Chemical or synthetic pesticides are of four types namely:
[a] Organochlorines-These are non- biodegradable and persist in soil for long time, eg, DDT, BHC, endrin etc.
[b] Organophosphates-These are esters of alcohols with phosphoric acid or with some other acids. These are very toxic acetylcholinesterase inhibitors as a result of which the breakdown of acetylcholine stops, accumulation of acetylcholine resulting in convulsions, paralysis and deaths, eg, malathion, parathion and fenitrothion.
[c] Carbamates-They are derived from carbamic acid, eg, carbaryl, dimetilan, aldicarb etc.
[d] Pyrethroids-These are synthetic pyrethrin, triazines etc.