Introduction to Phytoremediation - CLU-IN

• Thlaspi caerulescens (Alpine pennycress) for Ni and
Zn (Brown et al. 1994).
• Thlaspi rotundifolium ssp. cepaeifolium, a noncrop Brassica
and one of the few Pb accumulators mentioned in
the literature (Nanda Kumar et al. 1995).
• Alyssum wulfenianum for Ni (Reeves and Brooks 1983).
• Baker (1995) found 80 species of nickel-accumulating
plants in the Buxaceae (including boxwood) and
Euphoribiaceae (including cactus-like succulents) families.
Some euphorbs can accumulate up to 5% of their
dry weight in nickel.
• Indian mustard (Brassica juncea) and canola (Brassica
napus) have been shown to accumulate Se and B. Kenaf
(Hibiscus cannabinus L. cv. Indian) and tall fescue
(Festuca arundinacea Schreb cv. Alta) also take up Se,
but to a lesser degree than canola (Bañuelos et al.
1997b).
• Hybrid poplar trees were used in a field study in minetailing
wastes contaminated with As and Cd (Pierzynski
et al. 1994).
• Lambsquarter leaves had relatively higher As concentrations
(14 mg/kg As) than other native plant or poplar
leaves (8 mg/kg) in mine-tailing wastes (Pierzynski et
al. 1994).
• Sunflowers took up Cs and Sr, with Cs remaining in the
roots and Sr moving into the shoots (Adler 1996).
• Metal accumulator plants such as the crop plants corn,
sorghum, and alfalfa may be more effective than
hyperaccumulators and remove a greater mass of metals
due to their faster growth rate and larger biomass.
Additional study is needed to quantify contaminant removal.
The number of taxonomic groups (taxa) of
hyperaccumulators varies according to which metal is
hyperaccumulated:
Metal Number of Taxonomic Groups of Hyperaccumulators
Ni >300
Co 26
Cu 24
Zn 18
Mn 8
Pb 5
Cd 1
3.1.8 Site Considerations
Because potentially toxic levels of metals can accumulate
in the aboveground portion of the plant, access to the
plants must be controlled and plant debris must be monitored
more closely than with other phytoremediation technologies.
Thus, care must be taken to restrict access of
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browsing animals, and harvested plant material must be
properly disposed of.
3.1.8.1 Soil Conditions
Soil conditions must be appropriate for plant growth and
contaminant migration to the plant, yet not allow leaching of
the metals. The pH of the soil may need to be adjusted and/
or chelating agents may need to be added to increase plant
bioavailability and uptake of metals.
3.1.8.2 Ground and Surface Water
The primary considerations for phytoremediation in groundwater
are depth to groundwater and depth to contamination
zone. Groundwater phytoremediation is essentially limited
to unconfined aquifers in which the water table depths are
within reach of plant roots.
3.1.8.3 Climatic Conditions
Hyperaccumulators are often found in specific geographic
locations and might not grow under other climatic conditions.
3.1.9 Current Status
Both laboratory and field experiments have been conducted.
The first controlled field trial of Thlaspi caerulescens
in the UK was in 1994 (Moffat 1995). In this study, Thlaspi
caerulescens accumulated Zn and Cd to several percent
dry weight. A commercial operation, Phytotech, Inc., also
conducted field tests and small-scale field applications (including
the “Magic Marker” site in Trenton, NJ) with some
degree of success using Indian mustard (Brassica juncea)
to remove lead from soil.
Plant selection, breeding, and genetic engineering for fastgrowing,
high-biomass hyperaccumulators are active areas
of research. Information on uptake and translocation of metals
has been assessed by Nellessen and Fletcher (1993a).
3.1.10 System Cost
The estimated 30-year costs (1998 dollars) for remediating
a 12-acre lead site are $12,000,000 for excavation and disposal,
$6,300,000 for soil washing, $600,000 for a soil cap,
and $200,000 for phytoextraction (Cunningham 1996).
In a hypothetical study involving the remediation of a 20in.-thick
layer of sediments contaminated with Cd, Zn, and
137 Cs from a 1.2-acre chemical waste disposal pond,
phytoextraction cost was estimated to be about one-third
the cost of soil washing (Cornish et al. 1995).
Phytoextraction costs were estimated to be $60,000 to
$100,000 for remediation of one acre of 20-in.-thick sandy
loam, compared to a minimum of $400,000 for just excavation
and storage of this soil (Salt et al. 1995).
3.1.11 Selected References
Azadpour, A., and J. E. Matthews. 1996. Remediation of
Metal-Contaminated Sites Using Plants. Remed. Summer.
6(3):1-19.