| The presence of toxic organic chemicals in groundwater present a direct hazard to human health and to the environment. Examples of such pollutants are pyridine and its alkyl derivatives. These chemicals are found in groundwater as a consequence of industrial activities such as synthetic fuel production and chemical manufacturing. The acute toxicity of these compounds, their teratogenic properties, and their irritating odor require urgent remediation of pyridine-polluted groundwater.;Several treatments are commonly applied for the removal of organic pollutants from groundwater. They include physical, chemical, and biological treatments. In this investigation, the potential of a biological treatment was evaluated as a method for the clean-up of subsurface and groundwater contaminated with pyridine and its alkyl derivatives.;A pyridine-degrading denitrifying bacterium was isolated from a polluted aquifer. This bacterium, tentatively identified as an Alcaligenes sp., successfully mineralized pyridine in the subsurface sediment under anaerobic conditions. Moreover, the isolated bacterium was much more effective, when compared to chemical treatment (Fenton's reagent), in mineralizing pyridine in the groundwater and subsurface sediments.;In contrast to pyridine, alkylpyridines were not degraded under anaerobic conditions. However, under aerobic conditions indigenous bacteria were able to degrade all investigated contaminants. Thus, oxygen was the limiting factor for biodegradation of alkylpyridines. Degradation of these compounds also occurred in soil columns (containing subsurface sediment) leached with groundwater and operated under conditions similar to in situ conditions.;In addition, a mixed culture capable of degrading 14 different alkylpyridine isomers was selected from the sediment. This culture, grown in a chemostat, appeared to be very effective in removing pollutants from groundwater. Characterization of the different bacteria involved in the biodegradation of alkylpyridines showed that all strains were gram-negative rods. Pure cultures were isolated from the sediment on 2-,3-, 4-picoline and 2,4-, and 2,6-lutidine as a sole carbon source and each culture showed a distinct substrate specificity for alkylpyridines.;All the above findings clearly suggest that bioremediation of pyridine-contaminated groundwater is feasible. Bioremediation may be in situ using either inoculation of the subsurface with pyridine-degrading bacteria or stimulation of native microorganisms. |
