Increase in concentration of toxicant in the aquatic food chain is:

The correct answer is Option (2) → Bio-magnification

Option (2) Bio-magnification — Correct. Biomagnification is the increase in concentration of a toxicant at successive trophic levels. It happens because the toxicant (for example DDT or mercury) cannot be metabolised or excreted, so it passes on and builds up.

Note 1: A similar question was also asked in CUET (UG) 2023 on 28-05-2023 (Slot 1).

Note 2: 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 – “… 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 well-known 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.”