PURPOSE
The purpose of this experiment was to determine the toxicity threshold of bleach on wheat.
I became interested in this idea because I love plants, I also know that my family uses bleach in our house, both when washing clothes and when disinfecting some items. Water from the laundry goes into our septic tank and then into the drain field. I wondered if that could hurt trees and other plants in our yard. Bleach sprayed inside the house as a disinfectant could get into the air and possibly hurt houseplants. I especially wanted to know how much bleach was too much for the plants to tolerate.
The information gained from this experiment could help farmers, the wheat processing industry, and families, because most eat a lot of wheat in everyday life. It would also warn users of bleach, especially industries like paper mills, about discharging bleach into the environment.
My first hypothesis was that 10,000 ppm or 1.0 % bleach would meet the LC50 (50% die) toxicity level.
My second hypothesis was that 625 ppm or .0625% bleach would not meet the LC50 toxicity level.
My third hypothesis was that two concentrations would exist where the highest non-LC50 concentration would be ½ the strength of the lowest LC50 concentration.
I based my hypothesis on a previous science project done by Thomas Hepner in 2004 (determining the toxicity threshold concentration of herbicide on radishes). I also based my hypothesis on what I have read.
“People also use some bleaches as disinfectants.” Howard L. Needle (in the article “Bleach” on www.worldbook.com) says. In other words, people use bleaches to Kill germs and other organisms.
The constants in this study were:
• The amount of water given to each plant (5 ml. every 3 days)
• The room temperature (20 degrees Celsius)
• The depth that the seeds were planted (1cm.)
• The type of light (fluorescent light with two 40 watt “GroLux”
bulbs)
• How far away the light was from the soil
• The amount of bleach water given to the wheat every 3 days (5ml)
The manipulated variable was the concentration of bleach put on
the wheat.
The responding variables was the biomass of the wheat.
To measure the responding variable, I measured the growth of the wheat from the top of the soil to the tip of the wheat. Then I weighed the wheat in grams (g) to see how much biomass it has.
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QUANTITY
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ITEM DESCRIPTION
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6 (about)
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Syringe
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2
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Plastic plant holders
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1
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Fluorescent light
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2
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40 watt “GroLux” bulbs
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1
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Bag of planting soil
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580 (about)
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Seeds of wheat
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Various Amounts
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Pure well water
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1
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Bottle of bleach
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1
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Timer
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PROCEDURES
1. Plant the Wheat
a)
Fill all 72 cells in plastic planting tray with planting soil, but don’t
pack too tightly.
b)
Mark a pencil point exactly 1 cm. from its point with a permanent marker.
c)
Poke four equally spaced holes 1 cm. deep into the soil in each cell.
d) Place
one wheat seed into each hole.
e) Cover
holes with soil and pack lightly
f) Repeat all steps
above for second planting tray.
2. Start
Growing Process (Day 0)
a)
Water each cell with pure well water until soil is totally soaked.
b)
Allow excess water to drain through each cell. If this does not happen
each time after watering the wheat, the roots will rot.
c)
Place trays evenly spaced under fluorescent light with two 40 watt
“GroLux” bulbs. Bulbs should be 30 cm. above soil.
d)
Light should be attached to a timer so it is on for 16 hours a day.
e) Water
each cell every 3 days with 5 ml of pure well water, until wheat sprouts and is
1 cm tall on average.
3. Mix
the Chlorine Solutions.
a)
Using the graduated cylinder measure 990 ml of “pure” well water into a 1
liter beaker.
b)
Measure 10 ml of chlorine bleach and add that to the beaker. This
creates 1000 ml. of 1% or 10,000 ppm concentration (10/1000 = 1.0% = 10,000
ppm)
c)
Pour 500 ml. of this mixture into a plastic storage bottle and label
“10,000 ppm”
d)
Leave the remaining 500 ml. of this 10,000 ppm mixture in the beaker and
dilute it with 500 ml of well water. This creates 1000 ml. of 0.5% or 5,000 ppm
concentration. This is one-half as strong as the previous mixture.
e)
Pour 500 ml. of this mixture into a plastic storage bottle and label
“5,000 ppm”
f)
Leave the remaining 500 ml. of this 5,000 ppm mixture in the beaker and
dilute it with 500 ml of well water. This creates 1000 ml. of 0.25% or 2,500
ppm concentration. This is one-half as strong as the previous mixture.
