Hexane


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Introduction

n-Hexane (hereafter referred to simply as hexane) is a chemical made from crude oil. Pure hexane is a colorless liquid with a slightly disagreeable odor. It evaporates very easily into the air and dissolves only slightly in water. Hexane is highly flammable, and its vapors can be explosive.

Pure hexane is used in laboratories. Most of the hexane used in industry is mixed with similar chemicals in products known as solvents. Common names for some of these solvents are "commercial hexane", "mixed hexanes", "petroleum ether", and "petroleum naphtha". An older name for these types of solvents is "petroleum benzine". Several hundred million pounds of hexane are produced in the United States each year in the form of these solvents. The major use for solvents containing hexane is to extract vegetable oils from crops such as soybeans. They are also used as cleaning agents in the printing, textile, furniture and shoemaking industries. Certain kinds of special glues used in the roofing and the shoe and leather industries also contain hexane. Several consumer products contain hexane. For example, gasoline contains about 1-3% hexane. Hexane is also present in rubber cement.

Structural diagram: National Institutes of Health


Fate & Transport

Hexane enters the air, water, and soil during its manufacture and use. Wastes containing hexane are sometimes disposed of in landfills. Hexane can enter the environment from these landfills. Hexane also enters the environment from accidental spills during transport and leaks from storage containers.

Hexane evaporates very easily into the air. Once in the air, hexane can react with oxygen and be broken down. Hexane released into the air is broken down in a few days.

If hexane is spilled into a lake or river, a very small portion will dissolve in the water, but most will float on the surface. The hexane will then evaporate into the air. The hexane dissolved in the water can be broken down by certain types of bacteria, although it is not known how long this takes.

If hexane is spilled on the ground, much of it will evaporate into the air before it penetrates the soil. Any hexane that penetrated the soil would probably be broken down by bacteria. If hexane leaks from an underground storage tank, it will float on the groundwater, rather than mixing with it since hexane is lighter than water. Hexane is not stored or concentrated by plant, fish, or animals.

Exposure Pathways

Since gasoline contains hexane, almost everyone is exposed to small amounts of hexane in the air. The hexane in gasoline is released into the air at service stations and in automobile exhaust. Some people may also be exposed by spilling gasoline on their skin. The concentration of hexane in the air in Chicago was recently measured and contained 2 parts hexane per billion parts air (2 ppb). Hexane has generally not been found in most foods or drinking water, so you are not likely to be exposed by eating or drinking. Because cooking oils are processed with solvents containing hexane, very small amounts may be present in these products. However, the amounts in cooking oil are too low to have any effect on people.

People living near hazardous waste sites containing hexane or near its manufacturing, processing, or storage facilities could potentially be exposed. Because of the chemical properties of hexane, the most likely way a person would be exposed is by breathing in air contaminated with hexane. A less likely way for a person to be exposed is by drinking contaminated private well water.

You may be exposed to hexane if you use products containing it at work. This exposure will mainly be by breathing in air containing hexane, but you can also be exposed through your skin by contact with substances containing hexane. Some occupational groups that may be exposed to hexane include refinery workers, shoe and footwear assembly workers, laboratory technicians, workers operating or repairing typesetting and printing machinery, construction workers, carpet layers, carpenters, auto mechanics and gas station employees, workers in plants manufacturing tires or inner tubes, and workers in air transport and air freight operations. Exposure can also occur in the home if products containing hexane are used without proper ventilation.

Metabolism

Hexane can enter your body through your lungs if it is in the air you breathe. It can also enter your body through your stomach and intestines if it is in your drinking water or food, or through your skin if you come into contact with it. How much hexane enters your body depends on how long you are exposed and the amount to which you are exposed.

Once you inhale hexane, it goes into your bloodstream and is carried to all the organs in your body. Enzymes in your liver break down hexane. If you are exposed to high concentrations of hexane over a long period, one of these breakdown products may cause damage to your nervous system. Most of these breakdown products leave your body in the urine within a day or two. Hexane and its breakdown products are not stored in your body.

Health Effects

Almost all the people known to have had their health affected by exposure to hexane used it at work. In the 1960s and early 1970s, several outbreaks of nerve disorders occurred among shoe workers in Japan and Italy. Doctors determined the disease was caused by the workers breathing air containing high concentrations of hexane. The hexane came from glues and solvents the workers used in assembling the shoes. In one group of workers in Japan, it was estimated that the workers who became ill had been breathing air containing 500-2,500 parts hexane per million parts air (500-2,500 ppm) for 8-14 hours a day for 6 months to several years. The first symptom that the affected workers had was a feeling of numbness in their feet and hands. This was followed by muscle weakness in the feet and lower legs. If exposure continued, the symptoms grew worse. In some workers, paralysis of the arms and legs developed. When the affected workers were examined by doctors, the nerves controlling the muscles in their arms and legs were found to be damaged. The medical term for this condition is "peripheral neuropathy" (peripheral means outside the brain and spinal cord; neuropathy means nerve damage). Fortunately, once the workers were removed from exposure to hexane they recovered within 6 months to a year, although some of the more severely affected did not recover for 1-2 years.

Poor ventilation of the work area was a major factor in all of these cases. Workers who became ill usually worked in their homes or in very small workshops. Since the 1970s, workplace ventilation has been improved and levels of hexane in the air have been lower. There have been very few cases of nerve damage from hexane since 1980. A few people have also suffered nerve damage from "sniffing" products containing hexane. Like cases in the workplace, the number of cases due to sniffing has fallen since the 1970s.

It is not known if oral or skin exposure to hexane can cause these effects in people. There have been very few documented exposures to hexane by these routes in people.

When rats are exposed to hexane in the air, they show signs of damage to their nervous systems very similar to those seen in people who became ill after workplace exposure. As in people, these effects in rats depend on the concentrations of hexane in air and how long exposure lasts. Studies in rats showed that a breakdown product of hexane (called 2,5-hexanedione) causes the nerve damage, not hexane itself. Testing for 2,5-hexanedione in the urine can be used to determine if a person has been exposed to potentially harmful amounts of hexane. Studies in rats also showed that hexane can cause nerve damage when given orally in very large doses.

At very high levels of hexane in air (1,000-10,000 ppm), signs of damage to sperm-forming cells in male rats occurred. Damage to the lungs occurred in rabbits and mice. People have rarely been exposed to these high levels of hexane, so it is not known if these effects would occur in people.

It is not known if exposure to hexane can affect fertility in people. Experiments done with animals that were fed or breathed in hexane did not show any effect on fertility.

There is no evidence that exposure to hexane increases the risk of cancer in people. No reliable information is available on whether hexane causes cancer in animals. In an animal experiment with commercial hexane, an increase in liver cancer was found in female mice after exposure for 2 years. No increase was found in male mice or in rats of either sex. Commercial hexane is a mixture, and we do not know what parts of the mixture caused the cancer in the female mice. Hexane has not been characterized for carcinogenicity by the Department of Health and Human Services (DHHS), the International Agency for Research on Cancer (IARC), or the Environmental Protection Agency (EPA).

Information excerpted from:

Toxicological Profile for Hexane July 1999

Agency for Toxic Substances and Disease Registry
U.S. Dept. of Health and Human Services