phytoremediation of mercury by terrestrial plants

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PHYTO
-
REMEDIATION

Hg


Dikoleksi

oleh
:

Novie

A.S.
dan

Soemarno

PDKLP
-
PPSUB Mei 2012

FITOREMEDIASI

Sumber
: http://en.wikipedia.org/wiki/Phytoremediation ….
Diunduh

7/5/2012


Phytoremediation

(from Ancient Greek
φυτο (
phyto
)
, meaning "plant",
and Latin
remedium
, meaning "restoring balance") describes the
treatment of environmental problems (bioremediation) through the use
of plants that mitigate the environmental problem without the need to
excavate the contaminant material and dispose of it elsewhere.

Phytoremediation

consists of mitigating pollutant concentrations in
contaminated soils, water, or air, with plants able to contain, degrade, or
eliminate metals, pesticides, solvents, explosives, crude oil and its
derivatives, and various other contaminants from the media that contain
them.

Application

Phytoremediation

may be applied wherever the soil or static water environment has become
polluted or is suffering ongoing chronic pollution. Examples where
phytoremediation

has
been used successfully include the restoration of abandoned metal
-
mine workings, reducing
the impact of sites where polychlorinated biphenyls have been dumped during manufacture
and mitigation of on
-
going coal mine discharges.

Phytoremediation

refers to the natural ability of certain plants called
hyperaccumulators

to
bioaccumulate
,
degrade,or

render harmless contaminants in soils, water, or air.
Contaminants such as metals, pesticides, solvents, explosives, and crude oil and its
derivatives, have been mitigated in
phytoremediation

projects worldwide. Many plants such
as mustard plants, alpine pennycress, hemp, and pigweed have proven to be successful at
hyperaccumulating

contaminants at toxic waste sites.

Phytoremediation

is considered a clean, cost
-
effective and non
-
environmentally disruptive
technology, as opposed to mechanical cleanup methods such as soil excavation or pumping
polluted groundwater. Over the past 20 years, this technology has become increasingly
popular and has been employed at sites with soils contaminated with lead, uranium, and
arsenic. However, one major disadvantage of
phytoremediation

is that it requires a long
-
term
commitment, as the process is dependent on plant growth, tolerance to toxicity, and
bioaccumulation capacity.


KEUNTUNGAN DAN KETERBATASAN

FITOREMEDIASI

Sumber
: ….
Diunduh

7/5/2012

KEUNTUNGAN


1.
the cost of the
phytoremediation

is lower than that of traditional processes
both
in situ

and
ex situ

2.
the plants can be easily monitored

3.
the possibility of the recovery and re
-
use of valuable metals (by companies
specializing in “
phyto

mining”)

4.
it is potentially the least harmful method because it uses naturally occurring
organisms and preserves the environment in a more natural state.


KETERBATASAN


1.
Phytoremediation

is limited to the surface area and depth occupied by the
roots.

2.
Slow growth and low
biomass

require a long
-
term commitment with plant
-
based systems of remediation,

3.
It is not possible to completely prevent the leaching of contaminants into
the
groundwater

(without the complete removal of the contaminated
ground, which in itself does not resolve the problem of contamination)

4.
The survival of the plants is affected by the toxicity of the contaminated
land and the general condition of the soil.

5.
Bio
-
accumulation of contaminants, especially metals, into the plants which
then pass into the
food chain
, from primary level consumers upwards or
requires the safe disposal of the affected plant material.

BERBAGAI PROSES FITOREMEDIASI

Sumber
: ….
Diunduh

7/5/2012

A range of processes mediated by plants or algae are useful in treating environmental
problems:


1.
Phytoextraction



uptake and concentration of substances from the environment
into the plant biomass.

2.
Phytostabilization



reducing the mobility of substances in the environment, for
example, by limiting the leaching of substances from the soil.

3.
Phytotransformation



chemical modification of environmental substances as a
direct result of plant metabolism, often resulting in their inactivation, degradation
(
phytodegradation
), or immobilization (
phytostabilization
).

4.
Phytostimulation



enhancement of soil microbial activity for the degradation of
contaminants, typically by organisms that associate with roots. This process is also
known as
rhizosphere

degradation
.
Phytostimulation

can also involve aquatic
plants supporting active populations of microbial degraders, as in the stimulation
of
atrazine

degradation by hornwort.

5.
Phytovolatilization



removal of substances from soil or water with release into
the air, sometimes as a result of
phytotransformation

to more volatile and/or less
polluting substances.

6.
Rhizofiltration



filtering water through a mass of roots to remove toxic
substances or excess nutrients. The pollutants remain absorbed in or adsorbed to
the roots.


Sumber
: ….
Diunduh

7/5/2012

.

Phytoextraction

Phytoextraction

(or
phytoaccumulation
) uses plants or algae to remove contaminants
from soils, sediments or water into harvestable plant biomass (organisms that take
larger
-
than
-
normal amounts of contaminants from the soil are called
hyperaccumulators
).
Phytoextraction

has been growing rapidly in popularity
worldwide for the last twenty years or so. In general, this process has been tried more
often for extracting heavy metals than for organics. At the time of disposal,
contaminants are typically concentrated in the much smaller volume of the plant
matter than in the initially contaminated soil or sediment. 'Mining with plants', or
phytomining
, is also being experimented with.

The plants absorb contaminants through the root system and store them in the root
biomass and/or transport them up into the stems and/or leaves. A living plant may
continue to absorb contaminants until it is harvested. After harvest, a lower level of
the contaminant will remain in the soil, so the growth/harvest cycle must usually be
repeated through several crops to achieve a significant cleanup. After the process, the
cleaned soil can support other vegetation.

Advantages:

The main advantage of
phytoextraction

is environmental friendliness.
Traditional methods that are used for cleaning up heavy metal
-
contaminated soil
disrupt soil structure and reduce soil productivity, whereas
phytoextraction

can clean
up the soil without causing any kind of harm to soil quality. Another benefit of
phytoextraction

is that it is less expensive than any other clean
-
up process.

Disadvantages:

As this process is controlled by plants, it takes more time than
anthropogenic

soil clean
-
up methods.

Two versions of
phytoextraction
:

natural hyper
-
accumulation
, where plants naturally take up the contaminants in soil
unassisted, and

induced or assisted hyper
-
accumulation
, in which a conditioning fluid containing a
chelator

or another agent is added to soil to increase metal solubility or mobilization
so that the plants can absorb them more easily. In many cases natural
hyperaccumulators

are
metallophyte

plants that can tolerate and incorporate high
levels of toxic metals.

Examples of
phytoextraction

(see also
'Table of
hyperaccumulators
'
):

Arsenic
, using the Sunflower (
Helianthus
annuus
), or the Chinese Brake fern (
Pteris

vittata
), a
hyperaccumulator
. Chinese Brake fern stores
arsenic

in its
leaves
.

Cadmium
, using Willow (
Salix
viminalis
): In 1999, one research experiment performed
by Maria
Greger

and Tommy
Landberg

suggested Willow (Salix
viminlais
) has a
significant potential as a
phytoextractor

of Cadmium (
Cd
), Zinc (Zn), and Copper (Cu),
as willow has some specific characteristics like high transport capacity of heavy metals
from root to shoot and huge amount of biomass production; can be used also for
production of bio energy in the biomass energy power plant.
[3]

Cadmium

and
zinc
, using Alpine pennycress (
Thlaspi

caerulescens
), a
hyperaccumulator

of these metals at levels that would be
toxic

to many plants. On the other hand, the
presence of copper seems to impair its growth (see table for reference).

Lead
, using Indian Mustard (
Brassica

juncea
), Ragweed (
Ambrosia
artemisiifolia
),
Hemp Dogbane (
Apocynum

cannabinum
), or
Poplar

trees, which sequester lead in
their biomass.

Salt
-
tolerant (moderately
halophytic
)
barley

and/or
sugar beets

are commonly used for
the extraction of
Sodium chloride

(common salt) to reclaim fields that were previously
flooded by
sea water
.

Caesium
-
137

and
strontium
-
90

were removed from a pond using
sunflowers

after the
Chernobyl accident
.
[4]

Mercury
,
selenium

and organic pollutants such as
polychlorinated biphenyls

(PCBs)
have been removed from soils by
transgenic plants

containing
genes

for bacterial
enzymes.


Sumber
: ….
Diunduh

7/5/2012

.

