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Phytoremediation of Organics
to denote cannabis that contains 0.3% or less THC content by dry weight. In
recent years, C. sativa (hemp) has been studied as a bioenergy crop as it grows
well on marginal lands and has the capacity to produce high volumes of biomass (e.g., Kumar et al., 2017). Asquer et al. (2019) reported biogas production
using hemp straw was comparable to most other energy crops. This annual
crop can be grown in climates where winters are too cold, making successful
maintenance of perennial M. × giganteus unreliable.
C. sativa (hemp) was studied in the remediation of two PAHs, benzo[α]
pyrene and chrysene (Campbell et al., 2002). The authors carried out experiments over 45 days in soil spiked with benzo[α]pyrene and chrysene at 25, 50,
and 75 µg g −1 and found reductions in contaminants in all cases. They additionally found that the mass and growth of Cannabis plants to increase at
all three concentrations leading them to suggest that metabolites of the two
PAHs studied may have stimulated the growth of hemp.
Research to improve PHC phytoremediation processes is continuing, and
there has been significant progress in the last 6 years. In 2019, Tang reviewed
studies on the biodegradation of TPHs (Tang, 2019). Ren et al. (2017) discuss in
detail some of the complexity in remediating PHC because the larger aromatics are tightly sorbed to organic matter, and minerals of soil giving them very
low accessibility to organisms. The sorption/desorption processes are challenging to predict for the vast number of constituents in PHC mixtures such
as crude oil, and residuals from refining. Laboratory experimentation may
not align well with effects observed in the field with “aged” materials because
of the very slow rates of sorption/desorption observed in real soil structures,
particularly in micropores of mineral or biochar fractions (Ren et al., 2017).
3.2.2 Remediation of Explosives
Large areas of land are contaminated with explosives or their residues.
Landmines, unexploded ordnance (UXO), and explosive compounds in soil
are important issues in many countries. Globally more than 80 countries
have land contaminated by explosives (Robledo et al., 2009), including more
than 100 million antipersonnel mines (Hemapala, 2017). In Europe, there are
UXOs from World War 2 that still need to be removed. For example, Ukraine
has ~7000 km 2 of land with UXOs, and this resulted in 2078 casualties from
2014 to 2017 (Dathan, 2020). Due to military conflicts in Asia and the Middle
East, more than 150 million ha have explosives present as UXOs and/or as
contaminants in soil (Via, 2020). In the USA, there are more than 2000 sites
with soil contamination due to explosives (Via, 2020). Contaminated soil
locations include sites for the manufacture of explosives, assembly plants
where explosives are, or were, packed into shells, and sites where explosives
have been stored.
There has been good progress in developing robotic methods to identify and
remove landmines, one of the principal forms of UXO (Hemapala, 2017; Robledo
et al., 2009). Kalderis et al. (2011) provided a comprehensive review of research
Phytoremediation of Organics
to denote cannabis that contains 0.3% or less THC content by dry weight. In
recent years, C. sativa (hemp) has been studied as a bioenergy crop as it grows
well on marginal lands and has the capacity to produce high volumes of biomass (e.g., Kumar et al., 2017). Asquer et al. (2019) reported biogas production
using hemp straw was comparable to most other energy crops. This annual
crop can be grown in climates where winters are too cold, making successful
maintenance of perennial M. × giganteus unreliable.
C. sativa (hemp) was studied in the remediation of two PAHs, benzo[α]
pyrene and chrysene (Campbell et al., 2002). The authors carried out experiments over 45 days in soil spiked with benzo[α]pyrene and chrysene at 25, 50,
and 75 µg g −1 and found reductions in contaminants in all cases. They additionally found that the mass and growth of Cannabis plants to increase at
all three concentrations leading them to suggest that metabolites of the two
PAHs studied may have stimulated the growth of hemp.
Research to improve PHC phytoremediation processes is continuing, and
there has been significant progress in the last 6 years. In 2019, Tang reviewed
studies on the biodegradation of TPHs (Tang, 2019). Ren et al. (2017) discuss in
detail some of the complexity in remediating PHC because the larger aromatics are tightly sorbed to organic matter, and minerals of soil giving them very
low accessibility to organisms. The sorption/desorption processes are challenging to predict for the vast number of constituents in PHC mixtures such
as crude oil, and residuals from refining. Laboratory experimentation may
not align well with effects observed in the field with “aged” materials because
of the very slow rates of sorption/desorption observed in real soil structures,
particularly in micropores of mineral or biochar fractions (Ren et al., 2017).
3.2.2 Remediation of Explosives
Large areas of land are contaminated with explosives or their residues.
Landmines, unexploded ordnance (UXO), and explosive compounds in soil
are important issues in many countries. Globally more than 80 countries
have land contaminated by explosives (Robledo et al., 2009), including more
than 100 million antipersonnel mines (Hemapala, 2017). In Europe, there are
UXOs from World War 2 that still need to be removed. For example, Ukraine
has ~7000 km 2 of land with UXOs, and this resulted in 2078 casualties from
2014 to 2017 (Dathan, 2020). Due to military conflicts in Asia and the Middle
East, more than 150 million ha have explosives present as UXOs and/or as
contaminants in soil (Via, 2020). In the USA, there are more than 2000 sites
with soil contamination due to explosives (Via, 2020). Contaminated soil
locations include sites for the manufacture of explosives, assembly plants
where explosives are, or were, packed into shells, and sites where explosives
have been stored.
There has been good progress in developing robotic methods to identify and
remove landmines, one of the principal forms of UXO (Hemapala, 2017; Robledo
et al., 2009). Kalderis et al. (2011) provided a comprehensive review of research