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Age: Grades 7–8

Subject Areas: Science, Expressive Arts,Environmental Education

Duration: two 30- to 45-minute sessions,with research time in between the two

Group Size: minimum of 10 students

Setting: a large playing area

Conceptual Framework Topic Reference:HIIIB4

Key Terms: pesticide, insecticide,herbicide, food chain, accumulate, toxic,chemicals, trade-offs, organic, inorganic,biomagnification

Appendices: Using Local Resources, Agenciesand Organizations, Outdoors, Simulations

ObjectivesStudents will (1) give examples of ways inwhich pesticides enter food chains, (2) describepossible consequences of pesticides enteringfood chains, and (3) describe how regulationsattempt to control pesticide use.

MethodStudents become hawks, shrews, and grasshoppers in a physical activity.

MaterialsWhite and colored drinking straws; pipecleaners; poker chips or multicolored, dry dogfood—30 pieces per student, two-thirds white or plain and one-third colored; one bag pergrasshopper (approximately 18–20)

Hazardous Links,Possible Solutions

BackgroundPesticides are chemicals—often synthetic,inorganic compounds—developed to controlorganisms that have been identified as “pests”under some conditions. Herbicides are pesticidesthat control unwanted plants; insecticides arepesticides that control nuisance insects and soon. Although pesticides are useful to humanswhen used properly, they frequently end upgoing where they are not wanted. Many toxicchemicals have a way of persisting in the envi-ronment and often become concentrated in unexpected and undesirable places—fromfood and water supplies to wildlife and some-times people, too. The process where chemicalsaccumulate in organisms in increasingly higherconcentrations at successive trophic levels iscalled “biomagnification.” Biomagnificationresults in the storage of such chemicals in organisms in higher concentrations than are normally found in the environment. The resultscan be far-reaching.

For example, the insecticide dichlorodiphenyl-trichloroethane (DDT) was applied to controlinsects that were damaging crops. In the early1970s, it was discovered that DDT entered the food chain with damaging results. Fish ateinsects that were sprayed by the chemical;hawks, eagles, and pelicans then ate the fish.The poison became concentrated in the birdssystems, resulting in side effects such as thin egg shells. The weight of the adult bird wouldcrush the egg in the nesting process. The impacton species, including the bald eagle and thebrown pelican, has been well documented.

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Laws in the United States have now prohibitedthe use of DDT. However, DDT use is not prohibited worldwide. Resident and migratinganimal populations in the countries that stillallow the use of DDT are at particular risk.Even after the application of DDT is stopped,DDT and its by-products can affect the environment for decades.

Concerns over the growing use of pesticides ledto the establishment of the Federal Insecticide,Fungicide, and Rodenticide Act (FIFRA) in 1972. FIFRA gives federal government controlover pesticide sale, use, and distribution. UnderFIFRA, the U.S. Environmental ProtectionAgency (EPA) gained authority to study pesti-cide use consequences and also to require pesti-cide registration by farmers, businesses, and soon. FIFRA later was amended to require pesti-cide users to take certification exams. EPA mustregister pesticides used in the United States.

Congress also enacted the Toxic SubstancesControl Act (TSCA) in 1976 to regulate, test,and screen all chemicals imported or producedin the United States. TSCA requires that anychemical in the market place must be tested fortoxic effects before commercial manufacture.TSCA also tracks and reports chemicals thatpose health and environmental hazards.Authorization for toxic material cleanup hasbeen placed under TSCA. TSCA supplementsthe Clean Air Act and the Toxic ReleaseInventory. Like FIFRA, TSCA is a balancing law,which says that the EPA is to make decisions onany chemical by comparing the risks it posesagainst the benefits it produces for firms andconsumers.

Public pressure continues to force changes in the application and availability of pesticides.For example, there now is growing interest inintegrated pest management. This agriculturalapproach considers the entire farm and gardenecosystem. Integrated pest management caninclude using a pest’s predator as well as otherbiological controls to reduce crop damage.

Integrated pest management can include theselective use of naturally occurring and syntheticpesticides, as well as habitat manipulations.One concern with this approach is the possibleintroduction of non-native species.

The major purpose of this activity is for studentsto recognize the possible consequences of accu-mulation of some pesticides in the environmentand to evaluate measures to control pesticide use.

Procedure1. Discuss the term “food chain” with the

students. (Food chain: a sequence or “chain”of living things in a community, that is basedon one member of the community eating another, and so forth [e.g., grasshopper eatsplants like corn, shrews eat grasshoppers,hawks eat shrews])

2. Divide the group into three teams. In a classof 26 students, there would be 2 “hawks,” 6“shrews”, and 18 “grasshoppers.” (This activityworks best with approximately three times as many shrews as hawks and three times asmany grasshoppers as shrews.) OPTIONAL:Have grasshoppers, hawks, and shrewslabeled so they can be identified easily. Forexample, a green cloth flag (tied around thearm) for grasshoppers, red bandannas for“red-tail hawks”, and a brown cloth flag (tiedaround the arm) or caps for shrews.

3. Distribute a small paper bag or other small container to each “grasshopper.”The container is to represent the “stomach”of the animal.

4. With the students’ eyes closed, or otherwisenot watching where the food is placed,spread the white and colored straws (orwhatever material used) around in a largeopen space. Outside on a playing field (if it isnot windy) or on a gymnasium floor willwork; a classroom will also work if chairs and tables or desks can be moved.

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5. Give the students the following instructions:the grasshoppers are the first to go lookingfor food; the hawks and shrews are to sit qui-etly on the sidelines watching the grasshop-pers. After all, the hawks and shrews arepredators and are watching their prey.At a given signal, the grasshoppers areallowed to enter the area to collect as manyfood tokens as they can, placing the foodtokens in their stomachs (the bags or othercontainer). The grasshoppers have to movequickly to gather food. At the end of 30 seconds, the grasshoppers are to stop collecting food tokens.

