Determining the Toxicity Threshold Concentration of Herbicide on Radishes

student photo

Researched by Thomas H.


The purpose of this experiment was to determine the hormetic effect concentration of herbicide on radishes.  This information will help scientists understand how herbicide affects plants in both a damaging and beneficial way.

I became interested in this idea when I read an article showing that if you use a low enough concentration of herbicide it can actually have a beneficial effect on the plant.


My first hypothesis was that at least one of the plant groups would have a hormetic effect.

My second hypothesis was that 7.8 ppm mixture would provide the hormetic effect.

I based my first hypothesis on data collected from my previous science that showed the highest concentration at which most radishes lived and the lowest concentration at which most died. See Appendix 1 for Threshold Concentration Determination. This led me to the conclusion that I should predict in between the two and reduce concentrations from there. (I then based my second hypothesis on the selection of the midpoint between the two groups).


The constants in this study were: 
  • Type of plant
  • Seed age and storage
  • Soil moisture
  • Temperature
  • Amount of light
  • Pot size and shape
  • Amount of soil
  • Soil type
  • Testing procedure
  • Planting depth
  • The type of herbicide I used and how much I used for all plants of a specific test group

The manipulated variable was the amount of herbicide added to the radishes.

The responding variable was the height and weight of radishes. 

To measure the responding variable I measured the height and weighed the biomass using a triple beam balance. 

240 Radish seeds (radish champion)

Well water

Herbicide (2,4-D Weedar)
16 quart bag Natures Potting Soil
120 6.4 oz Styrofoam cups
cardboard trays lined with aluminum foil (which you line yourself)                                    
2 Grow-lights 49cm long (must be able to screw into wood)
1 179cm long by 99cm wide black cloth
2 A-frames
8 screws
1 screwdriver
1 graduated cylinder
1 pair of scissors
1 pencil
12 8.5 ounce Styrofoam cups (called herbicide cups)
1 syringe
500 ml flask
plastic sheet


1.    Plant seeds:
a)    Poke a pencil through the bottom side of 120 Styrofoam cups.
b)    Fill each cup with the potting soil to within 2 cm of the rim.
c)    Put the cups into 8 cardboard trays with 15 cups in each tray.
d)    Fill each cup with 50 ml of water.
e)    Place 2 radish seeds in each cup.
f)    Next cover the seeds with a large pinch of potting soil.
2.    Build the growing enclosure:
a)    Take one of the A-frames and 4 screws.
b)    Then carefully hold one of the grow lights up onto the bottom of the A-frame and put the screws into their holes.
c)    Repeat with the other A-frame.
d)    Place the A-frames structures relatively close to each other.
3.    Germinate seeds, grow seedlings:
a)    Next put 4 trays under one A-frame and 4 under the other.
b)    Drape the curtain over the two A-frames.
c)    Temp will fluctuate with garage temperature. 
d)    Cover cups with plastic to assist germination.
e)    Wait 1 day for the radishes to germinate.
f)    After the radishes have germinated turn on the grow lights.
g)    After 4 more days add 16 ml of water to each cup.
h)    Now add some topsoil to each cup so the plants don’t fall out.
i)    6 days later drench the soil with approximately 32 ml of water per cup.
j)    Sort the 120 Styrofoam plant cups into 12 groups and label the groups 1-12.
4.    Prepare herbicide concentrations:
a)    Take the twelve 8.5 ounce Styrofoam herbicide cups and label them #’s 1-12.
b)    Fill herbicide cup #1 with 160 ml of water and add NO Weedar.  This is the control.
c)    Fill a flask with 320 ml of H2O and apply 0.01 ml of 2,4-D. Pour 160 ml into cup #2. (Equals 31.3 ppm)
d)    Dilute 160 ml in flask with additional 160 ml of water. Pour 160 ml into cup #2.  (Equals 15.6 ppm = 100% solution)
e) Prepare a 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, and 10% solutions by
    Having the 100% solution diluted with clean water to the appropriate mix, for example, 9 part herbicide and 1 part water equals 90% herbicide; 3 parts herbicide and 7 parts water equals 30% herbicide.
f) The solution mixtures are:
    100% = 15.6 ppm 2,4-D
    90%  = 14.0 ppm 2,4-D
    80%  = 12.5 ppm 2,4-D
    70%  = 10.9 ppm 2,4-D
    60%  = 9.4 ppm 2,4-D
    50%  = 7.8 ppm 2,4-D
    40%  = 6.2 ppm 2,4-D
    30%  = 4.7 ppm 2,4-D
    20%  = 3.1 ppm 2,4-D
    10%  = 1.6 ppm 2,4-D
5.    Stir the mixture in herbicide cup #2 and apply 16 ml to each cup in group #2.
6.    Repeat step 5 for all other herbicide groups, being sure to use each on the respective plant group (for example, herbicide #6 goes only on plant group 6.)
7. Now water plants once a week for 53 days.
8. After the growth has occurred in all plants measure the height (cm) and weight (grams) plants. The height should be measured from soil level up not after taking the roots out. For the weight take the roots out of the cups gently and dab the roots to get the soil off. Then weigh.
9. Record results.