Phytostabilization

Phytostabilization

focuses on long
-
term stabilization and containment of the
pollutant. Example, the plant's presence can reduce wind erosion; or the
plant's roots can prevent water erosion, immobilize the pollutants by
adsorption or accumulation, and provide a zone around the roots where the
pollutant can precipitate and stabilize. Unlike
phytoextraction
,
phytostabilization

focuses mainly on sequestering pollutants in soil near the
roots but not in plant tissues. Pollutants become less
bioavailable
, and
livestock, wildlife, and human exposure is reduced. An example application
of this sort is using a vegetative cap to stabilize and contain
mine tailings


Sumber
: ….
Diunduh

7/5/2012

.

Phytotransformation

In the case of
organic

pollutants, such as
pesticides
,
explosives
,
solvents
, industrial
chemicals, and other
xenobiotic

substances, certain plants, such as
Cannas
, render
these substances non
-
toxic by their
metabolism
. In other cases,
microorganisms

living
in association with plant roots may metabolize these substances in
soil

or water. These
complex and recalcitrant compounds cannot be broken down to basic molecules
(water, carbon
-
dioxide, etc.) by plant molecules, and, hence, the term
phytotransformation

represents a change in chemical structure without complete
breakdown of the compound. The term "Green Liver Model" is used to describe
phytotransformation
, as plants behave analogously to the human
liver

when dealing
with these
xenobiotic

compounds (foreign compound/pollutant).
[7]

After uptake of the
xenobiotics
, plant enzymes increase the polarity of the
xenobiotics

by adding
functional groups such as hydroxyl groups (
-
OH).

This is known as Phase I metabolism, similar to the way that the human liver increases
the polarity of drugs and foreign compounds (
Drug Metabolism
). Whereas in the
human liver enzymes such as
Cytochrome

P450s

are responsible for the initial
reactions, in plants enzymes such as
nitroreductases

carry out the same role.

In the second stage of
phytotransformation
, known as Phase II metabolism, plant
biomolecules

such as glucose and amino acids are added to the polarized
xenobiotic

to
further increase the polarity (known as conjugation). This is again similar to the
processes occurring in the human liver where
glucuronidation

(addition of glucose
molecules by the UGT (e.g.
UGT1A1
) class of enzymes) and
glutathione

addition
reactions occur on reactive
centres

of the
xenobiotic
.

Phase I and II reactions serve to increase the polarity and reduce the toxicity of the
compounds, although many exceptions to the rule are seen. The increased polarity
also allows for easy transport of the
xenobiotic

along aqueous channels.

In the final stage of
phytotransformation

(Phase III metabolism), a
sequestration
[
disambiguation needed

]

of the
xenobiotic

occurs within the plant. The
xenobiotics

polymerize in a
lignin
-
like manner and develop a complex structure that is
sequestered in the plant. This ensures that the
xenobiotic

is safely stored, and does
not affect the functioning of the plant. However, preliminary studies have shown that
these plants can be toxic to small animals (such as snails), and, hence, plants involved
in
phytotransformation

may need to be maintained in a closed enclosure.

Hence, the plants reduce toxicity (with exceptions) and sequester the
xenobiotics

in
phytotransformation
.
Trinitrotoluene

phytotransformation

has been extensively
researched and a transformation pathway has been proposed


Sumber
: http://en.wikipedia.org/wiki/Phytoremediation,_Hyperaccumulators ….
Diunduh

7/5/2012

.

Hyperaccumulators

and biotic interactions

A plant is said to be a
hyperaccumulator

if it can concentrate the pollutants in a
minimum percentage which varies according to the pollutant involved (for example:
more than 1000

mg/kg of dry weight for
nickel
,
copper
,
cobalt
,
chromium

or
lead
; or
more than 10,000

mg/kg for
zinc

or
manganese
).
[10]

This capacity for accumulation is
due to
hypertolerance
, or
phytotolerance
: the result of
adaptative

evolution from the
plants to hostile environments through many generations. A number of interactions
may be affected by metal
hyperaccumulation
, including protection, interferences with
neighbour

plants of different species, mutualism (including
mycorrhizae
,
pollen

and
seed dispersal), commensalism, and
biofilm
.


Hyperaccumulators

and contaminants

:
Al
,
Ag
,
As
,
Be
,
Cr
,
Cu
,
Mn
,
Hg
,
Mo
, naphthalene,
Pb
,
Pd
,
Pt
,
Se
,
Zn



accumulation rates.


Contaminant

Accumulation
rates (in mg/kg
dry weight)

Latin name

English name

H
-
Hyperaccumul
ator or A
-
Accumulator P
-
Precipitator T
-
Tolerant

Notes

Sources

Al
-
Aluminium

A
-

Agrostis

castellana

Highland Bent
Grass

As
(A),
Mn
(A),
Pb
(A),
Zn
(A)

Origin
Portugal.

[1]

Hg
-
Mercury

A
-

Bacopa monnieri

Smooth Water
Hyssop

Cd
(H),
Cr
(H),
Cu
(H),
Hg
(A),
Pb
(A)

Origin India.
Aquatic emergent
species.

[1][17]

Hg
-
Mercury

xxx

Brassica napus

Rapeseed

plant

Ag
,
Cr
,
Pb
,
Se
,
Zn

Phytoextraction

[6][7]

Hg
-
Mercury

xxx

Eichhornia
crassipes

Water Hyacinth

Cd
(H),
Cr
(A),
Cu
(A),
Pb
(H),
Zn
(A)Also
Cs
,
Sr
,
U
,
[21]

and
pesticides.
[22]

Pantropical/Subtro
pical, 'the
troublesome
weed'.

[1]

Hg
-
Mercury

H
-

Hydrilla verticillata

Hydrilla

Cd
(H),
Cr
(A),
Pb
(H)

xxx

[1]

Hg
-
Mercury

1000

Pistia stratiotes

Water lettuce

Cd
(T),
Cr
(H),
Cu
(T)

35 records of
plants

[1][3][31][36]

Hg
-
Mercury

xxx

Salix

spp.

Osier

spp.

Ag
,
Cr
,
Se
,
Petroleum
hydrocarbures
,
Organic solvents,
MTBE
,
TCE

and by
-
products;
[7]

Cd
,
Pb
,
U
, Zn (
S.
viminalix
);
[8]

Potassium
ferrocyanide

(
S.
babylonica

L.)
[9]

Phytoextraction
.
Perchlorate

(wetland
halophytes)

[7]

Sumber
: http://en.wikipedia.org/wiki/Phytoremediation ….
Diunduh

7/5/2012

.

Phytoscreening

As plants are able to
translocate

and accumulate particular types of contaminants,
plants can be used as
biosensors

of subsurface contamination, thereby allowing
investigators to quickly delineate contaminant plumes.
[11][12]

Chlorinated solvents, such
as
trichloroethylene
, have been observed in tree trunks at concentrations related to
groundwater concentrations.
[13]

To ease field implementation of
phytoscreening
,
standard methods have been developed to extract a section of the tree trunk for later
laboratory analysis, often by using an
increment borer
.
[14]

Phytoscreening

may lead to
more optimized site investigations and reduce contaminated site cleanup costs.


Sumber
: ….
Diunduh

7/5/2012

Phytoremediation

plants

Phytoremediation

process and principles diagram.
(French)

Plants

used for
Phytoremediation

in sustainable
bioremediation

treatment

cleanup

restoration projects to contain, degrade, or eliminate
transient pollution

waste and/or on
-
site pollution

toxins


Sumber
: http://en.wikipedia.org/wiki/Rhizofiltration ….
Diunduh

7/5/2012

Rhizofiltration


Rhizofiltration

is a form of
bioremediation

that involves
filtering

water

through a mass
of
roots

to remove
toxic

substances or excess
nutrients
.


Rhizofiltration

is a type of
phytoremediation
, which refers to the approach of using
hydroponically cultivated plant roots to remediate contaminated water through
absorption, concentration, and precipitation of
pollutants
.It

also filters through water
and dirt.

The contaminated water is either collected from a waste site and brought to the
plants, or the plants are planted in the contaminated area, where the roots then take
up the water and the contaminants dissolved in it. Many plant species naturally uptake
heavy metals

and excess
nutrients

for a variety of reasons:
sequestration
,
drought

resistance, disposal by leaf
abscission
, interference with other plants, and defense
against
pathogens

and
herbivores
.
[1]

Some of these species are better than others and
can accumulate extraordinary amounts of these contaminants. Identification of such
plant species has led environmental researchers to realize the potential for using these
plants for
remediation

of contaminated soil and
wastewater
.


.

