Explain what is meant by 'biomagnification' using DDT as the example, and state why this property, together with its resistance to breakdown, led to restrictions on its agricultural use.

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DDT is highly fat-soluble (lipophilic) and only poorly water-soluble, so once absorbed by an organism it is stored in fatty tissue rather than being readily excreted, and because DDT's multiple stable carbon-chlorine bonds resist both hydrolysis and microbial breakdown, it is degraded only extremely slowly once released into the environment. An individual organism therefore accumulates DDT in its tissue over its lifetime (bioaccumulation), and because each predator consumes many prey organisms' worth of already-stored DDT, the concentration found in body fat increases at every successive step up a food chain -- this stepwise concentration increase is biomagnification, and it is why the highest DDT residues, and the clearest documented harm (such as eggshell thinning impairing reproduction in birds of prey), have historically been observed in top predators far removed from where the DDT was originally applied. It is precisely this combination -- resistance to breakdown (persistenc …

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CBSE 2025Set ANNUAL1 markMCQ
$Q. Which of the following compounds is known as DDT?$
(a) A benzene ring bearing two Cl substituents (one ortho, one shown below the ring) attached directly to -CH2-CCl3
(b) Two benzene rings, each bearing one Cl substituent, both attached to a central -CH- which is also bonded to -CCl3 (i.e. Cl-C6H4-CH(-C6H4-Cl)-CCl3, with the two Cl atoms drawn in an ortho-like arrangement)
(c) Two benzene rings, each bearing one Cl substituent, both attached to a central -CH- which is bonded to -CHCl2 (i.e. Cl-C6H4-CH(-C6H4-Cl)-CHCl2)
(d) Two benzene rings, each bearing one Cl substituent (para position), both attached to a central -CH- which is bonded to -CCl3 (i.e. Cl-C6H4-CH(-C6H4-Cl)-CCl3) — the standard DDT structure
›Reveal solutionSolution

DDT = 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane — two p-chlorophenyl rings on a CH carbon, with a $-CCl_3$ group.

DDT (dichlorodiphenyltrichloroethane) is a well-known chlorinated organic insecticide discussed under the environmental effects of haloarenes because of its persistence and bioaccumulation (it is non-biodegradable and builds up in fatty tissue up the food chain). Structurally it consists of two chlorobenzene rings (each chlorine substituted at the para position relative to the point of attachment), both attached to a single central CH carbon, which is in turn bonded to a trichloromethyl ( $-CCl_3$ ) group: $Cl$ - $C_6H_4$ - $CH$ ( $-C_6H_4$ - $Cl$ )- …

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CBSE 2016Set ANNUAL1 markMCQ
$Q. Which of the following is an example of freon?$
(a) BrCH2CH2Cl
(b) CCl2F2
(c) CCl2Br2
(d) ICH2CH2F
›Reveal solutionSolution

Freons are chlorofluorocarbon (CFC) compounds; among the given options, only CCl₂F₂ (Freon-12) fits that class.

"Freon" is the trade name for a family of chlorofluorocarbon (CFC) compounds — simple haloalkanes containing both chlorine and fluorine attached to carbon, historically used as refrigerants and aerosol propellants.

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Q.Explain what is meant by 'biomagnification' using DDT as the example, and state why this property, together with its resistance to breakdown, led to restrictions on its agricultural use.

Concept understanding — Environmental Effects of Halogenated Compounds

Q.Explain what is meant by 'biomagnification' using DDT as the example, and state why this property, together with its resistance to breakdown, led to restrictions on its agricultural use.

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