Crude oil PAH constitution, degradation pathway and associated bioremediation microflora: An overview

Crude oil, a dark sticky liquid, is a complex mixture of varying molecular weight which is used for the preparation of petroleum products. Crude oil contains more than 30 parent polyaromatic hydrocarbons (PAHs). The U.S.EPA has designated 16 PAH compounds (naphthalene, acenaphthylene, acenaphthene, fluorene, phenenthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[a, h]anthracene, benzo[g, h, i]perylene, and indeno[1,2,3-cd]pyrene) as priority pollutants. PAHs are one of the most widespread organic pollutants and potentially health hazard. Besides other environmental components, they are also found in foods (cereals, oils, fats, vegetables, cooked meat). They are carcinogenic, mutagenic, and teratogenic. Thus, key focus is to eliminate these hazardous pollutants from the environment. The present review highlights the presence of various PAHs in the crude oil, key metabolic pathway for the degradation and the associated microbial degraders. The current approach to bioremediation uses various bacterial and fungal genera under aerobic or anaerobic conditions to directly target the specific PAH. However, there is need to explore newer approaches to design an efficient, effective and ecofriendly bioremediation tool. The dearomatization of crude oil might be a useful comprehensive approach and one shot solution to multiple PAH population.