Is Dilution the Solution? An introduction to nonpoint source pollution

Purpose: This laboratory or classroom activity introduces students to water pollution concepts and demonstrates that even small amounts of pollution in a water supply can be harmful.

Summary: Students will learn about point source and nonpoint source pollution, learn to identify some pollution indicators, and attempt to clean up a contaminated sample by diluting the water.

Background: Water is a vital resource without which life cannot exist. While water has the capacity to cleanse itself when polluted, by depositing, breaking down, or diluting the materials, if too many pollutants enter a water body, its capacity to detoxify itself may be overwhelmed. Problems also arise when small amounts of highly toxic materials enter a stream or lake.

Water pollution can be categorized as point source pollution, in which the source of the pollution is easily determined, and nonpoint source pollution, which results from a variety of land uses. Point sources include factory discharges and wastewater treatment effluent that is discharged into a river or lake. Because the discharges reach the water from a known single source via an easily identified pipe, culvert, or other conveyance, it is possible to measure what is in the discharge and treat or control it before it enters a waterway.

Nonpoint source (NPS) pollution is much more difficult to control due to its diffuse nature. It occurs when water washes over the land surface, whether from rain, car washing, or the watering of crops or lawns, and then picks up an array of contaminants. These contaminants include sediment from storm water runoff, fertilizer from lawns and crops, leachate from landfills, and oil from leaky cars that washes off roads. Itπs impossible to trace NPS pollution to a single controllable source. Today, NPS pollution is our biggest water pollution challenge. Everyoneπs daily activities contribute to NPS pollution, so everyone needs to learn how it occurs and apply simple measures to decrease amounts.

There are six major types of water pollutants:

1. Nutrients are materials such as nitrogen and phosphorus that feed plants and stimulate their growth. We use fertilizers, which contain nutrients, to keep our lawns green and our plants and crops healthy and productive. Other sources of nutrients include sewage, septic tank effluent, animal waste, automotive exhaust, industrial wastes, and even car washing. It's been estimated that about 80 percent of nitrates and 75 percent of phosphates that are added to lakes and streams in the U.S. are the result of human activities. Plants require nitrogen and phosphorus to grow. When too many nutrients enter waterways, plants such as algae may grow explosively. These algal blooms can become so overwhelming that water becomes green, slimy, and smelly. This affects water clarity and blocks sunlight transmission, which harms other aquatic organisms. When the algae die, the decay process robs the water of oxygen, and fish death may occur. Nitrates in drinking water have been linked to "blue baby" syndrome in infants.
2. Pathogens are disease-causing microorganisms such as bacteria and viruses that come from the fecal waste of humans and animals. These substances may cause serious health problems, and can interfere with the use of water for recreation. Special treatment of drinking water may be required when it becomes contaminated with troublesome pathogens such as Giardia and Cryptosporidium. Pathogens wash off land from wild animal, farm animal, and pet wastes, and can also enter our waterways from improperly functioning septic tanks, leaky sewer lines, and boat sanitary disposal systems.
3. Sediment includes sand, dirt and gravel eroded by surface runoff. Our sandy Nevada soils are particularly vulnerable to erosion, and any activities that disturb the ground surface and remove rangeland or other plants may accelerate sediment production. Sediment usually ends up in stream beds, retention ponds, or at the shores of lakes and reservoirs. The sediment can alter stream flow and damage aquatic habitat. Sediment affects water clarity, may clog fish gills, and smothers spawning gravels. Poorly protected construction sites, bare soil at newly built sites, overly steep slopes resulting from poor construction methods, areas burned by wildfire, vacant agricultural fields, and suburban gardens can all be sources of sediment pollution.
4. Toxic chemicals are substances that may harm the health of human beings and aquatic life. These include heavy metals, pesticides, and organic compounds such as polychlorinated biphenyls (PCBs). Toxins result from a variety of human practices and products. Because many of these toxic substances are resistant to breakdown, they tend to be passed along the food chain and concentrated in large predators. Fish consumption health advisories may result from accumulation of toxins such as mercury. Oil, grease, and gasoline from roadways (called hydrocarbons), industrial practices, and chemicals used in homes, gardens, yards, and on farm crops are major sources of toxic contaminants. Few people know it, but storm drains dump runoff directly into the nearest river or lake. The storm water is not treated, and thus can be a source of dangerous pollution if people use storm drains as disposal sites for hazardous materials.
5. Trash (a.k.a. junk or debris) is something we all can recognize. Plastic bags, fast food wrappers, even shopping carts find their way into local streams and ditches. This type of pollution not only interferes with our enjoyment of our water resources, it also can be a health threat to aquatic organisms and other animals found in wetland habitats. Andäitπs just plain ugly. Trash often starts as street litter that is carried by the wind or by runoff into our waterways, or is directly dumped into streams, ditches and storm drains for disposal.
6. Increased temperatures result when streamside vegetation that shades and cools the water is removed. Paved surfaces, particularly asphalt, that transfer their heat to rainfall and runoff also are a source of temperature pollution. Shallow water impoundments and concrete canals will absorb heat and result in elevated temperatures in surface water. Elevated temperatures are harmful to aquatic life, and can even result in changes in fish species from those that require cool temperatures, such as trout, to those that will tolerate warm temperatures, such as carp. Warm temperatures also decrease oxygen concentrations, and create a more favorable environment for pathogen growth.

