Phytoremediation
Dawn Whitener
GLG 581
Dr. Erwin Mantei
Abstract
Four
heavy metal concentrations in soils Cu, Cr, As, and Pb were examined to see if removal
through the process of phytoremediation was possible. Through the use of Geochemical Techniques, an investigation was
conducted to evaluate the contaminations of heavy metals removed from the
contaminated soils. The heavy metals
were up taken through the roots of plants with phytoremediative qualities and
the soils analyzed. Tomato and lemon scented geranium plants were able to
extract different concentrations of each heavy metal from the soils. The length of time that the soils were
exposed to the contaminants affected the levels of concentrations. The soils located under older CCA treated
lumber decks had higher concentrations of Cu, Cr, and As. The soils that were around higher flows of
traffic also had higher instances of Pb contamination.
Introduction
There
is a remarkable agricultural practice that “is defined as the use of green
plants to remove pollutants from the environment or to render them harmless”
(Salt, 1). There are several species of
plants known for their phytoremediative abilities. Several of these plants are Indian mustard, Sudan grass,
sunflowers, and lemon-scented Geraniums.
Lemon-scented Geraniums are more importantly known as a hyperaccumulator. This means that they are able to uptake
large quantities of heavy metals and continue to thrive while storing these
heavy metals in its plant tissue.
CCA
treated wood is widely used because of its availability and its lower
cost. It reduces the amount of lumber
used because it preserves and protects the lumber from rot and insects. However, CCA can be very harmful to the
environment. CCA is named for the
presence of copper, chromium, and arsenic.
Trace amounts are found in rocks, animals, soil, food, and water, but
ingesting too much can have carcinogenic effects and even cause death. High concentrations of CCA have been found
in the soils below decks made from the treated lumber. Phytoremediation may help to solve this
problem. With the uptake of the heavy
metals Cu, Cr, and As, many backyard soils could have lower levels of these
heavy metals.
Lead
was in gasoline, which made it more efficient in car engines. The use of Pb in gasoline was banned after
research showed that the Pb was contaminating the air, water, and soil. This form of Pb that polluted the environment
has been found to be in an insoluble form.
Lower concentration levels of Pb can cause brain damage and
retardation. Phytoremediation has been
shown in studies to reduce the level of Pb in soils. There are several institutions that are currently investigating
the phytoremediative properties of plants, trees, and weeds such as Trinity
College in Hartford, Conn.
Phytoremediation is an alternative to the more expensive practices of cleaning up the soil, such as excavation and soil flushing. “Phytoremediation can be used to clean up metals, pesticides, solvents, explosives, crude oil, polyaromatic hydrocarbons, and landfill leachates” (USEPA, 1). Also, the practice of phytoremediation leaves the soil in better condition than before the plants were utilized. Through phytoremediation we will show that plants do uptake heavy metals from the soil they are grown in. The levels of heavy metals such as those leached from CCA treated lumber and Pb pollution will be reduced by phytoremediation. It is believe that the Lemon-scented Geranium plant will uptake more of the harmful heavy metals than the Tomato plant.
Methods
For
this study, the lemon-scented geranium was chosen because of its renowned
ability in phytoremediation, and the tomato plant because it also was a
remediator. Soils containing elevated
concentrations of lead were chosen. The high-density traffic intersection of
Battlefield and Glenstone was chosen for Site 1. The intersection of Cherry and Oak Grove was chosen as a less
dense traffic intersection and labeled Site 2.
Also, soils that were supposedly contaminated with CCA from the
treatment of deck lumber were also used.
Site 3 was chosen because the soil was located under a 12-year-old
treated lumber deck. Soil located under
a 19-year-old treated lumber deck was the area for Site 4. The control needed to be “free” of the
contaminants of lead and CCA. A field
located on Bennett east of Oak Grove as a control site was chosen.
The
soils were collected in the same manner.
The top layer of organic matter and about the first inch of soil was
removed. The next few inches of soil
were collected within a 14-inch diameter and placed in plastic bags. The points of the soil collection sites were
marked and stored using a GPS unit.
The
soil samples were brought to the lab and sieved using the parameters of 149 and
74 microns. The sieved soil samples
were placed in beakers and dried. They
were then stored until further analysis.
The
remaining amounts of soil were treated the following way; the tomato plants
were planted in half of the soil and the lemon-scented geraniums in the other
half. The plants were then allowed to
grow in the greenhouse for a span of three weeks.
After
the three weeks, the soils were removed and brought to the lab. The plants were discarded. The soil samples were dried overnight and
sieved using the same parameters of 149 and 74 microns. All of the soil samples were then weighed to
two grams, dissolved in a solution of nitric acid and doubly deionized water,
and placed in centrifuge tubes. The
centrifuge tubes were placed in a warm bath for over 24 hours. The soil samples were then placed in the
centrifuge for four minutes and the solution decanted. Standard solutions of 10 ppm and 2 ppm
concentrations were made for Pb, Cr,
Cu, and As. The decanted solutions and
the standards were taken to the ICP for analysis.
Results
The
data from the ICP analysis shows the concentrations of Pb.
In Site 1 and Site 2 the concentrations of Pb were lower than in the Control
Site. Site 1 did have a higher level of
Pb than the intersection with the less traffic, Site 2. However, the level of Pb in all of the soils
after the three weeks was reduced. In
the Control Site and Site 1, the Tomato plant showed the greatest amount of Pb
uptake. The Pb level in Site 2 was
reduced more by the Geranium plant.
For the element arsenic (As), the soil that had the
highest concentration at Site 4, followed by the Control Site, and finally Site
3. For this experiment, the Geranium
plant was the most effective in reducing the level of As in the soils taken at
Site 3 and Site 4. However, in the
Control Site the level of As increased.
The tomato plant did help to reduce the level of As in the Control Site,
Site 3, and Site 4.
For Cr, Site 4 contained the highest
concentrations. Site 3 had the next
highest level of Cr and the Control Site had the smallest amount. The Geranium plant up took more Cr than the
Tomato plant at each of the sites with the exception of the Control Site. The level of Cr in the Control Site
increased slightly for both the Tomato plant and the Geranium plant. Copper (Cu) concentrations were also the highest at Site
4. Site 3 had higher levels of Cu than
the Control Site did. The Geranium
plant worked best at removing the Cu level at Site 3 and Site 4. Moreover, the Tomato plant up took more Cu
for the Control Site.
Conclusion
I
believe that the results agreed for the most part with the hypothesis. The Lemon-scented Geranium plants absorbed
more of the Cr, Cu, As, and Pb concentrations from the soils at Site 3 and Site
4. The tomato plant, however, disproved
the hypothesis for the Pb levels for Site 1, Site 2, and the Control Site. The tomato plant also disproved the
hypothesis for the Control Site by up taking more Cu than the Geranium
plant. The lemon-scented Geranium plants
were more able to cope with the concentrations of heavy metals in the soils. The Geraniums all thrived and remained
green. The control tomato was the only
plant that thrived and remained green.
The other tomato plants yellowed and the tomato plant form Site 4 hardly
increased in size.
Phytoremediation
is an experiment that should be done when a longer interval of time can be
given to the growth of the plants in the sample soils. Different plants such as sunflowers and
possibly even several species of weeds should be tested to see if they have
phytoremediative properties. Better
soil removal techniques should be practiced to help provide more reliable
results. Above all, more elements
should be tested to see if plants through phytoremediation could up take them.