By
AHMED K. SALAMA, KHALED A. OSMAN AND NEAMA A. GUDA
Faculty of Science, Majmaah University and Alexandria
University
This report is based upon work supported by the Basic Science
Research Unit, Scientific Research Deanship, Majmaah
University 1435 H.
Environmental pollution has been increased because of
the human activities including emission, effluents and
solid discharge from industries, vehicle exhaustion,
smelting and mining and excessive use of pesticides
and fertilizers.
Soil contamination by metals is the most critical
environmental problems as it poses significant impacts
to the human health and ecosystems. Metals are able
to infiltrate deep into the layer of underground waters.
Metals in the soil subsequently enter the human food
web through plants and they constitute risk to the
ecosystem as they tend to bio-accumulate and can be
transferred from one food chain to another.
Soil contamination by metals is one of the most critical
environmental problems.
The currently used techniques either landfilling or metal
extraction using toxic agents as well as the use of
metal-chelating bio-surfactant for soil remedy need to be
replaced by green technology solution.
Therefore, the research was designated to study the
ability of plants to bio-accumulate, translocate and
remove some metals such as zinc, copper, lead and
cadmium from contaminated soil. This method does not
usually produce toxic by-products. It is also cheaper and
effective technology with minimal impact on the
environment and can be easily used for soil remedy.
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Soil were sieved, dried and the pH value and organic matter
were determined.
Seedlings of herbal plants were cultivated in pots containing
100 g soil without any fertilizer and the plant left to grow
under greenhouse conditions.
Metal salts of copper carbonate, zinc carbonate, lead
hydroxide carbonate and cadmium nitrate at different
concentration levels of 0, 100, 200, 400 and 600 µg/g soil
were spiked into the soil.
Plants were removed after 60 days and divided into roots
and shoots.
Plant and soil samples were dried at 105 °C in an oven for
24 h and powdered and digested with nitric acid.
Samples were put in a muffle furnace at 600°C for ashing.
The ash was rinsed with 1.0 M nitric acid and filtered to be
ready for analysis.
Samples of plant and soil were subsequently analyzed for
heavy metal contents, as dry weight basis, using an atomic
absorption spectrometer (AAS).
Measurements were made using the hollow cathode lamps for
Cu, Zn, Pb, and Cd at the proper wavelength.
Working solutions were prepared by dilution just before the
use of standard solutions for atomic absorption spectroscopy
(1000 ppm).
For the determination, two solutions were prepared for each
sample and three separate readings were made for each
solution. The means of these figures were used to calculate
the concentrations.
Mechanism of phytoremediation:
Phytoextraction (Phytoaccumulation):
Uptake and translocation of metals by plant roots into the above
ground portions of the plants.
Rhizofiltration: Adsorption of metals onto the plant roots.
Phytovolatilization:
Uptake metals from the soil and transforming them into less or non
toxic volatile forms into the atmosphere.
Phytostabilization: Immobilize metals in the soil through
absorption and accumulation by roots or adsorption onto roots.
Phytodegradation: Transformation of complex molecules to
simple forms or incorporation of these molecules into plant tissues.
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The plant used changes the soil chemistry because it releases
organic exudates from roots which can partially dissolve tightly
bound forms of metals and facilitate the metals uptake.
Soil-plant transfer index was calculated as metal concs. in plant to
metal concs. in soil. This value was more than 1.0 in case of all
tested metals.
The results explained that the investigated herbal plant is a good
accumulator for Cu, Zn, Pb or Cd.
The mechanism of soil remedy using the investigated plant is
phytoextraction where it is able to uptake and translocate Cu, Zn,
Pb, or Cd by plant roots into the above ground portions.
The method offers green technology solution to the problem
because it does not usually produce toxic by-products. It is also
cheaper and effective technologies with minimal impact on the
environment and can be easily used for soil remedy.
Thank you all