Ecology and Environmental Science Projects
Chemical Contamination of Lakes and Streams
One way to test for contamination in water from lakes, rivers and streams is with a bioassay.
A bioassay uses a living organism--usually a plant or a bacteria--as a test agent for the presence or concentration of a chemical compound or a disease. The idea is to choose a test agent that is very sensitive to the condition you are testing.
Have you ever read about how miners took canaries down into mines to act as early warnings of gas leaks? Because canaries are more sensitive to gas than people, the birds reacted to very small amounts of gas and gave miners a chance to escape. You could say canaries were a bioassay for underground gas.
Different plants are often used as bioassays because they respond in a predictable way and are often very sensitive to the condition that is being tested. A standard toxic dose--the level at which no seeds of the bioassay plant sprout or all the plants die--is established as a reference point. Then samples are tested and compared to the reference standard.
Of all the possible water-quality bioassay organisms, lettuce might be one of the last you would think of. Lettuce doesn't live in water, so why use it to test water quality? The reason is lettuce bioassays are inexpensive, easy to do, and the seeds are pretty sensitive to some types of contaminants in water, including heavy metals, pesticides and other organic toxins. Although any variety of lettuce may do, Lactuca sativa Buttercrunch is the standard variety recommended for bioassays by the U.S. Environmental Protection Agency, the Food and Drug Administration, and the Organization for Economic Cooperation and Development.
You might try taking a series of samples along one stream or compare streams near industry to water running though agricultural areas.
Directions for conducting experiments can be found at: Lettuce Bioassay. (http://ei.cornell.edu/toxicology/bioassays/lettuce/)
For most of the following experiments, you will need a pH indicator, such as wide-range litmus or pH paper, a garden soil pH testing kit, or a pH indicator that you can make yourself in Experiment 3. These pH indicators contain a chemical that changes color when it comes in contact with acids or bases.
For example, litmus and pH paper turn red in strong acids and blue in strong bases. Because only a few pH indicators measure pH over a wide range of pH values, you will need to find out the pH range of the indicator you use. Typically, the color chart provided with each pH indicator kit will show the pH range of that indicator.
Color pH indicators provide only an approximate measure of the pH, or the strength of the acid or base. They are not as accurate as the expensive instruments scientists use to measure pH, but they are adequate for the following experiments.
Measuring With pH Paper
When measuring pH with pH paper, dip the end of a strip of pH paper into each mixture you want to test. After about two seconds, remove the paper, and immediately compare the color at the wet end of the paper with the color chart provided with that pH indicator. Write down the pH value and color. Always use a clean, unused strip of pH paper for each mixture that you test
Measuring Liquids with a Garden Soil pH Test Kit
Soil pH test its are designed to measure the pH of soil, but they may also be used to measure the pH of liquids, such as water and water mixtures. Most of these kits contain a test solution (liquid pH indicator), color chart, and clear plastic test container, such as a test tube.
To measure pH, pour 1/4 teaspoon of the mixture you want to test into the test container, and add 1/4 teaspoon of the test solution provided in the kit. Cover the container and shake once or twice to mix, or stir if necessary. Compare with the color chart provided with the kit and write down the result.
- Except for pH test paper, all the materials called for in these experiments, including distilled water and borax, can be obtained at grocery stores or from local lawn and garden stores or nurseries.
- pH test paper can be ordered online at Amazon.com. Or, inexpensive garden soil pH testing kits are often available at lawn and garden stores or nurseries. These testing kits usually contain a pH indicator solution that covers a range of at least pH 4 to 10, which is wide enough for most of the following experiments.
- You may substitute baking soda for household ammonia in the experiments. If you do, be sure to stir well because baking soda does not dissolve easily in water unless heated. The pH of undissolved baking soda will not be the same as dissolved baking soda.
- You may substitute fresh-squeezed lemon juice for white vinegar. Lemon juice is slightly more acidic than the vinegar sold in grocery stores. White vinegar is preferred over cider vinegar or lemon juice because it is colorless and relatively free of impurities.
- Use clean, dry containers and utensils.
Experiment 1: Measuring pH
This experiment will illustrate how to measure the approximate pH of chemicals in water using a pH indicator. A pH indicator is a chemical that changes color when it comes in contact with acids or bases.
- pH paper and color chart (pH range 3 to 12) or garden soil pH testing kit distilled water (available at grocery stores and drug stores)
- white vinegar
- household ammonia (or baking soda)
- 3 small, clear cups or glasses
- 3 stirring spoons
- measuring cups and spoons (1/2 cup, 1/4 and 1 teaspoon)
- notebook and pencil
- ar, the second cup ammonia, and the third cup water.
- Pour 1/2 cup distilled water into each of the 3 cups.
- Add 1/2 teaspoon white vinegar to the vinegar cup and stir with a clean spoon.
- Add 1/2 teaspoon ammonia to the ammonia cup and stir with a clean spoon.
- Do not add anything to the water cup
- Dip an unused, clean strip of pH paper in the vinegar cup for about 2 seconds and immediately compare with the color chart. Write down the approximate pH value and set the cup aside. (If using a garden soil pH tester kit, pour 1/4 teaspoon of the contents of the vinegar cup into the test container, and add 1/4 teaspoon of the test solution. Cover the test tube and shake once or twice to mix, or stir if necessary. Compare with the color chart provided in the kit, and record the result.
