Health effects of n-hexane
Health effects of n-hexane may arise after human exposure to n-hexane, which may occur in the Earth's atmosphere, soil or water; however, most human exposure occurs by breathing atmopheric air. n-Hexane is a chemical molecule derived from crude oil, and pure n-hexane is a colorless liquid with a slightly disagreeable odor at normal atmospheric conditions. It evaporates very readily into the open air and dissolves only slightly in water. n-Hexane is highly flammable, and its vapors can be explosive.
Pure n-hexane is used in laboratories. Most of the n-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 n-hexane are produced in the United States each year in the form of these solvents. The major use for solvents containing n-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 n-hexane. Several consumer products contain n-hexane. For example, gasoline contains about one to three percent n-hexane. n-Hexane is also present in rubber cement.
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Pathways for n-hexane in the environment
n-Hexane enters the air, water, and soil during its manufacture and use. Wastes containing n-hexane are sometimes disposed of in landfills. n-Hexane can enter the environment from these landfills. n-Hexane also enters the natural environment from accidental spills during transport and leaks from storage containers.
n-Hexane evaporates very easily into the air. Once in the air, n-hexane can react with oxygen and be broken down. n-Hexane released into the air is broken down in a few days.
If n-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 n-hexane will then evaporate into the air. The n-hexane dissolved in the water can be broken down by certain types of bacteria, although it is not known how long this takes.
If n-hexane is spilled on the ground, much of it will evaporate into the air before it penetrates the soil. Any n-hexane that penetrated the soil would probably be broken down by bacteria. If n-hexane leaks from an underground storage tank, it will float on the groundwater, rather than mixing with it since n-hexane is lighter than water.
n-Hexane is not stored for any appreciable times or concentrated by plants, fish or animals.
Exposure to n-hexane
Since gasoline contains n-hexane, almost everyone is exposed to small amounts of n-hexane in the air. The n-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 n-hexane in the air in Chicago was recently measured and contained two parts n-hexane per one billion parts air (2 ppb). n-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 n-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 n-hexane or near its manufacturing, processing, or storage facilities could potentially be exposed. Because of the chemical properties of n-hexane, the most likely way a person would be exposed is by breathing in air contaminated with n-hexane. A less likely way for a person to be exposed is by drinking contaminated private well water.
You may be exposed to n-hexane if you use products containing it at work. This exposure will mainly be by breathing in air containing n-hexane, but you can also be exposed through your skin by contact with substances containing n-hexane. Some occupational groups that may be exposed to n-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 n-hexane are used without proper ventilation.
Pathways for n-hexane in the body
n-hexane can enter your body through the lungs, when n-hexane is present in the ambient air. 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 n-hexane enters your body depends on how long you are exposed and the amount to which you are exposed.
Once n-hexane is inhaled, it proceeds to the bloodstream and is carried to all the body organs.Liver enzymes break down n-hexane. Subsequent to exposure to high concentrations of n-hexane over a long time period, one of these breakdown products may cause damage to the nervous system. Most of these breakdown products leave the body in the urine within a day or two. n-Hexane and its breakdown products are not stored in the human body for any appreciable time period.
Health effects of n-hexane
Almost all the people known to have had their health affected by exposure to n-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 n-hexane. The n-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 n-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 n-hexane they recovered within 6 months to a year, although some of the more severely affected did not fully 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 n-hexane in the air have been lower. There have been very few cases of nerve damage from n-hexane since 1980. A few people have also suffered nerve damage from "sniffing" products containing n-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 n-hexane can cause these effects in people. There have been very few documented exposures to n-hexane by these routes in people.
To protect the public from the harmful effects of toxic chemicals and to find ways to treat people who have been harmed, scientists use many tests.
One way to see if a chemical will hurt people is to learn how the chemical is absorbed, used, and released by the body; for some chemicals, animal testing may be necessary. Animal testing may also be used to identify health effects such as cancer or birth defects. Without laboratory animals, scientists would lose a basic method to get information needed to make wise decisions to protect public health. Scientists have the responsibility to treat research animals with care and compassion. Laws today protect the welfare of research animals, and scientists must comply with strict animal care guidelines.
When rats are exposed to n-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 n-hexane in air and how long exposure lasts. Studies in rats showed that a breakdown product of n-hexane (called 2,5-hexanedione) causes nerve damage, not n-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 n-hexane. Studies in rats also showed that n-hexane can cause nerve damage when given orally in very large doses.
At very high levels of n-hexane in air (1000–10,000 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 n-hexane, so it is not known if these effects would occur in people.
It is not known if exposure to n-hexane can affect fertility in people. Experiments conducted with animals that were fed or breathed in n-hexane did not show any effect on fertility.
There is no evidence that exposure to n-hexane increases the risk of cancer in people. No reliable information is available on whether n-hexane causes cancer in animals. In an animal experiment with commercial hexane (which contains n-hexane), an increase in liver cancer was found in female mice after exposure for two 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. n-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).
Health effects in children
This section discusses potential health effects from exposures during the period from conception to maturity at 18 years of age in humans. Potential effects on children resulting from exposures of the parents are also considered.
Harmful effects from exposure to n-hexane have mainly occurred in adults. This is because most known cases have occurred in workers. However, it is probable that if children were exposed to n-hexane at levels that cause harmful effects in adults, similar effects would occur. We do not know whether children differ from adults in their susceptibility to health effects from n-hexane exposure. Only a few animal studies have compared the effects of n-hexane between adults and young animals. In these studies, the neonatal and young animals were somewhat less likely to have harmful effects on their nervous system from breathing n-hexane than the adults, but more likely to die from a large oral dose.
Experiments in rats and mice have shown little effect of n-hexane exposure on the development of the fetus. It is probable that n-hexane and its breakdown products can cross the placenta and also be excreted in breast milk, but no accurate measurements have been made in people. n-Hexane and its breakdown products have been detected in the fetus when pregnant rats were exposed to n-hexane.
Reducing risk of exposure to n-hexane
If one's doctor finds that exposure to significant amounts of n-hexane has occurred, one should ask whether one's children might also be exposed. The physician might need to ask the relevant state public health department to investigate.
Certain products used in the home may contain n-hexane, for example, some quick-drying glues and cements used in hobbies. These products should be kept out of the reach of children and only used with proper ventilation. One should always store household chemicals in their original, labeled containers. Household chemicals should not be stored in containers children would find attractive to eat or drink from, such as old drink bottles. An important precaution is to keep your Poison Control Center's number by the telephone.
Sometimes older children sniff household chemicals in an attempt to get high. Children may be exposed to n-hexane by inhaling products containing it. Talk with your children about the dangers of sniffing chemicals. Sniffing products containing n-hexane has caused paralysis of the arms and legs in teenagers in the United States and Europe.
Medical tests for exposure to n-hexane
After exposure to harmful amounts of n-hexane, the amount of one of its breakdown products (2,5-hexanedione) will probably be increased in urine. A physician will have to send a sample to a specialized laboratory. This test can only detect n-hexane exposure occurring within 2–3 days before the test, since 2,5-hexanedione leaves the body within a few days after exposure.
Further Reading
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