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Water pollution — What are we?
Grade Level: 6–12
Duration: 2 weeks
Subject: Water pollution
- Students will list and describe three types of surface water pollutants (nutrients, bacterial waste, toxic chemicals).
- Students will observe the effects of various water pollutants on algae growth.
- Students will list three causes of each surface water pollutant.
- Five 3-liter bottles (clear, not tinted)
- Five 2-liter bottles with pond water from same source and area
- Tap water that has been dechlorinated
- Five small jars (baby food jars)
- Measuring cup
- Soap or detergent
- Flea powder
- Food scraps
- Masking tape for labeling
- Waterproof markers or crayons
One type of water pollutant is nutrients. Nutrients from fertilizer have been major water pollutants since the 1940s. Although plants and animals need nutrients for growth, an overabundance of nutrients cause algae and other aquatic plants to grow too rapidly. Rapidly growing plants in water means a greater amount of plants that will die and decay, using up dissolved oxygen in the process. As a result, fish and other aquatic life die.
A second type of water pollutant is bacterial waste (human and animal). Lakes and beaches are often closed to swimmers and fishermen because of high counts of fecal coliform bacteria from sewage (human wastes), feedlot runoff, pet wastes, and improperly maintained septic tanks. Although fecal coliform bacteria are not harmful themselves, they usually indicate that pathogens, disease-causing organisms, are present.
A third type of water pollutant is toxic, or poisonous, chemicals. The most common sources of toxic pollution are from point sources of pollution (sources of pollution that are easily pinpointed) such as industrial discharges or oil spills. Toxic pollution can also come from less identifiable, or nonpoint, pollution sources, including runoff from urban and rural areas and fallout from the atmosphere. Point sources are the easiest to correct and can be dealt with directly. Nonpoint sources are more difficult to fix and require a lot of cooperation by every part of a community.
In the past, as we progressed as a nation, we were careless with our water. Farmers used chemicals to help crops grow and to kill insects, and later the rain and snow washed these chemicals into streams and lakes. Factories made many useful products from chemicals, such as medicine, clothes, automobile lubricants, and household goods. Water was always used in the process, and wastewater was discharged into rivers and streams. People added pollutants to water when they used it in their homes and on their lawns. They added soap, toothpaste, shampoo, bleach, detergents, fertilizers, insect spray, human wastes, paint, oil, and grease, and others.
Today, we are more aware of the damage that can be caused by water pollution, and many best management practices (BMPs) have been developed and are used to prevent water pollution. As we learn more about our natural systems and the impacts of our interactions on these systems, we are developing new laws, regulations, and BMPs to protect our water systems.
This activity can be done individually or in groups.
- Have students make three columns on a piece of paper and label each column with one of the three categories of pollutants: nutrients, bacterial waste, toxic chemicals.
- Ask students to identify the kinds of substances causing each kind of pollution. Lead them to summarize: nutrient — fertilizer; bacterial — human or animal wastes; toxic — chemicals/pesticides. Write these terms below the column headings.
- Have students list, in the appropriate columns, sources for each kind of pollution found in their area. List as many as possible and share with the entire class.
- Prepare the pollutant mixtures with the pond and tap water, using small jars. You may do this yourself or have the students do it.
- Pour ¼ cup (60 mL) of tap water into the first jar. This is the control; you will not add a pollutant to this jar.
- In a second jar, mix ½ teaspoon (2–3 mL) soap or detergent and ¼ cup of tap water.
- In a third jar, mix a solution of vinegar (1½ ounces or 45 mL) and ¼ cup of tap water.
- In a fourth jar, mix ½ teaspoon (2–3 mL) of flea powder and ¼ cup of tap water. (The powder is similar to chemicals used to kill pests in lawns and gardens.)
- In a fifth jar, mix ½ teaspoon (2–3 mL) food scraps and ¼ cup of tap water. (Bacteria will break down the food.) Note: Avoid using any meat scraps, because they will become very smelly.
- Cut the tops off five 3-liter plastic bottles or other clear containers. Fill each “pond model” with pond water. They will be identical.
- Add one jar mixture (steps a–e above) to each pond model. Point out to the students that the models are exactly the same except for the pollutants added to them. This is very important in the experiment.
- Label each pond model with pollutant and type: Pond Model 1 is the control; Pond Model 2 represents nutrient pollution, Pond Models 3 and 4 represent toxic pollution, and Pond Model 5 represents bacterial pollution.
- Have the students predict what will happen to each model.
- Next, the students will monitor the models for pollutants. They will make daily observations and record any differences in growth and development of the algae for about 10 days to 2 weeks. (Note: If the smell becomes too unpleasant in the food scraps pond, discard it.) Discuss the observations. The plain water model should look the same; the vinegar and flea powder models should show no growth (toxic); the detergent should have extensive growth of algae (nutrient); and the food scraps should be smelly (bacteria).
- Have students explain the results by comparing what was added to the models. (Algae and algae spores were present in the pond water that was collected for the experiment.)
- When observations have been completed, the algae and the water (with the additives) may be safely flushed down the sink.