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HCH
Editor	I.G. Ferris
Entity code	HCH
CAS registry No.	608-73-1
Family	Chlorinated hydrocarbons
Functions	Rodenticide, Insecticide
Chemical name	1,2,3,4,5,6-hexachlorocyclohexane (IUPAC and CAS) (EN)
Synonyms
Trade names	Agrocide; Ambrocide; Aparasin; Aphitiria; Benesan; Benexane; Benhexachlor; Benzene hexachloride; BHC; BoreKil; Borer-Tox; Exagama; Gallogama; Gamaphex; gamma-BHC; Gamma-Col; gamma-HCH; Gammex; Gammexane; Gamasan; Gexane; Hexachlorocyclohexane; HCH; Isotox; Jacutin; Kwell; Lindafor; Lindagronox; Lindaterra; Lindatox; Lintox; Lorexane; New Kotol; Noviagam; Quellada; Steward; Streunex; Tri-6
Other names
Last updated	17/2/2010

Fate
Breakdown in soil and groundwater
Alpha-hexachlorocyclohexane (alpha-HCH) biodegradation and beta-hexachlorocyclohexane (beta-HCH) undergo abiotic degradation (dechlorination) by ultraviolet irradiation in the environment. Degradation of alpha-HCH produces delta-3,4,5,6-tetrachloro-hexene and pentachlorocyclohexene (respectively). This breakdown process is slower than in the case of lindane. Beta-HCH is the most persistent HCH isomer. The persistence of alpha-HCH and Beta-HCH in soil is determined by environmental factors such as the action of microorganisms, organic matter content, and volatilization from soils. No isomerization occurs from lindane to alpha-HCH. A small portion of the beta-HCH may isomerize to alpha-, gamma-, and delta-HCH.
Lindane is highly persistent in most soils, with a field half-life of approximately 15 months. When sprayed on the surface, the half-life was typically much shorter than when incorporated into the soil. It shows a low affinity for soil binding, and may be mobile in soils with especially low organic matter content or subject to high rainfall. It may pose a risk of groundwater contamination.
Breakdown in water
Lindane is very stable in both fresh and salt water environments, and is resistant to photodegradation. It will disappear from the water by secondary mechanisms such as adsorption on sediment, biological breakdown by microflora and fauna, and adsorption by fish through gills, skin, and food.

Toxicology
Acute toxicity: The mean lethal dose of technical HCH may be about 400 mg/kg when ingested by man (Gosselin, 1984). Inhalation of more than 400 µg/kg within 3 days may cause toxic effects.
Relevant animal data: Oral LD50 (Guinea pig) 1400 mg/kg LD50 (Rat) 100 mg/kg LD50 (Mouse) 59 mg/kg
Dermal LD50 (Rat) 900 mg/kg (Lewis, 1996)
Inhalation: LC50 (Rat) 690 mg/m3 (LOLI, 2000)
In rats, the acute toxicity of isomers of HCH decreases in the order gamma < alpha < delta < beta. However, the toxicity of repeated doses decreases in the order beta < alpha < gamma < delta.
Chronic effects:
The long-term toxicity of the different isomers is directly related to their adipose tissue storage and inversely related to their rate of metabolism (Hayes, 1991).
Significant decreases in total white blood cell counts and clotting time were reported in rats fed Vitamin A free diets containing technical HCH at a dose level of 50 mg/kg/day for 7 weeks (Joseph et al, 1992).
Carcinogenicity:
The International Agency for Research on Cancer (IARC) has evaluated hexachlorocyclohexanes. They are classified under Group 2B. Evidence for carcinogenicity to humans is inadequate and evidence for carcinogenicity to animals is sufficient. (IARC, 1984).
Several case reports indicate a relationship between exposure to HCH or lindane and the occurrence of aplastic anaemia. An increase in lung cancer mortality was observed in agricultural workers who had used hexachlorocyclohexane (unspecified) and a variety of other pesticides and herbicides. Data available are insufficient for any conclusion to be drawn.
Technical grade alpha and beta-HCH and gamma isomer (lindane) produced liver tumours in mice when administered orally; the technical grade also produced lymphoreticular neoplasms. In two studies in rats, an increased incidence of liver tumours was observed with the gamma isomer, and in one study in rats a few thyroid tumours were observed with the gamma isomer; other studies were considered to be inadequate. Technical grade HCH and the gamma isomer were cancer tested inadequately by skin application in mice. alpha-HCH enhanced the incidence of liver neoplasms induced in rats by N-nitrosodiethylamine (IARC, 1979; IARC, 1984).

