Activities:
Effects of Pollution

Grades: 7 - 8

Purpose: To examine the effects of polluted air on plant life

Materials:

Time:

plant preparation - 2 - 3 weeks
setup: 30 minutes
observation: several days

CAUTION: Volatile liquids are harmful to inhale and should be used in well ventilated areas. Do not allow volatile liquids to contact skin, because they can be absorbed into the body.

Note: You may buy 5 small identical plants to use in the investigation. To eliminate variability in the age, condition, size, etc., of plants and to reduce costs, it is suggested that you grow your own plants from seed. One or two inches of potting soil can be placed in the bottom of each jar (prepare 7 jars, and later select the 5 most identical plants/jars for the investigation). Place approximately 4 seed (radish, corn, or another plant) in the soil of each jar (arrange seeds to sprout from one side of the jar bottom so a bottle cap can later be placed on the other side of the jar bottom), cover seeds with 1/4 to 1/2 inch of soil and moisten soil with water from a spray bottle. Lightly cover jars with plastic wrap to reduce evaporation but allow air to reach seeds. Place jars in a warm location, and as the seedlings begin to emerge, move all jars to a sunny window, and remove plastic wrap. Allow plants to grow for two to three weeks, watering them as needed and keeping them under identical conditions. Carefully pull out or trim out extra seedlings so that only 3 healthy plants remain in each jar, and them begin the investigation.

figure 1

Assemble 5 chambers as shown in figure 1. Each of the 5 jars should look identical, containing a purchased houseplant or 3 seedlings. Throughout the investigation, keep plants in sunlight to promote growth. Place a bottle cap in each jar. Place 1 ml of water in the bottle caps in jars #1 and #2. Place .01 ml of volatile liquid in the bottle cap in jar #3, 1 ml of volatile liquid in the bottle cap in jar # 4, and place 10 ml of volatile liquid in the bottle cap of jar #5. Immediately tighten lids on jars #2, #3, #4 and #5. Do not remove the lids during the observation period.

(It may be more convenient to vary the amount of volatile liquid in each jar by counting drops rather than measuring mls. For example, you might place 10 drops of water in bottle caps #1 and #2, 1 drop of volatile liquid in bottle cap #3, 10 drops of volatile liquid in bottle cap #4 and 100 drops of volatile liquid in bottle cap #5. Be sure to tighten lids on jars #2, #3, #4 and #5 immediately after adding pollutant, and do not remove lids during the observation period.)

Observe plants to determine the approximate threshold concentration of pollutant. The threshold concentration is the amount of pollutant needed to cause observable damage to the plant. What kind of damage are you able to observe? How soon is damage noticed? Record the observations on the data chart. What purpose did jars #1 and #2 serve? Could there be damage to the plants that we can not observe?

While this investigation should give you an approximate range for threshold, you could design another investigation to "pinpoint" a more exact threshold by using smaller increments of pollutant concentration, determined from what you observed during this investigation.

Expected results and the reasons they occur:

Depending upon the volatile liquid used, plant damage may be noticed at any of the concentrations and within any period of time. You may observe that the plants exposed to higher concentrations show damage first, and plants exposed to lower concentrations show damage at some time, while plants exposed to lower concentrations never show damage. jar #1 is included in the investigation to show the normal development of plants exposed to typical air movement with no "added" pollutant. jar #2 is included to show the development of plants exposed to a closed air system with no "added" pollutant. The two jars without pollutants serve as "controls", which provide comparisons for jars containing pollutants: If plants from all five jars show damage after a period of time, there would be no evidence that the pollutants could be causing the damage. Instead, it would provide evidence that something other than pollutants could be causing damage. If plants from jar #1 remain healthy but plants from jars #2 through #5 show damage, there would be no evidence that the pollutant could be causing damage. Instead, it would provide evidence that the closed air system cold be causing damage. If plants from jars #1 and #2 remain healthy but plants from jars #3 through #5 show damage, there would be evidence that the pollutant (i.e. volatile liquid) could be causing damage.

Activities adapted from the Puget Sound Air Pollution Control Agency's "Clean Air Express," and from "Where's the Air," Wisconsin Department of Natural Resources.