Heptachlor, chemical formula C10H5Cl7, is an organochlorine compound that was used as an insecticide. It is one of the cyclodiene insecticides. [1] Heptachlor is a white to light tan waxy solid with a camphor-like odour. It is insoluble in water and soluble in xylene, hexane, and alcohol. [2] Heptachlor was used extensively in the past for killing insects in homes, buildings, and on food crops. These uses stopped in 1988. [3] Due to its highly stable structure, heptachlor can persist in the environment for decades. [1] It is readily converted to more potent heptachlor epoxide once it enters the environment or the body. [4]

Uses [5]

  • Heptachlor is a constituent of technical grade chlordane, approximately 10 percent by weight.
  • Heptachlor was used as an insecticide in the United States from 1953 to 1974. In 1974, nearly all registered uses of heptachlor were cancelled.
  • Heptachlor was used from 1953 to 1974 as a soil and seed treatment to protect corn, small grains, and sorghum from pests. It was also used to control ants, cutworms, maggots, termites, and other pests in agriculture and in the home.
  • Its sole U.S. manufacturer voluntarily cancelled the sale of heptachlor in 1987.
  • In 1988, the sale, distribution, and shipment of existing stocks of all cancelled heptachlor and chlordane products were prohibited in the United States.
  • The only commercial use of heptachlor products still permitted is fire ant control in power transformers. In addition, homeowner’s use of existing stocks of heptachlor-containing termite control products is also allowed.

In the Environment [6]

  • When heptachlor is released into the environment it is converted to heptachlor epoxide, which degrades more slowly and is thus more persistent.
  • Heptachlor partitions somewhat rapidly to the atmosphere from surface water and that volatilisation is significant.
  • In contrast, heptachlor epoxide partitions slowly to the atmosphere from surface water.
  • Heptachlor in water has an estimated half-life of 3.5 days.
  • Heptachlor epoxide has a half-life in water of at least 4 years.
  • Heptachlor and heptachlor epoxide adsorb strongly to sediments.
  • Temperature and humidity affect the persistence of heptachlor and heptachlor epoxide in soil, as can the amount of organic matter present.
  • Heptachlor and heptachlor epoxide are also taken up by plants and both may bioconcentrate in aquatic and terrestrial food chains.

Sources & Routes of Exposure

Sources of Exposure [5]

  • People whose homes were treated for termites with heptachlor may be exposed to heptachlor in the indoor air for many years after treatment.
  • Workers who use heptachlor to kill fire ants or who manufacture the chemical may be exposed to it in the air or through the skin.
  • Heptachlor has been detected in food, including fish, shellfish, dairy products, meat, and poultry.
  • Another possible source of exposure is drinking water; heptachlor has been detected at low concentrations in drinking water wells in several states.

Routes of Exposure [6]

  • Inhalation – Minor route of exposure for the general population;
  • Oral – Primary route of exposure is through the diet;
  • Dermal – Minor route of exposure

Health Effects

Acute Effects

Acute inhalation exposure to heptachlor in humans has been associated with nervous system effects in a few case studies, while gastrointestinal effects, such as nausea and vomiting, have been reported to occur following accidental ingestion of heptachlor. Effects on the liver and central nervous system have been noted in animals acutely exposed to heptachlor via the oral route. Heptachlor is considered to have high to extreme acute toxicity based on short-term oral tests in rats.

Chronic Effects

Chronic inhalation exposure to heptachlor has been associated with blood effects in humans, while oral exposure has resulted in neurological effects including irritability, salivation, dizziness, muscle tremors, and convulsions. Animal studies have reported effects on the liver, kidney, and the immune and nervous systems from oral exposure to heptachlor. The Reference Dose (RfD) for heptachlor is 0.0005 milligrams per kilogram body weight per day (mg/kg/d) based on liver weight increases in males rats only. EPA has not established a Reference Concentration (RfC) for heptachlor.

Reproductive/Developmental Effects

Heptachlor has been shown to cross the placenta to the developing foetus in humans. However, inadequate information is available to determine whether heptachlor may cause developmental or reproductive effects in humans. Animal studies have reported developmental effects, including foetal resorptions, and decreased postnatal survival, as well as reproductive effects such as failure of animals to reproduce, following oral exposure to heptachlor.

Cancer Risk

Human studies on heptachlor exposure and cancer are inconclusive. There are several case reports describing a possible link between heptachlor exposure and leukaemia and neuroblastoma; however, insufficient information is available to confirm a causal effect. Several studies on workers exposed via inhalation to heptachlor are available; however, these are limited due to confounding factors and small sample size. Animal studies have reported liver tumours in mice exposed to heptachlor via ingestion. EPA considers heptachlor to be a probable human carcinogen (cancer-causing agent) and has classified it as a Group B2 carcinogen.

Safety [7]

First Aid Measures

  • Inhalation: Remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention immediately.
  • Ingestion: If swallowed, give large quantities of water to drink and get medical attention immediately. Never give anything by mouth to an unconscious person.
  • Skin Contact: Immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Get medical attention immediately. Wash clothing before reuse. Thoroughly clean shoes before reuse.
  • Eye Contact: Immediately flush eyes with plenty of water for at least 15 minutes, lifting lower and upper eyelids occasionally. Get medical attention immediately.

Exposure Controls & Personal Protection [8]

Exposure Controls

Methods that are effective in controlling worker exposures to heptachlor, depending on the feasibility of implementation, are as follows:

  • Process enclosure
  • Local exhaust ventilation
  • General dilution ventilation
  • Personal protective equipment

Personal Protective Equipment [9]

The following is a list of recommended personal protective equipment when handling heptachlor:

  • Respiratory protection: Where risk assessment shows air-purifying respirators are appropriate use a full-face particle respirator type N100 (US) or type P3 (EN 143) respirator cartridges as a backup to engineering controls. If the respirator is the sole means of protection, use a full-face supplied air respirator. Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN(EU).
  • Hand protection: Handle with gloves. Gloves must be inspected prior to use. Use proper glove removal technique (without touching glove’s outer surface) to avoid skin contact with this product. Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices. Wash and dry hands. The selected protective gloves have to satisfy the specifications of EU Directive 89/686/EEC and the standard EN 374 derived from it.
  • Eye protection: Face shield and safety glasses Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
  • Skin and body protection: Complete suit protecting against chemicals, the type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.

Regulations [8,10]

United States

OSHA: The United States Occupational Safety and Health Administration permissible exposure limit (PEL) for heptachlor is 0.5 milligrams per cubic metre (mg/m3) of air as an 8-hour time-weighted average (TWA) concentration. The OSHA PEL also bears a “Skin” notation, which indicates that the cutaneous route of exposure (including mucous membranes and eyes) contributes to overall exposure [29 CFR 1910.1000, Table Z-1].

NIOSH: The National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) for heptachlor of 0.5 mg/m3 as a TWA for up to a 10-hour workday and a 40-hour workweek. NIOSH also assigns a “Skin” notation to heptachlor. NIOSH considers heptachlor a potential occupational carcinogen [NIOSH 1992].

ACGIH: The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned heptachlor a threshold limit value (TLV) of 0.5 mg/m3 as a TWA for a normal 8-hour workday and a 40-hour workweek. The ACGIH also assigns a “Skin” notation to heptachlor. The ACGIH lists heptachlor as an animal carcinogen [ACGIH 1994, p. 22].


Safe Work Australia: Safe Work Australia have established a time weighted average (TWA) for heptachlor of 0.5 mg/m3 for a 40 hour work week.