Phytodegradation of organic compounds.
ABSTRACT The phytodegradation of organic compounds can take place inside the plant or within the rhizosphere of the plant. Many different compounds and classes of compounds can be removed from the environment by this method, including solvents in groundwater, petroleum and aromatic compounds in soils, and volatile compounds in the air. Although still a relatively new area of research, there are many laboratories studying the underlying science necessary for a wide range of applications for plant-based remediation of organic contaminants.
Article: Activity of Desulfitobacterium sp. strain Viet1 demonstrates bioavailability of 2,4-dichlorophenol previously sequestered by the aquatic plant Lemna minor.[show abstract] [hide abstract]
ABSTRACT: Aquatic plants take up and sequester organic contaminants such as chlorophenols through incorporation in cell wall materials and storage in vacuoles. The ultimate fate of plant-sequestered chlorophenols, however, remains unclear. This research investigated 2,4-dichlorophenol (2,4-DCP) sequestration by the aquatic plant Lemna minor and evaluated contaminant release and bioavailability after plant death and cellular disruption. 14C-labeled 2,4-DCP was used to establish that contaminant removed from the aqueous phase was retained internal to L. minor. An assay with Desulfitobacterium sp. strain Viet1 was used to assess the readily bioavailable fraction of plant-sequestered 2,4-DCP and plant metabolites of 2,4-DCP. In plant-free systems, strain Viet1 dechlorinated 2,4-DCP to stoichiometric amounts of 4-chlorophenol (4-CP) as a stable and quantifiable end product. Anaerobic microcosms containing inactivated L. minor, which had accumulated 3.8 micromol of 2,4-DCP equivalents/g of plant material (fresh weight) during a preceding aerobic exposure, were inoculated with strain Viet1. After 118 d of incubation with strain Viet1, 43.5% (+/-1.4%) of the contaminant was recovered as 4-CP, indicating a large portion of plant-sequestered 2,4-DCP was bioavailable for dechlorination by strain Viet1. In contrast, 4-CP formation was not observed in autoclaved microcosms, and only 26.1% (+/-1.0%) of plant-sequestered 2,4-DCP was recovered in the aqueous phase. These findings demonstrate contaminant cycling between plants and microorganisms, and emphasize that understanding the mechanisms and pathways of contaminant sequestration by plants is critical for predicting long-term contaminant fate.Environmental Science and Technology 02/2006; 40(2):529-35. · 5.23 Impact Factor
[show abstract] [hide abstract]
ABSTRACT: The paper reviews the essential roles of reinvention technology, focusing on the use of plants for design and process in environmental sanitation. Phytostructure consists of greenspace area and distribution which are addressed to sequestrate carbon dioxide released by human activities and to prevent environmental impact respectively. Cities may conduct an assessment for the required area based on population number and its distribution according to the local physical conditions. Phytoprocesses are controlling factors for quality of environmental resources to save quantity and sustainability. Conservative substances will be controlled by phytostabilization followed by rhizofiltration, phytoextraction and phytovolatilization to some extent, while non-conservative contaminants will undergo all processes. Phytosacrifice to disaster offers innovations in impact prevention due to natural disaster. Lesson from the extent of tsunami wave height, travel distance, and in analogy to open channel flow, it can be expected that coastal greenspace is promising measure to suppress wave travel into inland. Phytotoxicology is essential for using wastewater irrigation that should not create a risk towards crops. General assurance for safe and healthy living components and environmental media are addressed as well by the subject. These are challenging subjects in scientific innovations and can be put in reality for international consensus on sustainable development.Journal of Applied Sciences Research. 01/2007; 3:1037-1044.
[show abstract] [hide abstract]
ABSTRACT: Plant-microbe interactions are considered to be important processes determining the efficiency of phytoremediation of petroleum pollution, however relatively little is known about how these interactions are influenced by petroleum pollution. In this experimental study using a microcosm approach, we examined how plant ecophysiological traits, soil nutrients and microbial activities were influenced by petroleum pollution in Phragmites australis, a phytoremediating species. Generally, petroleum pollution reduced plant performance, especially at early stages of plant growth. Petroleum had negative effects on the net accumulation of inorganic nitrogen from its organic forms (net nitrogen mineralization (NNM)) most likely by decreasing the inorganic nitrogen available to the plants in petroleum-polluted soils. However, abundant dissolved organic nitrogen (DON) was found in petroleum-polluted soil. In order to overcome initial deficiency of inorganic nitrogen, plants by dint of high colonization of arbuscular mycorrhizal fungi might absorb some DON for their growth in petroleum-polluted soils. In addition, through using a real-time polymerase chain reaction method, we quantified hydrocarbon-degrading bacterial traits based on their catabolic genes (i.e. alkB (alkane monooxygenase), nah (naphthalene dioxygenase) and tol (xylene monooxygenase) genes). This enumeration of target genes suggests that different hydrocarbon-degrading bacteria experienced different dynamic changes during phytoremediation and a greater abundance of alkB was detected during vegetative growth stages. Because phytoremediation of different components of petroleum is performed by different hydrocarbon-degrading bacteria, plants' ability of phytoremediating different components might therefore vary during the plant life cycle. Phytoremediation might be most effective during the vegetative growth stages as greater abundances of hydrocarbon-degrading bacteria containing alkB and tol genes were observed at these stages. The information provided by this study enhances our understanding of the effects of petroleum pollution on plant-microbe interactions and the roles of these interactions in the phytoremediation of petroleum-polluted soil.PLoS ONE 01/2011; 6(3):e17961. · 4.09 Impact Factor
Phytodegradation of organic compounds
Lee A Newman1,2?and Charles M Reynolds3
The phytodegradation of organic compounds can take place
inside the plant or within the rhizosphere of the plant. Many
different compounds and classes of compounds can be
removed from the environment by this method, including
solvents in groundwater, petroleum and aromatic compounds
in soils, and volatile compounds in the air. Although still a
relatively new area of research, there are many laboratories
studying the underlying science necessary for a wide range
of applications for plant-based remediation of organic
1University of South Carolina Arnold School of Public Health, 800 Sumter
Street, Columbia, SC 29208, USA
2The Savannah River Ecology Laboratory Aiken, SC 29208, USA
3US Army Engineer Research Development Center, Cold Regions
Research and Engineering Laboratory, 72 Lyme Road, Hanover,
NH 03755-1290, USA
Current Opinion in Biotechnology 2004, 15:225–230
This review comes from a themed issue on
Edited by Michael Y Galperin and Alan JM Baker
Available online 8th May 2004
0958-1669/$ – see front matter
? 2004 Elsevier Ltd. All rights reserved.
polycyclic aromatic hydrocarbons
total petroleum hydrocarbon
Phytoremediation is the use of plants to remediate con-
taminants in the environment. With the high costs of site
remediation, it is important that we continue to develop
and refine innovative, low-cost methods for cleaning the
environment. Phytoremediation also has the benefit of
contributing to site restoration when remedial action is
ongoing. The phytoremediation of organic compounds
can take place from the soil, air, groundwater or surface
water. The action of plants can include the degradation,
adsorption, accumulationandvolatilization ofcompounds
or the enhancement of soil rhizosphere activity. Which
plant activity occurs can depend not only on the medium
to be remediated and the type of plant used, but also on
the physical properties of the contaminant. Thus, two
different compounds in the same medium can interact
with a plant in very different ways. In this review, we
classify compounds of a similar nature together and dis-
cuss how recent studies have helped to elucidate plant
interactions with those compounds.
A summary of the contaminants and plants discussed is
given in Table 1.
Phytoremediation of solvents
Thephytoremediationofsolventsisalmost atthe pointof
being considered an accepted technology, even as new
information on the fate of solvents in plants continues to
come to light. Shang and Gordon  showed that the
groundwater contaminant trichloroethylene (TCE) taken
up by suspension cell cultures of hybrid poplar becomes
part of the non-volatile, un-extractable portion of the
cells. In whole plant studies, however, Ma and Burken
[2??] demonstrated that the stems and trunks of plants
fate of TCE in whole plant systems, one of us (Newman)
is collaborating with Burken to better define the mass
balance and determine all fates of TCE in plants.
Other groundwater contaminants also continue to be
studied. Ma and Burken  looked at the diffusion of
compounds such as 1,1,2,2-tetrachloroethane and carbon
tetrachloride from the transpiration stream of mature
trees on contaminated sites and found that stem concen-
trations can be used as indicators of aquifer concentra-
tions. The fate of ethylene dibromide (EDB) and TCE
has also been studied in the tropical tree Leuceana leuco-
cephala  and the plant was shown to be highly effective
at taking up both compounds. Bromide levels in the
hydroponic solutions of plants exposed to EDB showed
a marked increase, indicating a dehalogenation activity in
the plants. Laboratory studies with a hairy root culture of
Brassica napus exposed to 2,4-dichlorophenol resulted in
greater than 90% removal of the compound from solution
over a range of pH values . The plant-based treatment
of benzotriazoles, corrosion inhibitors used in glycol-
based deicing fluids, has also been studied. Castro et al.
 observed that benzotriazoles appeared to be actively
taken up and then incorporated into plant tissue by sun-
flowers (Helianthus annuus) grown in hydroponic solution.
Advances in the phytoremediation of methyl-tert-butyl
ether (MTBE) have progressed more slowly. Although
previous studies have shown that a wide variety of plants
are capable of taking up the compound, little is known
about its fate. Trapp et al.  looked at the fate of MTBE
in a variety of plants including trees, grasses and herbs,
Current Opinion in Biotechnology 2004, 15:225–230
and found no evidence for its metabolism by the plants;
they proposed that volatilization was the main fate. It was
also shown by Ramaswami et al.  that rhizosphere
bacteria were not a significant source of MTBE degrada-
tion. In laboratory studies, Ma et al.  found that not only
previous studies, but it also diffused from the trunk of the
plants. A morerecent studyof fivemature Montereypines
exposed to MTBE in the aquifer reported much higher
levels of tert-butyl alcohol (TBA) than MTBE through
the transpiration stream, indicating that metabolism was
taking place either in the rhizosphere or within the
plant system [10??]. This study also showed a significant
decrease in MTBE levels in the aquifer as it passed under
the trees, indicating that phytoremediation may be a
viable option forMTBE, even if thefateof thecompound
in the plant is not yet fully understood.
Phytoremediation of pesticides
The area of pesticide phytoremediation has recently
yielded some interesting results. Li et al.  looked
at the uptake of trifluralin and lindane by ryegrass:
trifluralin appeared to be metabolized by the plant,
whereas lindane had minimal metabolism and instead
formed bound residues. A number of factors have been
shown to effect the phytoremediation of pesticides. For
example, White and colleagues [12,13??] showed that
organic acids increased the uptake of 2,2-bis(p-chloro-
phenyl)-1,1-dichlorethylene (DDE) and Knuteson et al.
 reported that younger plants (two weeks old) exhib-
ited greater uptake of simazine (2-chloro-4,6-bis(ethyla-
mino)-1,3,5-triazine) than plants that were just two
weeks older. Although it has long been known that the
species-specific, but also ecotype specific, White and
coworkers [15??,16] reported that the uptake of DDE
was also subspecies specific, with certain cultivars show-
difference was the result of higher exudation rates of low
molecular weight organic acids.
Phytoremediation of explosive compounds
interest to the Department of Defense, as they look for
innovative technologies to reduce the levels of contami-
nants onranges while still keeping the ranges operational.
