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Abstract
The persistence and recalcitrance of high molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) are potential threats to health and the environment. They result mainly from incomplete combustion of fossil fuels and organic materials, and they tend to accumulate in terrestrial and aquatic ecosystems (particularly in soils, sediments, and water sources). Chronic exposure to HMW PAHs is associated with some of the most dreadful health outcomes, including lung and skin cancers and disorders of the respiratory and immune systems. The study therefore proposes microbial degradation as a promising bioremediation technique for HMW PAHs: pyrene, benzo[a]pyrene, chrysene, and fluoranthene. Aerobic degradations mediated by dioxygenase and dehydrogenase enzymes, as well as anaerobic pathways involving sulfate- and nitrate-reducing bacteria, are discussed. Factors that promote microbial degradation include pH, temperature, nutrient availability, and salinity. While all factors can be biostimulation and bioaugmentation, the study emphasizes these two as effective methods to enhance bioavailability and degradation efficiency. The results provide insightful information for further development of microbial techniques in remediation of HMW PAH-contaminated sites.
Highlights
Bacterial strains capable of degrading Polycyclic aromatic hydrocarbons (PAHs) are isolated from the PAH-contaminated sites, and their degradation ability on HMW PAHs and mixture of PAHs are being studied
Aerobic biodegradation of PAHs is common in most of the cases the PAH-contaminated sites are always under anoxic conditions so anaerobic biodegradation of PAHs is reviewed in this study
The utilization of microbial consortium in remediation and degradation of PAHs is promising in achieving high efficiency of PAH degradation with higher versatility of PAH metabolism by different bacteria in the consortium
Summary
Concerns are raised on the persistence of the PAH pollutants in the environment including soil, marine water and surface water, and air due to the genotoxicity and carcinogenicity of the PAH pollutants especially HMW PAH. Most of the PAHs are genotoxic compounds, which indicate that they cause genetic mutations due to interaction with cellular DNA. The persistence and the low bioavailability of the HMW PAH are contributed by the sorption of HMW PAH compounds to the soils and sediments, added that they are hydrophobes, leading to the lower biodegradability of HMW PAHs compared to LMW PAHs. There are several existing remediation methods of PAH-contaminated sites including incineration and in situ thermal desorption (ISTD), solvent extraction, and chemical oxidation [1, 2]. The bioremediation and degradation of PAHs by bacteria are often limited by various abiotic factors including temperature, pH, and nutrients, and these factors affecting PAH degradation are discussed in this study
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