Methaemoglobinemia is caused by the drinking of water contaminated with
2023
Methaemoglobinemia is caused by the drinking of water contaminated with
Answer: A. nitrate — CONCEPTMethemoglobin forms when the iron in haemoglobin is oxidized from the ferrous (Fe2+) state to the ferric (Fe3+) state. Ferric haemoglobin cannot bind…
- A.
nitrate
- B.
cadmium
- C.
phosphate
- D.
More than one of the above
- E.
None of the above
Attempted by 2 students.
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Correct answer: A
CONCEPT
Methemoglobin forms when the iron in haemoglobin is oxidized from the ferrous (Fe2+) state to the ferric (Fe3+) state. Ferric haemoglobin cannot bind oxygen effectively, so excessive oxidation causes methaemoglobinemia.
APPLICATION
After nitrate-contaminated water is ingested, nitrate can be converted to nitrite, especially in infants. Nitrite oxidizes haemoglobin iron and increases methemoglobin, producing the characteristic disorder.
CONTRAST
Cadmium: classically associated with renal tubular toxicity and bone damage.
Phosphate: excess in water promotes eutrophication rather than this haemoglobin oxidation disorder.
More than one of the above: this would require at least two listed contaminants to share the direct association; the disease mechanism here is specifically linked to the nitrate–nitrite pathway.
None of the above: this would deny the documented nitrate–nitrite association.
CROSS-CHECK
The biochemical chain is nitrate → nitrite → oxidation of Fe2+ to Fe3+ → methemoglobin. Therefore, the relevant contaminant is nitrate.