Often, industrial pollutants which exist in trace amounts in the environment (such as certain heavy metals and organic agents found in pesticides) become concentrated in creatures near the top of the food chain. In an estuary, for example, microorganisms called plankton may absorb small amounts of pollutants such as PCBs (polychlorinated biphenyls); fish that eat lots of plankton might retain the pollutants in their tissues; birds or people that eat the fish might concentrate the pollutants still more. This process, called biomagnification, can produce health problems for animals in an ecosystem, including humans!

By the end of the 12th grade, students should be able to describe the effects of biological magnification on ecosystems. This lesson will focus on biomagnification as it relates to the ecosystems of the Great Lakes region in the mid-western United States. (For more background on the Great Lakes, see Environment Canada's Our Great Lakes.)

Geography, environmental studies, science

Standard 8: "The characteristics and spatial distribution of ecosystems on Earth's surface"

Two hours

• Computer with Internet access
• Drawing paper
• Blank Xpeditions outline maps of the Great Lakes region, one for each student
• Color pencils or markers
• Reference atlas (e.g., National Geographic Atlas of North America)
• Large sheet of paper with the Great Lakes region drawn on it

Students will

• draw a diagram of a food chain;
• label maps to show progress on environmental issues; and
• understand problems related to biomagnification in Great Lakes and other ecosystems.

Have students draw a diagram of a food chain found in the Great Lakes region, or in a typical aquatic ecosystem near your school. Each diagram should include energy (sunlight), producers (phytoplankton), and consumers (zooplankton, fish, birds, and humans). Photosynthetic plankton are microorganisms that turn solar energy into nutrients. These tiny creatures are consumed by zooplankton and fish. Fish in turn may be eaten by birds or humans—a food chain.

Explain to students that potentially toxic chemicals released or created by human activity often get into surface waters and, from there, into the food chain. When microorganisms ingest chemicals, those chemicals can be magnified further up the food chain. This may happen as fish ingest plankton that have higher than average levels of a toxin. As larger fish consume smaller fish, the concentration of toxins in animal tissues may increase. When a bird eats a number of large fish over time, the toxin may reach hazardous levels. Discuss some of the possible effects of biomagnification (e.g., fish tumors or kill-offs, bird ailments and soft eggs, human cancers or birth defects).

Note that many chemicals which appear to be non-hazardous at low concentrations may become hazardous at higher levels. Ask students to name some potential sources of hazardous chemicals. Make a list on the chalkboard. Examples could include factories, cities, shipping lanes, farm fields, etc.

Give each student an outline map showing the Great Lakes region, a set of colored pencils or markers, and an atlas. Have students work in pairs and look up information about places around the Great Lakes that may be in need of environmental restoration on Environment Canada's Our Great Lakes site. Have each pair of students choose one area that is in need of restoration.

Have students identify which of the following sorts of environmental impairments apply to the locations they chose:

• Degradation of phytoplankton and zooplankton
• Fish tumors and other deformities
• Bird or animal defects and reproduction problems
• Restrictions on fish and wildlife consumption by humans

Give each category a different color symbol, using lighter colors for the lower end of the food chain and darker colors for the higher end of the food chain. On their outline maps of the Great Lakes region, have students label the locations they are investigating, and add the color symbol or symbols for the environmental impairments at each location.

After all students have finished, have them transfer their findings onto a single map of the Great Lakes region.

Have the students analyze the patterns they see on the large map and offer explanations for them. Where are the greatest concentrations of impairments? Which sorts of impairments are the most and least widespread? Are there other patterns that are significant? Are certain patterns evident near obvious pollution sources? Are certain patterns located near cities? Which Great Lake has the most significant problems?

Discuss how the map illustrates the extent of contaminants in the food chain around the Great Lakes.

Have students look ahead 20 years and write a newspaper article on what they see. The article could warn of increased environmental degradation, based on projected levels of contamination. Students should be able to provide examples of affected members of the food chain and demonstrate knowledge of biomagnification. To illustrate their article, students might include a sketch map depicting the extent of contamination or a diagram depicting projected levels of contamination.

Have your students perform similar research on a watershed near your school. They could use a map to illustrate areas of environmental degradation and likely sources of pollutants, and suggest practical remedies.

Stanley Masters of Blissfield High in Blissfield, MI, contributed classroom ideas for Standard 8.

Canadian Museum of Nature
Environment Canada: Our Great Lakes
National Geographic: Xpeditions Activity—Preserving Biodiversity
World Wildlife Fund