Process

This process is very similar to
phytoextraction

in that it removes contaminants by
trapping them into harvestable plant
biomass
. Both
phytoextraction

and
rhizofiltration

follow the same basic path to remediation. First, plants are put in contact with the
contamination. They absorb contaminants through their root systems and store them
in root biomass and/or transport them up into the stems and/or leaves. The plants
continue to absorb contaminants until they are harvested. The plants are then
replaced to continue the growth/harvest cycle until satisfactory levels of contaminant
are achieved. Both processes are also aimed more toward concentrating and
precipitating heavy metals than organic contaminants. The major difference between
rhizofiltration

and
phytoextraction

is that
rhizofiltration

is used for treatment in
aquatic environments, while
phytoextraction

deals with soil remediation.


RHIZOFILTRASI

Sumber
: http://en.wikipedia.org/wiki/Rhizofiltration ….
Diunduh

7/5/2012

.

Applications

Weeping Willows

Rhizofiltration

may be applicable to the treatment of surface water and groundwater,
industrial and residential effluents, downwashes from power lines, storm waters,
acid
mine drainage
, agricultural runoffs, diluted
sludges
, and
radionuclide
-
contaminated
solutions. Plants suitable for
rhizofiltration

applications can efficiently remove toxic
metals from a solution using rapid
-
growth root systems. Various
terrestrial plant

species have been found to effectively remove toxic metals such as Cu
2+
, Cd
2+
, Cr
6+
,
Ni
2+
, Pb
2+
, and Zn
2+

from aqueous solutions.
[2]

It was also found that low level
radioactive

contaminants can successfully be removed from liquid streams.
[3]

A system
to achieve this can consist of a “feeder layer” of soil suspended above a contaminated
stream through which plants grow, extending the bulk of their roots into the water. The
feeder layer allows the plants to receive fertilizer without contaminating the stream,
while simultaneously removing heavy metals from the water.
[4]

Trees

have also been
applied to remediation. Trees are the lowest cost plant type. They can grow on land of
marginal quality and have long life
-
spans. This results in little or no maintenance costs.
The most commonly used are
willows

and
poplars
, which can grow 6
-

8’ per year and
have a high flood tolerance. For deep contamination, hybrid poplars with roots
extending 30 feet deep have been used. Their roots penetrate microscopic scale pores
in the soil matrix and can cycle 100 L of water per day per tree. These trees act almost
like a pump and treat remediation system.
[5]


RHIZOFILTRASI

Sumber
: ….
Diunduh

7/5/2012

.

Cost

Sunflowers used for
rhizofiltration

Rhizofiltration

is cost
-
effective for large volumes of water having low concentrations of
contaminants that are subjected to stringent standards.
[6]

It is relatively inexpensive,
yet potentially more effective than comparable technologies. The removal of
radionuclides

from water using
sunflowers

was estimated to cost between $2 and $6
per thousand gallons of water treated, including waste disposal and capital costs.
[7]

[
edit
] Advantages

Rhizofiltration

is a treatment method that may be conducted
in situ
, with plants being
grown directly in the contaminated water body. This allows for a relatively inexpensive
procedure with low capital costs. Operation costs are also low but depend on the type
of contaminant. This treatment method is also aesthetically pleasing and results in a
decrease of water infiltration and
leaching

of contaminants.
[5]

After harvesting, the
crop may be converted to
biofuel

briquette, a substitute for fossil fuel.
[8]

[
edit
] Disadvantages

This treatment method has its limits. Any contaminant that is below the rooting depth
will not be extracted. The plants used may not be able to grow in highly contaminated
areas. Most importantly, it can take years to reach regulatory levels. This results in
long
-
term maintenance. Also, most contaminated sites are polluted with many
different kinds of contaminants. There can be a combination of metals and organics, in
which treatment through
rhizofiltration

will not suffice.
[5]

Plants grown on polluted
water and soils become a potential threat to human and animal health, and therefore,
careful attention must be paid to the harvesting process and only non
-
fodder crop
should be chosen for the
rhizofiltration

remediation method.


BIO
-
RETENSI

Sumber
: http://en.wikipedia.org/wiki/Bioretention ….
Diunduh

7/5/2012

.

Bioretention

is the process in which contaminants and
sedimentation

are removed
from
stormwater

runoff
.
Stormwater

is collected into the treatment area which
consists of a grass buffer strip, sand bed,
ponding

area,
organic

layer or
mulch

layer,
planting
soil
, and plants. Runoff passes first over or through a sand bed, which slows
the runoff's velocity, distributes it evenly along the length of the
ponding

area, which
consists of a surface
organic

layer and/or
groundcover

and the underlying planting soil.
The
ponding

area is graded, its center depressed. Water is
ponded

to a depth of 15

cm
(5.9

in) and gradually infiltrates the
bioretention

area or is
evapotranspired
. The
bioretention

area is graded to divert excess runoff away from itself. Stored water in the
bioretention

area planting soil
exfiltrates

over a period of days into the underlying soils

A
bioretention

cell, also called a
rain garden
, in the
United States
. It is designed to treat
polluted
stormwater

runoff

from an adjacent parking lot. Plants are in winter
dormancy.

Merkuri

(Hg)

Sumber
: http://en.wikipedia.org/wiki/Mercury_%28element%29 ….
Diunduh

7/5/2012

.

Toxicity and safety

See also:
Mercury poisoning

and
Mercury cycle

Mercury and most of its compounds are extremely toxic and must be
handled with care; in cases of spills involving mercury (such as from certain
thermometers

or
fluorescent light bulbs
), specific cleaning procedures are
used to avoid exposure and contain the spill.
[77]

Protocols call for physically
merging smaller droplets on hard surfaces, combining them into a single
larger pool for easier removal with an
eyedropper
, or for gently pushing the
spill into a disposable container. Vacuum cleaners and brooms cause greater
dispersal of the mercury and should not be used. Afterwards, fine
sulfur
,
zinc
, or some other powder that readily forms an amalgam (alloy) with
mercury at ordinary temperatures is sprinkled over the area before itself
being collected and properly disposed of. Cleaning porous surfaces and
clothing is not effective at removing all traces of mercury and it is therefore
advised to discard these kinds of items should they be exposed to a mercury
spill.

Mercury can be inhaled and absorbed through the skin and mucous
membranes, so containers of mercury are securely sealed to avoid spills and
evaporation. Heating of mercury, or of compounds of mercury that may
decompose when heated, is always carried out with adequate ventilation in
order to avoid exposure to mercury vapor. The most toxic forms of mercury
are its
organic compounds
, such as
dimethylmercury

and
methylmercury
.
Inorganic compounds, such as
cinnabar

are also highly toxic by ingestion or
inhalation.
[78]

Mercury can cause both chronic and acute poisoning.


Merkuri

(Hg):

Pelepasan

ke

Lingkungan

Sumber
: http://en.wikipedia.org/wiki/Mercury_%28element%29 ….
Diunduh

7/5/2012

. Preindustrial deposition rates of mercury from the atmosphere may be about 4

ng

/(1
L of ice deposit). Although that can be considered a natural level of exposure, regional
or global sources have significant effects. Volcanic eruptions can increase the
atmospheric source by 4

6 times.
[79]

Natural sources, such as
volcanoes
, are responsible for approximately half of
atmospheric mercury emissions. The human
-
generated half can be divided into the
following estimated percentages:
[80][81][82]

65% from stationary combustion, of which
coal
-
fired power plants

are the largest
aggregate source (40% of U.S. mercury emissions in 1999). This includes power plants
fueled with gas where the mercury has not been removed. Emissions from coal
combustion are between one and two orders of magnitude higher than emissions from
oil combustion, depending on the country.
[80]

11% from gold production. The three largest point sources for mercury emissions in
the U.S. are the three largest gold mines.
Hydrogeochemical

release of mercury from
gold
-
mine tailings has been accounted as a significant source of atmospheric mercury
in eastern Canada.
[83]

6.8% from
non
-
ferrous metal

production, typically
smelters
.

6.4% from
cement

production.

3.0% from
waste disposal
, including
municipal

and
hazardous waste
,
crematoria
, and
sewage sludge

incineration.

3.0% from
caustic soda

production.

1.4% from
pig iron

and
steel

production.

1.1% from mercury production, mainly for batteries.

2.0% from other sources.

