contaminate the food chain as a result of bioaccumulation, affecting even humans far
from the site of contamination (Ite and Ibok 2019).
Petroleum hydrocarbons in the environment undergo “weathering.” This interaction with the environment may be physical (such as dispersion), physicochemical
(such as evaporation, dissolution, and sorption), as well as chemical (photo oxidation, auto-oxidation) and biological (such as natural catabolism of polluting hydrocarbons by plants and microbes) and has been reviewed recently (Truskewycz et al.
2019).
Volatilization—The lighter aromatics (BTEX) and other simple ringed aromatics
are generally volatile and therefore frequently separate from the more complex
fractions, enhanced by increasing environmental temperatures. Alkanes C8 are
completely evaporated while C9–C12 are partially evaporated in experimental flasks
containing 1% crude oil in aqueous medium (Perera et al. pers. comm.)
Dissolution—Solubility in aqueous environment decreases as aliphatic chain
length or number of rings in aromatics increase. However, the presence of polar,
non-hydrocarbon components will increase the solubility.
Sorption—Sorption of petroleum hydrocarbon (PH) fractions on to oil particles
may occur by various mechanisms such as diffusion into nanopores or bond formation with organic matter in the soil. Solubility of the hydrocarbon fractions also
affects sorption to soil (Truskewycz et al. 2019).
Dispersion—Oil spills in water spread and tends to form a viscous slick, cutting
off oxygen and nutrients to the aquatic microbes and animals, thus affecting the
ecosystem. Large masses of oil are generally not easily degraded by microbes due to
restricted accessibility, owing to the hydrophobic nature of the oil. However, oil in
water may also form emulsions as a result of wind and waves and due to microbial
secretion of biosurfactants. This is an important process as it increases the accessible
surface area, enhancing uptake of the hydrocarbons by microbes.
Unlike aquatic oil spills where the oil is dispersed horizontally on the surface of
the water, in terrestrial oil spills, the movement of oil is vertical into the soil. Such
infiltration hinders the evaporation of volatile hydrocarbons, which can be toxic to
microorganisms (Leahy and Colwell 1990).
11.4 Microbial Biodegradation of Petroleum Hydrocarbons
Both physical and chemical methods for remediation of petroleum hydrocarbon
pollution, particularly oil spills are used. However, they have limitations, both
cost-wise as well as toxicity—particularly with the use of chemical emulsifiers.
Bioremediation thus provides an alternative “green” mechanism for tackling this
issue.
Natural biodegradation of petroleum hydrocarbons is carried out primarily by
bacteria and fungi. Numerous species and strains that demonstrate varying capacities
for utilization of hydrocarbons have been identified and continue to be identified.
Microbes may use these for the production of energy or biomass. Biodegradation is
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from the site of contamination (Ite and Ibok 2019).
Petroleum hydrocarbons in the environment undergo “weathering.” This interaction with the environment may be physical (such as dispersion), physicochemical
(such as evaporation, dissolution, and sorption), as well as chemical (photo oxidation, auto-oxidation) and biological (such as natural catabolism of polluting hydrocarbons by plants and microbes) and has been reviewed recently (Truskewycz et al.
2019).
Volatilization—The lighter aromatics (BTEX) and other simple ringed aromatics
are generally volatile and therefore frequently separate from the more complex
fractions, enhanced by increasing environmental temperatures. Alkanes C8 are
completely evaporated while C9–C12 are partially evaporated in experimental flasks
containing 1% crude oil in aqueous medium (Perera et al. pers. comm.)
Dissolution—Solubility in aqueous environment decreases as aliphatic chain
length or number of rings in aromatics increase. However, the presence of polar,
non-hydrocarbon components will increase the solubility.
Sorption—Sorption of petroleum hydrocarbon (PH) fractions on to oil particles
may occur by various mechanisms such as diffusion into nanopores or bond formation with organic matter in the soil. Solubility of the hydrocarbon fractions also
affects sorption to soil (Truskewycz et al. 2019).
Dispersion—Oil spills in water spread and tends to form a viscous slick, cutting
off oxygen and nutrients to the aquatic microbes and animals, thus affecting the
ecosystem. Large masses of oil are generally not easily degraded by microbes due to
restricted accessibility, owing to the hydrophobic nature of the oil. However, oil in
water may also form emulsions as a result of wind and waves and due to microbial
secretion of biosurfactants. This is an important process as it increases the accessible
surface area, enhancing uptake of the hydrocarbons by microbes.
Unlike aquatic oil spills where the oil is dispersed horizontally on the surface of
the water, in terrestrial oil spills, the movement of oil is vertical into the soil. Such
infiltration hinders the evaporation of volatile hydrocarbons, which can be toxic to
microorganisms (Leahy and Colwell 1990).
11.4 Microbial Biodegradation of Petroleum Hydrocarbons
Both physical and chemical methods for remediation of petroleum hydrocarbon
pollution, particularly oil spills are used. However, they have limitations, both
cost-wise as well as toxicity—particularly with the use of chemical emulsifiers.
Bioremediation thus provides an alternative “green” mechanism for tackling this
issue.
Natural biodegradation of petroleum hydrocarbons is carried out primarily by
bacteria and fungi. Numerous species and strains that demonstrate varying capacities
for utilization of hydrocarbons have been identified and continue to be identified.
Microbes may use these for the production of energy or biomass. Biodegradation is
268
S. Jayasena and M. Perera