Middle School Science - an introduction to bioaccumulation and biomagnification in an ecosystem. Using DDT as an example and organic controls that can be used instead.

1. Bioaccumulation &
Biomagnification
Year 7 Ecosystems

2. Starter Activity
The following slides will help you recall the
connections in food chains and food webs.

3. Food Chains
Write down as many food chains as you can from
this food web.

4. Food Chains
How many carnivores are in the food web?
How many herbivores?
Name them!

5. Toxic Food Chains
Lesson learning Objectives:
• Name a pesticide that will not break down
in the environment
• Describe how pesticides can kill other
organisms
• Explain the advantages of using biological
control over pesticides

6. Toxic Food Chains
Pesticides are the only toxic substances released intentionally into
our environment to kill living things. This includes substances that
kill weeds (herbicides), insects (insecticides), fungus (fungicides),
rodents (rodenticides), and others.
• DDT, a useful pesticide, was found to have lots of toxic effects on
the environment, especially birds.
• DDT is not easily broken down by the environment.

7. Bioaccumulation
1. Each leaf receives one ‘dose’ of DDT when sprayed.
2. Each worm eats three leaves and receives three doses of DDT
3. Each robin eats 2 worms.
4. Each sparrowhawk eats 2 robins.
How many doses of DDT does the sparrowhawk eat?
If they eat enough DDT, birds lay eggs with very thin shells, which break
before they are ready to hatch.
How might this effect the sparrowhawk population, and the other members
of the food chain?

8. Biomagnification
Biomagnification is the increasing concentration of a
substance, such as a toxic chemical, in the tissues of
organisms at successively higher levels in a food chain.
By the time the sparrowhawk eats the two robins, it will be
consuming 12 doses of DDT.

9. Biological controls
It is possible to avoid using pesticides to control insects.
Let’s look at an example of Russian Wheat aphids and how to control
them

10. Traditional methods
Traditional methods of controlling aphids requires the
preparation and spraying of large volumes of pesticides.
These pesticides can run off the farm land and into rivers,
eventually reaching the ocean and having impacts on
structures like the Great Barrier Reef in Queensland.

11. Organic Methods
Pesticides are used because they are quick and cheap.
There are, however, methods that are better suited to the
ecosystems that reduce unwanted impacts. Both Ladybugs and
Lacewings are natural predators of the Russian wheat aphid.
These organisms also become part of the ecosystem themselves,
providing food for birds and other small creatures.

12. Recap
Bioaccumulation is the process of substances, such as
pesticides, building up within a organism at a rate that is greater
than the organism can get rid of it (through waste, etc.)
Biomagnification is the increasing concentration of a substance
at successively higher levels of the food chain.