Biodegradation kinetics of dicofol by selected microorganisms

The capacity of some plant growth promoters (seven species of bacteria namely, Azospirillium barasilense, Azotobacter chroococcum, Klebsilense pneumoneae, Pseudomonas cepacia, Bacillus subtilis, Pseudomonas fluorescens and Bacillus polymyxa) and some control agents for plant pathogens (two species of fungi namely, Trichoderma viride and Trichoderma harzianum) to degrade dicofol pesticide (DCF) in liquid culture media was investigated. The recovered amount of DCF was extracted based on the solid phase extraction (SPE) with methylene chloride and then analyzed by HPLC. Contrary to published reports, no intermediate or final degradation metabolites of DCF could be observed. About 26-33% of DCF degradation was observed after 3 days of incubation with the tested bacteria which increased to 61-80%, 74-85%, 77-87% and 75-94% after 7, 14, 21 and 28 days of incubation, respectively. On the other hand, the tested fungi removed roughly 35% of available DCF within the first three days of incubation which increased to 84-87%, 89-95%, 91-95% and 92-96% after 7, 14, 21 and 28 days of incubation, respectively. A biphasic model was assumed to explore the disappearance of DCF from media enriched with either bacteria or fungi, where the rate of disappearance in the first phase was faster than the second. This is clearly reflected in the half-life (t(1/2)) for the first and second phases, where the t1/2 values of DCF ranged from 2.82-4.42 to 19.32-29.73 days, respectively. The results have implications for the development of a bioremediation strategy. (C) 2008 Elsevier Inc. All rights reserved.