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ProEnvironment
ProEnvironment 8 (2015) 476 - 480
Original Article
Biosorption of Inorganic Mercury in Aqueous Solution by
some Aromatic Plants
VEREȘTIUC Paul Cristinel1, Oana Maria TUCALIUC1*, Gheorghe NEMȚOI2
1Al.I.Cuza
2Al.I.
University of Iasi, Faculty of Geography and Geology, Carol I Blvd., no. 20 A, 700505 Iasi, Romania
Cuza University of Iasi, Faculty of Chemistry, Carol I Blvd., no. 11, 700506 Iasi, Romania
Received 12 February 2015; received and revised form 20 June 2015; accepted 28 June 2015
Available online 1 September 2015
Abstract
Contamination of ecosystems with heavy metals is one of the major problems all over the world. Most of these
metals are present in the environment as a consequence of anthropogenic activities. Aromatic and medicinal plants have
an increasing economic importance and are used with success in pharmaceutic and food industry. Products based on
natural substances enjoy an increasing value. Some aromatic plants produce specific secondary metabolites, which can
detoxify some of toxic metals. Five aromatic plants (Salvia officinalis, Petroselium crispum, Artemisia dracunculus,
Mentha chrispa, Origanum vulgare) commonly known as sage, parsley, tarragon, mint and oregano were used to
remove inorganic mercury from aqueous solution. A sorbent was obtained from each plant leafs. Experiments were
carried out to determine the adsorption efficiency at a known pH and at a 180 seconds preconcentration time using
linear sweep voltammetry. The results in this study demonstrated that the cathodic discharge of mercury ions from
mercury (II) aqueous solutions can be pointed out by a relevant current pick, whose height, is dependent on the quantity
of plants. The study suggest that some of the plants hold great potential to be an effective biosorbent for removal of
mercury and other heavy metals from contaminated waters with good efficiency and low cost.
Keywords: mercury (II), aromatic plants, biosorption, linear sweep voltammetry.
1. Introduction
Mercury is and its compounds have been in
use for several millennia and the applications range
broadly from cosmetics, medicinal treatments,
dentistry, paints to electrical apparatus and batteries.
Mercury is liquid at room temperature and
mercury compounds are toxic, volatile and readily
dispersed through the atmosphere [6].
Mercury is widely considered to be among
the highest priority environmental pollutants of
continuing concern on the global scale [16].
This metal is among the most highly
bioconcentrated trace metals in the human food
chain, and many national and international
organizations have targeted mercury for emission
control [9].
The term of heavy metals defines metals with
specific weight higher than 5 g/cm3 [4]. Mercury has
natural sources such as volcanic activity, soil and
rock weathering and evaporation from oceans.
Between 70-80% of the Hg resealed in the
environment comes from anthropogenic sources
such as metal smelting, mining, cement production,
waste incineration and other industries [11].
* Corresponding author.
Tel: +40-755-156581
Fax: +40-332-881671
e-mail: [email protected]
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VEREȘTIUC Paul Cristinel et al./ProEnvironment 8(2015) 476 - 480
It is generally accepted that the major risks to
human health arise from the neurotoxic effects of
mercury: memory disturbance, tremors, deafness,
respiratory distress, renal failure, all of them are
reunited as symptoms of Minamata disease [8].
To grow and complete the life cycle, plants
must aquire not only macronutrients (N, P, K, S,
Ca), but also essential micronutrients as Fe, Zn, Mn,
Ni or Cu. Accumulation of these micronutrients
does not exceed their metabolic needs. In contrast,
some metal hyperaccumulator plants can accumulate
exceptionally high amounts of nonessential metals
(in the thousands of ppm) [15].
Salvia officinalis (sage) has been reported to
have a wide range of biological activities, such
antioxidant, antibacterial, hypoglycemic and antiinflammatory properties [2]. Petroselium crispum
(parsley) has been claimed to be antimicrobial,
antiseptic, astringent, gastrotonic, antispasmodic,
usually employed as food flavour [5]. Artemisia
dracunculus (tarragon) has a culinary and traditional
medicinally use, known
to improve
a
malfunctioning digestive system [13]. Mentha
chrispa (mint) posseses antioxidative, antimicrobial
and hepatoprotective activity due to phenolic
components [7]. Origanum vulgare species are a
rich source of carvacrol, a component of particular
biological importance: it is known for its
antibacterial and antifungal activities, antispasmodic
effects and radical scavenging effect [3]. Good
capacity of mercury adsorption was observed in
other studies for Coriandrum sativum [10], Ricinus
communis [1] or Bambusoideae subfamily [12].
The aim of the present work was to
investigate the capacity of mercury adsorption by
five different aromatic plants using linear sweep
voltammetry.