The above percentages are estimates of the global human
-
caused mercury emissions
in 2000, excluding biomass burning, an important source in some regions.
[80]

Current atmospheric mercury contamination in outdoor urban air is (0.01

0.02

µg/m
3
)
indoor concentrations are significantly elevated over outdoor concentrations, in the
range 0.0065

0.523

µg/m
3

(average 0.069

µg/m
3
).
[84]

Mercury also enters into the environment through the improper disposal (e.g., land
filling, incineration) of certain products. Products containing mercury include: auto
parts,
batteries
, fluorescent bulbs, medical products, thermometers, and
thermostats.
[85]

Due to health concerns (see below),
toxics use reduction

efforts are
cutting back or eliminating mercury in such products. For example, the amount of
mercury sold in thermostats in the United States decreased from 14.5 tons in 2004 to
3.9 tons in 2007.
[86]

Most thermometers now use pigmented
alcohol

instead of
mercury, and
galinstan

alloy thermometers are also an option. Mercury thermometers
are still occasionally used in the medical field because they are more accurate than
alcohol thermometers, though both are commonly being replaced by electronic
thermometers and less commonly by
galinstan

thermometers. Mercury thermometers
are still widely used for certain scientific applications because of their greater accuracy
and working range.

The United States
Clean Air Act
, passed in 1990, put mercury on a list of toxic
pollutants that need to be controlled to the greatest possible extent. Thus, industries
that release high concentrations of mercury into the environment agreed to install
maximum achievable control technologies (MACT). In March 2005 EPA rule
[87]

added
power plants to the list of sources that should be controlled and a national
cap and
trade

rule was issued. States were given until November 2006 to impose stricter
controls, and several States are doing so. The rule was being subjected to legal
challenges from several States in 2005 and decision was made in 2008. The Clean Air
Mercury Rule was struck down by a Federal Appeals Court on February 8, 2008. The
rule was deemed not sufficient to protect the health of persons living near coal
-
fired
power plants. The court opinion cited the negative impact on human health from coal
-
fired power plants' mercury emissions documented in the EPA Study Report to
Congress of 1998.
[88]

The EPA announced new rules for coal
-
fired power plants on December 22, 2011.
[89]

Cement kilns that burn hazardous waste are held to a looser standard than are
standard
hazardous waste

incinerators

in the United States, and as a result are a
disproportionate source of mercury pollution.
[90]

Historically, one of the largest releases was from the
Colex

plant, a lithium
-
isotope
separation plant at Oak Ridge. The plant operated in the 1950s and 1960s. Records are
incomplete and unclear, but government commissions have estimated that some two
million pounds of mercury are unaccounted for.
[91]

A serious
industrial disasters

was the dumping of mercury compounds into
Minamata

Bay, Japan. It is estimated that over 3,000 people suffered various deformities, severe
mercury poisoning symptoms or death from what became known as
Minamata

disease


Merkuri

(Hg)

Sumber
: http://en.wikipedia.org/wiki/Mercury_%28element%29 ….
Diunduh

7/5/2012

.

Chemistry

See also:
Category:Mercury

compounds

Mercury exists in two main oxidation states, I and II. Higher oxidation states are
unimportant, but have been detected, e.g.,
mercury(IV) fluoride

(HgF
4
) but only under
extraordinary conditions.
[29]

[
edit
] Compounds of mercury(I)

Different from its lighter neighbors, cadmium and zinc, mercury forms simple stable
compounds with metal
-
metal bonds. The mercury(I) compounds are
diamagnetic

and
feature the
dimeric

cation
, Hg2+

2. Stable derivatives include the chloride and nitrate. Treatment of Hg(I) compounds
complexation

with strong
ligands

such as sulfide, cyanide, etc. induces
disproportionation

to Hg
2+

and elemental mercury.
[30]

Mercury(I) chloride
, a colorless
solid also known as
calomel
, is really the compound with the formula Hg
2
Cl
2
, with the
connectivity
Cl
-
Hg
-
Hg
-
Cl. It is a standard in electrochemistry. It reacts with chlorine to
give mercuric chloride, which resists further oxidation.

Indicative of its tendency to bond to itself, mercury forms
mercury
polycations
, which
consist of linear chains of mercury centers, capped with a positive charge. One
example is Hg
3
2+
(AsF
6

)
2
.
[31]

[
edit
] Compounds of mercury(II)

Mercury(II) is the most common oxidation state and is the main one in nature as well.
All four mercuric halides are known. The form tetrahedral complexes with other
ligands

but the halides adopt linear coordination geometry, somewhat like Ag
+

does.
Best known is
mercury(II) chloride
, an easily
sublimating

white solid. HgCl
2

forms
coordination complexes

that are typically tetrahedral, e.g. HgCl
4
2

.

Mercury(II) oxide
, the main
oxide

of mercury, arises when the metal is exposed to air
for long periods at elevated temperatures. It reverts to the elements upon heating
near 400
°
C, as was demonstrated by Priestly in an early synthesis of pure
oxygen
.
[7]

Hydroxides of mercury are poorly characterized, as they are for its neighbors gold and
silver.

Being a
soft metal
, mercury forms very stable derivatives with the heavier
chalcogens
.
Preeminent is
mercury(II) sulfide
,
HgS
, which occurs in nature as the ore cinnabar and
is the brilliant pigment
vermillion
. Like
ZnS
,
HgS

crystallizes in two
forms
, the reddish
cubic form and the black
zinc
blende

form.
[5]

Mercury(II)
selenide

(
HgSe
) and
mercury(II) telluride

(
HgTe
) are also known, these as well as various derivatives, e.g.
mercury cadmium telluride

and
mercury zinc telluride

being
semiconductors

useful as
infrared detector

materials.
[32]

Mercury(II) salts form a variety of complex derivatives with
ammonia
. These include
Millon's

base (Hg
2
N
+
), the one
-
dimensional polymer (salts of HgNH
2
+
)
n
), and "fusible
white precipitate" or [Hg(NH
3
)
2
]Cl
2
. Known as
Nessler's

reagent
,
potassium
tetraiodomercurate
(II)

(HgI
4
2

) is still occasionally used to test for ammonia owing to its
tendency to form the deeply colored iodide salt of
Millon's

base.

Mercury fulminate

is a
detonator

widely used in
explosives
.
[5]

[
edit
] Compounds of mercury(IV)

Mercury(IV) is the rarest oxidation state of mercury which is known to exist. The only
known mercury(IV) compound is
mercury(IV) fluoride
.

[
edit
]
Organomercury

compounds

Main article:
Organomercury

compound

Organic mercury
compounds

are historically important but are of little industrial value
in the western world. Mercury(II) salts are a rare examples of simple metal complexes
that react directly with aromatic rings.
Organomercury

compounds are always divalent
and usually two
-
coordinate and linear geometry. Unlike
organocadmium

and
organozinc

compounds,
organomercury

compounds do not react with water. They
usually have the formula HgR
2
, which are often volatile, or
HgRX
, which are often
solids, where R is
aryl

or
alkyl

and X is usually halide or acetate.
Methylmercury
, a
generic term for compounds with the formula CH
3
HgX is a dangerous family of
compounds that are often found in
polluted

water.
[33]

They arise by a process known as
biomethylation
.


Merkuri

(Hg)

Sumber
: http://en.wikipedia.org/wiki/Mercury_%28element%29 ….
Diunduh

7/5/2012

.

Properties

[
edit
] Physical properties

A
pound coin

(density ~7.6 g/cm
3
) floats in mercury due to the combination of the
buoyant force

and
surface tension
.

Mercury is a heavy, silvery
-
white metal. As compared to other metals, it is a poor
conductor of heat, but a fair conductor of electricity.
[5]

Mercury has an exceptionally
low melting temperature for a d
-
block metal. A complete explanation of this fact
requires a deep excursion into
quantum physics
, but it can be summarized as follows:
mercury has a unique electronic configuration where electrons fill up all the available
1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d and 6s
subshells
. As such configuration
strongly resists removal of an electron, mercury behaves similarly to
noble gas

elements, which form weak bonds and thus easily melting solids. The stability of the 6s
shell is due to the presence of a filled 4f shell. An f shell poorly screens the nuclear
charge that increases the attractive
Coulomb interaction

of the 6s shell and the
nucleus (see
lanthanide contraction
). The absence of a filled inner
f

shell is the reason
for the somewhat higher melting temperature of
cadmium

and
zinc
, although both
these metals still melt easily and, in addition, have unusually low boiling points. Metals
such as
gold

have atoms with one less 6s electron than mercury. Those electrons are
more easily removed and are shared between the gold atoms forming relatively strong
metallic bonds
.
[3][6]

[
edit
] Chemical properties

Mercury does not react with most acids, such as dilute
sulfuric acid
, although
oxidizing
acids

such as concentrated
sulfuric acid

and
nitric acid

or
aqua
regia

dissolve it to give
sulfate
,
nitrate
, and
chloride

salts. Like silver, mercury reacts with atmospheric
hydrogen sulfide
. Mercury even reacts with solid sulfur flakes, which are used in
mercury spill kits to absorb mercury vapors (spill kits also use
activated carbon

and
powdered zinc).
[7]


FITOREMEDIASI
Merkuri

(Hg)

Sumber
: http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/homepage.html ….
Diunduh

7/5/2012

Mercury is an element






Mercury (Hg) is a silvery metallic liquid as
toom

temperature.