The original purpose of this experiment was to determine the hormetic effect concentration of herbicide on radishes.

The results shown from my experiment consisted of two different findings. My first was that 3.1 ppm group on average was 10.28% taller than the control group. This means that the average height for the control was 3.75 cm and the 3.1 ppm groups average height was 4.18. My second finding was that the 4.7 ppm group on average was 18.75% heavier than the control. That means that the whole control group weighed 1.6 grams and the 4.7 ppm group weighed 1.9 grams.

Also two other groups weighed, 1.7 grams and 1.6 grams. These groups were the 6.2 ppm group and the 1.6 ppm group. After that three other group’s height were slightly above the control. These were the 6.2 ppm group being 3.8 cm, the 4.7 ppm group with 3.85 cm, and 1.6 ppm group with 3.9 cm.

See my table and graphs


My first hypothesis was that at least one of the plant groups would have a hormetic effect.
The results indicate that this hypothesis should be accepted, because plants with 4.7 ppm and 3.1 ppm had significantly more growth (in height for the 3.1 ppm and weight for the 4.7 ppm group) over the control.

My second hypothesis was that the 7.8 ppm mixture would provide the hormetic effect.

This hypothesis should be rejected, because group 7, the 50% mixture did not have a hormetic effect in height or weight. However groups 9 and 10 with 4.7 and 3.1 ppm did have hormetic effects. One in height and the other in weight.

Because of the results of this experiment I wonder if a different herbicide would produce the same results as in this experiment. Also I wonder if a plant with a different root system would have the same results. I also wonder if there is a perfect amount of herbicide that would provide maximum growth stimulation. If I were to try to get the perfect stimulation I would probably try concentrations between 4.7 ppm and 3.1 ppm.

If I were to conduct this experiment again I would try it with better growth conditions:
real summer sunlight, natural soil, an additional week for maximum growth, and more accurate watering. I would also have more plants in the groups, and lastly pay more attention to the growth of my plants.


The graph also shows results from my 2003-04 experiment that established the Threshold Concentration. It shows that 7.8 ppm was the highest concentration at which almost all plants survived.


Dosage Rate Procedure

The Weedar reference recommended a rate of 1quart Weedar per acre for post-emergent ground treatment (1 quart Weedar contains 1 pound of the active ingredient 2, 4-D). The selected dose rates were chosen based on my previous research on calculating the threshold concentration of herbicide on radishes. Fractional dose rates that were selected were.15.6 ppm, 14 ppm, 12.5 ppm,, 10.9 ppm, 9.4 ppm, 7.8 ppm, 6.2 ppm, 4.7 ppm, 3.1 ppm, and 1.6 ppm.  Also, 1 group was chosen as a control group getting no herbicide added.


Introduction: Humans and animals need plants. Plants also need animals. Animals help spread the seeds from plants. Animals and humans need plants for food and shelter. Also plants create oxygen, which enables us to live so this is why humans and animals couldn’t live without plants. They all have a beneficial relationship to each other. One could not exist without the other.

Plants: Plants are important to our society. They provide food, lumber, clothing, paper, shelter, and many other products we use. Without them we wouldn’t be alive because we are omnivores eating both animals and plants, Animals that eat plants would not exist and carnivores would have no food source.

There are two main plant groups, flowering plants and non-flowering plants. Flowering plants include grasses, broadleaf plants, cacti and trees. Non-flowering plants include lichens, mosses, fungus, ferns, algae, and conifers. Flowering plants are generally plants that are eaten commonly.

Most plants live through photosynthesis where they make their own food using sunlight and an important plant chemical called chlorophyll. Chlorophyll gets its green color from its habit to absorb the red and blue portions of the electromagnetic spectrum giving it its color. The equation for photosynthesis is: 6 H2O+ 6 CO2 => C6H12O6 + 6 O2. Chlorophyll absorbs sunlight and this performs a chemical reaction, which provides its food. This chemical reaction then converts the carbon dioxide in the air and water to carbohydrates and oxygen. Animals then breath the oxygen keeping them alive, making plants an important part of our daily lives.

Agriculture: Agriculture is the most important industry in the world and is also the largest. When our ancestors began to grow food society was changed. Villages, cities, and towns began to grow rapidly due to agriculture. Communities, no matter how advanced, could not ignore agriculture’s importance. Now because of the new technologies we have obtained, people often don’t look at its importance. About half of all the world’s workers are in agriculture. It provides us food, clothing, and jobs. Farming is the common use of agriculture to grow natural resources like food, wood, and materials to make clothing. Farming provides us meat and plants. A few of the many plants farmers harvest  are beans, potatoes, fruits, nuts, tobacco, radishes, wheat, rice, vegetables, and many other plants.

