GETTING READY

Materials

• Library or Internet access
• Calculators
• Handouts

Student Prerequisites

• How to measure volume and square inches
• Parts of a circle
• Proportions
• Averages
• Ranges
• Computer skills
• Library skills

ACTIVITY PROCEDURE

Some groups might need a warm-up activity to get ready for some of the math-oriented questions within this activity. Here some important background concepts and conversions to go over with students if the reference sheet in the resource section below is not sufficient.

Math warm-up:

Convert the following:

Mass:

• 1.3 kilograms (kg) to grams (g), milligrams (mg), micrograms (mg), nanograms (ng)
• 4560 ng to mg, mg, g, kg

Volume:

• 4589 mL (microliters) to mL, L
• 0.76 L to mL, mL

Distance:

• 125 mm to cm, m

Geometry:

Say you dug out a bunch of soil and put it in a bucket. You dug out a square of soil 1 meter wide by 1 meter long. You dug out 50 cm of soil. How many cubic centimeters (cm³) do you have?

You want to know how much water it will take to fill up your hot tub. The tub is a circle 3 meters in diameter, and you want to fill it so there are 150 cm of water in the tub. How many cubic centimeters of water will it take?

A handy conversion is that 1 cubic centimeter (cm³) = 1 mL. How many liters of water would it take to fill the hot tub?

Chemical concentrations:

You have 10 grams of a chemical in 5 liters of water. What is the concentration in mg/L (milligrams per liter)?

You have 2 mg of a chemical in 8000 milligrams of soil. What is the concentration in mg/g (micrograms per gram)?

How many micrograms are in a gram? Express this as a mathematical relationship.

What is the concentration of the chemical in the soil above in parts per million (ppm), and in parts per billion (ppb)?

This activity involves doing some library or Internet research and then doing some calculations based on that research, to answer some questions. Access to the Internet or to the library will be essential. The students should also have access to calculators.

The Activity is built around having the students develop answers to a number of questions. Typically, students will work together in small groups (2-3 students), with different groups developing answers to different sets of questions. (Some sets are more difficult than others so you may want to review them first and assign accordingly.) We suggest having the questions printed off in advance for distribution to the groups. At the end of the activity the students will come back together to share what they have found. What follows are some good sets of starting questions. You might wish to add others. Some questions are more difficult or more involved than others so you may not want to use all of them with all students.

1. To get the students thinking about mercury, you might begin with a discussion to elicit what they already know. It is likely that they have heard something about the dangers of eating fish with mercury. They may also be aware of the dangers associated with mercury in fluorescent bulbs, thermostats, and other electronic devices.
2. Notions of scale are important to the work that the students will be doing. One of the question sets asks students to calculate the number of boxcars required to hold a billion ping pong balls. (The answer is 306 -- a good sized train.) You might "set up" this exercise by asking students--before they do the calculation--to estimate the answer. 
3. Divide the class into groups and distribute the question sets across the groups. Tell each group that they are expected to prepare material for presentation to the rest of the class. This presentation could take a number of forms. If computers are available, you might ask each group to put together a set of slides on the computer that includes pictures, when that is relevant, and that makes the calculations clear. 
4. After the groups have had time to develop their answers and presentations, have the groups present to the class as a whole. This is a good opportunity to focus on issues of scale and on flexibility in moving from one kind of unit to another. If this is a biology class, it is also a good opportunity to spend a bit of time talking about the significance of organic mercury -- and in general about why molecules that contain carbon are special when it comes to life processes.

Question Sets

Set 1 (Social Implications)

• What is "Minamata Disease"? What happened in Minamata?
• What concentration of mercury in hair is considered to be normal for people in the U.S.? What con-centrations were found in the people of Minamata? 
• Express this concentration in terms of parts per billion, parts per million, μg/g, and mg/kg

Set 2 (Social Implications)

• What was the source of mercury poisoning in Iraq in the early 1970s?
• What kinds of mercury concentrations in human hair were involved? 
• Express these concentrations in terms of parts per billion, parts per million, μg/g, and mg/kg

Set 3 (Least difficult)

• What is a typical mercury concentration for muscle tissue in swordfish? How about freshwater bass?
• Express these concentrations in terms of parts per billion, parts per million, μg/g, and mg/kg

Set 4 (All students should know, but chemistry teachers may want to take this further in terms of chemical interact tions)

• In what forms do we find mercury in the environment?
• What is special about "methyl mercury?" 
• What conditions are typically necessary to create methyl mercury?

Set 5 (Concentrations)

• What is the recommended maximum amount of mercury in drinking water?
• Nokomis Pond, the drinking water supply for Newport, covers approximately 119 acres, which is about 805,400 square meters. It is a fairly shallow pond -- 10 feet deep or less in most places, with a few places where it is about 20 feet deep. Assume an average depth of 3.5 meters (almost certainly an over estimate). A typical mercury thermometer of the kind that used to be common in high school laboratories contains about 3 grams of mercury. If you broke one of these thermometers in Nokomis pond, what would the mercury concentration of the water be? Would this be something to worry about?

Set 6 (Scale)

• The measurements we make with mercury are often in parts per billion. To make sense out of that, we need some physical notion of how big a billion is. Or, putting it in terms of parts per billion, if we have something that is, say, 11 parts per billion -- we need a way to understand how big a group those 11 items are a part of.
• Suppose we had a billion ping pong balls. Would they all fit in a boxcar? If not, how many boxcars would it take to hold them? Here is the basic information you need to figure this out for yourself:
  • The diameter of a ping pong ball is 40 mm. 
  • The volume inside a typical 50 foot boxcar is 148.32 m3. 
  • Because ping pong balls are round, there is unused space when you pack them together. A good estimate of the usable space when you are packing round things together is 74%.

REFLECTION/FORMATIVE ASSESSMENT IDEAS

For a quick check of understanding, ask the students to suppose that they found an old style mercury fever thermometer in a medicine cabinet at home and that it broke, leaving a little silver ball of mercury on the floor. Ask them to answer the following questions:

• What would probably happen if the dog ate the little ball of mercury?
• What if the dog just sniffed it? 
• What would be a good way to clean up the mercury? Would it be a good idea to vacuum it up to get all the little pieces?

Students could present their answers to the class. (Check in with students to make sure that they have the correct information before presenting to the class.)

EXTENSION IDEAS

Have the perfect extension for an activity like this? Share it with us in the comments section below.