Toluene is a clear, colorless liquid with a distinctive smell. It is added to gasoline along with benzene and tolueneylene. Toluene occurs naturally in crude oil and in the tolu tree. It is produced in the process of making gasoline and other fuels from crude oil, in making coke from coal, and as a by-product in the manufacture of styrene. Toluene is used in making paints, paint thinners, fingernail polish, lacquers, adhesives, and rubber, and in some printing and leather tanning processes. It is disposed of at hazardous waste sites as used solvent (a substance that can dissolve other substances) or at landfills where it is present in discarded paints, paint thinners, and fingernail polish. One can begin to smell toluene in air at a concentration of 8 parts of toluene per million parts of air (ppm), and taste it in water at a concentration of 0.04–1 ppm. (One part per million is equivalent to 1 minute in 2 years.)
Pathways for toluene in the environment
Toluene enters the environment from materials such as paints, paint thinners, adhesives, fingernail polish, and gasoline, from which toluene evaporates and becomes mixed with the air. Toluene enters surface water and groundwater (wells) from spills of solvents and petroleum products as well as from leaking underground storage tanks at gasoline stations and other facilities. Leaking underground storage tanks contaminate the soil with toluene and other petroleum-product components.
When toluene-containing products are placed in landfills or waste disposal sites, toluene can enter the soil and water near the waste site. Toluene does not usually stay in the environment; it is readily broken down to other chemicals by microorganisms in soil and evaporates from surface water and surface soils. Toluene dissolved in well water does not break down quickly while the water is under the ground because there are few microorganisms in underground water. Once the water is brought to the surface, toluene will evaporate into the air. Windows and doors in rooms where toluene-containing products are used should be opened to allow toluene gas to escape. When not in use, toluene products should be tightly covered to prevent evaporation. Toluene in air can combine with oxygen and form benzaldehyde and cresol, which can be harmful to humans.
Toluene can be taken up by fish and shellfish, plants, and animals living in water containing toluene, but it does not concentrate or build up to high levels because most animal species can convert toluene into water-soluble compounds that are excreted.
Exposure to toluene
One may be exposed to toluene from many sources, including drinking water, food, air, and consumer products, through breathing the chemical in the workplace or during deliberate glue sniffing or solvent abuse. Automobile exhaust can also put toluene into the air. People who work with gasoline, kerosene, heating oil, paints, and lacquers are at the greatest risk of exposure. Printers are also exposed to toluene in the workplace. Because toluene is a common solvent and is found in many consumer products, one can be exposed to toluene at home and outdoors while using gasoline, nail polish, cosmetics, rubber cement, paints, paintbrush cleaners, stain removers, fabric dyes, inks, and adhesives. Smokers are exposed to small amounts of toluene from cigarette smoke.
EPA reported in 1991 that toluene was found in well water, surface water, or soil at 63% of the hazardous waste sites surveyed. Those that live near a waste site and get drinking water from a well, might find toluene in the water or toluene vapors in the air.
Federal and state surveys do not show toluene to be a common impurity in drinking water supplies. Toluene was found in about 1% of the groundwater sources (wells) at amounts lower than 2 parts per billion (ppb). (This is like 1 second in 32 years). It was found more frequently in surface water samples at similar concentrations. If toluene is in drinking water, one can be exposed by drinking the water or by eating cold foods prepared with the water. Evaporation during cooking tends to decrease the amount of toluene found in hot foods or water. Additional exposure will occur through breathing in the toluene that evaporates from water while showering, bathing, cleaning, or cooking with the water.
The toluene level in the air outside homes is usually less than 1 ppm in cities and suburbs that are not close to industry. The toluene inside a house is also likely to be less than 1 ppm. The amount of toluene in food has not been reported, but is likely to be low. Traces of toluene were found in eggs that were stored in polystyrene containers containing toluene.
Unless one smokes cigarettes or works with toluene-containing products, they are probably only exposed to about 300 micrograms (µg) of toluene a day. A microgram is one one-millionth of a gram. If one smokes a pack of cigarettes per day, it adds another 1,000 µg to their exposure. People who work in places where toluene-containing products are used can be exposed to 1,000 milligrams of toluene a day when the average air concentration is 50 ppm and they breathe at a normal rate and volume. A milligram is one-thousandth of a gram.
