49
Phytoremediation of Organics
Recalcitrance of PAHs and PCBs varies widely so that success with a few
congeners or homologs is no guarantee of success with all forms. The earliest remediation study with Miscanthus that we can identify was by Wilke
and Metz (1993). They analyzed a suite of six PCB congeners and six PAHs
from a long-term contaminated site in Germany, which also had high levels
of toxic metals including Cd and Zn relative to regulatory standards. The
contamination source was sewage sludge irrigation and the soil total organic
carbon was 6.7%. Growth of Miscanthus sinensis (M. sinensis) or Polygonum
sachalinense was less effective in the undiluted soil containing 72 mg kg −1
of Cd and 1800 mg kg −1 of Zn, >1600 µg kg −1 of PCBs and 3062 µg kg −1 of
PAHs than in a soil diluted with brown podzol. That soil had only 0.77%
of TOC and a pH 4.1. It is not known which element or compound was the
main contributor to growth inhibition. Depending on bioavailability, Zn
at 1800 mg kg −1 at the pH < 5 (pH 4.8 in undiluted soil) could be strongly
inhibitory. Over a range of dilutions giving 1×, 5×, 10×, 20× of the regulatory
limit of 1.5 mg kg −1 for Cd, both PCBs and PAHs were accumulated only
in roots, to a maximum of 975 µg kg −1 of PCBs and 2083 µg kg −1 of PAHs at
approximately 1:1 dilution of the contaminated soil (to 20 × 1.5 mg kg −1 of
Cd). Degradation products were not measured. Neither PCB nor PAH congeners were detected in stems and leaves in this pot study. No more recent
studies with PCBs have been reported.
Little is known of the tolerance or degradation capacity of Miscanthus for
POPs including chlorinated pesticides. One study was completed with the
insecticide chlordecone (trade name Kepone) by Liber et al. (2018). This persistent material with a half-life of ~30 years may be present in soils at levels
of >1 mg kg −1 . Using 14-C labeled material in a greenhouse study with dense
planting of 49 plants in 0.81 m 2 , accumulation above soil level (expressed as
mg kg −1 ) was observed only in roots of both M. × giganteus (5 mg kg −1 in roots,
0.17 mg kg −1 in rhizomes, 0.15 mg kg −1 in shoots) and M. sinensis (15 mg kg −1 in
roots, 0.5 mg kg −1 in rhizome, 0.3 mg kg −1 in shoots) during the second growing period of 2 and then 6 months. In a second experiment with M. sinensis
over two growth periods of 10 months each, accumulation into aboveground
tissues from 8 mg kg −1 in soil was less in the second period, to only about
2 mg kg −1 , presumably because of increased organic matter in the root zone.
Calculated harvestable plant contamination under hypothetical field conditions (1 mg kg −1 soil) indicated about 1 g ha −1 year −1 would be removed by
harvesting Miscanthus. With a contaminant load of perhaps 2 kg ha −1 (~1 mg
kg −1 , ~20 cm depth). This is a trivial amount for recovery, though important
for appropriate use of the harvested crop.
A study by Nurzhanova et al. (2017) presented the application of M. sinensis
to phytoremediation of soil heavily polluted by DDT and its metabolites. The
aged contaminated soil was sampled around a destroyed storehouse for chlorinated pesticides in Kazakhstan, and chemical analysis showed large pesticide concentrations in the soil. For example, DDT concentrations in the soil
exceeded the maximum permissible concentration (MPC) limit value by 62
Phytoremediation of Organics
Recalcitrance of PAHs and PCBs varies widely so that success with a few
congeners or homologs is no guarantee of success with all forms. The earliest remediation study with Miscanthus that we can identify was by Wilke
and Metz (1993). They analyzed a suite of six PCB congeners and six PAHs
from a long-term contaminated site in Germany, which also had high levels
of toxic metals including Cd and Zn relative to regulatory standards. The
contamination source was sewage sludge irrigation and the soil total organic
carbon was 6.7%. Growth of Miscanthus sinensis (M. sinensis) or Polygonum
sachalinense was less effective in the undiluted soil containing 72 mg kg −1
of Cd and 1800 mg kg −1 of Zn, >1600 µg kg −1 of PCBs and 3062 µg kg −1 of
PAHs than in a soil diluted with brown podzol. That soil had only 0.77%
of TOC and a pH 4.1. It is not known which element or compound was the
main contributor to growth inhibition. Depending on bioavailability, Zn
at 1800 mg kg −1 at the pH < 5 (pH 4.8 in undiluted soil) could be strongly
inhibitory. Over a range of dilutions giving 1×, 5×, 10×, 20× of the regulatory
limit of 1.5 mg kg −1 for Cd, both PCBs and PAHs were accumulated only
in roots, to a maximum of 975 µg kg −1 of PCBs and 2083 µg kg −1 of PAHs at
approximately 1:1 dilution of the contaminated soil (to 20 × 1.5 mg kg −1 of
Cd). Degradation products were not measured. Neither PCB nor PAH congeners were detected in stems and leaves in this pot study. No more recent
studies with PCBs have been reported.
Little is known of the tolerance or degradation capacity of Miscanthus for
POPs including chlorinated pesticides. One study was completed with the
insecticide chlordecone (trade name Kepone) by Liber et al. (2018). This persistent material with a half-life of ~30 years may be present in soils at levels
of >1 mg kg −1 . Using 14-C labeled material in a greenhouse study with dense
planting of 49 plants in 0.81 m 2 , accumulation above soil level (expressed as
mg kg −1 ) was observed only in roots of both M. × giganteus (5 mg kg −1 in roots,
0.17 mg kg −1 in rhizomes, 0.15 mg kg −1 in shoots) and M. sinensis (15 mg kg −1 in
roots, 0.5 mg kg −1 in rhizome, 0.3 mg kg −1 in shoots) during the second growing period of 2 and then 6 months. In a second experiment with M. sinensis
over two growth periods of 10 months each, accumulation into aboveground
tissues from 8 mg kg −1 in soil was less in the second period, to only about
2 mg kg −1 , presumably because of increased organic matter in the root zone.
Calculated harvestable plant contamination under hypothetical field conditions (1 mg kg −1 soil) indicated about 1 g ha −1 year −1 would be removed by
harvesting Miscanthus. With a contaminant load of perhaps 2 kg ha −1 (~1 mg
kg −1 , ~20 cm depth). This is a trivial amount for recovery, though important
for appropriate use of the harvested crop.
A study by Nurzhanova et al. (2017) presented the application of M. sinensis
to phytoremediation of soil heavily polluted by DDT and its metabolites. The
aged contaminated soil was sampled around a destroyed storehouse for chlorinated pesticides in Kazakhstan, and chemical analysis showed large pesticide concentrations in the soil. For example, DDT concentrations in the soil
exceeded the maximum permissible concentration (MPC) limit value by 62