While some of these sources of pollution are visible, such as trash, others may be colorless and odorless, making them difficult to detect. Historically, humans have used large bodies of water, such as the oceans, to dilute and disperse wastes. During the 1860s through the 1890s, the Truckee River in Reno was used as a sewer. Raw wastes were dumped into the river, with the thought that they would move downstream and "go away". The river was also used to dispose of sawdust waste from paper mills. By the 1890s, it was no longer safe to drink the water due to pathogen contamination. Anecdotes from that time note that there was so much sawdust in the river, it looked like chowder.

Today, of course, we know that no water body is an infinite reservoir. Medical wastes are washing up on beaches. Sewage dumping has resulted in fish death and health problems. Swimmers become ill from a variety of infections, and beaches must be closed. Dilution is NOT the solution to all pollution!

Materials:

1. Categories of nonpoint source pollution handout
2. What you can do about nonpoint source pollution handout
3. Nonpoint source pollution cartoon handout
4. 6 plastic cups per group
5. 100-mL graduated cylinder
6. Water
7. Dropper
8. Plastic spoons for tasting and mixing
9. Colored powdered drink mix (such as Kool-Aid, etc.), without sugar
10. Colored powdered drink mix, with sugar (darker colors work well)
11. Sugar
12. Student worksheet for dilution exercise

Procedure: Provide a background to nonpoint source pollution to the students. Have them generate a list of all the types of pollutants they can think of.

1. Show students the cartoon handout and have them try to determine all of the visible sources of pollution in the picture.
2. Have students match the sources of pollution to the category of pollutant (nutrients, pathogens, sediment, toxic chemicals, trash, elevated temperature).
3. What are some local waterbodies that might be experiencing problems with nonpoint source pollution? Where is it coming from, and what kinds of pollution might be occurring?
4. Ask them to come up with some ways to decrease the pollution. How might they ensure a repeat accident or situation might not happen again?
5. To lead into the exercise, ask students how easy they think it might be to clean up the different types of pollutants.
6. Do the dilution exercise (adapted from The Water Sourcebook, Grades 6-8).
1. Mix up the unsweetened drink mix and have students taste it. Add small amounts of sugar, and have students keep continue to taste small amounts until it seems sweet. How much did it you add? Can the students see the sugar? Point out that pollutants may have neither a color NOR a taste, but may still be in the water threatening our health. An example is nitrate contamination, which has neither color, nor odor, nor taste.
2. Divide students into small groups. Each group needs 6 plastic cups. Have the students number the cups from one through six using a permanent marker.
3. Place 50 mL of water in cups 2 through 6 for each group. This represents the "pure" water that will be polluted by the drink mix.
4. Mix the powdered sweetened drink mix according to the directions.
5. Use the graduated cylinder to place 100 mL of the prepared sweetened drink mix into cup number 1 for each group. Explain to students that cup number 1 represents a source of pollution to local water, such as fertilizer running off a lawn. Have the students use a clean plastic spoon to taste the drink. Be careful - if they taste too much, you'll run out! Have students record the color and taste on the handout.
6. Place 50 mL of the "polluted" mix from cup 1 into cup 2 using the graduated cylinder and have students stir the mixture. Ask a single student to taste the mixture and decribe the difference in sweetness. Have them record their observations on the chart.
7. Ask the students to predict how dark the solutions will be in cups 3 - 6 after they are diluted, and how sweet they will be. Enter the predictions on the chart.
8. Continue to add 50 mL from the polluted water source into the clean water in cups 3 - 6. Have students mix the solutions and record their observations on the chart.
9. Have students compare the color of cup 1 to cup 3 and cup 6. Place white paper under the cups if needed for contrast. Compare tastes again, using clean spoons each time.
10. Have the students answer the questions on the chart. Ask them where they think pollution goes. Does it stay in the water forever? What happens to it? (it may wash downstream, be biodegraded, evaporate, stick onto sediments, etc.)

