BENZENE HEXACHLORIDE

(BHC) any of several isomeric compounds (i.e., of the same composition but different structures) formed by the reaction of chlorine with benzene in the presence of light; one of these isomers is an insecticide called Lindane, or Gammexane. Benzene hexachloride was first prepared in 1825; the insecticidal properties were identified in 1944 with the g-isomer, which is about 1,000 times more toxic than any of the other isomers formed in the reaction. The structural differences among these individuals are in the orientations of the chlorine atoms with respect to the ring of carbon atoms. The chemical addition of chlorine to benzene produces a mixture containing at least six of the eight possible isomers of BHC; the g-isomer, which makes up 2025 percent of this mixture, is more soluble than the other isomers in certain solvents and can therefore be extracted in concentrated form. More volatile than DDT, BHC has a faster but less protracted action upon insects. Its use had declined by the 1960s because of competition from other insecticides and its effects on fishes, which are killed by concentrations as low as one part per million in water.