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..
READ:
What is Bioamplification?

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.

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