Hexachlorocyclohexane (C6H6Cl6)

1,2,3,4,5,6-Hexachlorocyclohexane (HCH)

Other names

HCH, benzene hexachloride, 666

CAS Number



  • white or yellow powder
  • mouldy odour
  • mixture of alpha, beta, gamma and delta isomers: differing three-dimensional arrangement of the chorine atom on the cyclohexane ring
  • differ greatly in their biological activity
  • alpha-, beta- and gamma-HCH are persistent organic pollutants

Main sources

  • agriculture: insecticide

Thresholds for the reporting requirement of facilities in accordance with Annex 2 PRTRO

(Ordinance on the Register relating to Pollutant Release and the Transfer of Waste and of Pollutants in Waste Water)

  • Air               10 kg/year
  • Water          1 kg/year
  • Soil              1 kg/year


  • carcinogenic
  • toxic to humans, animals and aquatic organisms
  • alpha- and gamma-HCH: affect the central nervous system (effect of mixture depends on the exact composition)
  • beta- and delta-HCH: sedative (effect of mixture depends on the exact composition)
  • bioaccumulation
  • has a long half-life, very persistent in the environment


  • all isomers banned in Switzerland since 2005
  • included on the list of banned substances by the Stockholm Convention in May 2009

Further information

Last modification 16.12.2016

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