Student Worksheet - Dilution Exercise

Directions: Dilute each water sample and record your color and taste observations.

Starting liquid	100 mL drink mix	50 mL drink + 50 mL water	50 mL solution 2 + 50 mL water	50 mL solution 3 + 50 mL water	50 mL solution 4 + 50 mL water	50 mL solution 5 + 50 mL water
Color Predicted
Color Observed
Taste (how sweet is it?) Predicted
Taste (how sweet is it?) Observed

1. How could you tell that pollution still remained even when the solution was diluted?
2. How many more times do you think that the polluted water would need to be diluted in order not to cause color or taste changes? Why?
3. Do you think dilution is a good solution for pollution? Why or why not?

Additional Activity: Remove Oil Pollution from Water Using Different Methods

(Also adapted from the Water Sourcebook; or do activity "Cleaning Oil Spills" on p. 5-5 of the Sourcebook)

Materials:

Provide the following materials to each group:

1. Clear plastic cups
2. Large ladle, such as a gravy ladle or large serving spoon
3. Plastic teaspoon
4. Medicine dropper
5. Motor oil
6. Water
7. Graduated cylinder for measuring oil (100 mL)
8. Paper towels
9. Student worksheet

Procedure: Students will try three different physical procedures for removing oil from water.

1. Have students brainstorm ways to remove oil pollution from water. Have them research historic methods and compare to methods used today.
2. Divide students into groups.
3. Each group of students will need three samples consisting of approximately 1/2 cup of water contaminated by 50 mL of motor oil. Students should carefully measure the motor oil into each container. Use a plastic cup for the contaminated sample. Groups also need a large ladle like a gravy ladle, or a large spoon, a plastic spoon, a medicine dropper, paper towels, graduated cylinder, 3 cups for waste oil, and student worksheet.
4. Explain the three methods to be used (ladle, spoon, or dropper). Have the students enter their hypothesis (which method will work best?) on the worksheet.
5. Have groups attempt to remove as much oil as possible using the ladle. Dump the oil into the other plastic cup. When no more can be removed, measure the amount of oil removed using the graduated cylinder. Pour the oil from the plastic cup into the cylinder. Measure the oil in milliliters. Be careful not to measure the water! Enter the amount removed on the worksheet. Dump the oil into the used plastic cup for proper disposal.
6. Next, have groups repeat the procedure using the plastic teaspoon, and enter the amount removed on the worksheet.
7. Finally, have the groups repeat the procedure using the medicine dropper. Enter the amount removed on the worksheet.
8. Calculate the percent removed in each sample to determine which method worked best.
9. Have students complete the worksheet.

Student Worksheet - Oil Cleanup Exercise

I think this method will work best: ___________________________________________

	Method 1 (large ladle)	Method 2 (spoon)	Method 3 (medicine dropper)
Amount of oil contaminating water
Amount removed after treatment
Percentage of oil removed

To calculate the percentage of oil removed, divide the amount of oil removed by the amount of oil originally contaminating the water, and multiply by 100.