Nautral

sources of Hg
occur from
outgassing

of the earth's crust through volcanoes and evaporation from the
ocean.

It can be found in familiar items such as
lightbulbs
, batteries, thermometers,
pesticides, paint and some dental fillings (amalgams).

It is also sometimes used as a
catalyst in chemical reactions or in gold extraction procedures.

In nature, mercury
exists in several forms:

1) as ionic salts in either the
mercurous

(I) or mercuric (II)
states, 2) as an
organometallic

compound such as methyl mercury, or 3) as elemental
mercury Hg(0) in either liquid or vapor phase.

Mercury in the Environment






Mercury is believed to be transported throughout the environment by two
cycles.

On a global scale, Hg(0) vapor circulates through the earth's atmosphere from
land sources to the oceans
(3)
.

Researchers believe that the global amount of Hg has
increased by a factor of 2
-
5 since the advent of industry
(3)
.

This amounts to a total
estimate of approximately 10,000 tons of mercury being released worldwide into the
environment from both man
-
made and natural sources.

The second cycle occurs on a
local scale and involves
methylation

of atmospheric mercury, which is deposited into
bodies of water, by
methanogenic

bacteria to form methyl mercury.

This compound is
somewhat soluble in water and is taken up by organisms and concentrations are
"biomagnified" in animals such as fish, which are higher up in the food chain
(3)
.

FITOREMEDIASI
Merkuri

(Hg)

Sumber
: http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/homepage.html ….
Diunduh

7/5/2012

.

The Problem:

Mercury is toxic to many organisms






Because many animals, including humans, can potentially feed on contaminated
fish, shellfish, or sea mammals, contamination poses an immediate health threat.




Mercury is toxic to humans






During the 1950's the first major mercury
posioning

epidemic occurred in
Minamata

Bay in Kyushu, Japan.

Residents had cons

umed

methyl mercury
-
contaminated fish and shellfish.

The source of contamination
was effluent from a chemical manufacturing company,
Chisso
, which specialized in the
production of
acetylaldehyde
.

Mercury was used as a catalyst in the production
process and waste was released into
Minamata

Bay.

Many families who suffered
posioning

were associated with the local fishing industry.

Victims experienced ataxia
(loss of precise control of movement),

visual problems, loss of hearing and mental
confusion.

They became prone





























to shouting and violent behavior which often lead to coma
(1)
.

An estimated 1,435
people have died because of this contamination
(4)
.

Additional epidemics occurred
not long afterward in Niigata, Japan due to contaminated seafood
(1)

and in Iraq due
to consumption of seed grain that had been treated with a mercury
-
containing
fungicide
(2)
.

The largest concern, however, is that low levels of mercury exposure is
particularly harmful to the fetus.

Infants born to mothers who have been exposed to
mercury contamination while or before becoming pregnant have shown a high
incidence of mental retardation, ataxia, seizure, sensory disturbance, visual problems,
and hearing impairment
(1)
.

FITOREMEDIASI
Merkuri

(Hg)

Sumber
: http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/homepage.html ….
Diunduh

7/5/2012

Mercury is toxic to most plants






Plants that are exposed to mercury accumulate the metal, however
drastic decreases in growth are usually observed.

Plants exposed to ionic
mercury through the root exhibit reduced growth of shoots and roots.

They
also accumulate mercury in the root with slow movement to the
shoot.

Tree leaves can trap atmospheric mercury.

It is thought that
inorganic mercury may cause changes in root tip cell membrane integrity
while methyl mercury may affect organelle metabolism processes that
eventually
interrup

cell membrane integrity

FITOREMEDIASI
Merkuri

(Hg)

Sumber
: http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/homepage.html ….
Diunduh

7/5/2012

.

A solution:

Removing methyl mercury from water and soil
-

Phytoremediation

Technologies






Phytoremediation

or remedying a contaminated site using plants, is a
relatively new area of research.

Mercury
-
resistant bacteria have been
reported to produce enzymes that catalyze two reactions:

1)
organomercurial

lyase

-

which removes methyl groups from mercury to
create ionic mercury, and 2) mercuric ion
reductase

which converts ionic
mercury to volatile elemental mercury.

Plants engineered to express these
genes could have potential for relatively inexpensive clean
-
up of mercury
contaminated sites.

Additionally, many sites that are contaminated with
various metals are also contaminated with mercury which may be the most
toxic metal and is limiting to growth.

Volatilization of elemental mercury
would allow mercury to diffuse out of the plant and into the atmosphere at
diffuse and non
-
toxic concentrations
(15)
.

.

Phytoremediation

Technologies

-
Solutions
-

(
sumber
:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationt
echnologies.html )








Mercury pollution poses an immediate threat not only to human health, but also to
other plants, microorganisms and animals in the environment.

Methanogenic

bacteria
convert ionic and/or elemental mercury to methyl mercury, which is highly
toxic.

Other bacteria have been reported to produce enzymes that remove methyl
groups from mercury and reduce ionic mercury to less toxic elemental mercury Hg
(0).

Elemental Hg (0) is highly volatile and is readily converted from liquid to vapor
-
phase.

These bacteria could be used to volatilize Hg (0), however this process is
slow.

The genes involved in bacterial conversion of methyl mercury to ionic mercury
Hg+, to elemental mercury vapor Hg(0) are all a part of a mercury
-
responsive bacterial
operon
.

When a bacterium is exposed to

mercury, the gene products of the
operon

are expressed.

These include a mercury responsive regulatory protein, transport
proteins that bind and transport mercury into the cell,
organomercuric

lyase
, which
catalyzes the removal of the methyl group of methyl mercury converting it into ionic
mercury Hg+ (
merB
), and mercuric ion
reductase

which catalyzes the conversion of
ionic mercury to volatile elemental mercury (
merA
).

If the
merA

and
merB

are
expressed in plants, then these plants could clean up or
phytoremediate

a mercury
-
contaminated site with relatively low cost compared to current manual ex situ
processes.

Researchers have isolated the genes encoding these enzymes and
introduced them into plants.

The intention behind this research is to explore the
potential of plants to take up methyl mercury and convert it to volatile Hg(0).

The
following are summaries of some of the major contributing research in this area.

FITOREMEDIASI
Merkuri

(Hg)

Sumber
:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
Diunduh

7/5/2012

Rugh
, C.
, Dayton Wilde, H., Stack, N., Thompson, D.M., Summers A.O., and
Meagher, R.B.
,
(1996)

Mercuric ion reduction and resistance in transgenic
Arabidopsis thaliana

plants expressing
a modified bacterial
mer
A

gene.

Proc. Natl. Acad. Sci.

93:3182
-
3187.







The enzyme, mercuric ion
reductase
, encoded by the gene
merA
, reduces ionic
mercury (Hg+) to the less toxic volatile Hg(0) using NADPH reducing
equivalents.

Because the
merA

gene was found to be very G+C rich (~67%) and was
suited for expression only in a bacterial system, early attempts to express this gene in
plant systems were unsuccessful.



Rugh

et al.

replaced
codons

287
-
336, which constituted 9% of the coding region to
contain a sequence of DNA that had
codon

usage that was more suited to expression
in plant systems.

Transgenic
Arabidopsis thaliana

plants containing this modified
merApe9 expressed the gene product mercuric ion
reductase
.

Additionally, merApe9
seeds germinated and grew into seedlings on agar plates containing 50
micromolar

HgCl2 while control plants did not.




Mercury vapor analysis showed that transgenic merApe9 plants
volatilized significant amounts (~50
ng

Hg(0)/mg tissue of mercury
vapor.



Finally, Northern blots of total mRNA from transgenic plants
confirmed merApe9 gene expression.

These data suggest that the
potential for plants that volatilize Hg are viable.

FITOREMEDIASI
Merkuri

(Hg)

Sumber
:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
Diunduh

7/5/2012

Rugh
, C.
,
Senecoff
, J.,
Meagher, R.
, and
Merkle
, S. (1998)

Development of
transgenic yellow poplar for mercury
phytoremediation
.
Nature
Biotechnology.

16:925
-
928.

.


