UPPSC 2023 Prelims GS Paper-I · Question 66 of 150

Correct — D, Pesticide. Biodegradable pollutants are those that decomposer microorganisms (bacteria and fungi) can break down into simpler, harmless substances. Faecal matter, urine and ordinary domestic (organic) waste are all readily decomposed this way. Synthetic pesticides — the classic example being organochlorines such as DDT — resist microbial breakdown, so they persist in soil and water for years and biomagnify up the food chain; they are therefore non-biodegradable and are the odd one out.

• (a)Faecal matter — Human and animal excreta are organic and are readily broken down by bacteria and fungi — this is biodegradable, not the exception.
• (b)Urine — Urine is an organic, water-soluble waste that micro-organisms decompose quickly — it is biodegradable.
• (c)Domestic waste — Ordinary household (kitchen/organic) waste is decomposed by micro-organisms and is used to make compost — biodegradable, not the exception.

Pollutants are classified by whether nature can break them down. Biodegradable pollutants (sewage, faeces, urine, food and other organic waste) are decomposed by micro-organisms into harmless products and are recycled through natural cycles. Non-biodegradable pollutants (most pesticides such as DDT, plastics, heavy metals, glass) either cannot be decomposed by micro-organisms or degrade extremely slowly, so they accumulate in the environment.

Options (a)-(c) are all organic wastes a student intuitively links with sewage and composting — clearly biodegradable. The question therefore hinges on recognising that synthetic pesticides behave differently: because micro-organisms cannot break DDT-type compounds down, they persist and concentrate along the food chain. Spotting the one man-made, persistent chemical among natural organic wastes gives the answer.

• Biodegradable pollutants are broken down by decomposers (bacteria/fungi) into harmless substances; e.g., sewage, faeces, urine, organic domestic waste.
• Non-biodegradable pollutants resist microbial breakdown and persist; e.g., DDT and other synthetic pesticides, plastics, heavy metals, glass.
• Persistent pesticides like DDT undergo biomagnification — their concentration rises at each higher trophic level of a food chain.
• This persistence is why DDT and several organochlorine pesticides have been banned/restricted for agricultural use in India.

• Assuming every waste is biodegradable — synthetic chemicals like pesticides and plastics are not.
• Confusing 'biodegradable' (broken down by microbes) with merely 'soluble' or 'natural'.

UPPSC/UPSC ask this as 'which is/is not biodegradable' or through DDT/biomagnification — test whether you can separate microbe-degradable organic wastes from persistent synthetic pollutants.

• practice — not a real PYQ

  Increasing concentration of a pollutant at successively higher levels of a food chain is called:

  • (a)Eutrophication
  • (b)Biomagnification
  • (c)Bioremediation
  • (d)Biodegradation

  Answer(b) Biomagnification — e.g., DDT concentrates in top predators.

• practice — not a real PYQ

  Which one of the following is a non-biodegradable pollutant?

  • (a)Cattle dung
  • (b)Sewage
  • (c)Plastic
  • (d)Vegetable peels

  Answer(c) Plastic — micro-organisms cannot readily decompose it, so it persists.