HMX, an acronym for High Melting eXplosive, is also known as octogen and cyclotetramethylene-tetranitramine, as well as by other names. It is a colorless solid that dissolves slightly in water. Only a very small amount of HMX will evaporate into the air; however, it can occur in air attached to suspended particles or dust. The taste and smell of HMX are not known.
HMX is a manmade chemical and does not occur naturally in the environment. It is made from other chemicals known as hexamine, ammonium nitrate, nitric acid, and acetic acid. HMX explodes violently at high temperatures (534°F and above). Because of this property, HMX is used in nuclear devices, plastic explosives, rocket fuels, and burster chargers. A small amount of HMX is also formed in making cyclotrimethylene-trinitramine (RDX), another explosive similar in structure to HMX. The amount of HMX made and used in the United States at present is not known, but it is believed to be greater than 30 million pounds per year.
Pathways for HMX in the environment
Most of the HMX that enters the environment is released into waste water from places that make or use HMX. A small amount of HMX can be released to the air as dust or ash from facilities that burn waste contaminated with HMX. Some HMX may be released to soil as a result of accidental spills, the settling of HMX-containing dust particles from the air, or the disposal of waste that contains HMX in landfills.
Dust particles containing HMX may be carried by the wind for some distance. The distance depends on a number of factors, including particle size, wind velocity, and weather conditions. Eventually, these particles settle to the earth, depositing on soil and surface waters. The length of time that HMX remains in the air is not known.
In surface water, HMX does not evaporate or bind to sediments to any large extent. Sunlight breaks down most of the HMX in surface water into other compounds, usually in a matter of days to weeks. The amount of time HMX remains in surface water depends on how much light-absorbing material is present. A small amount of HMX may also be broken down by bacteria in the water. Some of the breakdown products of HMX (nitrite, nitrate, formaldehyde, 1,1-dimethylhydrazine) are also harmful to your health, although the amounts you may be exposed to as a result of HMX in your drinking water are not expected to be above trace levels.
Laboratory studies show that HMX is likely to move from soil into groundwater, particularly in sandy soils. For most soils, however, the movement of HMX into groundwater is expected to be slow. Bacteria in the soil are not expected to break down HMX to any large extent. Exactly how long HMX will remain in the environment is not known; however, HMX in soil and groundwater is expected to stay there for a long time. It is not known if plants, fish, or animals living in areas contaminated with HMX build up high levels of the chemical in their tissues.
Exposure to HMX
There is no information on how often you might be exposed to HMX in the environment or to how much. Most people, however, probably won't be exposed to HMX from the environment. People who work at facilities that make or use HMX or RDX, such as military personnel, may be exposed. These workers may be exposed by inhaling dusts that contain HMX or by getting HMX-containing liquids on their skin. People who live near facilities that make or use HMX, or near hazardous waste sites that contain HMX, may also be exposed. For these residents, exposure (if any) is most likely to occur from contaminated groundwater. However, exposures to small amounts of HMX from contaminated surface water, soil, and air are also possible.
Pathways for HMX in the body
HMX can enter your body if you breathe contaminated air, swallow contaminated water or soil, or get substances that contain HMX on your skin. Very little is known about how much and how fast HMX enters your body after you are exposed.
Limited information from laboratory studies in animals suggests that if you swallow HMX, only a small amount (less than 5 percent) will be absorbed into your blood. The rest of the HMX that is not absorbed leaves your body in your feces, usually within a day or two after you are exposed. Your blood carries the small amount of absorbed HMX to your tissues. Animal studies suggest that the resulting concentrations of HMX in your lungs, liver, heart, and kidneys may be slightly higher than the concentrations in other tissues.
HMX does not remain in any of your tissues for very long. Information from animal studies suggests that your body can transform HMX into other compounds called metabolites. At present, the identity and toxicity of these metabolites are not known. Most of these metabolites leave your body in your urine, usually within a few days after you are exposed. Smaller amounts of these metabolites may be released in your feces or in the air you breathe out.
Health effects of HMX
Information on the adverse health effects of HMX is limited. In one human study, no adverse effects were reported in workers exposed to HMX in air. However, the concentrations of HMX in the workplace air were not reported in this study, and only a small number of workers and effects were investigated.
You should know that one way to learn whether a chemical will harm people is to determine how the body absorbs, uses, and releases the chemical. For some chemicals, animal testing may be necessary. Animal testing may also help identify such health effects as cancer or birth defects. Without laboratory animals, scientists would lose a basic method for getting information needed to make wise decisions that protect public health. Scientists have the responsibility to treat research animals with care and compassion. Scientists must comply with strict animal care guidelines because laws today protect the welfare of research animals.
Additionally, there are vigorous national and international efforts to develop alternatives to animal testing. The efforts focus on both in vitro and in silico approaches and methods. For example, the National Toxicology Program (NTP) at the National Institute of Environmental Health Sciences (NIEHS) created the NTP Interagency Center for the Evaluation of Alternative Toxicological Methods (NICEATM) in 1998. The role of NICEATM is to serve the needs of high quality, credible science by facilitating development and validation—and regulatory and public acceptance—of innovative, revised test methods that reduce, refine, and replace the use of animals in testing while strengthening protection of human health, animal health and welfare, and the environment. In Europe, similar efforts at developing alternatives to animal based testing are taking place under the aegis of the European Centre for the Validation of Alternative Methods (ECVAM).
Studies in rats, mice, and rabbits indicate that HMX may be harmful to your liver and central nervous system if it is swallowed or gets on your skin. The lowest dose producing any effects in animals was 100 milligrams per kilogram of body weight per day (mg/kg/day) orally and 165 mg/kg/day on the skin. Limited evidence suggests that even a single exposure to these dose levels harmed rabbits. The mechanism by which HMX causes adverse effects on the liver and nervous system is not understood.
The reproductive and developmental effects of HMX have not been well studied in humans or animals. At present, the information needed to determine if HMX causes cancer is insufficient. Due to the lack of information, EPA has determined that HMX is not classifiable as to its human carcinogenicity.
Medical tests for exposure to HMX
You can find out if you have been exposed to HMX by having your blood, urine, or feces tested for HMX. Since HMX is poorly absorbed after it is swallowed, the levels of HMX in your blood and urine are likely to be lower than those in your feces. For best results, tests for HMX should be done within a few days after you are exposed. These tests cannot be used to tell how much HMX you have been exposed to or to predict whether or not you will experience adverse health effects. These tests are not usually done in a doctor's office, but require that the samples be sent to a laboratory for testing.
- The Agency for Toxic Substances and Disease Registry
- Interagency Coordinating Committee on the Validation of Alternative Methods
- European Centre for the Validation of Alternative Methods
- Institute for Laboratory Animal Research
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