Transgenic
Arabidopsis

plants expressing the merA9 gene construct converted ionic
Hg+ to volatile Hg(0).


Expression of this type of system in a high biomass plant with
potential environmental application, such as yellow poplar (
Liriodendron
tulipifera
)
may provide a means for
phytovolatilization

of mercury pollution.


The merA9
sequence was further modified to contain an additional 9% of the coding sequence
fragment of DNA with plant
-
like
codon

usage.


This further modified merA18 sequence
was transformed using particle bombardment of yellow poplar
proembryonic

masses.


Transgenic plantlets grew on agar plates containing 25microM and 50microM
HgCl2, whereas control plants did not.


Additionally significant Hg (0) volatilization was
observed by transgenic lines.


The demonstrated ability of genetically engineered
yellow poplar to grow on increased concentrations of ionic Hg+ may demonstrate the
potential for
phytovolitazion

methods of mercury remediation.


However, this research
is still in its infancy and future experiments may include growing transgenic poplar
plants on mercury
-
contaminated soils.

FITOREMEDIASI
Merkuri

(Hg)

Sumber
:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
Diunduh

7/5/2012

Bizily
, S.,
Rugh
, C.
, Summers, A.,
Meagher, R
. (1999)

Phytoremediation

of
methylmercury

pollution:

mer
B

expression in
Arabidopsis thaliana

confers resistance
to
organomercurials
.

Proc. Natl. Acad. Sci.

96:6808
-
6813.




Mercury deposited into bodies of water is typically converted to methyl
-
mercury by
methanogenic

bacteria.


Other mercury
-
resistant bacteria eliminate methyl mercury by
producing an enzyme,
organomercurial

lyase

encoded by the gene
merB
.


Because
most mercury
-
contaminated water contains methyl mercury, there would be a benefit
to producing a model system in which
merB

was expressed.


Bizily

et al
., report that
transformants

of
Arabidopsis

with
merB

grow on higher
concentrations of methyl mercury
-
like compounds than control plants.


The
merB

gene that was isolated from mercury
-
resistant bacteria was modified using PCR
techniques to contain flanking regions containing consensus plant sequences and
restriction sites.




The new
merB

gene was transformed into
Arabidopsis thaliana

by
Agrobacterium

tumefaciens
-
mediated transformation.


Transgenic
merB

plants grew on agar
plates containing
phenylmercuric

acetate or
methylmercuric

chloride while control
plants and transgenic
merA

plants did not.


Additional western blot studies
confirmed the expression of significant amounts of the
merB

gene product,
organomercruial

lyase
.





Results suggest that
merB

was successfully transformed and expressed in
Arabidopsis thaliana

plants as well as conferring resistance to
organomercurials
.

FITOREMEDIASI
Merkuri

(Hg)

Sumber
:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
Diunduh

7/5/2012

Bizily
, S.,
Rugh
, C.
,
Meagher, R.

(2000)

Phytodetoxification

of hazardous
organomercurials

by genetically engineered plants.

Nature Biotechnology.


18:213
-
217.







Methylmercury

is found in wetlands and aquatic sediments worldwide.

Both ionic
mercury and
methylmercury

are absorbed in the gastrointestinal tract of animals, but
methylmercury

is retained much longer in the body and is, therefore, is carried up
through the food chain more efficiently.

Plants engineered with both the
merA

and
merB

genes should be able to extract
methylmercury

from contaminated
environments and transpire Hg(0) into the atmosphere.







Because Hg(0) resides in the atmosphere for approximately two years, transpired
Hg(0) will be diluted to much lower concentrations before being
redeposited

into
terrestrial waters and sediments rather than being concentrated in one
area.

Additionally the amount of Hg(0) emitted from sites undergoing
phytovolitalization

can be regulated and will most likely be small in comparison to the
concentrations of Hg(0) already in the atmosphere.






Arabidopsis thaliana plants that had been separately transformed to contain
constructs that express
merA

and
merB
, respectively, were crossed.

F2
generation plants were analyzed for expression of both the
merA

and
merB

gene products in the same plant.

Plantlets containing
merA

or
merA

and
merB

grew on concentrations of
methylmercury
-
like compounds (mainly
CH3HgCl) up to 5
micromolar
.

Only plants expressing the gene products of
both
merA

and
merB

grew on concentrations of 10
micromolar

methyl
mercury.



Mercury vapor analysis showed significant Hg(0) volatilization emitted from
merA
/
merB

plants and western blots confirmed the expression of the gene
products of
merA

and
merB
.

These results demonstrate that transgenic plants
efficiently
phytovolatilize

methylmercury
.

FITOREMEDIASI
Merkuri

(Hg)

Sumber
:
http://rydberg.biology.colostate.edu/Phytoremediation/2003/Amy/phytoremediationtechnologies.html ….
Diunduh

7/5/2012

References


1.
Wantanabe
,
Chiho
, Satoh, Hiroshi.

(1996)

Evolution of our understanding of
methylmercury

as a
health threat.

Environmental Health Perspectives Supplements.


104(2):367.

2.
Wheeler, M. (1996) Measuring Mercury.

Environmental Health Perspectives.
104(8):

http://ephnet1.nih.gov/docs/1996/104
-
8/focus.html.

3.
Boening
, D.

(2000)

Ecological
effectws
, transport, and fate of mercury:

a general
review.

Chemosphere
.

40:1335
-
1351.

4.
Greimel
, H.

(2001)

Poisoning victims of Japan's mercury bay may be double previous
estimates.

http://www.enn.com/news/wire
-
stories/2001/10112001/ap
-
45234.asp

5.
Mercury Chemical Backgrounder.

http://www.nsc.org/library/chemical/Mercury.htm

6.
Mercury, chemical element:

The Columbia Encyclopedia, Sixth
Edition.

(2001).

http://www.bartelby.com/65/me/mercury/html

7.
Chemical Properties of Mercury.

http://pasture.ecn.purdue.edu/~mercury/src/props.htm

8.
Toxic Mercury Rains on U.S. Midwest. (1999)

http://www.uwsp.edu/geo/courses/geog100/ENS
-
Mercury.htm

9.
UGA Genetics
-

Richard B. Meagher.


http://www.genetics.uga.edu/faculty/bio
-
Meagher.html

10.
Phytoremediation

Research Lab, Michigan State University.

Department of Crop and Soil
Sciences.

http://www.css.msu.edu/phytoremediation/c_rugh.html

11.
Applied
PhytoGenetics

Inc.

Apgen's

phytoremediation

technologies.

http://www.applied
phytogenetics.com/
apgen
/technology.htm

12.
Rugh
, C., Wilde, H.D., Stack, N., Thompson, D., Summers, A., and Meagher, R. (1996)

Mercuric
ion reduction and resistance in transgenic
Arabidopsis thaliana

plants expressing a modified
bacterial
mer
A

gene.

Proc. Natl. Acad. Sci.

93:3182
-
3187.

13.
Rugh
, C.,
Senecoff
, J., Meagher, R., and
Merkle
, S. (1998)

Development of transgenic yellow
poplar for mercury
phytoremediation
.

Nature Biotechnology.


16:925
-
928.

14.
Bizily
, S.,
Rugh
, C., Summers, A., and Meagher, R. (1999)

Phytoremediation

of
methylmercury

pollution:

mer
B

expression in
Arabidopsis thaliana

confers resistance to
organomercurials
.

Proc.
Natl. Acad. Sci.

96:6808
-
6813.

15.
Bizily
, S.,
Rugh
, C., Meagher, R. (2000)

Phytodetoxification

of hazardous
organomercurials

by
genetically engineered plants.

Nature Biotechnology
. 18:213
-
217.

FITOREMEDIASI
Merkuri

(Hg)

Sumber
: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2590779/….
Diunduh

7/5/2012

.
Phytoremediation

of Mercury and
Organomercurials

in Chloroplast Transgenic Plants:
Enhanced Root Uptake, Translocation to Shoots, and Volatilization

Hussein S. Hussein,


Oscar N. Ruiz,

§

Norman Terry,


and Henry
Daniell

Environ
Sci

Technol. 2007 December 15; 41(24): 8439

8446.

