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Lesson 6-Environmental Hazards 
Evaluate

2. Distribute to each student one copy of Master 6.1, Heads or Tails? Tell students that they are going to determine their actions on the field trip based on a coin toss. For each action, if they get heads, they will check the box for the action on the left-hand side of the page. If they get tails, they will check the box for the action on the right-hand side of the page.

National Science Education Standards icon Content Standard A:
Students should develop abilities necessary to do scientific inquiry.

3. Next, distribute one Choice Card to each student. Tell students that they can use the Choice Card to overrule one of their coin flips if they would rather choose the opposite action.

4. Give each student one coin. Proceed as a class through the Heads or Tails? worksheet, one action at a time. Ask students to record the results of their coin toss by checking the appropriate box on the sheet. Remind students that they can use their Choice Card for one turn to choose the opposite action.

students working on Activity 1

5. After all the students have completed the worksheet, announce that some of the members of the class got sick after the field trip and ended up going to the emergency room with their parents because they had severe headaches and nausea. Circulate around the room, looking at all the students' sheets. With a red marker, write the words "Sick" or "Not Sick" on the top of each sheet.

Mark "Sick" on the worksheets if the student marked "you sat in the back of the yellow bus" (got "heads" in the coin toss for the last action). If the student marked "you sat in the front of the yellow bus" (got "tails" for the last action), then the student is not sick. Do not let the students know that you are looking only at the last action: Make it look like you are studying all the actions for the trip to decide if the student is sick.

Tip from the field test: To make the discussion more interesting and the problem harder and less obvious to solve, mark one or two students sick who did not sit at the back of the yellow bus. These students represent individuals who have higher susceptibility to carbon monoxide even though they did not sit in the back of the bus nearest to the faulty exhaust system. More-susceptible individuals would be affected by a lower concentration of carbon monoxide.

6. Discuss the problem of some students getting sick by asking these questions:

the principal of the school talking to a concerned parent the art teacher at the museum school bus

7. Ask each student who is sick to pair up with a student who is not sick.

Statistically, you should end up with nearly an equal amount of sick and healthy students. If the numbers are not even, make a few groups of three students.

Tell students that you want them to figure out what made one student sick in each pair. Ask students to work with their partners to determine what actions and chemicals could have caused the sickness in their pair.

Students will realize that they can compare the actions each took on the field trip. If there are actions that the sick student did that the other student did not do, students might hypothesize that those actions put the sick student more at risk of exposure to certain chemicals.

8. Ask the students what information they need to solve the problem of what caused the sickness in some students.

Help students realize that they need more information about the kinds of chemicals to which students were exposed and the symptoms caused by each.

Show students the sets of fact sheets at the front of the room. Tell the students that each fact sheet contains information about chemicals to which some students were exposed at specific locations during the field trip. Instruct students to go to the front of the room and select one fact sheet the pair would like to study based on their determination from Step 7 of what actions and chemical exposures might have caused the sickness. They can return that fact sheet and select another if time allows.

Direct students to read the information on the fact sheet, discuss it with their partner, and decide whether the chemical in the location could have caused the sickness.

Students should consider the chemical, the route of exposure, the dose, and the symptoms that a person exposed to the chemical exhibits. When they read the fact sheet, they may determine that the chemicals to which they were exposed in a certain location could not have caused the illness because there was not enough chemical there, the dose they might have received was too little, or the symptoms of the sick people do not match those produced by exposure to the chemicals.

Students probably will have more than one possible location of chemical exposure to check. They will need to study all the possible locations and chemicals to determine which one might have caused the sickness. It is possible that they will not be able to decide between two possibilities until the class meets together and compares notes.

9. Once students have come to some conclusions about the possible cause of sickness, discuss their solutions with the whole class.

There are two ways to figure out why some students became sick. The first is by the process of elimination. Help students narrow the possible chemicals that caused illness by determining how many of the sick students were exposed to chemicals at each location. Compare the total number of sick students with those sick students who were involved in actions at the various locations. For example, if the total number of sick students was 15, but only 6 sick students drank caffeine, what conclusions can students draw?

assessment iconTo assess your students' understanding of individual susceptibility, ask them to explain what could have happened to those few students who did not sit at the back of the bus but were sick anyway.

From the discussion, students can see that all of the students who sat at the back of the yellow bus became sick, while students who took part in each of the other actions were not universally sick. Ask the sick students how many were not sitting at the back of the yellow bus. Only those few students you purposely marked sick (if you chose to) should reply. Explain their illness in the context of individual susceptibility to chemical exposure.

The second way to figure out what made the students sick is to study the fact sheets. In all cases except carbon monoxide, the exposure the students received to the chemicals in each location is insignificant. Students can see that, even though there might be chemicals present in various locations or associated with various activities, their health is not at risk when they are exposed at the levels that were present on the field trip. Being able to recognize that an exposure to a chemical is not at a level that causes harm is an important part of the risk assessment process.

Students will make the correlation between sitting in the back of the yellow bus and carbon monoxide poisoning by referring to the fact sheets. They will reach the conclusion that the sick students were suffering from carbon monoxide poisoning, which was caused by a faulty exhaust system in the old yellow bus. Those in the back of the bus were exposed to more carbon monoxide than those in the front of the bus. Those who got sick who were sitting in places other than the back of the bus must be more sensitive to carbon monoxide than average.

10. To complete the discussion of the field trip, go to Activity 2.

National Science Education Standards icon Content Standard F:
Students should develop understanding of personal health, natural hazards, and risks and benefits.

ACTIVITY 2: WHAT CAN I DO?

1. Ask students whether some of the students on the field trip made choices that either limited or increased their exposure to chemicals on the museum field trip. Discuss how the choices the students on the field trip made are similar to decisions that they make in their own lives.

Students who did the Web version of the activity can refer to the records on the Web site to find out how exposure to the chemicals present at the field trip locations can be avoided.

If students did the print version of Activity 1, ask them how their use of the Choice Cards simulated decisions they make in their own lives that influence their exposure to chemicals.

Informed citizens can make decisions to limit or eliminate their exposure to environmental hazards. They can alter their lifestyles, their work, their use of materials that are made of hazardous chemicals, and so on.

2. Discuss with students the fact that the cause of the sickness in some of the field-trip students was related to a situation over which the students had no control. Ask students what they think they would be able to do about the faulty exhaust system in the bus. Go one step further and ask students what they think they can do about chemical exposure on a community level.

Some choices are not left to the individual because the decisions are made at a community or national level. For example, people could be at risk of exposure to radiation when they live near a nuclear power plant even if they do not support the decision to use nuclear energy to produce power. In the scenario in this activity, students did not know that the yellow bus had a faulty exhaust system, so they were unable to decide to limit their exposure to carbon monoxide. In response to the situation with the bus, students could write letters to their superintendent, petition the school for stricter safety standards, or raise money to support a better maintenance program. Share with students information about the various organizations and agencies whose mission it is to protect human health (see Background Information). Encourage students to investigate the organizations by logging on to the following Web sites:

(The following links open to a new browser window)

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