Water Quality & Health – Cause of “Blue Baby” (Methemoglobinemia) Infants suffering from blue baby syndrome (methemoglobinemia) typically do so due to excess of which contaminant in drinking water?

Introduction / Context:
Methemoglobinemia (blue baby syndrome) occurs when hemoglobin is oxidized to methemoglobin, which cannot carry oxygen effectively. Certain water contaminants trigger this condition in infants due to their unique physiology and gut chemistry.

Given Data / Assumptions:

• Population: infants consuming formula prepared with groundwater.
• Contaminants: common anions/cations found in water.
• Health endpoint: reduced oxygen transport (cyanosis).

Concept / Approach:

High nitrate (NO3−) in drinking water can be reduced to nitrite (NO2−) in the infant gut. Nitrite oxidizes Fe2+ in hemoglobin to Fe3+, forming methemoglobin. Infants are particularly susceptible due to higher gastric pH and lower methemoglobin-reductase activity. Guidelines set low permissible nitrate levels to prevent this condition.

Step-by-Step Solution:

Verification / Alternative check:

Epidemiological cases link shallow well waters in agricultural areas (fertilizer runoff) with infant cyanosis where nitrate exceeds guideline values.

Why Other Options Are Wrong:

• Chlorides, fluoride, lead: may cause taste, fluorosis, or neurotoxicity respectively, but not acute methemoglobinemia.

Common Pitfalls:

Confusing nitrate with nitrite; underestimating infant susceptibility compared to adults.

Final Answer:

Nitrates