Bioremediation of a pesticides mixture by a Streptomyces consortium in different systems

Abstract

Pesticides are usually applied simultaneously or one after another for crop protection, and their application often leads to a combined contamination of soils by these residues. Furthermore, it is important to characterize these mixtures due to their persistence, composition and geographical distribution. Organochlorine pesticides are persistent pollutants, and currently are still ubiquitous in the environment. The bioremediation offers the possibility to remove these toxic pollutants by using biological activity and the use of actinobacteria consortia is an attractive approach because of their ability to degrade pesticides and to increase the metabolic pathways to achieve it. The aim of this work was to study the ability of an actinobacteria consortium to remove an organochlorine pesticides mixture (lindane, chlordane and methoxychlor) under control laboratory conditions, in slurry and soil systems. The consortium Streptomyces sp. A2, A5, A11 and M7, previously selected for its ability to remove lindane, were pre-cultivated 72h as pure cultures in trypticase soy broth. Then these strains were inoculated as a defined consortium (2 g Kg-1 of soil or slurry), in sterile and non-sterile soil and in sterile slurry systems, and incubated for 16 days at 30 °C. The soil used was classified as silty clay loam. All tests were carried out in presence of the organoclorine pesticides mixture (1.66 mg Kg-1 each one). Respectively controls were carried out. Residual pesticides concentrations were measured by gas chromatography. The effect of the kind of system used for the mixture removal was analyzed by the main effect plot. The removal of the mixture was different for each pesticide and among the different systems. In the case of sterile soil the removal percentages were 38.9% for methoxychlor, 31.2% for lindane and 22.5% for chlordane. In non-sterile soil the removal percentages were 21% and 25.4% for methoxychlor and lindane. For the slurry system the removal percentages were 10.2% and 35.9% for methoxychlor and lindane respectively. Chlordane removal was no detected in both systems. The main effect plots analysis showed that the kind of system has a significant effect on the removal of methoxychlor and chlordane, showing statistically significant differences (P <0.05) in the different matrix; however this is not true for the case of lindane (P > 0.05). The type of systems used in the bioremediation process has a significant effect on the removal of the organochlorine pesticides mixture. The actinobacteria consortium has the ability to remove organoclorine pesticides in soil and slurry systems and could be a promising tool for ex-situ or in-situ bioremediation of this toxic compounds mixture.