'Blue baby syndrome' is due to the presence of which of the following in the blood ?

Question

UnlockIAS · Accepted Answer

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.

Why the other options are wrong — (a) 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) Wrong — lead in the blood causes lead poisoning (plumbism: anaemia, neurological and developmental damage), not blue baby syndrome.  (d) 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.

Concept: 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'.

State PCS 2021 Q38 — Science & Technology PYQ with Answer

State PCS 2021 Q38 — Science & Technology PYQ with Answer