A public health statement summarizes information about a hazardous substance. The information is taken from a toxicological profile developed by the Agency for Toxic Substances and Disease Registry's (ATSDR's) Division of Toxicology and Human Health Sciences (DTHHS). A toxicological profile is a thorough review of a hazardous substance.

This toxicological profile examines trichlorobenzenes. This public health statement summarizes the DTHHS's findings on trichlorobenzenes, describes the effects of exposure to them, and describes what you can do to limit that exposure.

The U.S. Environmental Protection Agency (U.S. EPA) identifies the most serious hazardous waste sites in the nation. U.S. EPA then includes these sites in the National Priorities List (NPL) and targets them for federal clean-up activities. U.S. EPA has found 1,2,3-, 1,2,4-, and 1,3,5-trichlorobenzene in at least 31, 187, and 4 of the 1,699 current or former NPL sites, respectively.

The total number of NPL sites evaluated for trichlorobenzenes is not known. But the possibility remains that as more sites are evaluated, the number of sites at which trichlorobenzenes is found may increase. This information is important; these future sites may be sources of exposure, and exposure to trichlorobenzenes may be harmful.

When a contaminant is released from a large area such as an industrial plant or from a container such as a drum or bottle, it enters the environment. But such a release does not always lead to exposure. You can only be exposed to a contaminant when you come in contact with it. That contact-and therefore that exposure-can occur when you breathe, eat, or drink the contaminant, or when it touches your skin.

Even if you are exposed to trichlorobenzenes, you might not be harmed. Whether you are harmed will depend on such factors as the dose (how much), the duration (how long), and how you are exposed. Harm might also depend on whether you have been exposed to any other chemicals, as well as your age, sex, diet, family traits, lifestyle, and state of health.

Trichlorobenzenes are human-made compounds that occur in three different chemical forms. Although they have the same molecular weight and molecular formula, they differ structurally by where the chlorine atoms are attached to the benzene ring. Compounds like these are referred to as isomers. 1,2,3 Trichloro¬benzene and 1,3,5 trichloro¬benzene are colorless solids, while 1,2,4-trichloro¬benzene is a colorless liquid.

Although the three isomers of trichlorobenzene are structurally similar, they each may have different chemical and toxicological properties.

Trichlorobenzenes have primarily been used as solvents and chemical intermediates to produce other compounds. In the past, mixed isomers of trichlorobenzene had been used for termite control, but this is not a current use. One of the isomers (1,2,4 trichlorobenzene) is produced in large quantities and is used as a solvent to dissolve such special materials as oils, waxes, resins, greases, and rubber. It is also frequently used to produce dyes and textiles. The other two isomers, 1,2,3 trichlorobenzene and 1,3,5 trichloro¬benzene, are produced in lower quantities and have fewer uses.

Trichlorobenzenes can be released into the air, water, and soil at places where they are produced or used.

Trichlorobenzenes can enter your body from the air, water, or soil.

There is no information regarding what happens to trichlorobenzenes in humans. In animals, trichlorobenzenes are transformed in the body into other chemicals.

There is no information on how these compounds could leave the body in humans, but based on studies in animals, they probably leave principally in the urine.

In animals, degradation products of trichlorobenzenes leave the body in the urine, feces, and bile in a few days following exposure.

Studies in animals suggest that trichlorobenzenes do not accumulate in the body of mammals, but can accumulate in fish to some extent.

The health effects of trichlorobenzenes depend on how much of these compounds you are exposed to and the length of that exposure. Environmental monitoring data suggest that any trichlorobenzene's levels that the public might encounter through contact or through water, soil, or food are much lower than animal-study levels.

There is no information regarding health effects of trichlorobenzenes in humans other than reports of minimal eye and throat irritation in certain people exposed to vapors of 1,2,4 trichlorobenzene.

Placing trichlorobenzenes on the skin or the eyes of animals produced irritation that eventually went away after time.

Very limited information exists regarding effects of long-term exposure in humans. There is a report of a woman who developed a blood disorder due to prolonged inhalation of trichlorobenzenes from her husband's work clothes.

Prolonged administration of 1,2,4-trichlorobenzene to rats did not affect their capacity to reproduce.

There are no studies of cancer in humans exposed to trichlorobenzenes.

Mice given 1,2,4-trichlorobenzene in the food for 2 years developed cancer of the liver

The EPA has stated that 1,2,4-trichlorobenzene is not classifiable as to human carcinogenicity. However, this was based on studies prior to 1990; newer information has not been evaluated.

There are no studies of children exposed to trichlorobenzenes. Therefore, we do not know whether children are more susceptible than adults to the effects of exposure to trichlorobenzenes.

We do not know whether exposure of women to trichlorobenzenes during pregnancy can produce birth defects in their babies.

For the most part, studies in rats and mice given 1,2,4 trichloro¬benzene orally during pregnancy did not cause effects in their pups at birth or later during the growing period. However, a study in rats found lesions in the eyes of the pups.

Trichlorobenzenes have been found in human breast milk, which means that mothers can transfer these chemicals to their babies by nursing.

Trichlorobenzenes tend to accumulate in the fatty tissue of fish; therefore, avoid eating large quantities of fish from areas contaminated with trichlorobenzenes. Avoid consumption of food crops grown in areas contaminated with trichlorobenzenes.

Avoid drinking water from sources that are known to be contaminated with trichlorobenzenes. Use bottled water if you have concerns about the presence of chemicals in your tap water. You may also contact local drinking water authorities and follow their advice.

Trichlorobenzenes have been detected in groundwater. Avoid contact with groundwater known to be contaminated with trichlorobenzenes.

Prevent children from playing in dirt if you live near a waste site that has trichlorobenzenes. Discourage your children from putting objects in their mouths. Make sure that they wash their hands frequently and before eating.

Trichlorobenzenes can be measured in blood and body fat, but the tests are not routinely available at the doctor's office. The detection of trichlorobenzenes cannot predict the kind of health effects that might develop from that exposure.

There is not enough information to determine whether trichlorobenzenes detected in your body indicate that you have been exposed recently to a high amount or you are continuously exposed to lower amounts.

Detecting trichlorobenzenes in your body generally means that you were exposed to these compounds. However, detecting breakdown products of trichlorobenzenes may mean that you were exposed to trichlorobenzenes or that you were exposed to other chemicals that produce the same breakdown products.

Regulations are enforceable by law. The U.S. EPA, the Occupational Safety and Health Administration (OSHA), and the Food and Drug Administration (FDA) are some federal agencies that have adopted toxic substances regulations.

The Agency for Toxic Substances and Disease Registry (ATSDR) and the National Institute for Occupational Safety and Health (NIOSH) have made recommendations about toxic substances. Unlike enforceable regulations, these recommendations are advisory only.

Regulations and recommendations can be expressed as "not-to-exceed" levels; that is, levels of a toxic substance in air, water, soil, or food that do not exceed a critical value usually based on levels that affect animals; levels are then adjusted to help protect humans. Sometimes these not-to-exceed levels differ among federal organizations. Different organizations use different exposure times (an 8-hour workday or a 24-hour day), different animal studies, or emphasize some factors over others, depending on their mission.

Recommendations and regulations are also updated periodically as more information becomes available. For the most current information, check with the federal agency or organization that issued the regulation or recommendation.

Some regulations and recommendations for trichlorobenzenes include: