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Advances in Environmental Biology, 6(10): 2663-2668, 2012
ISSN 1995-0756
This is a refereed journal and all articles are professionally screened and reviewed
ORIGINAL ARTICLE
Phytoremediation Using the Influence of Aromatic Crop on Heavy-Metal Polluted Soil,
a Review
1
Maryam Mashhoor Roodi, 1Md. Azlin Bin Md. Said, 2Houman Honari
1
Civil Engineering School, Engineering Campus, University Sains Malaysia, 14300 Nibong Tebal, Penang,
Malaysia.
2
Department of Medicinal and Aromatic Plants Torbat-e-Jam Branch, Islamic Azad University, Khorasan
Razavi, Iran.
Maryam Mashhoor Roodi, Md. Azlin Bin Md. Said, Houman Honari; Phytoremediation Using the
Influence of Aromatic Crop on Heavy-Metal Polluted Soil, a Review
ABSTRACT
Today, interests in aromatic crop usage worldwide are increasing. Production of these plants is used in the
food, confectionary, condiment, soap, mouthwash, and other industries. Product safety issue has just recently
been raised because of the presence of heavy metals. Modern industrial society discharges large quantities of
high level of gases and particles, which are harmful for human, plant, and animal lives. Some heavy metals,
such as lead, cadmium, arsenic, molybdenum, nickel, and zinc, can be found in the environment in trace
amount. The general presence of these metals in soil, water, air, and biota are increasing. In the current study,
the effect of heavy metals on aromatic crops (mint, lavender, Hypericum perforatum L., and Achillea
millefolium L.) is reviewed and investigated. In industrial region, result showed that edible crops are
contaminated. According to the research work carried out, instead of growing edible crops, growing some
aromatic species is possible, in which the final product is free from heavy metals. Studies on soil properties
show an advantage in reduced heavy-metal uptake by cultivation of appropriate plants using practical
techniques. In addition, some aromatic crops appear to be excellent choice for phytoremediation, such as
Hyssopus officinalis L. and Satureja montana L.
Key words: Heavy metal, aromatic crops, essential oil and phytoremediation
Introduction
Numerous studies on soils show that heavy
metal, particularly Lead and Cadmium, concentration
is increasing. High persistence and the dynamics of
heavy metals, such as Cadmium, contribute to
hazardous factors both in the solution phase and
available soil phase, as observed in plants. Their
introduction to plants and the food chain endangers
human health and animal life. Cd is considered nonessential for living organisms [11]. Some heavy
metals, like Fe +2, ZN +2, and Cu +2, are required
for metabolism, so they are essential micronutrient,
whereas doses in excess of the permitted one can be
toxic. Pb is recognized as a protoplasmic poison with
slow-acting penetrating aggregator characteristic. Pb
contamination in soil results in a sharp decrease in
crop production, thus considered a serious threat to
agriculture [22]. Modern industrial society produces
dangerous quantities of gases and particles. With the
industrialization process, expansion in cities, increase
in traffic, economic development, and increase
energy consumption cause air pollution [26]. Metals
from air are washed into and pollute the soil,
presenting a major cause for environment concern
[12]. The effect of air pollution on plants has long
been known. Various changes in plants in relation to
morphological, anatomical, physiological, and
biochemical characteristics induced by air pollutants
have been recorded. An ongoing effort has been
adopted to remediate heavy-metal polluted soil.
The surface enrichment of metals in soils may
have resulted from the fallout of wind-transported
contamination, accumulation of heavy metals in
plants from underground, or chemical composition of
metals from organic compounds [19]. In addition,
factors, like DTPA, EDTA (chelating agents'
diethylenetriamine
pentaacetic
acid
and
ethylenediamine tetraacetic acid) in detergents, such
as soaps, powders, and the like, increase the heavymetal solubility and accumulation in soil [28].
Among the soil factors that keep metals in soil are
PH, organic matter level, dissolved organic
compounds, clay, CEC (Cation-Exchange Capacity),
EC (electrical conductivity), oxides, iron hydroxides,
and other inorganic materials [1]. Ray [24]
discovered significant bioaccumulation of heavy
metals in endemic weeds and vegetables in polluted
Corresponding Author
Maryam Mashhoor Roodi, Civil Engineering School, Engineering Campus, University Sains
Malaysia, 14300 Nibong Tebal, Penang, Malaysia.
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Adv. Environ. Biol., 6(10): 2663-2668, 2012
regions. Most metal accumulation was found in the
edible parts compared with non-edible parts.
Mercury, thallium, vanadium, nickel, fluorine,
cadmium, and copper cause phytotoxicity. Sensitive
plant species effectively accumulate metals in their
tissues, which may have some influence on
chlorophyll reduction. Species such as Ficus
bengalensis, Psidium gujava, and Sygygium cuminii,
trap higher amount of metals in leaves around
thermal power stations [5]. Some higher doses of
heavy metals can cause metabolic disorders and
growth inhibition in most plant varieties.
Biological techniques use to remediate metalcontaminated soil, including the phytovolatization,
phytostabilization,
phytofiltration,
and
phytoextraction processes, are needed for plants and
organisms (Umeoguaju, 2009). Compared with some
methods, such as replacement of contaminated soils
with uncontaminated ones, the above techniques are
cheaper, as well as also conserve the soil
characteristic and help improve the soil organisms.
The main benefit from the heavy-metal absorption by
the biomass system is its role in reducing heavymetal concentration to a low level using inexpensive
biosorbent materials. Nevertheless, limitations exist:
it can be a time-consuming process and can increase
the clean-up process of the entire site. Further, it is
restricted by factors, such as root depth, weather,
pollution level, amount of produced biomass, and
soil chemistry. (Tangahu et al., 2011).
Experimental schedule:
Zheljazkov tested models for investigation in
some quantitative and qualitative characteristics of
Mentha piperita L. (cv Tundja and Clone No. 1) and
Mentha arvensis var piperascens Malinv. (cv
Mentolna – 14). The soils were taken from different
distances in polluted sites (soil 1=0.5 km, soil 2=3
km, soil 3=6 km, and soil 4 (control)=10 km).
Cadmium and lead concentration in plants
completely depends on soil accumulation. In all
variants, the maximum amounts of Cd and lead were
found in the root because of specific translocation. In
addition, soil 1 plants were able to accumulate more
elements than those in the control soil. Copper and
zinc can be a source of pollution to a large extent. Cu
and Zn accumulation in different plant parts is found
in the following order: roots> leaves> flowers>
stems. No cultivar response to Cu, Cd, and Zn was
found.
In oil samples, Cd and Pb were not found (using
GFAAS: Graphite furnace atomic absorption
spectrometry). The concentration of the other metals
was less than the maximum acceptable concentration.
The result shows that during the steam distillation
process, heavy metals were not removed from the
tissues, producing yields free of heavy metals.
Heavy-metal pollution in soil and air at a distance of
400 m from the source of pollution reduced the yield
of fresh herbage by 9%–16% and the yield of
essential oil by up to 14% compared with the control.
However, it did not affect the essential oil content
and soil quality.
Furthermore, investigations done on lavender
cvs. Hemus and Druzhba, which are the most grown
cultivars in Bulgaria, showed no decrease in the
product, which is not in accordance with the findings
of other researchers investigating the same problem
with other plant types. This difference can be
attributed to the great deal of good conformity
development of lavender roots or to the presence of
other heavy metals, a phenomenon discussed in some
papers. In fact, grass species that have root
penetration depth of up to 40 cm appear to be more
sensitive to high Cd concentration, whereas bushes
and woody species are less sensitive. The Cd and Pb
concentrations in different parts of the plant were at
critical level, although no toxicity symptoms were
observed. A cultivar response to Cd contamination
was found. The Pb concentration in the plant parts
was in the following order: stems>leaves = racemes>
roots. The Pb concentration in oil was very low
(0.03–0.04 mg/L), which is not a problematic
contamination. The Cu and Mn content concentration
in plant parts was found to be in following order:
roots>leaves = racemes> stems. The Zn content was
in the following order: leaves=stems>racemes>roots.
The zinc concentration value in oil was considered as
normal.
Iron was used as the "reference" element. The
role of iron was to cause zinc and copper absorption
to some extent. Higher concentration may show
toxicity in plants. Consequently, the pollution
content in oil was lower than that in the lavender
inflorescence, which has high heavy-metal content
used for the oil production [33]. High-quality
lavender oil can be produced from lavender plants
grown in polluted region [29].
Hyssopus officinalis L. and Satureja Montana L.
are two Mediterranean plants. Two concentrations
for each metal, namely, 200 and 1,400 ppm zinc and
21 and 108 ppm cadmium, respectively, were used.
After metal addition, the plant growth was monitored
for three months. The metal concentrations of the soil
dry weight are shown in Table 1.
The plant biomass was not affected by any of the
experimental treatments for both species under
consideration (Table 1), suggesting a lack of toxicity
of the used concentrations. Figures 1 and 2 show the
Cd and Zn accumulation during the experimental
period. Both species were able to extract and
accumulate great deal of these elements compared
with the control. The process was absolutely slow,
and the metal concentrations were obtained without
any toxicity symptoms.
The low concentration of zinc was quite the
same among organs in both species. In Hyssopus, the
zinc concentration increased as a function of
treatments in all organs, with especially higher rates
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in the roots. In fact, at 1,400 ppm, the zinc content
was 12-fold higher in roots and 3.5-fold higher in
leaves than those in the 200 ppm treatment. Further,
the addition of citric acid to the 200 ppm treatment
caused an increase in the total zinc accumulation
(twofold higher) both in the roots and leaves. In
Satureja, the increase of zinc concentration was
lower in leaves and stems compared with Hyssopus.
As a whole, Hyssopus was able to keep higher
amount of zinc than Satureja at 1,400 ppm in both
the leaves and roots.
Table 1: The H. officinalis L. and S. montana L total dry mass (g/pl) under different zinc and cadmium treatments after 90 days are
presented. Results are reported as means plus SD. All treatments are not significantly different (P<0.05) [20].
Treatments
Hyssopusofficinalis (g/pl)
Satureja Montana (g/pl)
1. Control
23.90 + 6.38
20.61 + 3.38
2. Zinc 200 ppm
22.62 + 2.30
19.84+1.78
3. Zinc 200 ppm + citric acid
21.15 + 5.62
19.20 + 1.70
4. Zinc 1400 ppm
5. Cadmium 21 ppm
19.12 + 4.06
25.97 + 1.63
18.67 + 1.92
22.34 + 3.53
6. Cadmium 21 ppm + citric acid
20.86 + 3.32
21.71+ 2.58
7. Cadmium 108 ppm
27.05 + 2.00
19.79 + 1.45
8. Cadmium 108 ppm + citric acid
25.94 + 4.06
21.98 + 1.50
Fig. 1: Cadmium content (ppm total plant dry weight) determined after 30, 60 and 90 days in (a)
Hyssopusofficinalis and (b) Saturejamontana [20].
Fig. 2: Zinc content (ppm total plant dry weight) determined after 30, 60 and 90 days in (c) Hyssopusofficinalis
and (d) Saturejamontana [20].
Other aromatic crops, such as Hypericum
perforatum L. and Achillea millefolium in the current
research, were collected in the wild in Yugoslavia
and Republic Srpska. Samples of H. perforatum L.
were collected at 11 different sites, whereas samples
of A. Millefolium L. originated from nine localities.
