P ART 4-L ESSON 1 The effect of excessive use and long-term consequences of using some pesticides

I NTRODUCTION The use of pesticides can have both positive and negative effects. It can eliminate pests which would otherwise destroy crops however it can initiate problems.

I NTRODUCTION A pesticide is a chemical specifically designed to kill insects, weeds and diseases. Their use at time is essential to protect crops. Today as we learn more and more about ecosystems and the environment we are becoming more concerned about the harms that they can cause.

I NTRODUCTION Farmers are being encouraged today to use alternates to pesticides which may eventually eliminate the use of chemicals all together.

A LTERNATIVES TO PESTICIDES There are several options to eliminate the use of pesticides. The first and most obvious is to choose plants appropriate for growth in the area. Native plants are often the best choice. Because most of our staple food crops are not native, growing native crops is not ideal.

A LTERNATIVES TO PESTICIDES Rotating crops is another solution. This can disrupt a ‘pests’ life cycle or create an environment not suitable for it’s survival. This would eliminate the possibility of a pest to infest an area.

A LTERNATIVES TO PESTICIDES Physical barriers can also be an effective way to fight pests. For example: Using nets to enclose crops protects them from insects and birds. Wide metal strips can stop slugs Tape around the base of trees Traps

A LTERNATIVES TO PESTICIDES Biological controls are another successful option. Introducing a predator species into the area can ensure pest populations are controlled. This option often has controversy attached to it. Can you think of a reason for this?

A LTERNATES TO PESTICIDES Genetic engineering is another controversial method to eliminate pesticides. This procedure genetically alters crops to become more resistant to pests. For example introducing genes from one crop to another to enable the new plant to produce toxic proteins which pests cannot tolerate.

A LTERNATIVES TO PESTICIDES Why would genetic manipulation be controversial? Many methods of biological control are currently being used but along with pesticides. This is called integrated pest management. This allows farmers to reduce the amount of chemicals being used and how often it’s used.

A LTERNATIVES TO PESTICIDES Plant derived pesticides are also being used. These can be just as potent and synthetic pesticides but break down more easily and rapidly without building up in the environment.

A CTIVITY Complete Activity 3.6 pg HSC Spotlight Text together.

H OMEWORK Read pages HSC Spotlight Text Update electronic vocabulary Complete DOT Point

P ART 4-L ESSON 2 The effect of excessive use and long-term consequences of using some pesticides

T HE LEGACY Pesticides have had a positive impact on farming. For example: Increased yields Enabled growth on unsuitable land Extended growing seasons However we need to consider the negative impacts too.

T HE L EGACY Pesticides are chemicals designed for killing weeds, insects and diseases. Most of which are applied by spraying. How do you think this affects the other organisms of the area?

T HE L EGACY Overspray and run-off can transport pesticides to other environments and even make their way into our water system. The pesticide is then said to be brought into contact with ‘non-target organisms’.

T HE L EGACY This can have negative effects and may cause problems worse than the initial pest problem. For example non-target organisms can be killed by the misuse of pesticides.

T HE L EGACY Pesticides that are absorbed into environments can also endanger non-target organisms. A famous example of this is DDT. (dichlorodiphenyltrich loroethane)

T HE L EGACY DDT was a great pesticide because it did not break down easily and killed pests for a long time. It was widely used during WWII to control mosquito populations.

T HE L EGACY DDT did reduce mosquito populations which led to good things such as reduce the spreading of malaria, however bad things were also happening.

T HE L EGACY DDT killed other insects. Some of these insects were eaten by lizards which in turn were eaten by cats. The DDT absorbed in the insects and lizards was strong enough to kill the cats.

T HE LEGACY Soon rat populations began to explode because the cat population decreased. This is one example of a negative effect of pesticides and there are many more including insects evolving to become resistant to the chemical.

T HE L EGACY Even worse problems were notices in the 1960’s. DDT was linked to Bioaccumulation and Biomagnification. Bioaccumulation is the increase in concentration of a pollutant from the environment into the first organism in a food chain. DDT was being detected in plants which meant it was accumulating in their tissues. These plants were then being eaten by other organisms which would also accumulate DDT in their systems but at higher concentrations because of repeat feeding.

T HE L EGACY DDT was being passed through food chains at higher and higher concentrations! This affects the non-target species in the area which eat the target species or any other organism living within the sprayed area.

T HE L EGACY In order to accumulate, a pesticide must be long lasting in the environment. DDT has a half life of 15 years. This means that if 100 kilograms of DDT was sprayed onto an area, 15 years later 50 kilograms would still be around.

T HE L EGACY DDT is also fat soluble. This means once in an organisms system it is not easily excreted. Bioaccumulation can produce concentrations is organisms which make them toxic to their predators.

T HE L EGACY Further study of animals have shown that DDT and other pesticides can cause cancers, mutations, birth defects and other life threatening defects. Today new pesticides undergo more rigorous testing.

T HE L EGACY Pesticide use is becoming less popular and the adoption of integrated pest control by many farmers is welcome and encouraged.

R EVIEW : Discuss Activity 3.9 pg 131 Science Skills pg 132

H OMEWORK Read pages Spotlight Text Update electronic vocabulary Complete ‘To Think About’ page 133 Complete DOT Point pages 66-67