Pathways for toluene in the body
Toluene can enter the body through breathing its vapors or eating or drinking contaminated food or water. When working with toluene-containing paints or paint thinners, the toluene can also pass through the skin into the bloodstream. One is exposed to toluene when they breathe air containing toluene. When this occurs the toluene is taken directly into the blood from the lungs. Where one lives, works, and travels and what one eats affects their daily exposure to toluene. Factors such as age, sex, body composition, and health status affect what happens to toluene once it is in the body. After being taken into the body, more than 75% of the toluene is removed within 12 hours. It may leave the body unchanged in air breathed out or in urine after some of it has been chemically changed to make it more water soluble. Generally, the body turns toluene into less harmful chemicals such as hippuric acid.
Health effects of toluene
A serious health concern is that toluene may have an effect on the brain. Toluene can cause headaches, confusion, and memory loss. Whether or not an individual is affected in this way depends on the amount taken in and the length of exposure. Low-to-moderate, day-after-day exposure in the workplace can cause tiredness, confusion, weakness, drunken-type actions, memory loss, nausea, and loss of appetite. These symptoms usually disappear when exposure is stopped. Researchers do not know if the low levels of toluene breathed in at work will cause any permanent effects on the brain or body after many years. One may experience some hearing loss after long-term daily exposure to toluene in the workplace.
If one is exposed to a large amount of toluene in a short time because they deliberately sniff paint or glue, they will first feel light-headed. If exposure continues, they can become dizzy, sleepy, or unconscious, and might even die. Toluene causes death by interfering with the way humans breathe and the way the heart beats. When exposure is stopped, the sleepiness and dizziness will go away and one will feel normal again.
If one chooses to repeatedly breathe in toluene from glue or paint thinners, they may permanently damage the brain. They may also experience problems with speech, vision, or hearing, have loss of muscle control, loss of memory, poor balance, and decreased mental ability. Some of these changes may be permanent.
Toluene may change the way the kidneys work, but in most cases, the kidneys will return to normal after exposure stops. If one drinks alcohol and is exposed to toluene, the combination can affect the liver more than either compound alone. This phenomenon is called synergism. Combinations of toluene and some common medicines like aspirin and acetaminophen may increase the effects of toluene on hearing.
In animals, the main effect of toluene is on the nervous system. Animals exposed to moderate or high levels of toluene may also show slightly adverse effects in their liver, kidneys, and lungs.
Several studies have shown that unborn animals were harmed when high levels of toluene were breathed in by their mothers. When the mothers were fed high levels of toluene, the unborn animals did not show any structural birth defects, although some effects on behavior were noted. It is not known if toluene would harm an unborn child if the mother were to drink water or breathe air containing low levels of toluene, because studies in people are not comprehensive enough to measure this effect. However, if one deliberately breathes in large amounts of toluene during pregnancy, their baby can have neurological problems and retarded growth and development.
Studies in workers and in animals exposed to toluene indicate that toluene does not cause cancer. The International Agency for Research on Cancer (IARC) and the Department of Health and Human Services (DHHS) have not classified toluene for carcinogenic effects. The EPA has determined that toluene is not classifiable as to its human carcinogenicity.
Medical tests for exposure to toluene
One can find out if they have been exposed to toluene by having their exhaled air, blood, and urine tested for toluene and/or its breakdown products. These tests may not be available at a doctor's office, but are easily done by special laboratories. To determine whether one has been exposed to toluene, their blood and urine must be checked within 12 hours of exposure for the presence of toluene breakdown products. Several other chemicals are also changed to the same breakdown products as toluene in the body, so these tests are not specific for toluene. Other factors, such as weight and body fat, sex, and the exposure conditions, may also influence the amount of the chemicals in one's urine.
Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Agency for Toxic Substances and Disease Registry. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Agency for Toxic Substances and Disease Registry should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.