An additional three Hypericum samples came from
cultivated production. Along with the herb samples,
corresponding soil samples were also taken. Positive
linear correlation coefficients between heavy-metal
content in the Achillea herb and the available
amounts in the soil were obtained for Cu, Pb, and Ni
and for the Pb in the Hypericum herb. The lack of
some expected correlation coefficients can be
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explained by the stronger influence of the genetic
characteristics on the investigated medicinal plant
species, as well as by some soil factors, which often
have opposite effects on heavy-metal uptake. The
Mn and Zn contents in both species had negative
correlation coefficients with the soil pH. Under low
pH conditions, due to higher solubility of their
compounds, the resulting higher Mn and Zn
availability was not unexpected. The Cu and Pb
contents in the herb have no correlation with the soil
pH. The Cu concentration of element in the soil
solution is not influenced by the soil pH but by its
absorption by soil particles. For Pb, several ideas are
proposed: its uptake is higher on acid soils, and
another opinion states that soil pH plays no role in its
uptake; thus, plants can accumulate Pb under both
acid and alkaline conditions. The main factor for
heavy-metal mobility is soil pH [8], but it is also
influenced by clay content, redox status, organic
matter, humus, carbonates, and soluble salts. In
addition, further Cd uptake and accumulation by
different plants depend greatly on variety or
genotype.
Fig. 3: Content of Cd in Hypericumperfuratum L. depending of soil pH [23].
Exponential dependence found in Cd is related
to the greater influence of soil pH on the Cd uptake
compared with other investigated elements. The Cd
content in Hypericum was mostly above the limit of
0.5 ppm when the soil pH was lower than 5.9 (Fig.
3). For yarrow, the herb Cd content was above the
limit (0.3 ppm) when the soil pH was lower than 5.1
(Fig. 4).
Fig. 4: Content of Cd in Achilleamillefolium L. depending of soil pH [23].
According to Yap et al. [10], heavy metals (Cd,
Cr, Cu, Fe, Mn, Pb, and Zn) in paddy plants
accumulated in the root except for Mn, which was at
the highest level in the leaves. Nevertheless, the low
level in the rice grain was below the allowable limits
stipulated under food regulation. The decrease in
soil-particle size and the increase in Hg and As
contents are believed to bind the heavy metals to soil
particles. In addition, the soil PH and the organic
matter content are considerable metal factors in the
soil. Most metals in low-PH soils are not in the
available form, and those that occur in ion exchange
fraction may be derived from different fertilizers and
pesticides applied to the soil. The reduced organic
carbon metal is lightly bound to organic matter and
does not create metal–chelate complex, thus
occurring in an available form that can be attracted
and accumulated easily by the plant parts.
The Zn, Cd, and Pb binding to water hyacinth
roots and leaves depend on the PH. The result
showed that at higher PH (PH=8.5), the highest
binding occurred, and it has the
accumulation in constructed wetland [11].
greatest
Conclusion:
Heavy-metal uptake by plants is a complex
process, influenced by numerous factors that interact
with one another and the availability and mobility of
metals in the soil, plant species, genotype, and soil
properties, such as pH, organic matter, clay content,
and so on. The tested cultivars of M.Piperita cvs
Tundja.arvensis
var
piperascens
Malinv.
(cvMentolna – 14), Lavandulaangustifolia Mill. cvs.
Druzhba and Hemus can be used as alternative for
other edible crops on heavy-metal polluted soils.
The research result did not show accumulation
of heavy metals in essential oil of aromatic species,
but some of these species can be well grown in
polluted sites without considerable decrease in yield.
Cd, Pb, and Zn are capable of passing into water
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during the distillation process; therefore, waste water
can be full of heavy metals and are hazardous.
Heavy metal contamination did not have a
negative effect on lavender in different stage; the
essential oil content, crop of fresh raceme, plant
branch, and essential oil. The different forms of
heavy-metal concentration in lavender are defined in
the following order:
Cd: leaves> roots = inflorescences = stems;
Pb: stems> leaves = inflorescences> roots;
Cu: roots> leaves = inflorescences = stems;
Mn: roots> leaves = inflorescences> stems;
Zn: leaves = stems> inflorescences> roots; and
Fe: roots> leaves> stems> inflorescences.
Some aromatic plants appear to be a good choice
for phytoremediation, such as Hyssopus officinalis
L., Satureja montana L., Hypericum perforatum L.
Achillea millefolium L. M. piperita and M. arvensis,
in a long term they could be used for contaminated
soils.
The roots are the primary plant organs that
sense, come in contact with, and accumulate heavy
metals from the substrate. Root growth has been
proven as indicator of metal tolerance in plants.
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