Pesticides are the chemicals that are used to kill or stop the growth of unwanted organisms. But these pesticides can affect the health of human beings. These are further classified as
a. Insecticides:
Insecticides like DDT ,BHC ,aldrin etc. can stay in soil for long period of time and are absorbed by soil . Th.y contaminate root crops like carrot, raddish, etc.
b. Fungicide :
Organo mercury compeunds are used as most common fungicide. They dissociate in soil to produce mercury which is highly toxic.
c. Herbicides :
Herbicides are the chemical compounds used to control unwanted plants. They are otherwise known as weed killers. Example sodium chlorate (NaClO₃) and sodium arsenite (Na₃ As O₃). Most of the herbicides are toxic to mammals.

a) The growth of algae in extreme abundance covers the water surface and reduces the oxygen concentration in water. Thus, bloom-infested water inhibits the growth of other living organisms in the water body. This process in which the nutrient rich water bodies support a dense plant population, kills animal life by depriving it of orygen and results in loss of biodiversity is known as eutrophication.
b) Chemicals from industries
c) Toxic pesticides
d) Detergents and oil floats
e) Acids from mine drianage and salts from various sources.

Ozone is formed by a series of reactions that occur from the sun shines

1. Waste management : Environmental pollution can be controlled by proper disposal of wastes. 
2. Recycling : a large amount of disposed waste material can be reused by recycling the waste, thus it reduces the land fill and converts waste into useful forms.
3. Substitution of less toxic solvents for highly toxic ones used in certain industrial processes. 
4. Use of fuels with lower sulphur content (e.g., washed coal)
5. Growing more trees
6. Control measures in vehicle emissions are adequate.
7. Green chemistry philosophy can be followed.
8. Eco-friendly compounds should be developed.
g. Greener routes should be followed in our day to day life.
10. For dry cleaning liquified CO₂ or H₂O₂ may be used.
11. Paper may be bleached by H₂O₂.
12. Methanol maybe used instead of petrol.
13. Neem based pesticides may be used.
14. Awareness among students and public may be created by using slogans like "Save water; Water will save You".

It binds with haemoglobin and form carboxy haemoglobin which impairs normal oxygen transport by blood and hence the oxygen carrying capacity of blood is reduced. This oxygen deficiency results in headache, dizziness, tension, Loss of consciousness, blurring of eye sight and cardiac arrest.