Environmental health: nitrates and methaemoglobinaemia: practice question

A PSM question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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PSM · Environmental health: nitrates and methaemoglobinaemia

Sample item

A 3-month-old bottle-fed infant in a farming area has cyanosis without respiratory distress. PaO2 is normal, and blood drawn is chocolate brown. Formula was prepared with well water near heavily fertilised fields. Which water contaminant is most likely responsible?

AFluorideBLeadCArsenicDNitrates

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Nitrates

Nitrate from fertilisers and sewage in shallow wells is reduced to nitrite in the infant gut, which oxidises haemoglobin to methaemoglobin and causes the so-called blue baby syndrome. Infants are particularly vulnerable because fetal haemoglobin is easily oxidised and gastric acidity is low. Treatment is intravenous methylene blue and a safe water source.

Option by option

A. Fluoride
Fluoride excess causes dental and skeletal fluorosis.
B. Lead
Lead causes anaemia, abdominal colic and neurodevelopmental effects.
C. Arsenic
Arsenic causes skin changes and cancers after chronic exposure.
D. Nitrates (correct)
Correct. Nitrate leads to methaemoglobinaemia in infants.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this PSM question

What is the answer to this PSM question?

The best answer is D, Nitrates. Nitrate from fertilisers and sewage in shallow wells is reduced to nitrite in the infant gut, which oxidises haemoglobin to methaemoglobin and causes the so-called blue baby syndrome.

Why is "Fluoride" not the answer?

Fluoride excess causes dental and skeletal fluorosis.

Why is "Lead" not the answer?

Lead causes anaemia, abdominal colic and neurodevelopmental effects.

Why is "Arsenic" not the answer?

Arsenic causes skin changes and cancers after chronic exposure.

What concept does this question test?

It tests Environmental health: nitrates and methaemoglobinaemia in PSM. Infants are particularly vulnerable because fetal haemoglobin is easily oxidised and gastric acidity is low. Treatment is intravenous methylene blue and a safe water source.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Environmental health: nitrates and methaemoglobinaemia?

Practise biostatistics with small calculations until sensitivity, predictive values and risk measures are automatic. Then use the flashcards and the other PSM questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.