A city is located near a river and an industrial area. Over time, scientists observed the following:

Question

A city is located near a river and an industrial area. Over time, scientists observed the following:

i. Fish in the river showed bioaccumulation of a persistent chemical that caused neurological disorders in humans who consumed them.

ii. The air contained high levels of a gas that reacts with water to form acid rain, damaging monuments and crops.

iii. Soil had elevated heavy metal concentrations, leading to reduced fertility and toxicity in plants.

On the basis of the given observations, pair each cause (i, ii, iii) with the corresponding pollutant (a, b, c) and answer the correct statement

a) Mercury

b) Sulfur dioxide

c) Lead

1. A. i → a, ii → b, iii → c (Correct answer)
2. B. i → a, ii → c, iii → b
3. C. i → b, ii → c, iii → a
4. D. i → c, ii → b, iii → a

Correct Answer

Option A — i → a, ii → b, iii → c

Detailed Solution & Explanation

The correct answer is i → a, ii → b, iii → c.

Key Points

• Observation (i) → Mercury. Mercury undergoes bioaccumulation and biomagnification in aquatic food chains, converting to methylmercury in fish. Consuming such fish causes severe neurological damage — the classic case being Minamata disease in Japan, first identified in 1956.
• Observation (ii) → Sulphur dioxide. SO₂ dissolves in atmospheric moisture to form sulphuric acid, producing acid rain that corrodes marble monuments and damages crops. The Taj Mahal's deterioration from emissions of the Mathura refinery is the standard Indian example.
• Observation (iii) → Lead. Lead is a heavy metal that accumulates in soil from battery waste, smelting, paint and formerly leaded petrol, reducing fertility and proving toxic to plants and to children.

Additional Information

• Acid rain chemistry:
  • $SO_2 + H_2O \rightarrow H_2SO_3 \qquad 2SO_2 + O_2 + 2H_2O \rightarrow 2H_2SO_4$
  • Nitrogen oxides contribute similarly, forming nitric acid. Normal rain is already mildly acidic at pH 5.6 because of dissolved CO₂; acid rain falls below pH 5.6.
• Biomagnification is the increase in concentration of a persistent pollutant at each successive trophic level. Substances that biomagnify are typically fat-soluble, non-degradable and long-lived — mercury, DDT, PCBs and arsenic.
• Marble cancer is the name given to the corrosion of marble monuments by acid rain: $CaCO_3 + H_2SO_4 \rightarrow CaSO_4 + H_2O + CO_2$.
• Health effects of lead poisoning (plumbism): anaemia, kidney damage, and impaired cognitive development in children. Itai-itai disease is the corresponding cadmium disorder, and Blackfoot disease the arsenic one.