is between 7 and 22
days with a mean value of 13 days. In the lower troposphere (up
to an altitude of approx. 1-2 km), the average values for the
half-life of benzene are between 3 and 10 days.
Degradation in surface water, groundwater and in soil is mainly by way of biodegradation (aerobic more readily than anaerobic). Microbial metabolites: 1,2-dihydroxy-1,2-dihydrobenzene, pyrocatechol. Metabolites in mammals: Phenols and related compounds (e.g. hydroquinone, pyrocatechol). 33% aerobic degradation in sewage treatment plants after 12h; aerobic degradation is slight compared to volatilisation. Thermal decomposition takes place at 600°C in the vapour phase; hydrolysis is unlikely under normal conditions.
ENVIRONMENTAL STANDARDS
| Medium/acceptor | Sector | Country/organ. | Status |
Value | Cat. | Remarks | Source |
| Water: | D | G |
3 | WGK | acc. RIPPEN, 1989 | ||
| Drinkw | A | L |
10 µg/l | acc. RIPPEN, 1989 | |||
| Drinkw | SU | G |
500 µg/l | Tox. tolerance value | acc. RIPPEN, 1989 | ||
| Drinkw | USA | G |
13 µg/l (7d) | Nat. Acad. Science | acc. RIPPEN, 1989 | ||
| Drinkw | USA | G |
0.35 µg/l (7d) | U.S.EPA | acc. RIPPEN, 1989 | ||
| Drinkw | USA | G |
0.67 µg/l | Chron. exposure | acc. RIPPEN, 1989 | ||
| Drinkw | USA | (L) |
5 µg/l | MCL | |||
| Drinkw | WHO | G |
10 µg/l | Risk of leukaemia | WHO, 1984 | ||
| Waste water | USA | G |
125 µg/l | Direct introduction | acc. RIPPEN, 1989 | ||
| Waste water | USA | G |
75 µg/l (average, 4d) | Direct introduction | acc. RIPPEN, 1989 | ||
| Groundw | D(HH) | G |
1 µg/l | Closer investigation | acc. LAU-BW1), 1989 | ||
| Groundw | D(HH) | G |
5 µg/l | Rehabilitation investigation | acc. LAU-BW1), 1989 | ||
| Groundw | NL | G |
0.2 µg/l | Reference | acc. TERRA TECH 6/94 | ||
| Groundw | NL | L |
30 µg/l | Intervention | acc. TERRA TECH 6/94 | ||
| Groundw | USA | L |
1 µg/l | Florida | acc. ORNL2), 1987 | ||
| Surface | USA | G |
3.1 mg/l (1 d, average) | Protect. of freshwater | acc. RIPPEN, 1989 | ||
| Surface | USA | G |
7 mg/l (max.) | Protect. of freshwater | acc. RIPPEN, 1989 | ||
| Surface | USA | G |
0.92 mg/l (1 d, average) | Protect. of saltwater | acc. RIPPEN, 1989 | ||
| Surface | USA | G |
2.1 mg/l (max.) | Protect. of saltwater | acc. RIPPEN, 1989 | ||
| Soil: | NL | G |
0.05 mg/kg DM | Reference | acc. TERRA TECH 6/94 | ||
| NL | L |
1 mg/kg DM | Intervention | acc. TERRA TECH 6/94 | |||
| Air: | Emiss. | D | L |
5 mg/m3 | mass flow > 25 g/h | acc. TA Luft, 1986 | |
| D | L |
10 mg/m3 | MIK | Short-time value | acc. RIPPEN, 1989 | ||
| D | L |
3 mg/m3 | MIK | Long-time value | acc. RIPPEN, 1989 | ||
| DDR | (L) |
0.3 mg/m3 | (MIK) | Short-time value | acc. HORN et al., 1989 | ||
| DDR | (L) |
0.1 mg/m3 | (MIK) | Long-time value | acc. HORN et al., 1989 | ||
| H | (L) |
0.8 mg/m3 | 30 min average3) | acc. STERN, 1986 | |||
| H | (L) |
1 mg/m3 | 30 min average4) | acc. STERN, 1986 | |||
| H | (L) |
0.3 mg/m3 | 24 h average4) | acc. STERN, 1986 | |||
| IL | (L) |
4.8 mg/m3 | 30 min average | acc. STERN, 1986 | |||
| IL | (L) |
1.6 mg/m3 | 24 h average | acc. STERN, 1986 | |||
| PL | (L) |
0.2 mg/m3 | 30 min average3) | acc. STERN, 1986 | |||
| PL | (L) |
1 mg/m3 | 30 min average4) | acc. STERN, 1986 | |||
| PL | (L) |
0.1 mg/m3 | 24 h average3) | acc. STERN, 1986 | |||
| PL | (L) |
0.3 mg/m3 | 24 h average4) | acc. STERN, 1986 | |||
| PL | (L) |
0.025 mg/m3 | a-average3) | acc. STERN, 1986 | |||
| PL | (L) |
0.043 mg/m3 | a-average4) | acc. STERN, 1986 | |||
| RO | (L) |
2.4 mg/m3 | 30 min average | acc. STERN, 1986 | |||
| RO | (L) |
0.8 mg/m3 | 24 h average | acc. STERN, 1986 | |||
| SU | (L) |
1 mg/m3 | 30 min average4) | acc. STERN, 1986 | |||
| SU | (L) |
0.3 mg/m3 | 24 h average4) | acc. STERN, 1986 | |||
| Workp | CS | (L) |
16 ppm | from 1969 | acc. ACGIH, 1982 | ||
| Workp | D | L |
16 mg/m3 | TRK5) | DFG, 1989 | ||
| Workp | D | L |
5 ml/m3 | TRK6) | DFG, 1989 | ||
| Workp | DDR | (L) |
5 mg/m3 | acc. HORN et al, 1988 | |||
