Tag: zoology

Some of the common pollutants are non biodegradable, e.g : persistent pesticides like organochlorine or chlorinated hydrocarbons like DDT. These chemicals pass into food chains and increase in amount per unit weight of organisms with the rise in trophic level due to their accumulation in animal fats. Higher the trophic level of an organism in the food chain, greater will be the accumulation of pollutant. As these chemicals are persistent and non biodegradable, they pollute air, soil and water and in which ever organism they reach they simply keep on increasing in concentration. The phenomenon is called biomagnification. 

Pesticides are important pollutants of soil. They include insecticides, fungicides, algicides, rodenticides and weedicides. Pesticides are generally broad spectrum and function as biocides. Organochlorines and chlorinated hydrocarbons are an important class of pesticides. The important ones are dichloro diphenyl trichloroethane (DDT), Benzene hexachloride (BHC), aldrin, dieldrin and endrin. They are persistent, fat soluble, and show biomagnification and hence, are harmful to higher trophic level of organisms. Aldrin was used in buildings to protect against insects, such as termites.

Zinc phosphide is a highly potent rodenticide. It has a wide range of uses commercially and residentially, including the protection of food crops and grasses. As a rodenticide, it can kill mice and voles and also be used as a fumigant in storehouse to control post - harvest pests such as rice weevils, grannary weevils, wheat moths, cotton red bollworms etc.

Bacterial blight is a serious disease of field peas that is caused by the pathogen Pseudomonas syringae. It can be controlled by crop rotation, time of sowing, farm hygiene, sowing disease free seed and using resistant varieties.

Bordeaux mixture was discovered by Pierre Marie Alexis Millardet in 1882. Its a mixture of copper sulphate and slaked lime. Its the most successful fungicide.

Paul Muller discovered that DDT (chemically, dichloro-diphenyl-trichloro-ethane) would kill insects in 1939 and used extensively by the U.S. military during the war. DDT led the way to develop other insecticides and herbicides. 

DDT was banned because of concern over carcinogenicity, bioaccumulation and health effects on wildlife. In addition to these concerns, resistance to DDT occurs in some insects (like the house fly) that develop the ability to quickly metabolize DDT into the lower toxicity breakdown product DDE. DDT affects the nervous system by interfering with normal nerve impulses. DDT causes the nerve cells to repeatedly generate an impulse which accounts for the repetitive body tremors seen in exposed animals.

DDT was used for malaria control at the end of WWII. National Malaria Eradication Programme (NMEP), started an attack phase for indoor residual spraying of DDT which resulted in malaria eradication. As a collateral benefit, DDT eliminated kala - azar and plague and wiped out nuisance of household insects. Such a spectacular success made the use of DDT popular.