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Phytoremediation of Organics
(Chan-Quijano et al., 2020; Fiorenza et al., 2000; McCutcheon & Schnoor, 2003;
Tang, 2019). Locations with petroleum and natural gas production operations, pipelines, refineries, storage sites, gasoline stations, vehicle maintenance shops, and parking lots are some of the places where hydrocarbons
are routinely found in soils. Leaking underground storage tanks have been
found at many locations including service stations, buildings where heating
oil is used, and on farms where fuel for vehicles is stored.
Most PHCs have very low solubility in water and often the separation of
a two-phase mixture of oil and water allows some valuable recovery of the
oil phase when a “pump and treatment” system is used to recover product.
Gasoline, kerosene, and diesel fractions are liquid at ambient temperature;
however, some petroleum compounds are solids under ambient temperatures. When microorganisms feed on petroleum compounds, they may
be found at oil phase surfaces. Polycyclic aromatic hydrocarbons (PAHs)
are natural petrogenic materials although they can also be products of
incomplete combustion of hydrocarbon fuels. Often, they are the most
hazardous components of fuel spills because many PAHs are classified as
carcinogenic (Cachada et al., 2016; Henner et al., 1997). Loss from soil to
atmosphere is an important route of dispersal for petroleum fractions with
reasonable vapor pressures, and fairly low water solubility. For instance,
gasoline, kerosene, and jet fuel will dissipate from soils relatively quickly
if the soil is porous. Plants which remove water from soils often facilitate
diffusive loss of contaminants trapped beneath the water table by lowering the water table.
Petroleum compounds provide carbon and energy, but nitrogen (N) and
phosphorus (P) are also needed to support growth of both the plants and
microorganisms. Because N and P are needed, fertilizer is often added as
part of the phytoremediation plan. Organic fertilizers such as manure add
to microbial diversity, which is often beneficial (Chan-Quijano et al., 2020).
Many different bacteria participate in the biodegradation of PHCs, and some
authors have generated lists of different species that have been isolated
(e.g., Chan-Quijano et al., 2020). Research on the biodegradation of hydrocarbons was ongoing when phytoremediation research to address PHCcontaminated soil began in the 1990s.
Several of the early field studies in the 1990s were carried out by Banks
and coworkers (Fiorenza et al., 2000). The results from several field studies
are included in McCutcheon & Schnoor (2003). Grasses have been among
the more beneficial plants in the research on biodegradation of petroleum
compounds (Chapter 11 by Hutchinson, Banks and Schwab in McCutcheon
& Schnoor (2003)). Although many forage grasses have only very limited use
in industrial biomass production, the early research demonstrated beneficial
effects of plants in field-scale PHC degradation. Plant roots provide an active
environment, which contains compounds and organisms that are beneficial
for microbial degradation processes. Often, they enhance soil aeration by