UPPSC 2022 Prelims GS Paper-I · Question 9 of 150

Correct — A, Non-biodegradable pollutant. DDT is a synthetic organochlorine insecticide, and the chlorinated aromatic structure that makes it so effective against insects also makes it very hard for soil and gut micro-organisms to break down. It therefore persists in soil, sediment and water for years rather than weeks — the defining property of a non-biodegradable pollutant. Two consequences follow, and they are what examiners actually want. First, because DDT is fat-soluble rather than water-soluble, an organism cannot excrete it; it is stored in body fat, so the load accumulates over the animal's lifetime (bioaccumulation). Second, when a predator eats many contaminated prey animals, it inherits all of their stored DDT, so the concentration rises at each higher trophic level (biomagnification), with top predators carrying the heaviest burden. This persistence is why DDT is classed internationally as a persistent organic pollutant and is listed under the Stockholm Convention, which permits its use only for disease-vector control such as malaria.

• (b)Biochemical pollutant — Not a recognised category for DDT. The standard classification of pollutants is by degradability — biodegradable against non-biodegradable — and DDT is a manufactured organochlorine compound, not a substance produced by biochemical or metabolic processes. The word 'biochemical' also invites confusion with biochemical oxygen demand, which measures the oxygen consumed while micro-organisms decompose organic matter in water: DDT is precisely the kind of substance that resists such decomposition.
• (c)Non-pollutant — Plainly wrong. DDT is one of the most intensively documented pollutants in environmental science — it accumulates in the tissues of fish, birds and mammals, is transported far from where it was sprayed, and is the substance around which Rachel Carson's Silent Spring (1962) and much of the modern environmental movement were built.
• (d)Biodegradable pollutant — The exact opposite of the truth, and the option a careless reader picks. Biodegradable pollutants — sewage, faecal matter, urine, domestic organic waste — are broken down by decomposers within a short time. DDT resists microbial breakdown, which is why residues remain in soils and in animal tissue long after spraying has stopped.

Pollutants are sorted first by whether decomposers can break them down. Biodegradable pollutants — sewage, food and farm waste, faecal matter — are degraded by micro-organisms and become a problem only when the rate of release exceeds nature's capacity to process them, as in a river whose dissolved oxygen collapses under a heavy organic load. Non-biodegradable pollutants — organochlorine pesticides such as DDT, plastics, heavy metals like mercury, lead and arsenic, and radioactive waste — resist breakdown and therefore persist. Persistence combined with fat solubility produces the two effects that define this family: bioaccumulation, the build-up of the substance within one organism over time, and biomagnification, the increase in concentration from one trophic level to the next, so that a top predator may carry a burden many times that of the producers at the bottom of the chain.

The question can be answered from the name alone, without any recall of pesticide history. 'Dichloro-diphenyl-trichloroethane' announces a chlorinated aromatic compound, and carbon–chlorine bonds on a benzene ring are exactly the structures that soil bacteria and digestive enzymes handle badly. Two of the four options are ruled out before that: 'non-pollutant' is untenable for a compound whose environmental effects gave rise to modern pollution regulation, and 'biochemical pollutant' is not a category in the standard classification at all. That leaves the biodegradable–non-biodegradable pair, and DDT is the textbook example of the non-biodegradable side. The word to attach permanently to DDT is 'persistent': it is what makes DDT a persistent organic pollutant, what makes it biomagnify, and what makes it the answer here.

• DDT — dichlorodiphenyltrichloroethane — is a synthetic organochlorine insecticide whose chlorinated aromatic structure resists microbial breakdown, so it is non-biodegradable and persists in soil, water and sediment.
• DDT is fat-soluble rather than water-soluble, so organisms store it in fatty tissue instead of excreting it — this is bioaccumulation within a single organism over its lifetime.
• Because each predator inherits the stored residues of all the prey it eats, DDT concentration rises at each trophic level — biomagnification — and top predators carry the highest burden.
• DDT is listed as a persistent organic pollutant under the Stockholm Convention, which restricts its use to disease-vector control such as malaria control.
• Rachel Carson's Silent Spring (1962) documented the ecological effects of DDT and is generally credited with launching the modern environmental movement.
• Biodegradable pollutants, by contrast, include sewage, faecal matter, urine and domestic organic waste, which decomposers break down comparatively quickly.

• Reading the option list too fast and picking 'biodegradable' — the two key options differ by a single prefix.
• Assuming that a substance banned or restricted for agriculture is no longer an environmental issue; DDT's problem is precisely that residues outlast its use.
• Confusing bioaccumulation (build-up inside one organism over time) with biomagnification (increase in concentration from one trophic level to the next).

UPPSC asks this as a one-line classification — 'which is not a biodegradable pollutant', 'DDT is a …' — and repeats it across years; UPSC prefers the consequence, asking which organism in a food chain carries the highest residue or which convention governs persistent organic pollutants.

• practice — not a real PYQ

  DDT is described as a persistent organic pollutant chiefly because

  • (a)it dissolves readily in water and spreads quickly through rivers
  • (b)it resists microbial degradation and is stored in the fatty tissue of organisms
  • (c)it is produced naturally by soil bacteria
  • (d)it decomposes into harmless products within a single cropping season

  Answer(b) it resists microbial degradation and is stored in the fatty tissue of organisms — persistence plus fat solubility is what produces bioaccumulation and biomagnification.

• practice — not a real PYQ

  Which one of the following international conventions specifically addresses persistent organic pollutants such as DDT?

  • (a)The Basel Convention
  • (b)The Montreal Protocol
  • (c)The Stockholm Convention
  • (d)The Cartagena Protocol

  Answer(c) The Stockholm Convention — Basel deals with hazardous waste movement, Montreal with ozone-depleting substances and Cartagena with biosafety.