Radishes: A radish is a fast maturing plant known for spiciness and its fleshy root. The scientific name for radish is Raphanus sativus. Radishes are found all over the world. There are two main types of radishes, spring radishes and winter radishes. Radishes maturing times range from 20 to 60 days after planting. Radishes that mature in 30 days or less are called spring radishes, which can be grown in fall gardens. Winter radishes are radishes that take 50 or more days to mature. Skin colors of radishes vary. There are red radishes, white ones, lavender radishes, scarlet radishes, and many other colors.
Radishes are typically disease free but there are some pests, which are aphids, cabbage maggots, and flea beetles, which tunnel, eat, and damage the radishes. A few reasons radishes die are because of pollution and insects.

Herbicides: Herbicides are used for the eradication of unwanted plants (usually weeds). However herbicide can harm animals and people. That is why people must be extremely careful with herbicide.

There are two different types of herbicide, selective and non-selective. Non-selective herbicide will kill any plant it comes in contact with if there is enough of it. An example would be Round-Up. It is used in places where people don’t want any plants at all. These places include cracks in cement, alleys, and other the road. Selective herbicide is the type of herbicide that will only kill a certain type of plant for example the herbicide Weedar (2,4-D) only kills broadleaf plants such as a radish plant.

Herbicides can also be dangerous to people and animals. The danger varies on what age you are, the dose you get, and what type it is. An example would be how the herbicide 2,4-D is corrosive. Thus it does more damage to the eye and skin than a no-corrosive herbicide. Also it is most likely fatal if swallowed.

2, 4-D: 2,4-D was the first successful selective herbicide made. It was made in 1946 and is currently the herbicide used most in the world. It is also the most researched herbicide in the world. Its major use in agriculture is with wheat, grains, corn, soybeans, and other vital crops.

Also it is used to kill weeds, aquatic weeds, and other unwanted plants. The herbicide is a growth inhibitor, which when sucked into the plant and causes abnormal growth blockage throughout the system, which stops the plant from taking in liquids and nutrients. This starves the plant, causing it to die.

However herbicides are extremely dangerous because this specific weed killer 2, 4-D is corrosive, its effects are it causes irreversible damage to the human eye, can be fatal if absorbed through skin, and is also extremely dangerous if swallowed or inhaled.

Hormesis: What is hormesis? Hormesis occurs when a toxin is administered to a plant. But for it to have a hormetic effect the plant has to receive a beneficial effect. Almost always the dose given to have this effect is unbelievably low. 

The concept of hormesis is not new and his been around for over a century. However in the 16th century Paracelsus had the idea that low enough doses of poison would not hurt a plant at all. Just the main idea has been around for over a century.

Based on information from Edward Calabrese’s studies the maximum tested amount of stimulation received from hormesis was on average 50% more than the control. Hormetic effects generally received from toxins were wide-ranged root or shoot growth. However toxicologists have found that hormesis is very unpredictable and is not easily reproduced in an experiment, if at all.

Summary: Although herbicides are useful in the destruction of unwanted plants they continue to be a threat to humans, plants (including radishes), and wildlife through pollution. Unfortunately the escape of herbicides and other pollutants continues to contaminate our water and hurt plants and animals alike.


“A little poison can be good for you,” November 12, 2003.,15704,454888,00.html 
Arnold P. Appleby. “The Practical Implications of Hormetic Effects of Herbicides on Plants.” October 1, 2004
Calabrese, Edward”6th Grade Hormesis Science Project Interview.” December 9, 2003 Personal e-mail
Cathy, Henry.  “Plants,” World Book Encyclopedia, 1999.
Cobbe, Harold. “Herbicide,” World Book Encyclopedia, 1999.
“Easy Gardening…. Radishes,” November 19, 2003
Edward J. Calabrese and Linda A. Baldwin. “Hormesis as a Biological Hypothesis.”
October 7, 2004
“Farm and Garden.” November 5, 2003.
Freeborn, Joel. “Agriculture,” December 10, 2003. F.html
Freeborn, Joel. Personal Interview. November 12, 2003.
“Herbicides,” November 19, 2003
Hughes, George R. “Radishes,” World Book Encyclopedia, 1999.
Mortazavi, Javad. “An Introduction to Radiation Hormesis.” December 3, 2003.
“Radish. “Microsoft Encyclopedia Deluxe.2001
“Radish.” November 12, 2003. http://www.urbanext.uiuc.edc/
Shconeweis, Susan D.” Growing Radishes and Table Beets.” November 5, 2003.
 “The Importance of Agriculture,” December 17, 2003
Welsh, Frank.” Kinds of Poisons,” World Book Encyclopedia, 1999.

  • I would like to thank the following people for helping make my project possible:
  • My parents, especially my dad for helping me conduct my science experiment, helping me e-mail an expert, also for helping record my results, and giving me an idea for my science experiment.
  • I would also like to thank Mr. Newkirk and Mrs. Helms for helping me get resources for my experiment and project board.

Top of page

Menu of 2004-2005 Science Projects

Back to the Selah Homepage