Bioremediation of Hexachlorocyclohexane Contaminated Soil: Field Trials

Hexachlorocyclohexane or the abbreviation HCH is identified as a monocyclic chlorinated hydrocarbon. HCH was discovered in 1825by Faraday, who just had discovered benzene. By reacting benzene with chlorine in bright sunlight, formation of HCH was observed. Neither Faraday nor the Dutch chemist Van der Linden, who in 1912 isolated the pure -isomer from a HCH mixture, realized the insecticidal potential of the compounds they produced (Amadori, 1993). The insecticidal properties of HCH were however first mentioned by Bender in a patent paper. HCH was first patented in the 1940s.. Dupire conducted detailed investigations on the insecticidal properties in 1940, and HCH was first used to combat the Colorado beetle (Stoffbericht, 1993). In 1942 Slade proved that -HCH was the sole carrier of the insecticidal properties of technical HCH (Stoffbericht, 1993). HCH production started commercially since 1947 in Germany. The common name of Hexachlorocyclohexane is “benzene hexachloride”, which is incorrect according to the IUPAC rules (Galvan, 1999). Nevertheless it is still widely used, especially in the form of its abbreviation “BHC” Technical HCH consists mainly of a mixture of various stereo-isomers, which are designated by Greek letters. Only one of these stereoisomers, -HCH, is the carrier of the insecticidal properties, while the other isomers are sometimes collectively referred to as “inactive isomers”. The raw product from the chlorination of benzene contains about 14% -HCH and 86 % of inactive isomers, i.e. 65-70% -, 7-10% ┚-,, 14-15% -, approximately 7% ├-,, 1-2% ┝HCH, and 1-2% other components. Therefore, in the production of one ton of technical HCH, 140 kg is -HCH and 860 kg is “inactive isomers”. The latter is potentially waste and predestined for disposal. It is possible to extract and purify the active -HCH. If the purity is 99.0% or more it may be called “Lindane”, which is an accepted common name for this substance. Lindane is also called -HCH, or BHC and by FAO BHC (technical grade). Technical grade HCH and fortified HCH (FHCH) containing a varying mixture of at least 5 isomers, with a minimum of 40% -isomer was available commercially. HCH is no longer produced in USA and few other European countries and cannot be sold for domestic use by EPA regulation as well as many other countries (FCH, 1984). However, in some developing countries HCH especially -isomer continues to be used because of economic purposes and also in public health programmes. Thus Technical grade HCH continues to be produced and