UPPSC 2021 Prelims GS Paper-I · Question 38 of 150

Correct — B, Methemoglobin. 'Blue baby syndrome' (infantile methemoglobinemia) develops when nitrate in drinking water is converted by gut bacteria into nitrite, which oxidises the iron in haemoglobin from the ferrous (Fe2+) to the ferric (Fe3+) state, forming methemoglobin. Methemoglobin cannot bind and carry oxygen, so the infant's blood becomes oxygen-poor and the skin takes on a bluish tinge (cyanosis). Since the question asks what is present in the blood that causes the condition, the answer is methemoglobin.

• (a)Haemoglobin — Wrong — normal haemoglobin is the healthy oxygen-carrying pigment; its presence is normal, not a disease. Blue baby syndrome is caused by the abnormal form, methemoglobin.
• (c)Lead — Wrong — lead in the blood causes lead poisoning (plumbism: anaemia, neurological and developmental damage), not blue baby syndrome.
• (d)Nitrate — Tempting but wrong — nitrate in contaminated water is the environmental CAUSE that triggers the syndrome, but it is not the blood substance responsible for the blue colour. It is reduced to nitrite, which then forms methemoglobin; the question asks what is present in the blood, i.e. methemoglobin.

Methemoglobin is a form of haemoglobin in which the iron is in the ferric (Fe3+) state instead of the normal ferrous (Fe2+); in this state it cannot carry oxygen. In infants, high nitrate in drinking water — often from nitrogenous-fertilizer runoff or contaminated wells — is reduced to nitrite in the gut, which oxidises haemoglobin to methemoglobin, producing methemoglobinemia, popularly called 'blue baby syndrome'.

The tempting answer is Nitrate, because nitrate contamination is the classic environmental trigger discussed in ecology chapters. But the question specifically asks what is present in the blood causing the syndrome — that is the abnormal pigment methemoglobin. Separate the CAUSE (nitrate in water) from the blood-level MECHANISM (methemoglobin).

• Blue baby syndrome = infantile methemoglobinemia.
• Pathway: nitrate → nitrite (by gut bacteria) → oxidises haemoglobin Fe2+ to Fe3+ → methemoglobin, which cannot carry oxygen.
• Result: cyanosis (bluish skin), most dangerous in infants under about six months.
• Main environmental cause: high nitrate in drinking water from fertilizer runoff or contaminated wells.

• Choosing 'Nitrate' — it is the cause in water, not the substance in the blood asked for
• Confusing methemoglobin (oxidised, non-functional) with normal haemoglobin

UPPSC/UPSC ask blue baby syndrome via cause (nitrate in water) or mechanism (methemoglobin in blood) — read whether the stem asks for the environmental cause or the blood substance.

• practice — not a real PYQ

  Blue baby syndrome in infants is chiefly linked to excess of which contaminant in drinking water?

  • (a)Fluoride
  • (b)Arsenic
  • (c)Nitrate
  • (d)Iron

  Answer(c) Nitrate — nitrate in water is reduced to nitrite, which forms methemoglobin and causes blue baby syndrome.

• practice — not a real PYQ

  Methemoglobin differs from normal haemoglobin because its iron is in which oxidation state?

  • (a)Ferrous (Fe2+)
  • (b)Ferric (Fe3+)
  • (c)Metallic (Fe0)
  • (d)It contains no iron

  Answer(b) Ferric (Fe3+) — in this state it cannot bind oxygen, unlike normal ferrous haemoglobin.