| Workp | S | (L) |
10 ppm | from 1975 | acc. ACGIH, 1982 | ||
| Workp | SU | (L) |
5 mg/m3 | acc. RIPPEN, 1989 | |||
| Workp | USA | (L) |
10 ppm | TWA | acc. AUER TECHNIKUM 1988 | ||
Note:
1) Baden-Württemberg Regional Environment Office
2) Oak Ridge National Laboratory
3) Specially protected areas
4) Protected areas
5) Dusts
6) Gases and vapours
Further benzene-specific legislation in the Federal Republic
of Germany can be found in:
the Gefahrstoffverordnung (Ordinance on Hazardous
Substances), the Bundesimmissionsschutzverordnung (Federal
Immission Control Ordinance); the Störfallverordnung (Hazardous
Incident Ordinance), the Gefahrgutverordnungen (ordinances
governing hazardous materials), the Abfallgesetz-Sonderabfall
(Waste Avoidance and Waste Management Act - Special Waste), the Benzinqualitätsangabeverordnung
(ordinance on the indication of fuel grade), the Kosmetikverordnung
(ordinance on cosmetics), the Verordnung über die
Einschränkung und Verbote für bestimmte Stoffe in Spielwaren
und Scherzartikeln (ordinance on the restriction and banning
of certain substances in toys and joke-shop articles).
Comparison/reference values
| Medium/origin | Country | Value |
| Water | ||
| Rhine (Basle, 1976) | CH | 0.2 µg/l |
| Rhine (Cologne, 1976) | D | 0.3 µg/l |
| Rhine (Duisburg, 1976) | D | 0.8 µg/l |
| Tees River Estuary (1984) | GB | 0.1-200 µg/l |
| Groundwater (not contaminated) | NL | <0.01-0.03 µg/l (n=8) |
| Groundwater (contaminated) | NL | 100 µg/l |
| Groundwater (contaminated) | USA | 1.0-470 µg/l (n=9 of 13) |
| Dump seepage water | USA | 17-540 µg/l (n=6) |
| Drinking water | USA | <0.5-15 µg/l (n=945; 11 >=0.5 µg/l) |
| Rainwater | GB | 87 µg/l |
| Soil/sediment: | ||
| Sewage sludge | USA | 0.05-11.3 mg/kg (n=11 of 13) |
| Tees River Estuary (1986) | GB | 1.5-3.9 µg/kg (n=4) |
| Air: | ||
| Clean air, Southern hemisphere 1980-1983 | <5-80 pptv (average values) | |
| Clean air, Northern hemisphere 1980-1983 | 100-260 pptv (average values) | |
| Arctic (July 1982) | 66 pptv (n=8; average value) | |
| Arctic (spring 1983) | 307 pptv (n=10; average value) | |
| Deuselbach ('clean air', 1983) | D | 0.10-0.12 ppbv (average values) |
| Various (background impact) | Brazil | 0.31-0.72 ppbv (n=8) |
| Various | Kenya | 0.07-0.85 ppbv (n=13) |
| Various (desert) | Egypt | 0.19 ppbv (n=5; average value) |
| Berlin (1976/77) | D | 0.6-60 ppbv (n>200; 24 h values) |
| 7 cities (1980/81) | USA | 1.4-5.8 ppbv (average values) |
| Leningrad (1977-79) | SU | 5.4-204 ppbv (n=30; 20-50 min values) |
| Respiratory air: | ||
| At petrol stations (1970-80) | 100-10,000 µg/ m3 (n>130; 2-14 h values) | |
| Petrol-tanker drivers | 30-100,000 µg/m3 | |
| Petrol-tanker drivers | 540 µg/m3 (8 h average value) | |
| Tanker crew | 2,400-170,000 µg/m3 | |
| Tanker crew | 4200 µg/m3 (8 h average value) | |
| Foodstuffs: | ||
| Various fish (Los Angeles Bay, 1980/81) | <1-52 µg/kg FS (n=4) | |
| Eggs | 0.5-1.9 mg/kg | |
| Beef | 2-19 µg/kg | |
| Rum | 0.12 µg/kg | |
Note: 1) All data as per RIPPEN, 1989
Assessment/comments
In view of the fact that benzene readily ingresses into the atmosphere on account of its physical properties, it can be transported over long distances despite relatively short transformation reactions. The advantages of relatively rapid benzene degradation are offset by numerous toxic degradation products. In addition to workplace exposure, humans are threatened above all by the intake of benzene caused by smoking and traffic emissions. The limit values and guide values vary in the atmospheric sector and particularly in the drinking water sector. The values recommended by the WHO are 15 - 30 times in excess of the proposals made by the U.S. EPA which should be used for orientation at least in those instances where drinking water is primarily used for human consumption.
Further information on benzene is to be found in RIPPEN (1989), OAK RIDGE NATIONAL LABORATORY (1987) and BUA, 1988.