Bioaccumulation & BiomagnificationYear 7 Ecosystems

Starter ActivityThe following slides will help you recall the connections in food chains and food webs.

Food ChainsWrite down as many food chains as you can from this food web.

Food ChainsHow many carnivores are in the food web?How many herbivores?Name them!

Toxic Food ChainsLesson 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

Toxic Food ChainsPesticides 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.

Bioaccumulation

1. Each leaf receives one ‘dose’ of DDT when sprayed.2. Each worm eats three leaves and receives three doses of DDT3. 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?

BiomagnificationBiomagnification 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.

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

Traditional methodsTraditional 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.

Organic MethodsPesticides 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.

RecapBioaccumulation 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.