1. Which method worked best? Which method was least effective? Why?

2. Which method resulted in the most spills during cleanup?

3. Which method removed the least water?

4. Were all three methods equally effective in helping you remove 50% of the pollution?

5. How might you improve your method to clean up even more oil?

Impacts of Nonpoint Source Pollutants on Water Resources

	Fisheries	Water Supply	Wetlands	Recreation
Nutrients (nitrogen & phosphorus)	Promotes algae blooms, inhibiting aquatic plant growth Favors survival of less desirable species Reduces dissolved oxygen levels through increased productivity and decays of organic matter	Promotes algae blooms,resulting in odors and poor taste Increases treatment costs Increases nitrate concentration (drinking water limit is 10 mg/L)	Alters wetland vegetation and habitat	Promotes eutrophication of lakes and rivers Increases algae growth, which may create public health risks Decreases aesthetic value Interferes with fishing and boating activities Reduces tourism and property values
Pathogens (bacteria & viruses)	Introduces disease-bearing organisms to aquatic life	Increases public health risks Increases treatment costs for drinking water supplies	Results in loss of wetland recreation areas Introduces harmful organisms to aquatic life and food chain	Closes swimming areas
Sediment	Decreases light transmission Increases surface water temperature Decreases spawning habitat Transports contaminants	Damages water treatment pumps, equipment Increases treatment cost Reduces reservoir volume Nutrients increase, stimulating algae growth Decreases river bottom infiltration, reducing well yields	Reduces flood storage Increases peak discharges Alters habitat	Decreases water clarity, affecting public health and safety Reduces aesthetic and recreational value Reduces sport fishing populations
Toxic Contaminants (metals, pesticides)	Accumulate in sediments, affecting bottom feeders Bioaccumulate in fish tissue May kill fish and other aquatic organisms Hinder photosynthesis in aquatic plants	Increase treatment costs Form deposits in pipes (metals) Cause odors in water supplies(pesticides) Color water and stains clothing and fixtures Public health risks	Bioaccumulate in food web Hinder photosynthesis in aquatic plants Affect reproductive rates and life spans of wetland organisms	Reduce waterfront property values May restrict sport fishing
Salts	Favors salt-tolerant species Creates stressful environment Destroys habitat and food source plants for some species Alters species composition	Reduces drinking water quality	Alters wetland vegetation and species composition Destroys habitat and food sources for wetland animals	May cause skin or eye irritations
Thermal	Reduces growth and health of fish Reduces resistance to disease Dissolved oxygen concentration decreases ads temperature increases Alters fishery from cold water species to warm water species	Accelerated pump or equipment corrosion Promotes increased biological activity, producing odors and poor taste Creates a more favorable environment for pathogens		May stimulate growth of algae and aquatic plants, reducing water clarity, aesthetic value, sport fishing populations and tourism

Adapted from Nonpoint Source Pollution: A Handbook for Local Governments, 1997

What You Can Do About Nonpoint Source Pollution

• Never pour, dump, or place trash or yard wastes in a storm drain, ditch, or stream.
• Make sure your parents recycle their used motor oil, rather than dumping it on the ground.
• Pick up after your pets, and dispose of their wastes in the landfill.
• Never dump anything down a storm drain. Ask if you can join in a storm drain stenciling program, to pain the words "No Dumping: Drains to River" on storm drains in your neighborhood.
• If you're going to use chemicals or fertilizers, always read the label first and follow the directions carefully. Don't use them if they are not needed
• .If you have a horse, or other livestock, make sure to clean up the manure on a regular basis. Compost the manure and add it to your garden, or give it to gardeners, or take it to a recycling facility.
• Use nontoxic products whenever possible. Dispose of hazardous household chemicals at approved disposal sites.
• Educate your parents! Encourage them to have the septic tank pumped on a regular basis, and to make sure to minimize any bare erodible ground on your property. Don't let them be a source of nonpoint pollution!

Resources

The Watershed Game, 1998, web resource developed by Minnesota IDEALS and Educational Web Adventures, www.aces.edu/crd/wqc.html

NOAA. The Nonpoint Source Pollution Matching Game. www.

University of South Alabama. 1998. The Water Sourcebook, Grades 6-8, Water Environment Federation. EPA/904-R-94-017(c). Available online at www.epa.gov/safewater/kids/wsb/

Also see fact sheets at www.epa.gov/safewater/kids/wsb/FACTS.pdf

Vocabulary Words

Algal bloom	A heavy growth of algae in and on a body of water, usually resulting from high nitrate and phosphorus concentrations in the water resulting from pollution. May occur naturally under certain conditions.
Contamination	The addition of any substance to water that makes it unfit for use.
Fertilizer	Chemicals used to enhance plant growth.
Nonpoint source pollution	Pollution that enters water from a variety of land use activities over a widespread area.
Nutrient	A substance such as nitrogen or phosphorus that is necessary for plant growth.
Point source pollution	Pollution that can be traced to a single, identifiable source, such as a pipe or culvert.
Pollutant	Something added to water that causes an undesirable change in the physical, chemical, or biological characteristics of the air, water, or land that may harm or affect humans or other living organisms.
Runoff	Precipitation that flows overland to streams, rivers and lakes.
Surface water	All water on the surface of the earth, including lakes, rivers, streams, ponds, oceans, and runoff.