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Bioremediation for Sustainable Environmental Cleanup

1.5 Different types of Pollutants in the Environment and their

Bioremediation

Many organic pollutants, such as polychlorinated biphenyls (PCBs), Polycyclic Aromatic

Hydrocarbons (PAHs), pesticides, oil spills and dyes have been found to be toxic in the environment.

They can be detrimental to other species and human health due to their large-scale manufacturing

and use, toxicity, bioaccumulation and persistence in the environment (Figure 1.2). Inorganic

pollution by Heavy Metal (HM) is less visible and direct than other types of pollutants, but its effects

on marine ecosystems and humans are concentrated and very extensive (Necibi and Mzoughi 2017).

Figure 1.2. Different types of pollutants in the environment.

1.5.1 Bioremediation of Polycyclic Aromatic Hydrocarbons (PAHs)

Polycyclic Aromatic Hydrocarbons (PAHs) consist of a large and diverse class of organic compounds

consisting of fused aromatic rings in various forms. They are colorless, white or pale yellow-green

solids, have low water solubility and vapor pressure, and a high octanol/water partitioning coefficient

and low microbial bioavailability which are produced as a result of incomplete combustion of organic

compounds (wood, coal, oil and gasoline). US Environmental Protection Agency (USEPA) has

identified a collection of 16 different PAHs as priority pollutants. PAHs are used to make pesticides,

dyes, plastics and medicines. PAHs are widely distributed in environments which are toxic and

persistent for a long period (Cerniglia 1984, Wang 2009). Due to their mutagenic and carcinogenic

toxicity, PAH’s outcome in nature is of major environmental concern.

Bioremediation is a natural process that recovers PAH-polluted environments by converting

hazardous PAHs into non-toxic products. The number and kind of microorganisms present, as well

as the nature and chemical structure of the chemical component being degraded, all influence PAH

breakdown. Some of the microorganisms that are used in the degradation of PAHs are given in

Table 1.1. During biodegradation, microorganisms either convert or mineralize PAHs and other

xenobiotic chemicals to CO2 and H2O. The rate of biodegradation is influenced by factors like

pH, temperature, oxygen, microbial population, degree of acclimation, nutrient accessibility, the

chemical structure of the substance, cellular transport characteristics and chemical partitioning

in growing media (Haritash and Kaushik 2009). Benzo[a]pyrene (BaP) is a PAH that consists

of five fused benzene rings and is one of the most potent carcinogenic PAHs. In mammals and