Which of the following pollutants is responsible for causing blue baby disease?

CONCEPT

When a dissolved substance changes haemoglobin into a form that cannot carry oxygen efficiently, tissues receive too little oxygen. Infants are especially vulnerable because their protective enzyme systems are still developing.

APPLICATION

1. Drinking-water nitrate can be converted to nitrite in an infant’s digestive system.

2. Nitrite oxidizes the iron in haemoglobin and forms methaemoglobin, which has a reduced ability to transport oxygen.

3. The resulting oxygen shortage can produce cyanosis, the bluish skin colour associated with blue baby disease.

CONTRAST

• Mercury primarily causes neurological and renal toxicity; methylmercury is especially harmful to the developing nervous system.

• Particulate matter is mainly inhaled and causes respiratory and cardiovascular inflammation.

• Sulphur dioxide irritates the respiratory tract and can aggravate asthma.

CROSS-CHECK

The nitrate-to-nitrite pathway directly explains impaired oxygen transport and cyanosis, whereas the other listed pollutants have different principal toxic effects.

Therefore, the pollutant is nitrates.