4 Types of Pesticides
- Herbicides : kills plants
- Insecticides : kills insects
- Fungicides : kills fungi
- Bactericides : kills bacteria
First-Generation Pesticides
- inorganic biocides (eg. Metals such Lead, mercury, arsenic, cyanide)
- Found to be toxic to humans, polluted water and soil and were not biodegradable (not able to break down naturally).
- Materials from a non-living origin which is harmful to almost all living things
Second-Generation Pesticides
- 20th century pesticides
- Generally man made organic chemicals
- Less toxic to humans
- More biodegradable
- However, it was found that some of these chemicals were fat soluble and became stored within animal tissues. This created a problem known as bioaccumulation.
- products of synthetic organic chemistry (eg. Chlorinated hydrocarbons, organophosphates, pyrethroids, triazines)
- Swiss chemist Paul Muller gets Nobel Prize for DDT in 1948
Bioaccumulation & Bioamplification
- Bioaccumulation – An increase in the concentration of a pesticide within the body of an organism over time.
- Bioamplification – The increase in pesticide levels in organisms of higher trophic levels.
- Thus, top consumers are affected the most
- For Bioamplification to occur, the pesticide must be…long-lived (Present for a long time in the system)
- mobile- Easily passed up the food chain
- soluble in fats (Dissolves in, and is stored in fatty tissue)
- biologically active (Affects biological body tissue_
Past vs. Present
- Past Chemical Pesticides were:
- Stored in fat tissue
- Not soluble in water
- Modern Chemical Pesticides are:
- Not stored in fat tissue
- Soluble in water
Pesticide Resistance:
- Over time some species of ‘pests’ become resistant to the pesticide. Meaning the pesticide no longer effects them.
- The survivors then have offspring which are mostly resistant.
- These organisms survive the next spraying. If a similar pesticide is continually used, resistant pests will soon make up most of the population.
- Dichloro, Diphenyl Trichloroethane (DDT)
- Pesticide that is suitable for bioamplification
- Has a half-life of 15 years
- That is, every 15 years the amount left in the system will be reduced by one half.
- If you use 100 kg of DDT, after 15 years it will be reduced to 50 kg, and after another 15 years it will be 25 kg, and so on..
Effects of DDT in Birds
- Carnivorous birds such as ospreys and bald eagles eat other birds, dead animals and fish which contain a build-up of DDT
- DDT causes the shells to become too thin to allow the large females to sit on the eggs without them breaking.
- Both effects have resulted in decreases in bird populations
- However, after DDT was banned in the US and Canada in the early 1970’s the bird populations of began to recover.
- Not all countries, like Mexico for example, have banned the use of DDT.
