AIPMT Biology Aspirants, read out the next AIPMT Biology Study material/ Notes of Biomagnification, important topic for AIPMT Biology. Free online notes for AIPMT.

Biomagnification refers to increase in concentration of the toxicant/pollutant at successive trophic levels, i.e. concentration of the toxic substance increases as it goes to organisms of higher trophic levels.

  • Increase in concentration occurs because a toxic substance accumulated/taken by an organism cannot be metabolized or excreted, and is as it is passed on to the next higher trophic level.
  • Biomagnification is well-known for Mercury and DDT (POP, Persistant Organic Pollutant).
  • Also called as Bioaccumulation.
  • DDT is most famous POP, as it is resistant to environmental degradation.
  • Toxic substances which result in biomagnification, often are present in industrial waste waters and are major cause of biomagnification in the aquatic food chain.
  • You must have heard to avoid eating fishes of mercury-contaminated water, because these fishes are at high risk of mercury biomagnification.
  • Biomagnification begins when toxicants like mercury and DDT (Dichlorodiphenyltrichloroethane) are taken up from air or water by primary producers.

    AIPMT Biology - Biomagnification


  • Biomagnification of DDT in an aquatic food chain is shown in figure.
  • DDT is a fat-soluble chemical that can accumulate in the fatty tissues of animals.
  • Primary producers take these toxicants from water. Zooplankton eating phytoplankton retains this toxicant. Small fish eating thousands of zooplankton stores even larger units of DDT in fatty tissues. Toxicants become more concentrated as it moves up each trophic level. The greater the number of trophic levels, the higher the consequences to the top consumers. Humans are top predators too, so are vulnerable to biomagnification.
  • High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations.
  • DDT was previously used as a pesticide to control mosquitoes. Soon, DDT sprayed areas showed decrease in bird population because pesticide caused birds to lay thin-shelled eggs that became crushed in the nest.
  • Ecologist Rachel Carson paid attention to DDT Biomagnification in birds, and wrote famous book Silent Spring in 1962, referring to Pesticide (DDT) pollution.
  • Soon after in 1970s, DDT was banned in the U.S. and population of birds once again increased.
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