Detection

Sampling

Methods

MRLs

Uses
HCH is a mixture of isomers of hexachlorocyclohexane. It was used to control leafhoppers and stem borers in lowland rice. Seed treatment were used to reduce wireworm damage in winter and spring sown cereals. Other uses include control of pests of cereals, sugar beets and oilseed rape.

HCH was subject to the PIC procedure in 1991.

Notes
Lindane (or hexachlorocyclohexane, HCH) has historically and widely been inappropriately referred to as "benzene hexachloride" or "BHC". This compound should not be confused with hexachlorobenzene, or HCB.

Bibliography
IPCS INCHEM Hexachlorocyclohexane (mixed isomers) http://www.inchem.org/documents/pims/chemical/pim257.htm
IPCS Environmental Health Criteria 123 alpha- and beta- hexachlorocyclohexanes (http://www.inchem.org/documents/ehc/ehc/ehc123.htm)

Mode of action
HCH isomers differ quantitatively and qualitatively in biological activity. The alpha and gamma HCH isomers are central nervous system stimulants causing violent epileptiform convulsions. The beta and delta isomers are mainly depressant (Gosselin, 1984; Lewis, 1999).
Chlorinated hydrocarbon insecticides act by altering the electrophysiological and associated enzymatic properties of nerve cell membranes, causing a change in the kinetics of Na+ and K+ ion flow through the membrane. Disturbances of calcium transport or Ca2+ - ATPase activity may also be involved, as well as phosphokinase activities (Hayes 1991). A major site of action of HCH and its isomers appear to be at the synapse in the rat (Hayes and Laws, 1991).
It seems that HCH and its isomers could act on the GABA receptor-linked chloride channel although the mechanism is highly complex and is still not completely elucidated (Hayes & Laws, 1991). In the nervous system, gamma-HCH is thought to interfere with the gamma-aminobutyric acid (GABA) system by interacting with the GABA-A receptor-chloride channel complex at the picrotoxin binding site. Thus the seizures caused by gamma-HCH can be antagonized by GABA-A mimetics. Other suggestive data concerning mechanisms by which HCH causes neurological effects in animals includes enhanced synaptic activity, altered GABA functional activity, and inhibition of Na+ -K+-ATPase. (ATSDR, 1994, Ratra et. al, 2001).
In the liver, gamma-HCH is thought to act by interfering with hepatic oxidative capacity and glutathione metabolism. Another possible mechanism for hepatic toxicity is the increased lipid metabolism. Inhibition of Mg2+ATPase activity has been observed in rat liver tissue, suggesting an ATPase enzyme sensitivity to the action of gamma-HCH. The researchers suggested that some toxic effects appearing in mammals as a result of gamma-HCH exposure may arise from its influence on this ATPase activity. (ATSDR, 1994).

Ecotoxicology
Effects on birds
Lindane is moderately to practically nontoxic to bird species, with a reported LD50 of more than 2000 mg/kg in the mallard duck. The 5-day dietary LC50 of lindane in Japanese quail is 490 ppm. The LC50 values of lindane in pheasant and bobwhite quail are 561 ppm and 882 ppm, respectively. Egg-shell thinning and reduced egg production has occurred in birds exposed to lindane. Lindane can be stored in the fat of birds. Residues can also find their way into egg yolks at measurable concentrations for 32 days after dosing.
Effects on aquatic organisms
Lindane is highly to very highly toxic to fish and aquatic invertebrate species. Reported 96-hour LC50 values range from 1.7 to 90 ug/L in trout (rainbow, brown, and lake), coho salmon, carp, fathead minnow, bluegill, largemouth bass, and yellow perch. Water hardness did not seem to alter the toxicity to fish, but increased temperature caused increased toxicity for some species and decreased toxicity for others. Reported 96-hour LC50 values in aquatic invertebrates were: in Daphnia, 460 ug/L; in scuds, 10-88 ug/L; and in Pteronarcys (stone flies), 4.5 ug/L. The bioconcentration factor for the compound is 1400 times ambient water concentrations, indicating significant bioaccumulation.
Effects on other organisms
Lindane is highly toxic to bees.

Plant metabolism & residues
HCH residues may occur in plants from not only direct application, but through water and vapour phase transfers. Residues are more persistent when plants are rich in lipid content. Crops like cauliflower and spinach will accumulate less residue than crops like carrots. The metabolism in plants is not well understood. Carrots are estimated to metabolize lindane with a half-life of just over 10 weeks (based on plant uptake) whereas it may have a half-life in lettuce of only 3 to 4 days.

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