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-Trichlorobenzene and 1,3,5-trichloro­benzene are colorless solids, while 1,2,4-trichloro­benzene is a colorless liquid.

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

Uses

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-trichlorobenzene, are produced in lower quantities and have fewer uses.

Trichlorobenzenes are volatile substances and may therefore partition to air when released to the environment. The half-life (the time it takes for 50% of the compound to degrade) of trichlorobenzenes in air is about 1 month.

Water

Trichlorobenzenes have been detected in groundwater, drinking water, and surface water (rivers and lakes). Trichlorobenzenes have a tendency to evaporate over time from water, but can also adsorb to suspended solids and sediment in water.

Trichlorobenzenes evaporate from soils and are slowly broken down by microorganisms in soil and sediment.

Trichlorobenzenes in water and soil may be absorbed or ingested by animals. High levels of trichlorobenzenes are often detected in fish or other species living in contaminated waters because trichlorobenzenes can accumulate in fatty tissues.

Monitoring data suggest that the general population may be exposed to trichlorobenzenes by inhaling air and through the ingestion of food and drinking water. Other substances that have been released into the environment, such as higher chlorinated benzenes, or the formerly used pesticide, lindane, can break down into trichlorobenzene. Therefore, if you live in an area where these products were used or disposed of (hazardous waste sites) you may potentially be exposed to trichlorobenzenes as well.

Trichlorobenzenes have been identified in a variety of food items including vegetables, milk, eggs/meat, and oils produced from corn, soybeans, peanuts, walnuts, hazelnuts, and rape, sunflower, sesame, and poppy seeds. People who eat large quantities of fish from areas contaminated by trichlorobenzenes may have higher exposure to these substances since fish tend to accumulate trichlorobenzenes in their fatty tissues.

You can be exposed to trichlorobenzenes by inhalation and dermal contact with these substances if you are employed in an occupation where trichlorobenzenes are manufactured or used. According to the National Occupational Exposure Survey (NOES), workers employed in textile mill production and electric and electronic manufacturing tend to have the greatest potential exposure to trichlorobenzenes.

Enter your body

There is not enough information to determine how much or how fast trichlorobenzenes can enter your body if you inhale vapors or contaminated air, if you swallow these chemicals, or if they get onto your skin.

Studies in animals suggest that trichlorobenzenes can rapidly enter the body through the lungs and the gastrointestinal tract. Less is known about entering the body through the skin.

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, trichlorobenzenes are transformed in the body into other chemicals, which are eliminated in the urine, feces, and bile in a few days.

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

Effects in humans

There is virtually 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 and a report of a woman who developed a blood disorder due to prolonged inhalation of trichlorobenzenes from her husband’s work clothes.

However, based on results from studies in animals, it is reasonable to predict that humans exposed to high amounts of trichlorobenzenes may develop liver problems.

Laboratory animals

Studies in animals indicate that oral administration of trichlorobenzenes for short or long periods produces mainly alterations in the liver and kidneys.

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

Placing trichlorobenzenes on the skin or the eyes of animals produced transitory irritation.

It should be noted that, in general, animals have been exposed to considerably higher amounts of trichlorobenzenes than the amounts that humans can encounter in the environment.

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 conducted prior to 1990; newer information has not been evaluated.

There are no studies of children exposed to trichlorobenzenes.

For the most part, studies in rats and mice given 1,2,4-trichlorobenzene during pregnancy have not found adverse 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 do not have widespread use in consumer products that are readily available to the general public. However, 1,2,4-trichlorobenzene is often detected in air, water, and aquatic species such as fish. The highest levels are typically encountered near facilities that manufacture and use trichlorobenzenes and other chlorinated substances or hazardous waste sites at which these substances may have been disposed of. Avoiding these areas will reduce your risk of exposure to trichlorobenzenes and other chemicals.

Avoiding high consumption of root crops and fish living in contaminated environments will reduce the risk of exposure.

Trichlorobenzenes can be measured in blood and body fat, but the tests used are not routinely available in the doctor’s office.

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.

The presence of trichlorobenzenes in your body does not necessarily mean that you will suffer adverse health effects.

The EPA has determined that exposure to 1,2,4-trichlorobenzene and 1,3,5-trichlorobenzene in drinking water at concentrations of 0.1 and 0.6 milligrams per liter (mg/L), respectively, for 1 or 10 days is not expected to cause any adverse effects in a child.

The EPA has determined that lifetime exposure to 0.07 mg/L 1,2,4-trichlorobenzene and 0.04 mg/L 1,3,5-trichlorobenzene is not expected to cause any adverse effects.

The EPA established a maximum contaminant level (MCL) of 0.07 mg/L for 1,2,4-trichlorobenzene in drinking water.

The FDA has determined that the concentration of 1,2,4-trichlorobenzene in bottled drinking water should not exceed 0.7 mg/L.