benzene

CAS71-43-2

Molecular formulaC6H6

Molar mass78.11 g/mol

Hazardous

Hazards Summary | Benzene is a colorless liquid with a sweet odor. It evaporates into the air very quickly and dissolves slightly in water. It is highly flammable and is formed from both natural processes and human activities. Benzene is widely used in the United States; it ranks in the top 20 chemicals for production volume. Some industries use benzene to make other chemicals which are used to make plastics, resins, and nylon and synthetic fibers. Benzene is also used to make some types of rubbers, lubricants, dyes, detergents, drugs, and pesticides. Natural sources of benzene include volcanoes and forest fires. Benzene is also a natural part of crude oil, gasoline, and cigarette smoke.

Scientific Grain Officer - Dictionary Editorial Department, revised at:2026-10-19

Toxicity

Body Burden

In a 1980's study of non-occupational benzene exposure, it was found that smokers had an average benzene body burden about 6 to 10 times that of nonsmokers, and received about 90% of their benzene exposure from smoking(1). The mean benzene concentration found in the breath and blood of 1,683 individuals was 13.1 and 131 ng/L, respectively(1).

Fate Summary

ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), benzene, which has a vapor pressure of 94.8 mm Hg at 25 °C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase benzene is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 13 days(SRC), calculated from its rate constant of 1.23X10-12 cu cm/molecule-sec at 25 °C(3). The half-life in polluted atmospheres which contain nitrogen oxides or sulfur dioxide has been observed to shorten to 4-6 hrs(4). Vapor-phase benzene is also degraded in the atmosphere by atmospheric ozone radicals at an extremely slow rate; the half-life for this reaction in...

Soil Adsorption / Mobility

An experimentally derived log Koc of 1.93 (Koc = 85) was obtained via reverse phase HPLC (high performance liquid chromatography) with a cyanopropyl column and a mobile phase of water(1). According to a classification scheme(2), this estimated Koc value suggests that benzene is expected to have high mobility in soil. The sorption equilibrium for benzene in a soil/water mixture (ratio soil/water 0.12 kg/l) took 72 hrs(3). The Koc for benzene has also been experimentally determined to be 79(4).

Environmental Biodegradation

ANAEROBIC: Benzene was degraded under methanogenic conditions in an enrichment culture fed ferulic acid for five years. It was also degraded under sulfate-reducing conditions in microcosms containing benzene-contaminated aquifer sediment(1). Benzene was not biodegraded in aquifer sediment down gradient of the Wilder's Grove sanitary landfill near Raleigh, NC(1). In a study of chemical biotransformation under nitrate- and sulfate-reducing conditions, benzene was found to be stable under these anaerobic conditions for 60 days(2). In a related study, benzene did not undergo biodegradation in situ nor in laboratory controlled soil samples under denitrifying conditions(3). Although benzene appears to be recalcitrant under anaerobic conditions, there was one experiment in which benzene underw...

Environmental Bioconcentration

Benzene has BCFs ranging from 1.1-20(1). According to a classification scheme(2), this BCF range suggests the potential for bioconcentration in aquatic organisms is low. The uptake and elimination rate constants for benzene in fathead minnows were studied(3). Fathead minnows were found to have an average uptake rate of 7 L/kg/hr with an average elimination rate of 0.384/hr which corresponds to a BCF of 19(3). In a study of BCF values for various aquatic species, benzene was found to have a BCF value of 3.5 in eels(4), 4.4 in pacific herring(5), and 4.3 in goldfish(6).

Volatilization from Water / Soil

The Henry's Law constant for benzene is 5.56X10-3 atm-cu m/mole(1). This Henry's Law constant indicates that benzene is expected to volatilize rapidly from water surfaces(2). Based on this Henry's Law constant, the volatilization half-life from a model river (1 m deep, flowing 1 m/sec, wind velocity of 3 m/sec)(2) is estimated as 1 hr(SRC). The volatilization half-life from a model lake (1 m deep, flowing 0.05 m/sec, wind velocity of 0.5 m/sec)(2) is estimated as 3.5 days(SRC). Benzene's Henry's Law constant(1) indicates that volatilization from moist soil surfaces may occur(SRC). The potential for volatilization of benzene from dry soil surfaces may exist(SRC) based upon a vapor pressure of 94.8 mm Hg(3).

Environmental Abiotic Degradation

While benzene is considered to be relatively unreactive in photochemical smog situations (in the presence of nitrogen oxides), its rate of degradation is accelerated with about 16% decrease in concentration in 5 hr(1). A typical experiment in the presence of active species such as NOx and SO2 showed that benzene photodegradation was considerably accelerated above that in air alone(2). Its half-life in the presence of active species was 4-6 hr with 50% mineralization to CO2 in approximately 2 days(3). Products of degradation include phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitrophenol, nitrobenzene, formic acid, and peroxyacetyl nitrate(4-6). Benzene has an estimated lifetime under photochemical smog conditions in southeastern England of 28 hrs(3). Benzene has an es...

Environmental Water Concentrations

RAIN/SNOW/FOG: Benzene was detected in rainwater in Japan and in the UK at a concentration of 87.2 ppb(1,2).

Food Survey Values

In 1990, benzene was detected in fruit flavored mineral waters at concentrations greater than 5.0 ug/kg in Canada(1). When an investigation of benzene concentrations in beverages was performed, benzene was found at an average concentration of 0.042, 0.67, 0.056, 0.14, 0.29, 0.12, 0.95, 0.062, 0.79, and 0.55 ug/kg in freshly squeezed fruit, retail juice (with benzoate additive), retail juice (without benzoate), fruit drinks (with benzoate), fruit drinks (with cranberry, without benzoate), fruit drinks (excluding cranberry, without benzoate), cranberry drinks (without benzoate), carbonated soft drinks (without benzoate), carbonated soft drinks (with benzoate), and ice tea (with benzoate), respectively(1). These data suggest the natural occurrence of benzene in fruits and fruit juices, esp...

Milk Concentrations

Benzene was detected in all 8 samples of mothers milk from women in 4 US urban areas(1).

Ecotoxicity Excerpts

/PLANTS/ In higher plants, benzene administered in aqueous solution or as vapor is translocated and metabolized. The proposed sequence of benzene metabolism in plants is benzene /to/ phenol /to/ pyrocatechol /to/ o-benzoquinone /to/ muconic acid.

Effluent Concentrations

In 4 municipal landfill gases in Southern Finland (1989-1990 data), benzene's average concentration ranged from 0.17-9 mg/cu m with a max concentration of 11 mg/cu m(1). Benzene emissions were studied from seven Swedish incineration plants before and after air pollution control systems (APCS) were introduced(2). Benzene concentrations emitted from plant A (3 incinerators) without APCS were 1.93, 1.95, and 21.16 ug/cu nm and with APCS were 2.46, 0.83 and 1.81 ug/cu nm, respectively. Plant B (3 incinerators) benzene levels were 21.23, 10.81, and 1.63 ug/cu nm before APCS and 14.37, 444.20, and 0.14 ug/cu nm after APCS, respectively(2). Oddly, benzene levels rose on an incinerator after APCS. At the third plant, benzene concentrations were 2.57 ug/cu nm before APCS and 0.79 ug/cu nm after...

ICSC Environmental Data

The substance is toxic to aquatic organisms. The substance may cause long-term effects in the aquatic environment.

Natural Pollution Sources

Benzene is found naturally in the environment from volcanoes, as a natural constituent of crude oil, from forest fires and as a plant volatile(1,2). Benzene concentrations range from 100-200 parts per trillion over the Pacific and Atlantic Oceans due to seepage and spillage of oil into the oceans(3).

Fish/Seafood Concentrations

Benzene was detected in 5 oyster samples from the Inner Harbor Navigational Canal in Lake Pontchartrain, LA at 220 ppb wet weight(1). Composite clam samples from Chef Menteur Pass in Lake Pontchartain, LA contained benzene at 260 ppb wet weight; however clam samples from The Rigolets did not contain benzene(1).

Artificial Pollution Sources

Benzene is the largest volume aromatic petrochemical; ethylbenzene is the largest chemical outlet for benzene, and nearly all is consumed for the production of styrene(1). Benzene has been detected in cigarette smoke ranging from 47-64 ppm(2). The world wide release of benzene into the environment is estimated to be 4-5 Tg/yr with 0.6 Tg/yr coming from the United States alone(3). Leachate from landfills is also a source of benzene in the environment(4).

Sediment/Soil Concentrations

SOIL: Soil near factories where benzene was used or produced contained benzene ranging from 2-191 ug/kg(1).

Environmental Fate / Exposure Summary

Benzene's production, existence in gasoline, and use in the production of ethylbenzene and styrene as well as many other chemicals may result in its release to the environment through various waste streams. Benzene is found in volcanoes, as a constituent of crude oil, from forest fires, and as a plant volatile. If released to air, a vapor pressure of 94.8 mm Hg at 25 °C indicates benzene will exist solely as a vapor in the ambient atmosphere. Vapor-phase benzene will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 13 days. Vapor-phase benzene is also degraded by ozone radicals and nitrate found in the atmosphere but at such low rates as to not be important. A half-life of 16.9 days was r...

