Unraveling the Role of Microbes in Remediation of High Molecular Weight Polycyclic Aromatic Hydrocarbon Persistence in the Environment.

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.