Which one of the following organisms is likely to show the highest- concentration of DDT once it has been introduced into the ecosystem ?

DDT is a persistent, chlorinated pesticide that biomagnifies—its concentration increases at successive trophic levels—so top predators accumulate the highest burdens. Field and textbook accounts show that DDT sprayed into the environment moved up food chains and became highly concentrated in consumers at upper trophic levels (e.g., fish-eating birds, humans), and was even deposited in animal fat such as butterfat [1]. Trophic-level structure places grasshoppers and cattle as primary consumers and toads typically as secondary consumers, while snakes occupy a higher (tertiary) predator position; therefore, snakes will concentrate more DDT than organisms lower in the chain [1]. Thus, the snake (option 3) is most likely to show the highest DDT concentration.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 29: Environment Issues and Health Effects > 29.1.6. DDT > p. 414
2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > z.r.r. Trophic level interaction > p. 11