Reductive dechlorination of hexachlorocyclohexane (HCH) isomers in soil under anaerobic conditions

The biological anaerobic reductive dechlorination of β- hexachlorocyclohexane under methanogenic conditions was tested in a number of contaminated soil samples from two locations in the Netherlands. Soils from a heavily polluted location showed rapid dechlorination of β- hexachlorocyclohexane to benzene and chlorobenzene with lactate as electron donor. Soils from an adjacent slightly polluted location did not show substantial dechlorination of β-hexachlorocyclohexane within 4 months. A heavily polluted sample was selected to optimise the dechlorination. All tested hexachlorocyclohexane isomers (α-, β-, γ-, and δ-), either added separately or simultaneously, were dechlorinated in this soil sample. The most rapid dechlorination was observed at a temperature of 30°C. Dechlorination of β-hexachlorocyclohexane was observed with acetate, propionate, lactate, methanol, H2, yeast extract and landfill leachate as electron donors. In a soil percolation column, packed with a selected heavily polluted soil sample, the presence of 10 mM sulphate in the influent led to simultaneous dechlorination of β-hexachlorocyclohexane and sulphate reduction. When the column was fed with 10 mM nitrate instead of sulphate, dechlorination ceased immediately. After omitting nitrate from the influent, dechlorination activity recovered in about 1 month. Also in a separate column, the addition of nitrate from the start of the experiment did not result in dechlorination of β-HCH. The significance of these experiments for in situ bioremediation of polluted soils is discussed. Chemicals / CAS: acetic acid, 127-08-2, 127-09-3, 64-19-7, 71-50-1; hexachlorocyclohexane, 608-73-1; hydrogen, 12385-13-6, 1333-74-0; methanol, 67-56-1; propionic acid, 72-03-7, 79-09-4; Chlorine, 7782-50-5; Lindane, 58-89-9; Soil Pollutants