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close this bookBasic Concepts in Environment, Agriculture and Natural Resources Management: An Information Kit (IIRR, 1993, 151 p.)
close this folderEcological basics
View the documentEcosystem degradation
View the documentHabitat and niche
View the documentThe food chain
View the documentBiological magnification
View the documentNitrogen cycle
View the documentSociety and the carbon-oxygen cycle
View the documentHealth consequences of environmental degradation
View the documentPopulation and the environment

Biological magnification

Biological magnification


· In an ecosystem, any change in the population of one organism is likely to have effects on other organisms in the same food chain or food web.

· This fact is illustrated by what is known as biological magnification. Biological magnification is the increase in concentration of certain fat-soluble chemicals in successively higher trophic levels of a food chain or food web. In other words, as chemical compounds move up through the various links of a food chain by being consumed by different organisms, the toxic effect of these compounds is magnified.

· Biological magnification plays a devastating role in certain types of pollution. Many air end water pollutants are either diluted to relatively harmless levels or are degraded to harmless forms by decomposition and other natural processes. This is true as long as the amount of these chemicals entering the environment is not excessive. However, some synthetic chemicals, such as the pesticide DDT, some radioactive materials and some toxic mercury and lead compounds, become more concentrated in the fatty tissues of organisms at successively higher trophic levels in various food chains and food webs.

· Biological magnification depends on two factors: chemicals that are soluble in fat, but insoluble in water; and, chemicals that either are not broken down or are broken down slowly in the environment.

· To illustrate the process of biological magnification, the example of the pesticide DDT moving through an estuarine ecosystem can be given. DDT is insoluble in water, soluble in fat and breaks down slowly in the environment. Thus, if each phytoplankton concentrates one unit of water-insoluble DDT from the water, a small fish-eating thousands of phytoplankton will store thousands of units of DDT in its fatty tissue. Then, a large fish that eats ten of the smaller fish will receive and store tens of thousands of units of DDT. A bird or human that feeds on several large fish can ingest hundreds of thousands of units of DDT. Of course, ingestion of high levels of DDT in plants and animals, including humans, can lead to chronic health problems and even death.

· Biological magnification of certain chemicals helps explain why dilution is not always the solution to some - forms of air and water pollution.