Degradation and detoxification of hexachlorocyclohexane isomers by Pseudomonas aeruginosa ITRC-5

Technical-hexachlorocyclohexane (t-HCH) consists of four major isomers i.e. α-, β-, γ- and δ-HCH. The insecticidal γ-HCH is separated from it by solvent extraction, and the remaining 'muck' is discarded. HCH-isomers from the 'muck' can potentially enter the environment and impart toxicity. For its biological treatment, biodegradation of HCH-isomers by the isolated bacterium Pseudomonas aeruginosa ITRC-5 was evaluated. In its presence, from 1.7 mM 'muck', >98% α- and >80% β-, γ- and δ-HCH were degraded after 24 days of incubation. The degradation was optimal at 1.7 mM input concentration of 'muck', pH 9.0, and temperature 20-30°C. Under these conditions, from 2 g 'muck', >90% Σ-HCH, i.e. the sum of α, β, γ, and δ-HCH, were degraded in a 1.0-liter batch-reactor after incubation for 4 cycles of 5 weeks each. The degradation was accompanied with 90% reduction in the toxicity of 'muck' to the aquatic test organism Daphnia magna. The isolated bacterium ITRC-5 can therefore be used for the degradation and detoxification of HCH-wastes, prior to their disposal.