The Toxicity Threshold of  Bleach Concentrations on Wheat Growth
Photo of Mary Michael @ Mid Columbia Science Fair

Researched by Mary Michael G.
2005-2006


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.

HYPOTHESIS

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.

EXPERIMENT DESIGN

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.
 
MATERIALS

QUANTITY ITEM DESCRIPTION
6 (about) Syringe
2 Plastic plant holders
1
 Fluorescent light
2
 40 watt “GroLux” bulbs
1
 Bag of planting soil
580 (about)
 Seeds of wheat
Various Amounts
 Pure well water
1
 Bottle of bleach
1
 Timer

              
                     
                                 
                                 
                                
                                          
                
        
                                 
                                 
 
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.

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.

See the table and graph below.
 
 CONCLUSION

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 worth while

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.
 


RESEARCH REPORT

Introduction

Humans, like all animals, need food for survival. Wheat is a significant part of our diet. Chlorine bleach is used widely in homes and factories. As this chemical is discarded it causes serious problems in the environment, including damage to plants.

Wheat

The Growth and Reproduction of Wheat

Wheat is a very important food source for most societies around the world. A wheat kernel (seed) starts to absorb moisture shortly after it is planted. The “primary roots” begin to appear and the stem starts to reach toward the surface of the soil. One to two weeks later, the stem pops out of the soil. In under four weeks, leaves, tillers, and “secondary roots” begin to grow. Wheat finishes ripening in 30 to 60 days, mostly depending on the weather. The whole plant becomes dried-out and turns to golden brown. Ripe wheat kernels can be white, red, yellow, or even purple; it depends on the type of wheat.

How Wheat is Grown

Wheat can be grown in many climates and soils, but the best way to grow wheat is in the proper soil and the proper climate for the specific variety. To have the highest yields, farmers have to use healthy seeds. Wheat farmers also must plant and harvest their wheat at a precise time. They must be sure to keep their crops free from disease, insects, and other pests.

Wheat farmers in nonindustrial countries do all their plowing and planting by hand or with the help of animals. In industrial countries though, farmers use machinery almost all of the time.

Soil Conditions

Wheat grows best in the soil called clay loam or silt loam (Loam: “Soil composed of sand, clay, silt, and decayed plant matter”- The American Heritage Student Dictionary). In order to provide nutrients for wheat, soil needs to have a lot of decayed organisms. If the soil doesn’t have these nutrients, farmers can add them with the fertilizer. To reduce the amount of soil acid, farmers can add lime into the soil.

Climate Conditions

Wheat is grown in dry and mild climates. When the weather is overly wet, dry, cold, or hot the wheat gets killed easily, both summer and winter varieties. Wheat has less chance of dying in the spring than in the winter because there are fewer weather hazards. If wheat growers plant wheat seeds too early or too late, it can reduce the yield. If planted too late (in addition to less yield) the wheat’s chance of dying or getting damaged, during the winter, increases.

Types of Wheat

Most of the time, winter wheat is planted in the fall and during the following spring or summer the wheat is harvested. Usually, spring wheat is planted in areas with harshly cold weather. It’s planted in the spring and ripens in the summer.

There have been only thirty types of wheat scientists have discovered. Three main types of wheat are frequently used in the U.S, common wheat, club wheat, and durum wheat. Bread wheat (otherwise known as common wheat), includes both winter and spring wheat and is the most widely grown wheat species in the world. Bread wheat kernels are usually red, yellowish-brown, white, purple, or blue. Sometimes the kernel is hard and sometimes the kernel is soft.

A close species to common wheat is club wheat (also including winter and spring varieties). Its kernels are usually white or red, most of the time it is soft.

There are two types of durum wheat: ground durum wheat and plain durum wheat. Durum wheat’s kernels are white, red, yellowish-brown, or purple in color. The kernels of durum wheat are very hard. Ground durum wheat is put into pasta, because it is very firm and paste-like.

History

Scientists believe that some grain species closely related to wheat began growing in the Middle East about 11,000 years ago. It was one of the first plants to be grown by humans. Some other species that come from around that area are einkorn, wild emmer, and some types of wild grasses. In the olden days, men would sit around and talk, while chewing on the wheat kernels. In time people learned to toast, grind, and boil the kernels, which turned it into porridge. Then people figured out how to fry the porridge, which became a type of flat bread, sort-of like pancakes. There has been some old, old wheat kernels found in Syria by archaeologists. They also found bone hoes, flint sickles, and tools that were used for grinding stones. Archaeologists believe that these tools were used for planting, harvesting, and grinding wheat. Lives were changed all around the world by crops of various kinds, especially wheat and corn. Parents searching for food for their children, and for themselves, was over. The crops also helped make people healthier, happier, and handier. Since people could get food for their family so close to their home, they had more free time on their hands. Some places grew enough extra food to feed other towns and villages.

Bleach

The two main bleaches are chlorine bleach and oxygen bleach. All varieties of
bleach take color out of color giving molecules. (Color giving molecules are little
microscopic organisms that make all clothing colorful.)

