Sunday, 9 September 2012

Bioaccumulation and Biomagnification

(Prepared by P.H.Poh and C.F.Kuan) 

One of the classic examples of bioaccumulation that resulted in biomagnification occurred with an insecticide called dichlorodiphenyltrichloroethane (DDT). 

DDT is an insecticide that was sprayed in the ABC farm to help the control of mosquitoes and other insects because the insecticide is cheap and highly effective against the mosquitoes that spread malaria. During rainy day, the rain water washed away the DDT, infiltration of liquid state and leachate of DDT into creeks, where it eventually found its way into lakes and the ocean.

The toxic pollutant bioaccumulated within each organism and then biomagnified through the food web to very high levels in predatory birds such as bald eagles, osprey, peregrine falcons and brownpelicans that ate the fish.

Levels of DDT were high enough that the birds' eggshells became abnormally thin. As a result, the adult birds broke the shells of their unhatched offspring and the baby birds died. The population of these birds plummeted.

Marine fish such as swordfish, shark, and tuna often have bioaccumulated levels of the toxic pollutant from DDT will finally hunted by human beings as protein sources. Pregnant women exposed to the insecticide DDT are much more likely to give birth prematurely, or to full-term but low birth weight babies. Studies in mice have found that DDE blocks the binding of the hormone progesterone to its receptors, and in theory, this could cause both prematurity and low birth weight in humans. DDT concentrations are especially high in human milk. Milk production depends heavily on the use of stored body fat, and this is where DDT tends to stay in our bodies. At concentration above 236 mg DDT per kg of body weight, you'll die. Concentration of 6-10 mg/kg leads to such symptoms as headache, nausea, vomiting and confusion.

DDT was sprayed in the United States prior on 1972 to help the control ofmosquitoes and other insects.  Because the population of those birds plummeted. DDT was finally banned in the United States in 1972, and since that time there have been dramatic increases in the populations of many predatory birds.
Example : Food Chain Story


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