In this regard, Wang et al.  studied the interactions
between 2,4,6-trinitrotoluene (TNT) and Myriophyllum
aquaticum, looking at transformation rates. Planting with
Johnsongrass or wild ryegrass has been shown to decrease
soil concentrations of TNT  and it has been reported
that the use of plants to remediate surface waters con-
taminated with TNT could reduce toxicity in the system
. A newly discovered endophytic bacterium, Methylo-
bacterium sp. (isolated from hybrid poplar), was shown by
van Aken et al. [20??] to be capable of degrading TNT,
Summary of contaminants and plants discussed in the text*.
ClassContaminant Plants studiedEffect studied
volatilization from trunk [2??]
Volatilization from trunk
Volatilization from trunk
TNT, RDX, HMX
Leuceana , poplar rhizosphere 
Herbaceous plants , pine [10??]
Parrot feather, canna
Parrot feather , Arabidopsis 
Poplar , bean, alfalfa, canola 
Tobacco , poplar 
Sorghum , alfalfa , clover, rye ,
poplar [42,43], willow 
Rye , fescue [30??], Kandelia , Bruguiera 
Grasses native to California (US) 
Diesel, heavy oil
*This does not reflect what was done in previous studies and should not be considered an inclusive list of all plant and contaminants studied.
CT, carbon tetrachloride; DDE, 2,2-bis(p-chlorophenyl)-1,1-dichlorethylene; EDB, ethylene dibromide; HMX, octahydro-1,3,5,7-tetranitro-
1,3,5-tetrazocine; RDX, hexahydro-1,3,5-trinitro-1,3,5-triazine.
Current Opinion in Biotechnology 2004, 15:225–230www.sciencedirect.com
hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octa-
hydro-1,3,5,7-tetranitro-1,3,5-tetrazocine (HMX); it may
be that this bacterium has a major role in the degradation
of explosive compounds in plants. However, Ekman et al.
 found that the detoxification enzymes cytochrome
P450, glutathione S-transferase, an ABC transporter, and
a probable nitroreductase were all induced in Arabidopsis
roots following TNT exposure, which opens the possi-
bility of these enzymes being involved in plant degrada-
tion of TNT. In contrast to the promising results seen
with TNT, Yoon et al.  showed that HMX has limited
metabolism in plants, and could result in accumulation
of the compound in plants. Likewise, Groom et al. 
looked at HMX uptake using alfalfa (Medicago sativa),
bush bean (Phaseolus vulgaris), canola (Brassica rapa), and
other plants and saw the same limited uptake and meta-
bolism in the plants, suggesting reduced potential for the
phytoremediation of this compound.
Diverse results have also been observed for the remedia-
tion of perchlorate. Although one study reported the
accumulation of perchlorate in the leaves of tobacco
plants  another showed that poplars were able to
reduce perchlorate, albeit at a low level .
Phytoremediation of petroleum compounds
The rhizosphere degradation of chlorinated solvents
under new plantations is limited, but work by Godsy
et al.  indicates that as the trees age the microbial
populations might change and foster anaerobic degrada-
tion. With compounds such as the polycyclic aromatic
hydrocarbons (PAHs), petroleum compounds and poly-
chlorinated biphenyls (PCBs), the role of the rhizosphere
is much more critical.
