Presentation is loading. Please wait.

Presentation is loading. Please wait.

Pesticides: Poisons in the food chain. Pesticides  As much as 30% of the annual crop in Canada is lost to pests.  The pests include weeds, rusts and.

Similar presentations


Presentation on theme: "Pesticides: Poisons in the food chain. Pesticides  As much as 30% of the annual crop in Canada is lost to pests.  The pests include weeds, rusts and."— Presentation transcript:

1 Pesticides: Poisons in the food chain

2 Pesticides  As much as 30% of the annual crop in Canada is lost to pests.  The pests include weeds, rusts and moulds, birds, small mammals, and insects.  For each of these pests, we have created a pesticide.  Pesticides are chemicals designed to reduce the populations of unwanted organisms, both plant and animal.

3 Tires and Mosquitoes  What do we do with worn out old tires?  Can’t bury them in landfills – they just keep popping up.  Can’t burn them – thick choking smoke – bad for the environment  Let them sit???

4 Still water – breeding ground

5 Still Water  The still water – warmed by the sun hitting black rubber, makes an agreeable ecosystem for hatching mosquitoes.  Why is it a problem to create a favourable ecosystem for mosquitoes??

6 Mosquitoes and Disease  Some mosquitoes carry microbes that cause disease. Malaria is one such disease.  Thousands of people in tropical areas of the world die of this disease every year.  Used tires are often stored in one area and then moved to another area for disposal. What problem might this cause?

7 Using Pesticides  Scientists developed a pesticide spray that could eliminate mosquitoes. When it was tried on an island, other effects were soon noted.  Insects other than mosquitoes began to disappear, and then the number of lizards began to fall.  What do you think caused some other insects to begin to disappear?  Why did the lizards begin to disappear?

8 The Problems Spreads  Most people on the island were not too worried about the disappearance of a few insects and some lizards.  However, they took notice once the local wildcats, which had fed on lizards, began to get sick and die.  Without cats the rat population soon increased.  Fearing an outbreak of diseases linked with rats, the local people imported domestic cats.  What problem could be caused by bringing in domestic cats?

9 The Invasion  Changes to the food web became even more obvious when caterpillar populations began to increase  The pesticide affected wasps and other predators of the caterpillar, but had little effect on the caterpillar.  One the predators were gone, the caterpillar population increased greatly.  Eventually hungry caterpillars moved into the fields and devastated food crops

10 Biological Amplification  Pesticides tend to stay in the bodies of animals that come in contact with them.  The result is that the concentration of harmful pesticides increases at each level in a food chain.  Predators always have more toxic chemicals in their bodies than their prey.

11 Biological Amplification  If the body of a prey contains harmful pesticides, the pesticides will be taken in by the predator.  Predators eat many prey over their lifetimes. Each time prey is eaten, the amount of pesticide in the predator increases.  This process is called biological amplification.  Predict how scavengers, such as beetles, might be affected by biological amplification.


Download ppt "Pesticides: Poisons in the food chain. Pesticides  As much as 30% of the annual crop in Canada is lost to pests.  The pests include weeds, rusts and."

Similar presentations


Ads by Google