Module 8. Pollution

(Level of difficulty ***)

Question: How do chemicals and pollutants in the environment affect plant health?

Materials you will need:
• 2 or more empty rinsed plastic yogurt containers or single-use cups (any size, preferably 3-10 oz)
• 2 or more larger plastic or Styrofoam trays or bowls
•An awl
•Soil (dirt from outside should work)
•Seeds (bean, pea, cucumber, tomato, sunflower, corn, pumpkin or squash)
•Water (tap water is fine)
•Household chemicals, such as salt, sugar, baking soda, vinegar, laundry detergent, dish soap, Windex, etc.
•A measuring cup or spoon

•Poke small holes (1-3 per container) on the bottom of yogurt containers or cups using an awl (have an adult help you with that!)
•Fill containers with soil and place them in a larger bowl/tray (to capture spills and leaks)
•Prepare your chemicals by mixing them with water (see below for mixing suggestions)
•Put the seeds in soil (it is OK to put multiple seeds into each container, but keep the number of seeds in both containers the same) and cover them with a little bit of soil (finger-thick layer or less)
•Pour your chemicals (one chemical per pot) or water onto the soil to make it moist, but do not overwater (stop watering as soon as you see excess water/chemicals coming out from the holes onto the tray)
•Cover the pots with seeds with some plastic wrap (to keep soil from drying), leaving some space on the top of the container for the seeds to grow
•Put all containers next to the source of light (a windowsill)
•Wait for 3-14 days for the seeds to germinate
•Unwrap the pot with dark-grown plants and examine how it looks in comparison to the light-grown pot

Helpful hints and suggestions:
•Don’t forget to label the containers (for example, “water”, “salt”, “soap”, and so on), so after your experiment is done you will not get confused which pot is which.
•You can compare the effect of several different chemicals on plant growth (do not forget to include water only as your control!), or test different amounts (concentrations) of a single chemical.
•Some plant varieties are more sensitive to certain chemicals than others and some chemicals are more harmful to plants than others, but as a general guideline, try adding 1 teaspoon of the chemical to each 5 ounces of water (have an adult help you with the measurements).
•To avoid cross-mixing of chemicals, place individual pots watered with different chemicals in separate trays (for collecting spills).

Expected results:
•Seeds watered with chemicals will not germinate, will germinate later and grow poorly compared to the seeds watered with clean water.
•Some chemicals, such as sugar, may promote (or speed up) germination and growth.

Follow-up questions:
•Why do you think chemicals affect plant growth?
•Do you think all chemicals are bad for the plants or some are good?
•What can you and your family do to reduce amount of chemicals dumped into environment?
•If you were to repeat the experiment, would you get the same results?
•Do you think the results of your experiment would be different if you used a different amount (concentration) of the same chemical?
•Do you think the results of your experiment would be different if you grew your plants in the dark or used a different kind of seeds?
•If you first germinated the seeds in the presence of clean water and then watered the plants with the chemical, what do you think would happen to those plants?