How did DDT affect fish and bird populations?
D.D.T. is a highly persistant chemical called an organophosphate. It is readily absorbed by the soil and is hydrophobic. It was used extensively during W.W.II against malaria and to control the insect vectors of Typhus. In 1962, Rachel Carson wrote the book, Silent Spring, detailing the dangers to the environment of pesticide use. By 1972, the use of this pesticide was banned in the United States as well as many other countries for agricultural reasons and new insecticides were developed to control insect pests. D.D.T. is problematic because it stays in the ecosystem for many, many years. It enters food chains and bioaccumulation occurs. At each trophic level of the food chain, the amount of D.D.T. accumulating in the organisms' tissues magnifies. Unfortunately for birds, many of their eggshells became weakened due to this pesticide and reproductive failure of the embryos occurred. The bald eagle almost went extinct but their population began to rebound once the ban on the use of D.D.T. went into effect. When runoff occurs on areas that were sprayed with D.D.T., the pesticide can be transported to lakes, streams, rivers, etc. This again caused problems to various fish species whose eggs develop in the water and many did not develop properly. D.D.T. is an agent known to be carcinogenic. It is also an endocrine disrupter and can cause reproductive and developmental problems in humans and other species.
One of the major effects of DDT, and one that led in many ways to its ban was the effect it had on the eggshells of predatory birds. Because they are such a visible member of the animal kingdom, much more than fish or other underwater life, people noticed when the populations dropped precipitously. As it thinned out the shells of the eggs the birds laid, the chicks would not survive.
The chemical is also toxic and deadly to many marine species as it filled lakes and rivers through ground run-off and concentrations arose it led to drops in those populations as well.
DDT (dichloro-diphenyl-trichloroethane) is a pesticide widely used for protection of crops as well as for prevention of diseases like malaria. Though DDT has been found to be very effective and economical for the basic function of destroying pests, it also has many harmful side effects.
Harmful effects of DDT are directly linked to the fact that DDT decays very slowly. Thus the DDT that is sprayed gets collected on land and in water. This DDT then gets absorbed by the plants that grow in such environment. Similarly, cells of animals living in water polluted by DDT also absorb it. The DDT then gets transferred to other animals that eat animals and plants containing DDT. In this way, because of the very slow decay rate of DDT, the chain of transfer of DDT from one organism to others continues.
In this way birds, fishes, and even humans develop high levels of DDT, with negative effect on their health. Among other effects, accumulation of DDT in fishes and birds causes sharp drop in their reproductive rate and population. Because of such harmful effects, use of DDT has been banned in many countries.