Abstract
Petroleum hydrocarbon contamination is an environmental concern. Of the various hydrocarbons, polycyclic aromatic hydrocarbons (PAHs) are a major worry because they cause many health problems including cancer and the inflammation of tissue in humans. So, it is necessary to remediate contaminated sites. Sites with diffuse low to medium level pollution can be remediated with the use of biological techniques, such as phytoremediation. Phytoremediation is a low input biotechnology approach: it relies on the knowledge that natural attenuation by biodegradation and physicochemical mechanisms will decrease the pollutant concentration. Limited PAH uptake by plant roots also takes place. This is influenced by both the organic content of the soil in which the plants are grown and the plant root lipid contents. Plant responses to growth in soils contaminated with petroleum hydrocarbons need to be taken into account, if plants are to be used to clean up petroleum hydrocarbon contamination. Different plant species show various stress responses and adaptations to survive the stress conditions caused by hydrocarbonpollution. The responses of plants also vary with the type and amount of the contaminant as well as duration of exposure. Phytoremediation can be feasible if appropriate plant species are selected. They must show sufficient morphological plasticity to survive stress situations induced by hydrocarbon-contamination, have an extended rhizosphere and appropriate root exudate patterns, positively influence the growth of hydrocarbon-degrading microorganisms in contaminated soil, and should also limit the uptake of toxic molecules through various adaptations to the root ultrastructure and cell wall components. Plants chosen should also be native to the area to be remediated so that they will be tolerant to the soil and environmental conditions. Additionally, plants that require little attention are preferable because cost is an important factor. Plants with deep, fibrous roots and fast growth, such as grasses, are generally considered useful in phytoremediation.
Highlights
Petroleum hydrocarbons are prevalent in our environment due to industrial activities such as gasification and liquefaction of fossil fuels, and accidental oil spills, with at least 350,000 contaminated sites in Western Europe [1]
The main objective of this review is to identify the shortcomings with regard to the use of plants in remediation of hydrocarbon-polluted sites and finding solutions to overcome these limitations
It has been demonstrated that when grown in hydrocarbon-contaminated soil, plants increase the catabolic potential of rhizospheric soil by altering the composition of the indigenous microbial communities and proliferating the polycyclic aromatic hydrocarbons (PAHs)-degrading microorganisms within the dynamic region of the rhizosphere [10]
Summary
Petroleum hydrocarbons are prevalent in our environment due to industrial activities such as gasification and liquefaction of fossil fuels (gaswork sites), and accidental oil spills, with at least 350,000 contaminated sites in Western Europe [1]. Engineering techniques based on physical, chemical and thermal processes have been used for remediation purposes, but these methods are very expensive and not always effective [7,8] Another option is landfilling of contaminated soil, but this is expensive and becomes an increasingly greater problem as landfill sites are in short supply and apart from this, it is not deemed a sustainable approach to solving the problem. The presence of petroleum hydrocarbons in soil poses many challenges to plant root growth such as water stress, chemical toxicity, mechanical impedance and nutrient deficiency as reported in many studies [11,12,13,14]. Little is known about the bioavailability of bound metabolites, but there may be a need to prevent the movement of PAHs into wildlife food chains [17]
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