2-Hexanone (methyl butyl ketone, MBK) is a ketone used as a general solvent and in paints. It dissolves cellulose nitrate, vinyl polymers and copolymers, and natural and synthetic resins. It is recommended as a solvent because it is photochemically inactive;however it has a very low safe threshold limit value. 2-Hexanone is absorbed through the lungs, orally and dermally and its metabolite, 2,5-hexanedione, is neurotoxic.Animal tests have shown that the neurotoxic effect of 2-hexanone may be potentiated by simultaneous administration of 2-butanone (methyl ethyl ketone, MEK).
2-Hexanone is also known as methyl n-butyl ketone, MBK, or propyl acetone. It is a clear, colorless liquid with a sharp odor. It dissolves very easily in water, and can evaporate easily into the air as a vapor. It was used in the past in paint and paint thinner, to make other chemical substances, and to dissolve oils and waxes. It is no longer made or used in the United States because it has harmful health effects. It is formed as a waste product resulting from industrial activities such as making wood pulp and producing gas from coal, and in oil shale operations.
You can be exposed to 2-hexanone if you live near an industry or hazardous waste site that releases the liquid into wastewater or the gas form into the surrounding air. These industries include coal gasification plants, oil shale operations, and wood pulping mills. We have no information on background levels of 2-hexanone in the environment.
2-Hexanone has been found as a natural substance in foods such as cheese, nectarines, nuts, bread, and chicken muscle. We do not know the levels of 2- hexanone in these foods. 2-Hexanone has been found in milk and cream at levels up to 0.018 ppm (0.018 parts of 2-hexanone in one million parts of liquid). These levels are far below the levels that have caused harmful effects in animals. It has also been found in drinking water and soil near hazardous waste sites. Exposures at these sites may take place if you drink the contaminated water or bathe in it, if you get contaminated soil on your skin, or if you breathe the contaminated air.
2-Hexanone can enter your body when you breathe its vapors, eat food or drink water that contains it, or when you come in contact with it through your skin. When 2-hexanone is breathed in, about 75% of it is taken up and remains in the body unchanged or as a breakdown product for an unknown length of time. If it enters the body by mouth, about 65% of the chemical leaves the body slowly (in about a week), either unchanged or as breakdown products, in the breath and urine. The rest may either stay in the body or may leave the body slowly through the breath or urine. One of the breakdown products, called 2,5-hexanedione, may be responsible for the harmful effects on the nervous system (see Section 1.4). When 2-hexanone gets in through the skin, some leaves the body through the lungs and urine within a few hours. We have no information on how much stays in the body or for how long. If you live or work near a hazardous waste site, you may be exposed to 2-hexanone in the air that you breathe or in the water you drink or bathe in, if it contains small amounts of this.
The most important health concern for humans from exposure to 2-hexanone is its harmful effects on the nervous system. These effects were seen in workers who were exposed to 2-hexanone for almost a year. The major effects were weakness, numbness, and tingling in the skin of the hands and feet. Similar effects were seen in animals that ate or breathed high levels of 2-hexanone; these effects included weakness, clumsiness, and paralysis.
We do not know whether 2-hexanone can cause cancer or birth defects. In one study, when pregnant rats were exposed to 2-hexanone in the air, fewer offspring lived after birth, and those that did survive had low birth weights.
Many of the studies in which the health effects of 2- hexanone in humans or animals were reported did not use pure 2-hexanone. Therefore, we do not know whether the results were caused by 2- hexanone itself or by the other chemicals in the mixture.
Tests can be used to find out whether you have recently been exposed to 2-hexanone. The tests measure levels of 2-hexanone or its breakdown products in blood or urine. These tests require special equipment and are done in a special laboratory, so they are usually not available in a doctor's office. However, these tests cannot be used to predict whether harmful effects will occur.
The federal government has set certain regulations and guidelines to help protect people from the possible health effects of 2-hexanone in the workplace. The Occupational Safety and Health Administration (OSHA) has set a limit of 5 ppm (5 parts of 2-hexanone in 1 million parts of air) as an average exposure level to this chemical over a 40- hour work week. The American Conference of Governmental Industrial Hygienists (ACGIH) has made the same recommendation. The National Institute for Occupational Safety and Health (NIOSH) recommends an even lower limit, 1 ppm, as an average exposure during a 10-hour period.