Technical Factsheet on: BENZENE
List of Contaminants
As part of the Drinking Water and Health pages, this fact sheet is part of a larger publication:
National Primary Drinking Water Regulations
Drinking Water Standards
MCLG: Zero
MCL: 0.005 mg/L
HAL: 1 to 10 day: 0.2 mg/L; Longer-term: 0.2 mg/L
Health Effects Summary
Acute: Acute exposure to high levels of benzene produces central nervous system (CNS) effects and
death. At lower levels, above the MCL, mild CNS effects appear to be concentration dependent and
rapidly reversible. Other effects include immune system depression and bone marrow toxicity leading to
aplastic anemia.
Drinking water levels which are considered "safe" for short-term exposures: For a 10 kg (22 lb.) child
consuming 1 liter of water per day: upto a ten-day exposure to 0.2 mg/L.
Chronic: Benzene has the potential to cause chromosomal aberrations in people who are chronically
exposed at levels above the MCL.
Cancer: Benzene has the potential to cause cancer from a lifetime exposure at levels above the MCL.
Usage Patterns
Production of benzene in the USA in 1993 was over 12 billion lbs.
Used for printing & lithography, paint, rubber, dry cleaning, adhesives & coatings, detergents, extraction
and rectification, preparation and use of inks in the graphic arts industries, as a thinner for paints and as a
degreasing agent. In the tire industry and in shoe factories, benzene is used extensively.
Used primarily as a raw material in the synthesis of styrene (polystyrene plastics and synthetic rubber),
phenol (phenolic resins), cyclohexane (nylon), aniline, maleic anhydride (polyester resins), alkylbenzenes
(detergents), chlorobenzenes, and other products used in the production of drugs, dyes, insecticides, and
In future, coal will increasingly replace petroleum & natural gas as a source of hydrocarbons both for fuel
& petrochemicals. Processes such as USA Steel Corporation's Clean Coke process, which yields 38%
coke & 20% chemical by-products compared to 73% coke & 2% chemical by-products in conventional
coking technology, should soon be used commercially. New coking, liquefaction, & gasification processes
for coal are all potential sources of benzene.
Release Patterns
Benzene will enter the atmosphere primarily from fugitive emissions and exhaust connected with its use
in gasoline. Another important source is emissions associated with its production and use as an industrial
intermediate. In addition, there are discharges into water from industrial effluents and losses during spills.

Benzene is also released from its indirect production in coke ovens; from nonferrous metal manufacture,
ore mining, wood processing, coal mining and textile manufacture. Although most public drinking water
supplies are free of benzene or contain <0.3 ppb, exposure can be very high from consumption of
contaminated sources drawn from wells contaminated by leaky gasoline storage tanks, landfills, etc.
From 1987 to 1993, according to the Toxics Release Inventory, releases of benzene to water totalled
583,210 lbs. Releases to land totalled 1,566,900 lbs. As indicated in the Table below, these releases
were primarily from petroleum refining industries, with the greatest releases occuring in Texas and
Environmental Fate
If benzene is released to soil, it will be subject to rapid volatilization near the surface and that which does
not evaporate will be highly to very highly mobile in the soil and may leach to groundwater. It may be
subject to biodegradation based on reported biodegradation of 24% and 47% of the initial 20 ppm
benzene in a base-rich para-brownish soil in 1 and 10 weeks, respectively. It may be subject to
biodegradation in shallow, aerobic groundwaters, but probably not under anaerobic conditions.
If benzene is released to water, it will be subject to rapid volatilization; the half-life for evaporation in a
wind-wave tank with a moderate wind speed of 7.09 m/sec was 5.23 hrs; the estimated half-life for
volatilization of benzene from a model river one meter deep flowing 1 m/sec with a wind velocity of 3
m/sec is estimated to be 2.7 hrs at 20 deg C. It will not be expected to significantly adsorb to sediment,
bioconcentrate in aquatic organisms or hydrolyze.
It may be subject to biodegradation based on a reported biodegradation half-life of 16 days in an aerobic
river die-away test. In a marine ecosystem biodegradation occurred in 2 days after an acclimation period
of 2 days and 2 weeks in the summer and spring, respectively, whereas no degradation occurred in
winter. According to one experiment, benzene has a half-life of 17 days due to photodegradation which
could contribute to benzene's removal in situations of cold water, poor nutrients, or other conditions less
conductive to microbial degradation.
If benzene is released to the atmosphere, it will exist predominantly in the vapor phase. Gas-phase
benzene will not be subject to direct photolysis but it will react with photochemically produced hydroxyl
radicals with a half-life of 13.4 days calculated using an experimental rate constant for the reaction. The
reaction time in polluted atmospheres which contain nitrogen oxides or sulfur dioxide is accelerated with
the half-life being reported as 4-6 hours. Products of photooxidation include phenol, nitrophenols,
nitrobenzene, formic acid, and peroxyacetyl nitrate.
Benzene is fairly soluble in water and is removed from the atmosphere in rain. The primary routes of
exposure are inhalation of contaminated air, especially in areas with high traffic, and in the vicinity of
gasoline service stations and consumption of contaminated drinking water.
Chemical/Physical Properties
CAS Number: 71-43-2
Color/ Form/Odor: Clear, colorless aromatic liquid; highly flammable M.P.: 5.5 C B.P.: 80.1 C
Vapor Pressure: 100 mm Hg at 26.1 C
Octanol/Water Partition (Kow): Log Kow = 2.13
Density/Spec. Grav.: 0.8787 at 15 C

Solubilities: 1.8 g/L of water at 25 C; Slightly soluble in water;
Soil sorption coefficient: Koc estimated at 98; high to very high mobility in soil
Odor/Taste Thresholds: Taste threshold in water is 0.5 to 4.5 mg/L
Bioconcentration Factor: 3.5 to 4.4 in fish; not expected to bioconcentrate in aquatic organisms.
Henry's Law Coefficient: 0.0053 atm-cu m/mole;
Trade Names/Synonyms: Benzol 90, Pyrobenzol, Polystream, Coal naphtha, Phene
Other Regulatory Information
-For Ground/Surface Water Sources:
Initial Frequency- 4 quarterly samples every 3 years
Repeat Frequency- Annually after 1 year of no detection
-Triggers - Return to Initial Freq. if detect at > 0.0005 mg/L
Reference Source	Method Numbers
EPA 600/4-88-039	502.2; 524.2
Treatment/Best Available Technologies: Granular Activated Charcoal and Packed Tower Aeration
Toxic Release Inventory - Releases to Water and Land, 1987 to 1993 (in pounds):
Top Six States*
Major Industries*
Petroleum refining
Primary Metal Ind.
Industrial chemicals
Alkalies, chlorine
* Water/Land totals only include facilities with releases greater than a certain amount - usually 1000 to
10,000 lbs.
For Additional Information
EPA can provide further regulatory or other general information:
EPA Safe Drinking Water Hotline - 800/426-4791

Other sources of toxicological and environmental fate data include:
Toxic Substance Control Act Information Line - 202/554-1404
Toxics Release Inventory, National Library of Medicine - 301/496-6531
Agency for Toxic Substances and Disease Registry - 404/639-6000