. Transgenic tobacco plants engineered with bacterial
mer
A

and
mer
B

genes via the
chloroplast genome were investigated to study the uptake, translocation of different
forms of mercury (Hg) from roots to shoots, and their volatilization. Untransformed
plants, regardless of the form of Hg supplied, reached a saturation point at 200 µM of
phenylmercuric

acetate (PMA) or HgCl
2
, accumulating Hg concentrations up to 500 µg
g
−1

with significant reduction in growth. In contrast, chloroplast transgenic lines
continued to grow well with Hg concentrations in root tissues up to 2000 µg
g
−1
.
Chloroplast transgenic lines accumulated both the organic and inorganic Hg forms to
levels surpassing the concentrations found in the soil. The organic
-
Hg form was
absorbed and
translocated

more efficiently than the inorganic
-
Hg form in transgenic
lines, whereas no such difference was observed in untransformed plants. Chloroplast
-
transgenic lines showed about 100
-
fold increase in the efficiency of Hg accumulation in
shoots compared to untransformed plants. This is the first report of such high levels of
Hg accumulation in green leaves or tissues. Transgenic plants attained a maximum rate
of elemental
-
Hg volatilization in two days when supplied with PMA and in three days
when supplied with inorganic
-
Hg, attaining complete volatilization within a week. The
combined expression of
merAB

via the chloroplast genome enhanced conversion of
Hg
2+

into Hg,
0

conferred tolerance by rapid volatilization and increased uptake of
different forms of mercury, surpassing the concentrations found in the soil. These
investigations provide novel insights for improvement of plant tolerance and
detoxification of mercury.

FITOREMEDIASI
Merkuri

(Hg)

Sumber
: http://www.ncbi.nlm.nih.gov/pubmed/11642409….
Diunduh

7/5/2012

Differential mercury volatilization by tobacco organs expressing a
modified bacterial
merA

gene.

He YK
,
Sun JG
,
Feng

XZ
,
Czakó

M
,
Márton

L
.

Cell Res.

2001 Sep;11(3):231
-
6.

. Mercury pollution is a major environmental problem accompanying industrial
activities. Most of the mercury released ends up and retained in the soil as complexes
of the toxic ionic mercury (Hg2+), which then can be converted by microbes into the
even more toxic
methylmercury

which tends to
bioaccumulate
. Mercury detoxification
of the soil can also occur by microbes converting the ionic mercury into the least toxic
metallic mercury (Hg0) form, which then evaporates. The remediation potential of
transgenic plants carrying the
MerA

gene from E. coli encoding mercuric ion
reductase

could be evaluated. A modified version of the gene, optimized for plant
codon

preferences (merApe9,
Rugh

et al. 1996), was introduced into tobacco by
Agrobacterium
-
mediated leaf disk transformation. Transgenic seeds were resistant to
HgCl2 at 50
microM
, and some of them (10
-
20% ) could germinate on media containing
as much as 350
microM

HgCl2, while the control plants were fully inhibited or died on
50
microM

HgCl2. The rate of elemental mercury evolution from Hg2+ (added as
HgCl2) was 5
-
8 times higher for transgenic plants than the control. Mercury
volatilization by isolated organs standardized for fresh weight was higher (up to 5
times) in the roots than in shoots or the leaves. The data suggest that it is the root
system of the transgenic plants that volatilizes most of the reduced mercury (Hg0). It
also suggests that much of the mercury need not enter the vascular system to be
transported to the leaves for volatilization. Transgenic plants with the merApe9 gene
may be used to mercury detoxification for environmental improvement in mercury
-
contaminated regions more efficiently than it had been predicted based on data on
volatilization of whole plants via the upper parts only (
Rugh

et al. 1996).

FITOREMEDIASI
Merkuri

(Hg)

Sumber
: http://www.ncbi.nlm.nih.gov/pubmed/21518240….
Diunduh

7/5/2012

.

Plant
Biotechnol

J.

2011 Jun;9(5):609
-
17.
doi
: 10.1111/j.1467
-
7652.2011.00616.x.
Epub

2011 Apr 24.

Metallothionein

expression in chloroplasts enhances mercury accumulation and
phytoremediation

capability.

Ruiz ON
,
Alvarez D
,
Torres C
,
Roman L
,
Daniell

H
.


. Genetic engineering to enhance mercury
phytoremediation

has been accomplished
by expression of the
merAB

genes that protects the cell by converting Hg[II] into Hg[0]
which volatilizes from the cell. A drawback of this approach is that toxic Hg is released
back into the environment. A better
phytoremediation

strategy would be to
accumulate mercury inside plants for subsequent retrieval. We report here the
development of a
transplastomic

approach to express the mouse
metallothionein

gene
(mt1) and accumulate mercury in high concentrations within plant cells. Real
-
time PCR
analysis showed that up to 1284 copies of the mt1 gene were found per cell when
compared with 1326 copies of the 16S
rrn

gene, thereby attaining
homoplasmy
. Past
studies in chloroplast transformation used qualitative Southern blots to evaluate
indirectly
transgene

copy number, whereas we used real
-
time PCR for the first time to
establish
homoplasmy

and estimate
transgene

copy number and transcript levels. The
mt1 transcript levels were very high with 183,000 copies per
ng

of RNA or 41% the
abundance of the 16S
rrn

transcripts. The
transplastomic

lines were resistant up to 20
μ
m mercury and maintained high chlorophyll content and biomass. Although the
transgenic plants accumulated high concentrations of mercury in all tissues, leaves
accumulated up to 106
ng
, indicating active
phytoremediation

and translocation of
mercury. Such accumulation of mercury in plant tissues facilitates proper disposal or
recycling. This study reports, for the first time, the use of
metallothioneins

in plants for
mercury
phytoremediation
. Chloroplast genetic engineering approach is useful to
express metal
-
scavenging proteins for
phytoremediation
.

J.
Ind

Microbiol

Biotechnol
.

2005 Dec;32(11
-
12):502
-
13.
Epub

2005 Jul 2.

Strategies for the engineered
phytoremediation

of toxic element pollution: mercury and
arsenic.

Meagher RB
,
Heaton AC
.


Sumber
: ….
Diunduh

7/5/2012

Plants have many natural properties that make them ideally suited to clean up polluted
soil, water, and air, in a process called
phytoremediation
. We are in the early stages of
testing genetic engineering
-
based
phytoremediation

strategies for elemental
pollutants like mercury and arsenic using the model plant Arabidopsis. The long
-
term
goal is to develop and test vigorous, field
-
adapted plant species that can prevent
elemental pollutants from entering the food
-
chain by extracting them to aboveground
tissues, where they can be managed. To achieve this goal for arsenic and mercury, and
pave the way for the remediation of other challenging elemental pollutants like lead or
radionucleides
, research and development on native
hyperaccumulators

and
engineered model plants needs to proceed in at least eight focus areas: (1) Plant
tolerance to toxic elementals is essential if plant roots are to penetrate and extract
pollutants efficiently from heterogeneous contaminated soils. Only the roots of
mercury
-

and arsenic
-
tolerant plants efficiently contact substrates heavily
contaminated with these elements. (2) Plants alter their
rhizosphere

by secreting
various enzymes and small molecules, and by adjusting pH in order to enhance
extraction of both essential nutrients and toxic elements. Acidification favors greater
mobility and uptake of mercury and arsenic. (3) Short distance transport systems for
nutrients in roots and root hairs requires numerous endogenous transporters. It is
likely that root plasma membrane transporters for iron, copper, zinc, and phosphate
take up ionic mercuric ions and arsenate. (4) The electrochemical state and chemical
speciation of elemental pollutants can enhance their mobility from roots up to shoots.
Initial data suggest that elemental and ionic mercury and the
oxyanion

arsenate will be
the most mobile species of these two toxic elements. (5) The long
-
distance transport
of nutrients requires efficient xylem loading in roots, movement through the xylem up
to leaves, and efficient xylem unloading aboveground. These systems can be enhanced
for the movement of arsenic and mercury. (6) Aboveground control over the
electrochemical state and chemical speciation of elemental pollutants will maximize
their storage in leaves, stems, and vascular tissues. Our research suggests ionic Hg(II)
and
arsenite

will be the best chemical species to trap aboveground. (7) Chemical sinks
can increase the storage capacity for essential nutrients like iron, zinc, copper, sulfate,
and phosphate. Organic acids and
thiol
-
rich
chelators

are among the important
chemical sinks that could trap maximal levels of mercury and arsenic aboveground. (8)
Physical sinks such as
subcellular

vacuoles, epidermal
trichome

cells, and dead vascular
elements have shown the evolutionary capacity to store large quantities of a few toxic
pollutants aboveground in various native
hyperaccumulators
. Specific plant
transporters may already recognize
gluthione

conjugates of Hg(II) or
arsenite

and
pump them into vacuole.

Environ
Sci

Pollut

Res Int.

2009 Mar;16(2):162
-
75.
Epub

2008 Dec 6.

Implications of metal accumulation mechanisms to
phytoremediation
.

