Study of metabolites from the degradation of polycyclic aromatic hydrocarbons (PAHs) by bacterial consortium enriched from mangrove sediments

The PAH metabolites produced during degradation of fluorene, phenanthrene and pyrene by a bacterial consortium enriched from mangrove sediments were analyzed using the on-fiber silylation solid-phase microextraction (SPME) combining with gas chromatography–mass spectrometry (GC–MS) method. Seventeen metabolites at trace levels were identified in different PAH degradation cultures based on the full scan mass spectra. In fluorene degradation cultures, 1-, 2-, 3- and 9-hydroxyfluorene, fluorenone, and phthalic acid were detected. In phenanthrene and pyrene degradation cultures, various common metabolites such as phenanthrene and pyrene dihydrodiols, mono-hydroxy phenanthrene, dihydroxy pyrene, lactone and 4-hydroxyphenanthrene, methyl ester, and phthalic acid were found. The detection of various common and novel metabolites demonstrates that SPME combining with GC–MS is a quick and convenient method for identification as well as monitoring the real time changes of metabolite concentrations throughout the degradation processes. The knowledge of PAH metabolic pathways and kinetics within indigenous bacterial consortium enriched from mangrove sediments contributes to enhance the bioremediation efficiency of PAH in real environment.     

INFLUENCE OF SOIL ORGANIC MATTER ON THE LEACHING OF POLYCYCLIC AROMATIC HYDROCARBONS IN SOIL

Polycyclic aromatic hydrocarbons (PAHs) are one of the main classes of contaminants in the terrestrial environment. Aside from total organic carbon, the ratio among the different organic matter fractions [dissolved organic matter, fulvic acid (FA), humic acid (HA) and humin] can also affect the mobility of these hydrocarbons in soils. In this study the effect of the whole organic carbon pool has been compared with that of HA and FA on the translocation of four PAHs (biphenyl, fluorene, phenanthrene and pyrene) in soil columns. Oxidized and untreated soil columns with and without HA or FA, were prepared, spilled with hydrocarbons and leached with a 0.01 M CaCl₂ solution. The influence of HA and FA on PAH translocation was investigated through determinations of the PAH contents and total organic carbon (TOC) in the layers of the columns. All molecules were moved vertically by the percolating solutions, their concentrations decreasing with depths. The non-oxidized soil tended to retain more PAHs (96%) than the oxidized one (60%), confirming that organic matter plays an important role in controlling PAH leaching. The whole organic matter pool reduced the translocation of pollutants downward the profile. The addition of HA enhanced this behaviour, by increasing the PAH retention in the top layers (7.55 mg and 4.00 mg in the top two layers, respectively) while FA increased their mobility (only 2.30 and 2.90 mg of PAHs were found in the top layers) and favoured leaching. In fact, in the presence of HA alone, the higher amounts of PAHs retained at the surface and the good correlation (r²=0.936) between TOC and hydrocarbon distribution can be attributed to a parallel distribution of PAHs and HA, while in the presence of FA, the higher mobility of PAHs can be attributed to the high mobility of the humic material, as expected by its extensive hydrophilic characteristics.     

The efficacy of an oxidation pond in mineralizing some industrial waste products with special reference to fluorene degradation: a case study

The efficacy of the oxidation pond on the outskirts of the 10th of Ramadan, the main industrial city, in Egypt was examined. Samples of wastewater collected from the inlet and the outlet were screened for some priority pollutants. Acenaphthene and fluorene were the most frequently detected polycyclic aromatic hydrocarbons, while dimethyl phthalate was the most frequently detected phthalate ester. The spectrum of pollutants, their concentrations and frequencies were similar in the inlet and the outlet, indicating an inferior mineralization capability of the pond. Several degradative bacterial strains were isolated from the pond and grown on M56 minimal media supplemented with different pollutants as the carbon source. The efficacy of pure and mixed cultures to break down fluorene, the most frequently detected pollutant was examined. Fluorene degradation was fast in the first 10 days, then followed by a slow phase. Mixed culture had a higher rate of fluorene degradation in comparison to pure cultures. High performance liquid chromatography analysis of fluorene degradation showed three degradative metabolites. But GC/MS analysis detected one compound, identified as acetamide. The present work has indicated the poor efficacy of the pond. Lack of primary treatment of industrial effluent at factory level, coupled with shock loads of toxicants that may damage the microorganisms and their degradative capabilities are presumably main factors behind such inferior performance. Moreover, the type of pollutants discharged into the pond tend to fluctuate and change depending on the rate from the factories discharge and work shifts. Such irregular feeding of persistent pollutants may have led to a wash out of specialized strains of bacteria capable to degrade such persistent pollutants.