6. Next, allow the shrews to hunt the grass-hoppers. The hawks are still on the sidelinesquietly watching the activity. The amount of time available to the shrews to huntgrasshoppers should take into account thesize area in which you are working. In a classroom, 15 seconds may be enough time;on a large playing field, 60 seconds may bebetter. Each shrew should have time to catchone or more grasshoppers. Any grasshoppertagged or caught by the shrew must give itsbag or container of food to the shrew andthen sit on the sidelines.

7. Next, allow from 15 to 60 seconds (or whatever set time) for the hawks to hunt theshrews. The same rules follow. Any shrewsstill alive may hunt for grasshoppers. If ahawk catches a shrew, the hawk gets the food bag and the shrew goes to the sidelines.At the end of the designated time period,ask all students to come together in a circle,bringing whatever food bags they have with them.

8. Ask students who have been “consumed” toidentify what animal they are and whatanimal ate them. If they are wearing labels,this will be obvious. Next, ask any animalsstill alive to empty their food bags out ontothe floor or on a piece of paper where theycan count the number of food pieces theyhave. They should count the total number of white food pieces and total number ofmulticolored food pieces they have in their

food sacks. List any grasshoppers and thetotal number of white and multicolored foodpieces each has. List the number of shrewsleft and the number of white and multicol-ored pieces each has. Finally list the hawksand the number of white and multicoloredfood pieces each has.

9. Inform the students that there is somethingcalled a “pesticide” in the environment.This pesticide was sprayed onto the crop the grasshoppers were eating in order to prevent a lot of damage by the grasshoppers.If there were substantial crop damage by thegrasshoppers, the farmers would have less of their crop to sell, and some people anddomestic livestock might have less of thatkind of food to eat—or it might cost more to buy the food because a smaller quantitywas available. This pesticide accumulates infood chains and can stay in the environmenta long time. In this activity, all multicoloredfood pieces represent the pesticide. Allgrasshoppers that were not eaten by shrewsmay now be considered dead if they haveany multicolored food pieces in their foodsupply. Any shrews for which half or more of their food supply was multicolored pieceswould also be considered dead from chem-ical side effects. The one hawk with thehighest number of multicolored food pieceswill not die. However, it has accumulated somuch of the pesticide in its body that the eggshells produced by it and its mate during thenext nesting season will be so thin that theeggs will not hatch successfully. The otherhawks are not visibly affected at this time.

10. Talk with the students about what they justexperienced in the activity. Ask for theirobservations about how the food chain seemsto work and how toxic substances can enterthe food chain with a variety of results.Introduce the term “biomagnification,” anddiscuss how it can result in the accumulationof chemicals in species higher in the foodchain. The students may be able to giveexamples beyond those of the grasshopper—shrew—hawk food chain affected by the pesticide in this activity.

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11. Divide the class into two, four, or moregroups. Ask one or two groups of students toresearch other chemicals—such as tributyltin(TBT), polychlorinated biphenyls (PCBs), ordieldrin—that have demonstrated the abilityto persist and accumulate through foodchains. What are the effects of such chemi-cals on organisms? What limitations havebeen set on the use of such substances? Havethe other groups research legislation such asFIFRA and TSCA to determine how theselaws work to control toxic chemicals. Allowall groups to present their findings in class,and then have the students hypothesize theeffectiveness of the laws in controlling thevarious chemicals that were researched.

Extensions1. Consider and discuss possible reasons for use

of such chemicals. What are some of the ben-efits? What are some of the consequences?

2. Offer and discuss possible alternatives to usesof such chemicals in instances where it seemsthe negative consequences outweigh the ben-efits. For example, some farmers are success-fully using organic techniques (e.g., sprays oforganic, nontoxic substances; crop rotation;companion planting); biological controls (e.g.,predatory insects); and genetic approaches(e.g., releasing sterile male insects of the pestspecies) in efforts to minimize damages totheir crops.

3. What research is being developed and tested on the effects of pest control efforts—from effects of possibly toxic chemicals tonontoxic alternatives? What are the benefits?Consequences? Potential?

4. Review news media for relevant local,national, or international examples of such issues.

Aquatic Extensions1. See the Project WILD activity “What’s in

the Water?”

2. Have the students describe how pesticidescan enter an aquatic food chain. Also,describe how pesticides can enter aquaticenvironments and can end up in food chainsof terrestrial environments (e.g., mosquitolarvae, fish, birds). Show how pesticides can enter the food chains in terrestrial environments and can end up in aquaticenvironments (e.g., grasshoppers, small fish,large fish).

Evaluation1. Identify examples of how pesticides could

enter a food chain.

2. Discuss two possible consequences of pesticides entering the food chain for each of the examples given above.

3. A group of ecologists studied the presence of a toxic chemical in a lake. They found thewater had one molecule of the chemical forevery 1 billion molecules of water. This con-centration is called one part per billion(ppb). The algae had one part per million(ppm) of the toxic chemical. Small animals,called zooplankton, had 10 ppm. Small fishhad 100 ppm. Large fish had 1,000 ppm.How do you explain this increase in thistoxic chemical to 1,000 ppm for the largefish? Use a drawing to help support youranswer. The ecologists found the chemicalwas a pesticide that had been sprayed oncropland 100 miles away from the lake.How did so much of the chemical get into the lake?

4. Evaluate the effectiveness of at least one lawthat regulates hazardous chemical usage.

Additional Resources

www.3dchem.com/molecules.asp?ID=90

www.pmac.net