g)
Pour 500 ml. of this mixture into a plastic storage bottle and label
“2,500 ppm”
h)
Leave the remaining 500 ml. of the 2,500 ppm mixture in the beaker and
dilute it with 500 ml of well water. This creates 1000 ml. of 0.125% or 1,250
ppm concentration. This is one-half as strong as the previous mixture.
i)
Pour 500 ml. of this mixture into a plastic storage bottle and label
“1,250 ppm”
j)
Leave the remaining 500 ml. of the 1,250 ppm mixture in the beaker and
dilute it with 500 ml of well water. This creates 1000 ml. of 0.0625% or 625
ppm concentration. This is one-half as strong as the previous
mixture. This is the smallest dilution planned for this experiment.
k)
Pour 500 ml of this mixture into a plastic storage bottle and label “625
ppm” Discard the remainder.
l)
Measure 500 ml of pure well water and pour it into a plastic storage
bottle and label “Control – 0 ppm”
m)
Label all of the cells, then treat according to their label of
concentration.
4. Water the Plants
a)
Water the 24 cells in the “Control” zone of the planter with 10ml of
water from its matching water container.
b)
Water the 24 cells in the “10,000 ppm” zone of the planter with 10ml of
water from its matching water container.
c)
Water the 24 cells in the “5,000 ppm” zone of the planter with 10ml of
water from its matching water container.
d)
Water the 24 cells in the “2,500 ppm” zone of the planter with 10ml of
water from its matching water container.
e)
Water the 24 cells in the “1,250 ppm” zone of the planter with 10ml of
water from its matching water container.
f)
Water the 24 cells in the “625 ppm” zone of the planter with 10ml of
water from its matching water container.
g)
Repeat steps “4-A through 4-5” in three days, but water with only 5ml.
h) Water the plants
every third day until 5 weeks are over.
5. Finding the Mass
a)
Use a triple beam balance to measure the mass of the wheat.Pull all
plants in one group (zone) out of the soil (not all at the same time) with
care, make sure to pull the wheat out by the roots.
b) Then
wash the soil off of each strip of wheat.
c)
Then dry the wheat off with a paper towel, try not to damage the plants.
d) Then
weigh the plants.
e) Count
the number of plants in each group.
f)
Divide total mass for each group by the number of plants in each group to
calculate the average mass.
g)
Compare results.
The original purpose of this experiment was to determine the toxicity threshold of bleach on wheat.
For the control group there were 66 wheat stalks (69%) survived, with a total mass of 2.7 grams, and an average mass of .040 grams.
For the 625 ppm group there were 65 wheat stalks (68%) survived, with a total mass of 2.6 grams, and an average mass of .040 grams.
For the 1,250 ppm group there were 62 wheat stalks (65%) survived, with a total mass of 2.4 grams, and an average of .038 grams.
For the 2,500 ppm group there were 56 wheat stalks (58%) survived, with a total mass of 2.0 grams, and an average of .035 grams.
For the 5,000 ppm group there were 49 wheat stalks (51%) survived, with a total mass of 1.6 grams, and an average of .032 grams.
For the 10,000 ppm group there were 46 wheat stalks (48%) survived, with a total mass of 1.4 grams, and an average of .030 grams.
My 1st hypothesis was that 10,000 ppm or 1.0% bleach would meet the LC50 (50% die) toxicity level.
The
results indicate that my 1st hypothesis should be accepted, because the 10,000
ppm group did reach the LC50 level.
My 2nd
hypothesis was that 625 ppm or .0625% bleach would Not meet the LC50 toxicity
level.
The
results indicate that my 2nd hypothesis should be accepted because 65%
survived.
My 3rd
hypothesis was that two concentrations would exist where the highest non-LC50
concentration would be ½ the strength of the lowest LC50 concentration.
The
results indicate that my 3rd hypothesis should be accepted because in my 5,000
ppm group (highest non-LC50 level), there were 51% that survived, and in my
10,000 ppm group (lowest LC50 level), there were only 48% that survived.
After
thinking about the results of this experiment, I wonder if a very small amount
of bleach would actually help the wheat grow.
Perhaps
by keeping mold in the soil. Also testing bleach concentrations on a different
type of plant. Like tomatoes or soybeans would be worthwhile.
If I
were to conduct this project again I would make a larger amount of each bleach
concentration (500ml) so I wouldn’t have to re-make it so often. I would also
grow many more plants per group. I would grow them outside in the sunlight in
the spring. I would also grow the wheat 2-3 times longer (or until the seed
heads become ripe) before I weighed them.
Researched
by ----- Mary Michael G
