Populus × generosa · Atlas of Contaminated Sites

How it works

Mechanisms: phytodegradationhydraulic controlphytovolatilisationrhizodegradation
Native range: Cultivated hybrid

Contaminants

Contaminant	Evidence	What was shown
Chlorinated solvents (TCE, PCE, chloroform)	field	Three-year controlled field study in lined cells fed with contaminated water: during the growing seasons the trees removed over 99% of the added TCE; less than 9% was transpired to the air in the second and third years, and soil chloride rose by about the amount of TCE lost (Newman et al. 1999). Metabolites in tissues are trichloroethanol, trichloroacetic acid and dichloroacetic acid (Newman et al. 1997). At a Superfund site in California, poplars inoculated with a TCE-degrading endophytic bacterium: from 300 µg/L upstream to under 5 µg/L (Doty et al. 2017). Newman et al., Remediation of trichloroethylene in an artificial aquifer with trees: a controlled field study, Environ. Sci. Technol. 33:2257, osti.gov, 1999 Newman et al., Uptake and biotransformation of trichloroethylene by hybrid poplars, Environ. Sci. Technol. 31:1062, 1997 Doty et al., Enhanced degradation of TCE on a Superfund site using endophyte-assisted poplar tree phytoremediation, Environ. Sci. Technol. 51:10050, 2017
Polychlorinated biphenyls	field	An area near Taranto historically contaminated by PCBs and metals, planted with clone Monviso: at 420 days a significant decrease in PCB congeners and a reduction in all metals where poplars were present, none in unplanted soil; microbial activity raised up to 1 m from the trunk and 40 cm deep (Ancona et al. 2017). Ancona et al., Plant-assisted bioremediation of a historically PCB and heavy metal-contaminated area in Southern Italy, New Biotechnol. 38:65, 2017

Contaminant

Evidence

What was shown

Chlorinated solvents (TCE, PCE, chloroform)

field

Three-year controlled field study in lined cells fed with contaminated water: during the growing seasons the trees removed over 99% of the added TCE; less than 9% was transpired to the air in the second and third years, and soil chloride rose by about the amount of TCE lost (Newman et al. 1999). Metabolites in tissues are trichloroethanol, trichloroacetic acid and dichloroacetic acid (Newman et al. 1997). At a Superfund site in California, poplars inoculated with a TCE-degrading endophytic bacterium: from 300 µg/L upstream to under 5 µg/L (Doty et al. 2017).

Polychlorinated biphenyls

field

An area near Taranto historically contaminated by PCBs and metals, planted with clone Monviso: at 420 days a significant decrease in PCB congeners and a reduction in all metals where poplars were present, none in unplanted soil; microbial activity raised up to 1 m from the trunk and 40 cm deep (Ancona et al. 2017).

Ancona et al., Plant-assisted bioremediation of a historically PCB and heavy metal-contaminated area in Southern Italy, New Biotechnol. 38:65, 2017

Limits

The TCE result comes from controlled cells; in a real aquifer roots must reach the contaminated water, usually within a few metres, and transpiration stops in winter. Part of the volatile compounds leaves through the foliage to the air. The Taranto study covers just over a year and a 40 cm layer. Single-clone plantations are exposed to disease.

Where it has been tried

Taranto

PhytoremediationField scale, 2013–2017

Populus generosa × Populus nigra 'Monviso'

CNR-IRSA (Ancona, Barra Caracciolo and colleagues) planted about 650 cuttings of the Monviso poplar clone on 785 m² in April 2013, after a compost dressing. Soil and its microbial community were analysed at planting, after 420 days and after 55 months, at several distances from the trunk and at two depths.

Outcome After 420 days PCB congeners and metals had fallen in the soil under the poplars and not in unplanted soil. At 55 months PCBs, 240 ng/g on average at the start, were below the legal limit of 60 ng/g in the planted plots; nearly all metals were below the limits, cobalt excepted. The unplanted control soil held about 1,400 ng/g of PCBs, more than the starting average of the planted plots, so the comparison with the control should be read with care.