Memon

AR
,
Schröder

P
.

Sumber
: ….
Diunduh

7/5/2012

.

BACKGROUND, AIM, AND SCOPE:

Trace elements (heavy metals and metalloids) are important environmental pollutants, and many of
them are toxic even at very low concentrations. Pollution of the biosphere with trace elements has
accelerated dramatically since the Industrial Revolution. Primary sources are the burning of fossil fuels,
mining and smelting of
metalliferous

ores, municipal wastes, agrochemicals, and sewage. In addition,
natural mineral deposits containing particularly large quantities of heavy metals are found in many
regions. These areas often support characteristic plant species thriving in metal
-
enriched
environments. Whereas many species avoid the uptake of heavy metals from these soils, some of
them can accumulate significantly high concentrations of toxic metals, to levels which by far exceed
the soil levels. The natural phenomenon of heavy metal tolerance has enhanced the interest of plant
ecologists, plant physiologists, and plant biologists to investigate the physiology and genetics of metal
tolerance in specialized
hyperaccumulator

plants such as Arabidopsis
halleri

and
Thlaspi

caerulescens
.
In this review, we describe recent advances in understanding the genetic and molecular basis of metal
tolerance in plants with special reference to
transcriptomics

of heavy metal accumulator plants and
the identification of functional genes implied in tolerance and detoxification.

RESULTS:

Plants are susceptible to heavy metal toxicity and respond to avoid detrimental effects in a variety of
different ways. The toxic dose depends on the type of ion, ion concentration, plant species, and stage
of plant growth. Tolerance to metals is based on multiple mechanisms such as cell wall binding, active
transport of ions into the vacuole, and formation of complexes with organic acids or peptides. One of
the most important mechanisms for metal detoxification in plants appears to be
chelation

of metals by
low
-
molecular
-
weight proteins such as
metallothioneins

and peptide
ligands
, the
phytochelatins
. For
example, glutathione (GSH), a precursor of
phytochelatin

synthesis, plays a key role not only in metal
detoxification but also in protecting plant cells from other environmental stresses including intrinsic
oxidative stress reactions. In the last decade, tremendous developments in molecular biology and
success of genomics have highly encouraged studies in molecular genetics, mainly
transcriptomics
, to
identify functional genes implied in metal tolerance in plants, largely belonging to the metal
homeostasis network.

DISCUSSION:

Analyzing the genetics of metal accumulation in these accumulator plants has been greatly enhanced
through the wealth of tools and the resources developed for the study of the model plant Arabidopsis
thaliana such as transcript profiling platforms, protein and metabolite profiling, tools depending on
RNA interference (
RNAi
), and collections of insertion line mutants. To understand the genetics of metal
accumulation and adaptation, the vast arsenal of resources developed in A. thaliana could be extended
to one of its closest relatives that display the highest level of adaptation to high metal environments
such as A.
halleri

and T.
caerulescens
.

CONCLUSIONS:

This review paper deals with the mechanisms of heavy metal accumulation and tolerance in plants.
Detailed information has been provided for metal transporters, metal
chelation
, and oxidative stress in
metal
-
tolerant plants. Advances in
phytoremediation

technologies and the importance of metal
accumulator plants and strategies for exploring these immense and valuable genetic and biological
resources for
phytoremediation

are discussed.

RECOMMENDATIONS AND PERSPECTIVES:

A number of species within the
Brassicaceae

family have been identified as metal accumulators. To
understand fully the genetics of metal accumulation, the vast genetic resources developed in A.
thaliana must be extended to other metal accumulator species that display traits absent in this model
species. A. thaliana microarray chips could be used to identify differentially expressed genes in metal
accumulator plants in
Brassicaceae
. The integration of resources obtained from model and wild species
of the
Brassicaceae

family will be of utmost importance, bringing most of the diverse fields of plant
biology together such as functional genomics, population genetics,
phylogenetics
, and ecology. Further
development of
phytoremediation

requires an integrated multidisciplinary research effort that
combines plant biology, genetic engineering, soil chemistry, soil microbiology, as well as agricultural
and environmental engineering.


.

Environ
Sci

Pollut

Res Int.

2009 Mar;16(2):162
-
75.
Epub

2008 Dec 6.

Implications of metal accumulation mechanisms to
phytoremediation
.

Memon

AR
,
Schröder

P
.


Sumber
: http://www.ncbi.nlm.nih.gov/pubmed/19067014 ….
Diunduh

7/5/2012.

.

BACKGROUND, AIM, AND SCOPE:

Trace elements (heavy metals and metalloids) are important environmental pollutants, and many of
them are toxic even at very low concentrations. Pollution of the biosphere with trace elements has
accelerated dramatically since the Industrial Revolution. Primary sources are the burning of fossil
fuels, mining and smelting of
metalliferous

ores, municipal wastes, agrochemicals, and sewage. In
addition, natural mineral deposits containing particularly large quantities of heavy metals are found in
many regions. These areas often support characteristic plant species thriving in metal
-
enriched
environments. Whereas many species avoid the uptake of heavy metals from these soils, some of
them can accumulate significantly high concentrations of toxic metals, to levels which by far exceed
the soil levels. The natural phenomenon of heavy metal tolerance has enhanced the interest of plant
ecologists, plant physiologists, and plant biologists to investigate the physiology and genetics of metal
tolerance in specialized
hyperaccumulator

plants such as Arabidopsis
halleri

and
Thlaspi

caerulescens
.
In this review, we describe recent advances in understanding the genetic and molecular basis of metal
tolerance in plants with special reference to
transcriptomics

of heavy metal accumulator plants and
the identification of functional genes implied in tolerance and detoxification.

RESULTS:

Plants are susceptible to heavy metal toxicity and respond to avoid detrimental effects in a variety of
different ways. The toxic dose depends on the type of ion, ion concentration, plant species, and stage
of plant growth. Tolerance to metals is based on multiple mechanisms such as cell wall binding, active
transport of ions into the vacuole, and formation of complexes with organic acids or peptides. One of
the most important mechanisms for metal detoxification in plants appears to be
chelation

of metals
by low
-
molecular
-
weight proteins such as
metallothioneins

and peptide
ligands
, the
phytochelatins
.
For example, glutathione (GSH), a precursor of
phytochelatin

synthesis, plays a key role not only in
metal detoxification but also in protecting plant cells from other environmental stresses including
intrinsic oxidative stress reactions. In the last decade, tremendous developments in molecular biology
and success of genomics have highly encouraged studies in molecular genetics, mainly
transcriptomics
, to identify functional genes implied in metal tolerance in plants, largely belonging to
the metal homeostasis network.

DISCUSSION:

Analyzing the genetics of metal accumulation in these accumulator plants has been greatly enhanced
through the wealth of tools and the resources developed for the study of the model plant Arabidopsis
thaliana such as transcript profiling platforms, protein and metabolite profiling, tools depending on
RNA interference (
RNAi
), and collections of insertion line mutants. To understand the genetics of
metal accumulation and adaptation, the vast arsenal of resources developed in A. thaliana could be
extended to one of its closest relatives that display the highest level of adaptation to high metal
environments such as A.
halleri

and T.
caerulescens
.

CONCLUSIONS:

This review paper deals with the mechanisms of heavy metal accumulation and tolerance in plants.
Detailed information has been provided for metal transporters, metal
chelation
, and oxidative stress
in metal
-
tolerant plants. Advances in
phytoremediation

technologies and the importance of metal
accumulator plants and strategies for exploring these immense and valuable genetic and biological
resources for
phytoremediation

are discussed.

RECOMMENDATIONS AND PERSPECTIVES:

A number of species within the
Brassicaceae

family have been identified as metal accumulators. To
understand fully the genetics of metal accumulation, the vast genetic resources developed in A.
thaliana must be extended to other metal accumulator species that display traits absent in this model
species. A. thaliana microarray chips could be used to identify differentially expressed genes in metal
accumulator plants in
Brassicaceae
. The integration of resources obtained from model and wild
species of the
Brassicaceae

family will be of utmost importance, bringing most of the diverse fields of
plant biology together such as functional genomics, population genetics,
phylogenetics
, and ecology.
Further development of
phytoremediation

requires an integrated multidisciplinary research effort
that combines plant biology, genetic engineering, soil chemistry, soil microbiology, as well as
agricultural and environmental engineering.


.

Ying Yong
Sheng

Tai
Xue

Bao
.

2003 Apr;14(4):632
-
6.

[
Phytochelatin

and its function in heavy metal tolerance of higher plants].

[Article in Chinese]

Wu F
,