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Biomagnification

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  • Biomagnification

Biomagnification is the process where pollutants become concentrated in the tissues of organisms at higher trophic levels. In this activity students analyse and explain some simple data from a food chain including ring-billed gulls and discuss the trade-off between control of the malarial parasite and DDT pollution.

Lesson Description

Guiding Question

At times the fishing of certain carniverous fish is banned because of dangers to human health.  Fish like farmed Salmon can also contain high concentrations of DDT. What could cause this toxicity?

Activity 1 - Global biomagnification of DDT

The interactive Thinglink map shows examples of animals which accumulate pesticides, Sparrowhawk, Orcas, Bald eagles and Nile crocodiles are just four examples.  There are many others.

Explore the examples on the map, then answer the three short questions below.

Questions

1.  What are the properties of DDT or PCB which allow these chemicals to bioaccumulate?

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2. Why does a preditor accumulate a higher concentration of DDT than the prey which it eats?

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3  Name two examples of Bioaccumulation.

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Suggested answers

1.  What are the properties of DDT or PCB which allow these chemicals to bioaccumulate?

They are fat soluble, but not water soluble

They a persistent in the environment, they don't get broken down

They are not metabolised by organisms

2. Why does a preditor accumulate a higher concentration of DDT than the prey which it eats?

Preditors eat many of the prey, and they gradually accumulate all of the DDT which they have consimed, because it is not excreted (not water soluble) and it is not metabolised.

3 Name two examples of Bioaccumulation.

Sparrowhawks in the UK

Bald Eagle in the USA

Nile crocodile in Zimbabwe

Orca, killer whales in New Zealand

Activity 2 - IB style question

Answer the following data based question on this  Biomagnification IB-style questions worksheet below​.

Activity 3 - Video extension

Rachel Carson was the first scientist to suggest that DDT was causing harm in natural ecosystems. Through a best selling book, Silent spring, she brought about a change in the way in which scientists thought about the balance of nature..

Watch the short   Biomagnification video and the historical DDT footage (10 minutes)    Pesticides DDT Rachel Carson Silent spring

  1. What do you think could be the next case like DDT? 
  2. Are there any chemicals used widely in the world today which could be having a bad long-term affect on human health?
  3. How would you communicate today your concerns about this 'silent danger'?

Teacher's notes

The first activity is a short introduction to the concept of biomagnification, and how top predators in a food chain can accumulate high concentrations of a toxin.

Activity two gives students an opportunity to explain these ideas, and practice a straightforward data analysis question.

There are some suggestions for the answers on this page Biomagnification IB style questions - model answers

The last activity is really extension. The historical video is really quite shocking, now that we know that DDT is quite toxic for human health.

 

Differentiation / Extension ideas

Polar bears in peril is an interesting way to introduce the concept of biomagnification as a "wide game" an activity where students chase each other over a limited area, like a sports field or an outdoor classroom.

Interactive game, Secrets at Sea from Vacouver aquarium is quite nice online puzzle and addresses killer whales, food webs and bioaccumulation. Learning