CBSE Class 10 Answered

The  intensity  of  accumulation  of toxic  substances  such  as  DDT  increases  as  we move  from  a  lower  trophic  level  to  a  higher  trophic  level  in  a  food  chain.  This phenomenon is called biomagnification.

Let’s  take  the  example  of  DDT  which has been  applied  on  farm  lands to eradicate pests.

DDT gets washed off from the farm land and reaches the water body. In water, small phytoplankton (producers) would accumulate certain amounts of DDT which would  be  passed  on to  the  next  trophic  level,  the zooplankton (primary  consumers),and  then  to  fish (secondary  consumers) which  feed  on these zooplankton and finally to tertiary consumers. Concentration  of  DDT  would  increase  with each  trophic  level,  with  producers having  the  minimum  concentration, while  the  tertiary  consumers  having the highest concentration of DDT accumulation. This  is because tertiary consumers have consumed many  secondary consumers which  in  turn had consumed many  primary  consumers.In  this  way, tertiary consumers accumulate the maximum concentration of toxic chemicals.