Insecticides are the pesticides used against insects. Organochlorines are class of synthetic organic insecticides.

Organochlorines are chlorinated hydrocarbons and contains the elements carbon and chlorine. They have been used extensively from the 1940s through the 1960s.

Bioaccumulation

They break down slowly in the environment and accumulate in the fatty tissues of animals and they stay in the environment and food web long after the being applied (Bioaccumulation).

OCs in Food Chain

They have long chemical half-life (7-30 years), which makes them highly persistent. So, most people have organochlorine pesticides present in their bodies. It cause reproductive failure among birds.

Organochlorine are persistent organic pollutants (POPs). They act primarily by altering the movement of ions across the nerve cell membranes, thus changing the ability of the nerve to fire and interfere Na⁺and K⁺ion permeation.

Examples

1. DDT

First commercially produced insecticide (1940’s). Banned in the US in the 1970’s but is still manufactured and exported

2. Cyclodienes

Most toxic (CNS) and persistent pesticides known

3. HCH and Cl-benzene

Mixtures of isomers

Medicinal use (lice shampoo) (lindane)

These insecticides are

1. Non-selective

2. Endocrine disrupter

3. Reproductive toxins

4. Neurotoxins (Lindane)

DDT (1,1,1-trichloro-2,2-bis-chlorophenyl ethane or Dichloro diphenyl trichloro ethane)

DDT stands for 1,1,1-trichloro-2,2-bis-chlorophenyl ethane or Dichloro diphenyl trichloro ethane and it is one of the most well known and oldest organochlorine pesticides. DDT was synthesized first by Zeidler in 1874.

Its insecticidal properties were discovered by the Swiss scientist Paul Muller in 1942. Originally used during World War II to control typhus. It was also used to kill moths and carpet beetles in 1939. Used on humans to control typhus epidemic by killing lice in Italy in winter of 1943-1944.

Historical Use of DDT

Properties of DDT

· --> Oral LD50 is 250 mg/kg for mammals

· --> As little as 10 mg/kg will produce signs of poisoning in human

· --> DDT is highly fat soluble

· --> But poorly soluble in water

· --> DDT is highly persistent and has longer residual effects

· --> Soil half-life for DDT is from 2 to 15 years while in an aquatic environment is about 150 years

· --> DDT use was banned in 1972 by the United States Environmental Protection Agency (U.S. EPA).

Common formulations

1. Wetable powders (WP)

2. Dusts (D)

3. Flowables (F)

4. Aerosols (A)

5. Emulsifiable concentrates (EC)

Mode of action of DDT

DDT affects the nervous system by interfering with normal nerve impulses. It causes the nerve cells to repeatedly generate an impulse which accounts for the repetitive body tremors. It causes repetitive discharge of axonal action potentials in response to a single stimulus. Its action produces hyper-excitability, tremor and muscular weakness.