has role cyclodiene organochlorine insecticide fungicide hexachlorocyclohexane gamma-hexachlorocyclohexane 1,2,3,4,5,6-Hexachlorocyclohexane CHEBI:32888 antibacterial agent agrochemical rodenticide alicyclic compound pediculicide ectoparasiticide GABA-gated chloride channel antagonist persistent organic pollutant