- Dip an unused, clean strip of pH paper in the ammonia cup for about 2 seconds and immediately compare with the color chart. Write down the approximate pH value and set the cup aside. (If using a garden soil pH tester kit, repeat the same process in step 6 using the contents of the ammonia cup instead of the vinegar cup.)
- Dip an unused, clean strip of pH paper into the water cup for about 2 seconds and immediately compare with the color chart. Write down the approximate pH value. (If using a garden soil pH tester kit, repeat the same process above using the contents of the water cup instead of the ammonia cup.)
Questions and Answers
Is vinegar an acid or a base?
Vinegar is an acid, and in this experiment it will display a pH of about 4. Vinegar at pH 4 turns pH paper yellow and most other pH indicators red.
Is ammonia an acid or a base?
Ammonia is a base and in this experiment it will display a pH of about 12. Bases turn most pH indicators blue.
Did distilled water have a neutral pH?
PURE distilled water would have tested neutral, but pure distilled water is not easily obtained because carbon dioxide in the air around us mixes, or dissolves, in the water, making it somewhat acidic. The pH of distilled water is between 5.6 and 7. To neutralize distilled water, add about 1/8 teaspoon baking soda, or a drop of ammonia, stir well, and check the pH of the water with a pH indicator. If the water is still acidic, repeat the process until pH 7 is reached. Should you accidentally add too much baking soda or ammonia, either start over or add a drop or two of vinegar, stir, and recheck the pH.
3. Which way is up? - Tropism and Auxin
Many seeds and bulbs have a definite top and bottom. What happens if you plant them upside down or sideways? Will the seeds still grow; will it take longer for leaves to start showing up?
What happens if you change a seed's direction once it starts to sprout? You'll learn about the chemical auxin, which affects where roots and stems grow.
- Divide 10 bean seeds into 2 groups of 5. - a control group and the experimental group.
- Spread the seeds out on moist paper towels then wrap them a pieces of folded aluminum foil.
- Label one side of control group packet "Up". Label the sides of the experimental group "A" and "B". Place the sprouts where they will not be observed.
- Allow the beans to sprout for 3 days.
- Carefully open the foil and towels and observe the seedlings. Moisten the towels if necessary, then refold the foil. Turn the experimental set of the seeds upside down. Make sure to keep the control seeds right-side up.
- Open and observe the sprouts every 2 days, making sure to keep the control sprouts right-side up and turning the experimental group over.
If you have access to an old record player turntable, you can take it a step further by using it to simulate changing gravity's pull on seeds. Tape the experimental packet onto the turntable and set it for 78 RPM. Allow the machine to rotate continuously for 5 days. After the 5 days are up, turn off the record player and without changing the position of the foil, open them up and observe the beans. The rotating turntable creates a gravity with an outward force instead of the normal down.
Materials: Greenhouse or sunny window sill, 10 bean seeds, 10 small pots, water, ruler, potting soil, pencil.
- Fill the 10 small pots with equal amounts of dampened potting soil.
- With a pencil, make holes about 2 centimeters deep in each pot.
- Place the 10 bean seeds, one per pot, and cover the seeds with some of the soil.
- Place 5 of the pots in the greenhouse or on a window sill on the sunny side of the house.
- Place the other 5 on a window sill that does not receive bright sunlight.
- Be sure to water the plants as needed.
- Seeds will germinate within 7 days, and you can begin making stem measurements. Take stem measurements for 14 days. Note the difference in stem length for each set of plants, and write down your observations.
Results: What differences did you observe between seedlings that grew in the bright sunlight compared to less bright light? (color of leaves, length of stems, etc.) What caused those differences?
4. What happens when you grow sweet potatoes next to other plants? - Allelopathy
Compare how fast other plants grow at different distances from sweet potatoes. Remember to grow some control plants nowhere near the sweet potato.
Background Info: Allelopathy is a chemical process that a plant uses to keep other plants from growing too close to it. Some plants that use allelopathy are black walnut trees, sunflowers, wormwoods, sagebrushes, and trees of heaven.
There are several ways in which an allelopathic plant can release its protective chemicals:
- Volatilization - Allelopathic trees release a chemical in the form of a gas through small openings in their leaves. Other plants absorb the toxic chemical and die.
- Leaching - Some plants store protective chemicals in the leaves they drop. When the leaves fall to the ground, they decompose, giving off chemicals that protect the plant.
- Exudation - Some plants release defensive chemicals into the soil through their roots. Those chemicals are absorbed by the roots of other nearby plants, which are damaged.
5. How do different conditions affect the speed at which fruit and vegetables ripen?
Temperature, light, placement in sealed bags, exposure to other ripe fruit--all have different effects on different fruits and vegetables. Design an experiment to test two or more of these variables.
Background Info: Ethylene gas is the ripening agent that many fruits and vegetables produce naturally. Ethylene causes them to ripen--and then overripen. While refrigeration and humidity slow the effects of ripening, they don't stop the production of ethylene gas.
The more the fruit ripens, the more ethylene gas it makes. This has a big effect on how--and when--farmers harvest their fruits and vegetables for market. Most commercial tomatoes are picked before ripening is completed, so the fruit won't spoil before it gets to your market. But picking early also means the tomato spends less time on the vine, where ethylene would help build more of the sugars and acids that create tip-top tomato flavor.
6. The effects of light on seedlings germination
How do light and dark conditions affect the germination and growth of seedlings....