Gamma-1,2,3,4,5,6-Hexachlorocyclo-Hexane

OVERVIEW

Gamma-1,2,3,4,5,6-hexachlorocyclohexane (GAM-uh one two three four five six HEK-sa-KLOR-oh-SYE-kloh-HEK-sane) exists in four isomeric forms. Isomers are two or more forms of a chemical compound with the same molecular formula, but different structural formulas and different chemical and physical properties. The isomer of greatest commercial interest is called the gamma (γ) isomer and is also known as lindane. It is sold commercially in more than a hundred commercial products under trade names such as 666, Africide, Agrocide, Aparasin, Arbitex, Ben-Hex, Bentox, Devoran, Entomoxan, Exagamma, Forlin, Gamaphex, Gammalin, Gammex, Gexane, Hexachloran, Isotox, Jacutin, Kwell, Lindafor, Lindatox, Lin-O-Sol, Lintox, Streunex, Tri-6, and Vitron.

KEY FACTS

OTHER NAMES:

Benzene hexachloride; BHC; HCCH; HCH; TBH

FORMULA:

C₆H₆Cl₆

ELEMENTS:

Carbon, hydrogen, chlorine

COMPOUND TYPE:

Chlorinated aromatic hydrocarbon (organic)

STATE:

Solid

MOLECULAR WEIGHT:

290.83 g/mol

MELTING POINT:

112.5°C (234.5°F)

BOILING POINT:

323.4°C (614.1°F)

SOLUBILITY:

Insoluble in water; soluble in absolute alcohol, chloroform, and ether

Gamma-1,2,3,4,5,6-hexachlorocyclohexane is normally available as a white to yellowish powder or crystalline solid with a musty odor. Its color, odor, melting point, and other characteristics differ depending on the relative amount of the four isomers present in the final product. Gamma-1,2,3,4,5, 6-hexachlorocyclohexane is non-flammable and stable in the presence of heat, light, strong acids, and carbon dioxide. The compound has two primary commercial uses: as a pesticide in agriculture and as a treatment for head lice, scabies, and other external parasites.

HOW IT IS MADE

Gamma-1,2,3,4,5,6-hexachlorocyclohexane is made by treating benzene (C₆H₆) with chlorine gas. In the process, each of the six hydrogen atoms in the benzene ring is replaced by a chlorine atom, resulting in the formation of a fully chlorinated benzene ring. That is, all of the original six hydrogen atoms have been replaced by chlorine atoms.

COMMON USES AND POTENTIAL HAZARDS

About 80 percent of all γ-1,2,3,4,5,6-hexachlorocyclohexane produced worldwide is used in agriculture, especially for treating soil and seeds. The wood and timber industries also use the product to protect trees from insects that attack them. In some places, γ-1,2,3,4,5,6-hexachlorocyclohexane is used as a spray to control the spread of mosquitoes. Veterinarians sometimes use the compound to treat or prevent fleas and other external parasites on animals. Gamma-1,2,3,4,5,6-hexachlorocyclohexane is also a major ingredient of products used to treat head lice, scabies, and similar pests that infest body hair.

Gamma-1,2,3,4,5,6-hexachlorocyclohexane is a member of the family of compounds known as the organochlorides, organic compounds that include one or more atom of chlorine in their molecular structure. The family also includes a number of other well-known products, such as DDT, dieldrin, aldrin, endrin, dinoseb, and chlordane. These compounds kill pests by attacking and incapacitating their nervous systems. Unfortunately, they have somewhat similar effects on the nervous systems of higher animals, including humans. Many of these organochlorides have been banned in commercial applications and many nations around the world.

The status of γ-1,2,3,4,5,6-hexachlorocyclohexane is still a matter of some controversy. It is banned for medicinal uses in many countries of the world, including Bangladesh, Belize, Bolivia, Brazil, Bulgaria, Chad, Denmark, Ecuador, Egypt, Finland, Guatemala, Honduras, Hong Kong, Hungary, Indonesia, Japan, Kuwait, Mozambique, New Zealand, The Netherlands, Nicaragua, Paraguay, the Republic of Korea, Singapore, Sweden, Taiwan, and Yemen. Its use is still permitted in the United States, although it has been banned as a known carcinogen in the state of California. The product has also been banned for some or all agriculture applications in more than 50 nations.

Gamma-1,2,3,4,5,6-hexachlorocyclohexane poses a health hazard to humans if ingested, inhaled, or deposited on the skin. It may cause skin irritation or rashes, nausea and vomiting, nervousness or irritability, accelerated heartbeat, convulsions or seizures, and dizziness or clumsiness. In rare cases, the ingestion of the compound has resulted in a person's death. It has also been classed as a likely carcinogen by the U.S. Environmental Protection Agency. The compound has been ranked in the top 10 percent among the most hazardous chemicals in ten out of eleven systems for making such rankings. It is ranked number thirty-two on the U.S. Agency for Toxic Substances and Disease Registry's list of 275 "priority" hazardous chemicals.

In spite of the apparent risk that γ-1,2,3,4,5,6-hexachlorocyclohexane poses to human health and the environment, its use is still permitted for many applications in the United States. A number of consumers' groups are currently working, however, to have the compound's use totally or partially banned.

FOR FURTHER INFORMATION

"Drug Information for Gamma Benzene Hexachloride." Drugs.com. http://www.drugs.com/cons/Gamma_benzene_hexachloride.html (accessed on October 10, 2005).

"Hexachlorocyclohexane (Mixed Isomers)." International Labour Organization. http://www.oit.org/public/english/protection/safework/cis/products/icsc/dtasht/_icsc04/icsc0487.htm (accessed on October 10, 2005).

"Lindane." IPCS International Programme on Chemical Safety. http://www.inchem.org/documents/hsg/hsg/hsg054.htm (accessed on October 10, 2005).

"Lindane Education and Research Network." National Pediculosis Association. http://www.headlice.org/lindane/ (accessed on October 10, 2005).