Efforts to demonstrate plant or rhizosphere effects on
petroleum degradation, particularly PAHs, continue. In a
greenhouse study, Banks et al.  observed generally
greater remediation efficiency in soil planted with four
genotypes of Sorghum bicolor (L.) compared with unve-
getated controls. Although the genotypes were selected
for different root characteristics and root exudate levels,
these differences were not reflected in remediation effi-
ciencies. Measuring plant effects on PAH degradation in
soil remains difficult, and our ability to measure phyto-
remediation treatment effects is confronted by numerous
interactions among the soil-rhizosphere-microbial-plant
system. Parts of the system interact on a continuous basis,
interactions vary with conditions, such as moisture and
temperature, as well as with the growth stage of both
plants and microorganisms. These interactions make
understanding and monitoring phytoremediation com-
plex. Results from studies are mixed. Using small field
with pyrene, mixed and then either revegetated with
annual ryegrass (Lolium multiflorum Lam.) or kept fallow,
Lalande et al.  reported greater pyrene loss from
unvegetated treatments and suggested that microorgan-
isms may use easily degradable organic matter as a carbon
source rather than pyrene. Joner et al.  suggested that
priming effects associated with experimental protocols
were large, and may tend to mask beneficial effects from
the synergistic effects of fertilizing and planting. Solid
evidence for increased degradation with plants continues
to be reported. Using14C-labeled pyrene, Chen et al.
[30??] showed 38% and 30% pyrene mineralization in tall
fescue (Festuca arundinacea) and switchgrass (Panicum
virgatum L.), respectively, compared with 4.3% in the
affects the carbon:nitrogen (C:N) ratio in soil and can
lead to nitrogen immobilization. Adam and Duncan 
evaluated leguminous plants in diesel-contaminated soil
and found that contaminated soil had fewer nodules, but
that these nodules were more developed. White et al. 
investigated soil amendments with different C:N ratios
for their effects on both seed germination and plant
growth. Addition of boiler litter, which had a C:N ratio
of approximately eight, resulted in lower soil total pet-
roleum hydrocarbons (TPHs) compared to amendments
with higher C:N ratios.
In field soils, numerous soil–plant interactions and soil
conditions, including soil moisture and temperature, may
influence contaminant fate. Plants can affect soil water
content and movement in several ways. Karthikeyan et al.
 used column studies to demonstrate that transport
and biodegradation of jet fuel (JP-8) were affected by soil
water, and that soil columns planted with fescue grass
(Festuca arundinacia) had less leaching of JP-8. They
suggested that plant transpiration and associated water
movement could favor biodegradation by keeping mobile
contaminants near the soil surface, and they developed a
modeling approach to describe water and JP-8 transport
 (Table 1).
Although field studies are more difficult to conduct and
monitor than greenhouse studies, results are encouraging.
Banks etal. foundthat vegetative treatmentofdiesel-
and heavy-oil-contaminated soil yielded both lower TPH
values in the vegetated soil and reduced toxicity. They
suggested that longer term treatment may be needed for
further reductions in TPH concentration. Robson et al.
contaminated soils and cold regions.
Our understanding of rhizosphere microbiology and its
changes during phytoremediation is improving. Siciliano
et al.[37??] observed greater levels of hydrocarbon-related
catabolic genes (ndoB, alkB and xylE) in rhizosphere soils
relative tobulk soil.Muratova etal. used fluorescence
microscopy to show that the microflora in the rhizosphere
of bitumen-contaminated soil was greater than in
Phytodegradation of organic compounds Newman and Reynolds 227
Current Opinion in Biotechnology 2004, 15:225–230
unplanted soil, and that the community structure was also
different. Differences between alfalfa (Medicago sativa)
and reed (Phragmites australis) rhizospheres were also
observed. Additionally, alfalfa enhanced the PAH-
degrading population in the rhizosphere . In a pot
study, Joner and Leyval  found that in PAH-contami-
nated soil planted with a clover–ryegrass mix PAH con-
centrations decreased as a function of proximity to the
roots, and that mycorrhiza generally enhanced plant
growth and favored growth of clover at the expense of
ryegrass. Singer et al.  repeatedly augmented Aro-
chlor1242-contaminated soil with PCB-degrading bac-
teria, carvone and salicyic acid as enzyme inducers, a
surfactant and minimal salts medium, and compared
Brassica nigra to non-vegetated controls. The B. nigra-
planted treatments resulted in 61% PCB removal in the
top 6 cm after nine weeks of bioaugmentation, compared
with 43% and 14% PCB removal in the 0–2 and 2–6 cm
depths, respectively, in unplanted controls.