Symptoms

Breathing benzene can cause drowsiness, dizziness, rapid heart rate, headaches, tremors, confusion, and unconsciousness. Ingestion can result in vomiting, irritation of the stomach, dizziness, sleepiness, convulsions, and rapid heart rate. (L5)

Treatment

There is no known antidote for benzene and poisoning is first treated by preventing further exposure. If inhaled, respiratory assist may be necessary. If ingested, gastric lavage may be performed, or activated charcoal can be administered. (T8)

Cancer Sites

[leukemia]

Target Organs

Eyes, skin, respiratory system, blood, central nervous system, bone marrow

Toxicity Data

LD50: 3306 mg/kg (Oral, Rat) (T14) LD50 340 mg/kg (Intraperitoneal, Mouse) (T14) LC50: 9980 ppm (Inhalation, Mouse) (T14)

Health Effects

Benzene causes harmful effects on the bone marrow and also decreases blood cell counts, leading to blood disorders such as anemia. It can also cause excessive bleeding and affect the immune system, increasing the chance for infection. Benzene is also a known carcinogen, as chronic exposure to high levels has been shown to cause leukemia, particularly acute myelogenous leukemia. (L5)

Adverse Effects

ACGIH Carcinogen - Confirmed Human.

Exposure Routes

Inhalation (L5)

Toxicity Summary

The toxic agents of benzene are its metabolites. Benzene is able increase its toxicity by inducing cytochrome P450 2E1, its main metabolic enzyme. Benzene's primary toxic effects are decreases in haematological cell counts and bone marrow cellularity. The decrease in blood cell count may be due to the binding of metabolites such as benzene oxide to the blood proteins albumin and haemoglobin. In the bone marrow, phenolic metabolites can be metabolized by bone marrow peroxidases to highly reactive semiquinone radicals and quinones that stimulate the production of reactive oxygen species. This and direct metabolite binding leads to damage to tubulin, histone proteins, and topoisomerase II. Some metabolites also exert mutagenic effects by inhibiting other DNA associated proteins, such as mi... CDC-ATSDR Toxicological Profile

Minimum Risk Level

Acute Inhalation: 0.009 ppm (L134) Intermediate Inhalation: 0.006 ppm (L134) Chronic Inhalation: 0.003 ppm (L134) Chronic Oral: 0.0005 mg/kg/day (L134)

Average Daily Intake

Two studies of benzene levels in foods have confirmed the conclusion that ingesting food and beverages are an unimportant pathway for benzene exposure. In a study of more than 50 foods, most contained benzene below 2 ng/g ppbw. A Canadian review of benzene exposures concluded that food and drinking water each contributed only about 0.02 ug/kg benzene per day compared to a total intake of 2.4 ug/kg per day from airborne exposures (3.3 ug/kg/day if exposed to cigarette smoke). In a 1980's study of non-occupational benzene exposure, it was found that more than 99% of the total personal exposure was through air and that a global average personal exposure for benzene was about 15 ug/cu m. Roughly half the total benzene exposure in the United States was borne by smokers. For non-smokers, most...

RAIS Toxicity Values

Oral Slope Factor Reference: IRIS Current

Human Toxicity Values

Immediately dangerous to life and health = 500 ppm

Acceptable Daily Intakes

Insufficient data are available to calculate a one-day Health Advisory for benzene. The Ten-day Health Advisory (0.235 mg/l) is considered to be adequately protective for a one-day exposure as well. ... Longer-term Health Advisories have not been calculated because of the carcinogenic potency of benzene.

Carcinogen Classification

1, carcinogenic to humans. (L135)

Populations at Special Risk

... It has been suggested that Thalassemia minor, and presumably other disorders in which there is increased bone marrow turnover, may predispose a person to benzene-induced aplastic anemia.

1 or Cancer Risk Level 1E-06

Soil Saturation Concentration (mg/kg): 1.82e+03

Evidence for Carcinogenicity

Benzene: known to be a human carcinogen. Carcinogenicity: Benzene is known to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in humans.

Hazard Quotient Level 3 or Cancer Risk Level 1E-04

Soil Saturation Concentration (mg/kg): 1.82e+03

USGS Health-Based Screening Levels for Evaluating Water-Quality

Reference: Smith, C.D. and Nowell, L.H., 2024. Health-Based Screening Levels for evaluating water-quality data (3rd ed.). DOI:10.5066/F71C1TWP