Moving through water: How can pesticides affect nontarget plant life?
Leaching and runoff can cause pesticides to move away from their target location. When pesticides mix with rain or irrigation water, they can seep into the soil and travel to another area where they can affect the plant, animals, and environment. In this experiment, you will examine the effects of pesticides on new growth. You will plant a lettuce seed and nurture it with water that has insecticide in it. Planting three sets of seeds, you will add two varying amounts of insecticide to the water and compare them to lettuce grown in unaltered water.
Before you begin, make an educated guess about the outcome of this experiment based on your knowledge of leaching, runoff, and pesticides. Here is one possible hypothesis: "Water with the greatest amount of pesticide will result in stunted or no plant growth."
Level of Difficulty
Easy to moderate.
Materials Needed
- 15 lettuce seeds
- peat pots, with moist to dry soil (available at garden stores)
- water
- liquid synthetic insecticide
- marking pen
- masking tape
- ruler
- area with light
- paper towels
- plastic wrap
- two rubber bands
- plastic teaspoon
- measuring cup
- three disposable plastic cups
Approximate Budget
- $7
Timetable
20 minutes setup; about 5 minutes daily for 8 to 12 days (longer if desired).
How to Experiment Safely
Have an adult present for this experiment. Be careful when working with the pesticide. Measure the pesticide outside or in a sink. Follow the warnings carefully and wash your hands afterwards. Make sure you throw away the disposable cups and spoons that come into contact with the pesticide. Keep younger children away from the cups containing the pesticide mixtures.
Step–by–Step Instructions
- Label the disposable cups: "Low Pesticide," "High Pesticide," and "Control." Label each peat pot "Low," "High," and "Control." The dirt should be dry to moist
- In the Low Pesticide cup, use the plastic spoon to place 2 teaspoons (about 10 milliliters) of the pesticide in the cup.
- In the High Pesticide cup, use the plastic spoon to place 5 teaspoons (about 25 milliliters) of the pesticide in the cup.
- Measure and pour 0.5 cup (about 125 milliliters) of water into each of the cups. The Control cup should have plain water. Use plastic spoons to stir the High and Low cups, making sure to throw the spoons away when you have finished.
- In each peat pot, plant five lettuce seeds per the instructions on the package.
- Working over a sink or paper towels, pour the High pesticide water into the peat pot labeled High. Pour enough water to saturate the lettuce seeds. Water will start to drip out the bottom when you have poured enough.
- Repeat with the Low water, and the Control water. Set the plants on a plastic container or holder to catch the water dripping out the bottom.
- To seal in the water, tightly cover the disposable cups (not the peat pots) with plastic wrap and wrap a rubber band around the plastic. Place the water cups aside near the plants and make sure labeling is clearly visible.
- After the seeds sprout (about 5 days), start daily observations of the plants. Count how many sprouts there are in each pot and measure the height. Make your measurements at the same time every day.
- When the seeds need more water, use the water from its designated cup until the water is gone. (You may need to restir.)
Summary of Results
Examine the height and number of sprouts from each peat pot. Average the heights of each group and graph the results. Is there a difference between the experimental trials and the control? Are there any other physical characteristics that are different among the groups of lettuce sprouts? Write up a brief summary of the experiment.
Troubleshooter's Guide
Problem: None of the plants grew.
Possible cause: Make sure you are following instructions as to the amount of light and warmth the seeds need. You may also have bought defective seeds. Try the experiment again with a new packet, making sure to follow the instructions.
Problem: There was not much difference between the two groups of seeds watered with the pesticides.
Possible cause: All the pesticide water may not have soaked into the plants. Make sure you stir the water thoroughly before applying it to the seeds, and repeat the experiment.