In addition to grasses and legumes, trees such as Populus
are increasingly being considered for use in PAH and
TPH degradation. In short-term tests, Wittig and collea-
gues [42,43] found that poplar cuttings grown in a PAH-
amended sand-nutrient solution had similar shoot bio-
mass, growth and leaf water content to the controls, but
that transpiration, nutrient solution uptake, and root mass
among plants from the PAH-contaminated soils and con-
trols. The effects were also dependent on the PAH under
study. Willow (Salix viminalis L. ‘Orm’) has been eval-
uated for the dissipation of mineral oil and PAHs in
decreased 57% after 1.5 years in the willow-planted
treatment compared to 15% in the control. In the vege-
tated soil, mineral oil degradation was greater in the roots
zone than in the total column of soil.
Mineral oil concentration
Because the volume of soil affected by rhizosphere pro-
cesses is related to root morphology and size, there is
continued interest in rooting patterns. Rentz et al. [45??]
investigated five passive methods for increasing oxygen
delivery to enhance root development and plant growth.
Using commercial oxygen release compounds stimulated
suggest that there may be effective ways to enhance root
growth in oxygen-limiting situations and to couple phy-
toremediation with other technologies to enhance both.
Ke etal. investigatedusing mangrove (Kandelia candel
and Bruguiera gymnorrhiza) wetland systems to treat pyr-
ene-contaminated sediments. After six months, pyrene
concentrations decreased in the mangrove treatments
relative to the controls. Although there was a measurable
increase in pyrene concentrations in the roots relative to
the non-pyrene control roots, the increase was minor
compared with the total pyrene removed from the sedi-
ment, suggesting that plant uptake was not a significant
path for pyrene loss. The authors found that adding
humic acid (HA) to the soil reduced both plant growth
limited its bioavailability .
Although most problems with petroleum compounds are
associated with contaminated soils and groundwater, the
atmospheric release of gasoline compounds also needs to
be addressed. Oyabu et al.  investigated the ability of
Epipremnum aureum (golden pothos) to remove gasoline
from the air and found that the plants purification ability
reached a maximum value 40 h after gasoline vapors were
inroduced into the growth chamber. The authors did not
separate soil effects from plant effects in their study.
Models of phytoremediation
ing treatment times, and developing monitoring schemes
are recognized as current limitations to using phytoreme-
diation. Developing effective models may help to address
these limitations and might help the research community
to understand the interactions among the many processes
that contribute to phytoremediation. Thoma and collea-
gues [49,50] developed a model for screening grass spe-
cies for the phytoremediation of weathered petroleum.
Models for calculating hydraulic control based on tran-
spiration and groundwater characteristics have been dis-
cussed and evaluated, with the suggestion that field
measurements be used to verify model predictions when-
ever possible . International interest in using phytor-
emediation has lead to reviews that discuss both models
and processes thought to be important , as well as
performance evaluations of existing models against
experimental datasets . Matthews et al.  used a
numerical groundwater flow model and evaluated how
variations in hydrogeologic and seasonal growth para-
meters influenced the minimum plantation area needed
for plume capture. They found that the aquifer horizontal
hydraulic conductivity and saturated thickness directly
influenced the plantation size.
Reviews and conference summaries of phytoremediation
ofinternationalphytoremediationefforts [55–63]. As more
researchers, site owners and regulators become aware of
and soil remediation continue to lead to a better under-
standingof themany processes by which plants canhave a
positive impact on contamination in the environment.
The authors gratefully acknowledge the efforts of SE Hardy and support
from the US Army Environmental Quality Basic Research Program, the
Department of Energy and the US-NIEHS, grant P42 ES04696, in
developing this review.
Current Opinion in Biotechnology 2004, 15:225–230www.sciencedirect.com
References and recommended reading
Papers of particular interest, published within the annual period of
review, have been highlighted as:
? of special interest
??of outstanding interest
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