Dichloro-diphenyl-trichloroethane (DDT) is a

Question

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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.

Why the other options are wrong — (b) 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) 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) 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.

Concept: 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.

State PCS 2022 Q9 — Environment & Ecology PYQ with Answer

State PCS 2022 Q9 — Environment & Ecology PYQ with Answer