Arrange the stages of bio magnification of DDT.
(A) Fish eating birds (DDT 25 ppm)
(B) Small fish (DDT 0.5 ppm)
(C) Zooplankton (DDT 0.04 ppm)
(D) Water (DDT 0.003 ppb)
(E) Large fish (DDT 2 ppm)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (D) → (C) → (B) → (E) → (A)
(A) Fish eating birds (DDT 25 ppm) — fifth and last. They are at the top of the food chain and eat many large fish, so the DDT of all of them collects in their bodies.
(B) Small fish (DDT 0.5 ppm) — third. They feed on zooplankton and keep the DDT of every one they eat.
(C) Zooplankton (DDT 0.04 ppm) — second. They take in DDT from the water and from the phytoplankton they eat.
(D) Water (DDT 0.003 ppb) — first. DDT washed into the lake is at its lowest concentration here; 0.003 parts per billion is far less than any value in ppm.
(E) Large fish (DDT 2 ppm) — fourth. They eat many small fish, so the DDT rises again before it reaches the birds.
The concentration rises at every step because DDT cannot be broken down or excreted; it stays in the body and passes to the next trophic level.
Note: This question is from Chapter 16, Environmental Issues, of the pre-rationalised NCERT book. This chapter is not in the present NCERT book (2026-27). The extract below is from the pre-rationalised edition.
NCERT Extract (Pre-rationalised edition, Chapter 16, Environmental Issues):
Domestic Sewage and Industrial Effluents – “… A few toxic substances, often present in industrial waste waters, can undergo biological magnification (Biomagnification) in the aquatic food chain. Biomagnification refers to increase in concentration of the toxicant at successive trophic levels. This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted, and is thus passed on to the next higher trophic level. This phenomenon is wellknown for mercury and DDT. Figure 16.5 shows biomagnification of DDT in an aquatic food chain. In this manner, the concentration of DDT is increased at successive trophic levels; say if it starts at 0.003 ppb (ppb = parts per billion) in water, it can ultimately reach 25 ppm (ppm = parts per million) in fish-eating birds, through biomagnification.”
Figure 16.5 Biomagnification of DDT in an aquatic food chain