2. Material and Method
For the study, dried leafs of five aromatic
plants (Salvia officinalis, Petroselium crispum,
Artemisia dracunculus, Mentha chrispa, Origanum
vulgare) commercially used were purchased and
milled afterwards. A quantity (P) of 2 mg, 4 mg, 6
mg, 8 mg, 10 mg, 12 mg and 14 mg was used in
order to determine the capacity of mercury
adsorption. For this, an aqueous solution was
obtained using tap water with a pH value of 7.79 to
which was added 4 mL of HgCl2 with a
concentration of 2.736 x 10-4 M. Each quantity of
leafs was introduced into 30 mL of aqueous solution
for a time of 30 minutes at a temperature of
25°Celsius. Further, the vegetal material was
separated from the aqueous solution using filter
paper. The aqueous solutions obtained after
separation was investigated using linear sweep
voltammetry. The linear sweep voltammetry was
performed using the electrochimical combine
VoltaLab 32. The satureted calomel electrode was
used as the reference electrode, while the platinum
wire was used as auxiliar electrode and as working
electrode was utlized a carbon paste electrode. The
working carbon paste electrode had an adsorption
surface of 19.63·10-2 cm2.
3. Results and Discussions
Studying the electrochemical behavior of
mercuric ion it was noticed that the different current
peak of the plant sorbent shown in Figs 1 - 5,
mercury adsorption is directly proportional with the
plant quantity introduced in the tap water, at a
concentration of 2.736 x 10-4 M. It also proves that
the processes that are taking place are slow and
quasi-irreversible.
Different accumulation potentials were tested
with the aim to find the best reduction potential for
mercury (II). Potentials from 500 mV to -500 mV
were applied. The peak currents increases when
reduction potentials were changed from 500 mV to 200 mV. The peak current values of the sorbent
were stabilized within the potential range of 50 mV
and 150 mV.
Salts of divalent mercury are readily soluble
in water, and, by this, highly toxic. The extreme
high affinity of mercury (II) to sulfhydryl groups of
amino acids as cysteine and methionine in enzymes
explains its high toxicity [14].
The preconcentration time was established
after testing the preconcentration process at 30 s, 60
s, 90 s, 120 s, 150 s and 180 s. after this time, no
significant variation was noticed. For a better
accuracy of the result a precocentration of 180 s was
used for the determinations.
The biosorption efficiency of mercury (II)
increased rapidly during the first 5 minutes and
remained nearly constant after 30 minutes. The
mercury sorption was relatively fast suggesting that
the system reached the final equilibrium plateau
within 30 minutes. The increase of contact time
beyond 30 minutes has no significant effect on
biosorption efficiency. Most of mercury sorption
was during the first 10 minutes.
Other parameters such as surface charge
capacity, composition of plant sorbent, metal
affinity and experimental conditions play a role in
the adsorption mechanism.
Figs. 1 - 5 show the current peak of mercury
(II) removal as a function of initial concentration
with 2 mg to 14 mg of plant sorbent (pH 7.79 and
30 minutes).
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VEREȘTIUC Paul Cristinel et al./ProEnvironment 8(2015) 476 - 480
Figure 1. Linear cathodic voltammograms of mercury
adsorption by oregano at different quantity
of plants
Figure 2. Linear cathodic voltammograms of
mercury adsorption by minth at different quantity of
plants
Figure 3. Linear cathodic voltammograms of mercury
adsorption by sage at different quantity
of plants
Figure 4. Linear cathodic voltammograms of
mercury adsorption by parsley at different quantity
of plants
Figure 5. Linear cathodic voltammograms of mercury
adsorption by tarragon at different quantity of plants
Figure 6. Adsorption of aromatic plants at different
quantity of plants
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VEREȘTIUC Paul Cristinel et al./ProEnvironment 8(2015) 476 - 480
This electrochemical behavior of plant
sorbent leads to the following dependence equations
for the cathodic peaks, as a expresion of the
discharge of mercuric ion on the carbon paste
electrode, in all investigation plants:
1. Oregano: I (mA) = -0.00297 + 0.1037 P –
1.03287 P2 (R = 0.99465);
2. Minth: I (mA) = -0.0105 + 2.11661 P –
0.23882 P2 (R = 0.99692);
3. Sage: I (mA) = -0.00713 + 0.26413 P –
2.96068 P2 (R = 0.97652);
4. Parsley: I (mA) = -0.0121 + 0.24772 P –
0.2838 P2 (R = 0.99936);
5. Tarragon: I (mA) = -0.00617 + 0.21172 P –
1.99687 P2 (R = 0.99085);
where P is the quantity of plant sorbent in mg from
34 mL aqueous solution.
4. Conclusions
In this study it was demonstrated that the
cathodic discharge of mercury ions from mercury
(II) aqueous solutions can be pointed out by a
relevant current pick, whose height, is dependent on
the quantity of plants. Best results of mercury
adsorption were obtained during the first 10 minutes
while the increase of contact time beyond 30
minutes has no significant effect on biosorption
efficiency.
The current peak of the plant sorbent in
mercury adsorption was directly proportional with
the plant quantity introduced in the tap water.
The cathodic discharge of mercury of the
mercury ion on tap water it is a slow process, quasiireversible.
The best results in mercury adsorption was
given in ther following order: oregano > tarragon >
sage > minth > parsley. Furthermore, it can be
concluded that oregano leveas hold great potential to
be an effective biosorbent for removal of mercury
and other heavy metals from contaminanted waters
with good eficiency and low cost.
Acknowlegments. This work was supported by the
strategic grant POSDRU/159/1.5/S/133652, cofinanced by the European Social Fund within the
Sectorial Program Human Resources Development
2007-2013.
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