Hexachlorobenzene (HCB), is a chlorocarbon with the molecular formula C6Cl6. [1] It is a fully chlorinated industrial hydrocarbon chemical, which is insoluble in water, but is very soluble in fat, oils, and organic solvents. Hexachlorobenzene is one of the most persistent environmental pollutants, and bioaccumulates in the environment, in animals, and in humans. It is not currently manufactured as a commercial product in the United States, and virtually all commercial production ended in the late 1970s. However, some hexachlorobenzene is produced as a by-product or impurity in the manufacture of chlorinated solvents and other chlorinated compounds, including several pesticides currently in use (pentachloronitrobenzene, chlorothalonil, Dacthal®, picloram, pentachlorophenol, atrazine, simazine, and lindane). [2] HCB has been banned globally under the Stockholm Convention on persistent organic pollutants. [1]

Uses [3]

There are currently no commercial uses of hexachlorobenzene. It was previously used as a pesticide but is no longer registered for this use. In addition, HCB was used in the production of fireworks, ammunition, rubber, aluminium, and dyes, and in wood preservation. Hexachlorobenzene was widely used as a pesticide to protect the seeds of onions and sorghum, wheat, and other grains against fungus. It is formed as a by-product during the manufacture of chemicals used as solvents (to dissolve other substances), other chlorine-containing compounds, and pesticides. Furthermore, it is formed as a by-product in the waste streams of chloralkali and wood-preserving plants, and when burning municipal waste.

HCB in the Environment [4]

  • Hexachlorobenzene can remain in the environment for a long time.
  • It breaks down very slowly.
  • It does not dissolve in water very well, so most of it will remain in particles on the bottom of lakes and rivers.
  • Hexachlorobenzene sticks strongly to soil.
  • High levels can build up in fish, marine mammals, birds, lichens, and animals that eat lichens (like caribou) or fish.
  • It can also build up in wheat, grasses, some vegetables, and other plants.

Sources & Routes of Exposure

Sources of Exposure [4,5]

  • Inhalation exposure to hexachlorobenzene may occur through proximity to industrial sites where it is formed as a by-product or to waste facilities where it is disposed.
  • Occupational exposure, via inhalation and dermally, can occur at industries where hexachlorobenzene is produced as a by-product.
  • Exposure to hexachlorobenzene can also occur through consuming foods tainted with hexachlorobenzene including fish and dairy products or meat from cattle grazing on contaminated pastures.
  • Drinking small amounts in contaminated water.
  • Eating or touching contaminated soil.
  • For babies, drinking contaminated breast milk from exposed mothers.
  • Hexachlorobenzene has been listed as a pollutant of concern to EPA’s Great Waters Program due to its persistence in the environment, potential to bioaccumulate, and toxicity to humans and the environment

Routes of Exposure [6]

  • Inhalation – A minor route of exposure for the general population.
  • Oral – The predominant route of exposure for the general population through ingestion of contaminated food.
  • Dermal – Skin contact with contaminated soil may be an important route of exposure, for those living near waste sites, especially children

Health Effects [5]

Acute Effects

  • No information is available on the acute (short-term) effects of hexachlorobenzene in humans.
  • Acute animal tests in rats and mice have shown hexachlorobenzene to have low-to-moderate acute toxicity from oral exposure.

Chronic Effects

  • Humans who ingested hexachlorobenzene in heavily contaminated bread during a 4-year poisoning incident were sickened with a liver disease with associated skin lesions (porphyria cutanea tarda).
  • Very little data is available on the health effects of hexachlorobenzene in humans or animals following inhalation exposure.
  • Animal studies have reported effects on the liver, skin, immune system, kidneys, and blood from chronic oral exposure to hexachlorobenzene.
  • EPA has determined that there is inadequate data to establish a Reference Concentration (RfC) for hexachlorobenzene.
  • The California Environmental Protection Agency (CalEPA) has established a chronic inhalation reference exposure level of 0.003 milligrams per cubic metre (mg/m3) for hexachlorobenzene.
  • The Reference Dose (RfD) for hexachlorobenzene is 0.0008 milligrams per kilogram body weight per day (mg/kg/d) based on liver effects in rats.

Reproductive/Developmental Effects

  • One human study reported abnormal physical development in young children who ingested contaminated bread during a 4-year poisoning incident.
  • Hexachlorobenzene has been found to decrease the survival rates of newborn animals and to cross the placenta and accumulate in foetal tissue in several animal species.
  • Neurological, teratogenic, liver, and immune system effects have been reported in the offspring of animals orally exposed to hexachlorobenzene while they were pregnant.

Cancer Risk

  • Human data regarding the carcinogenic effects of hexachlorobenzene are inadequate.
  • Hexachlorobenzene, when administered orally, has been shown to induce tumours of the liver, thyroid, and kidney in several animal species.
  • EPA has classified hexachlorobenzene as a Group B2, probable human carcinogen.
  • EPA calculated an inhalation unit risk estimate of 4.6 x 10-4 (µg/m3)-1.

Safety [7]

First Aid Measures

  • Eyes: Flush eyes with plenty of water for at least 15 minutes, occasionally lifting the upper and lower eyelids. Get medical aid.
  • Skin: Flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Wash clothing before reuse. Get medical aid.
  • Ingestion: If victim is conscious and alert, give 2-4 cupfuls of milk or water. Never give anything by mouth to an unconscious person. Get medical aid.
  • Inhalation: Remove from exposure and move to fresh air immediately. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical aid.

Exposure Controls & Personal Protection

Engineering Controls

Use adequate general or local exhaust ventilation to keep airborne concentrations below the permissible exposure limits.

Personal Protective Equipment

  • Eyes: Wear appropriate protective eyeglasses or chemical safety goggles as described by OSHA’s eye and face protection regulations in 29 CFR 1910.133 or European Standard EN166.
  • Skin: Wear appropriate protective gloves to prevent skin exposure.
  • Clothing: Wear appropriate protective clothing to prevent skin exposure.
  • Respirators: Follow the OSHA respirator regulations found in 29 CFR 1910.134 or European Standard EN 149. Use a NIOSH/MSHA or European Standard EN 149 approved respirator if exposure limits are exceeded or if irritation or other symptoms are experienced.


United States [4,8]

  • The EPA has recommended that drinking water should not contain more than 0.05 milligrams of hexachlorobenzene per litre of water (0.05 mg/L) in water that children drink, and should not contain more than 0.2 mg/L in water that adults drink for longer periods (about 7 years). The EPA has set a maximum contaminant level of 0.001 mg/L in drinking water.
  • The EPA requires that spills or accidental releases into the environment of 10pounds or more of hexachlorobenzene be reported to the EPA.
  • ACGIH: The American Conference of Governmental Industrial Hygienists has set a time weighted average threshold limit value (TLV) of 0.002 mg/m3; Skin; Appendix A3 – Confirmed Animal Carcinogen with Unknown Relevance to Humans

Australia [3]

  • No national guidelines.