Chlorine bleach is the variety that is mostly used in homes and factories. It
removes most color from textiles, wood pulp, pottery, and many other objects.

Oxygen bleaches are milder than chlorine bleaches. People use oxygen bleach
(also known as hydrogen peroxide) to lighten their hair and to make colored
fabrics brighter.

Another type of bleach is a certain sulfur compound, used to bleach silk,
different types of fibers, and some wools.

Optical bleach (another variety) sometimes hides the yellow coloring in
materials. This bleach is also known as fabric brightener. Fabric brighteners
take in ultraviolet light and change it to a blue light. The blue light and the
yellow coloring must work together to make a white light, which makes the
material brighter. Many laundry detergents contain optical bleach, to hide any
coloring that is not wanted.

History

People from centuries ago used to use bleach on textiles. They made bleach from plants or plant ashes. Sometimes these people used smoke from burning sulfur to take stains and/or coloring out of clothing. Then they lay that clothing spread out on the ground, waiting for the sun to whiten it.

In the 1700’s, manufactured bleaches were used in about the same way. Now factories (depending on the type of cloth) use bleach in different ways. A common method that is used goes like this-
Step 1) Take the cloth and wash it.
Step 2) Soak the cloth in a bleach solution.
Step 3) Then take the cloth and put it in other types of chemicals (to connteract the toxic bleach).
Step 4) The cloth is washed again and dried.

Chlorine

Chlorine, a yellow/green gas with a strong odor, causes irritation just about everywhere in your body, your eyes, your nose, and definitely your mouth. When chlorine and metal sodium combine, it creates table salt.

Chlorine is a word in the English language close to a word, which means greenish-yellow in Greek.

You can only find chlorine in compounds. Such as chloride minerals (like sodium chloride). There are many types of chlorides, they are mostly found in seawater, salt lakes, and small pieces of rock salt.


Uses of Chlorine

Chlorine is the substance used for killing germs and other types of bacteria. Chlorine is mostly used to clean water before it is safe to drink. It is also used in swimming pools. Hydrogen chloride is made when chlorine acts explosively with hydrogen. Later on, hydrogen chloride dissolves in the water and then turns into hydrochloric acid. Hydrochloric acid is used when people want to dye or clean metal.

Manufacturing companies use chlorine to make many things such as paper, plastics, insecticides, cleaning fluids, and antifreeze. These companies also use chlorine to make medicines, paints, and petroleum products-better.

Chemical Properties

Halogen (meaning salt forming), is the chemical group chlorine falls in to. If you use pure chlorine as a chemical in pools or on plants, it is deathly. Chlorine, like other types of halogens, often mixes with other substances by taking electrons from them. Chlorine makes the other substances give their electrons to it. When the temperature hits 20°c, chlorine’s density is .00295 grams (per cubic inch) at sea level. It can be made into a liquid that freezes at the temperature of about -101°c, and boils at the temperature of about 34°c.

Summary

Wheat

Wheat is a very important food source for most societies around the world. It can be grown in many different conditions. It is grown best in a soil called clay loam. Wheat is better grown in spring rather than winter. There are 30 types of wheat that have been discovered.  Common, club, and durum wheat are the three main types of wheat. Wheat began in the Middle-East about 11,000 years ago. Lives were changed by wheat crops.

Bleach

Bleach is a disinfectant. There are two main bleaches, oxygen bleach and chlorine bleach. Bleach takes the color out of clothing. Chlorine bleach is used in homes and factories. Oxygen bleaches are milder than chlorine bleaches. There are also bleaches called optical bleach and a bleach called certain sulfur compound. Bleach is made of plants and plant ashes.

 

BIBLIOGRAPHY

Appleman, Evan H. Chlorine. 2004 ed. CD-ROM.

Croy, Lavoy I.  “Wheat.” World book. 2004 ed. CD-ROM.

Hart, John. “Water Pollution.” Encarta. 2005 ed. CD-ROM.

Houghton Mifflin. “Loam.” The American Heritage Student Dictionary. 1994.

Needle, Howard L. "Bleach." Worldbook. 2004 ed. CD-ROM.

Ocko, Stephanie. Water. Scarborough, Ontario, Canada: Library of Congress Cataloging in-publication data, 1995. Pg. 129 & 130

Train, Russell E. The Fragile Earth. United States of America: Chelsea House Publishers, 1994. Pg. 65 & 71
 


ACKNOWLEDGEMENTS

I would like to thank the following people for helping make my project possible:

•    My parents for providing transportation to get to after school science classes, and to get materials for my experiment.

•    My friends Lyndsey, Jack, Austin, and Conner, and my cousin Scotty, for helping me to stay on-task…most of the time!

•    My sister, Lacie, for helping me make my concentrations and helping me water my plants.

•    Mr. Kenneth A. Newkirk and Mrs. Robbi M. Veirnes (my teachers) for teaching me so much about science. Also for providing a triple beam balance.

•    My cousin Brett G. for watching over my plants when I was in Hawaii for Christmas  vacation.

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