What health risk is associated with nitrate in water?

Nitrate in water primarily poses a health risk associated with methemoglobinemia, commonly known as "blue baby syndrome." This condition occurs when nitrate is converted to nitrite in the body, which can then interfere with the ability of red blood cells to carry oxygen. The internal conversion leads to methemoglobin, a form of hemoglobin that does not effectively bind to oxygen.

This condition is particularly dangerous for infants, as their developing systems are more susceptible to this change and can have serious health implications, including difficulty breathing and blue-tinged skin due to oxygen deprivation. When assessing the health risks of nitrate exposure through contaminated water, the focus is on this oxygen transport issue, making methemoglobinemia the correct answer in this context.

Though the other options may describe significant health risks, they are not specifically associated with nitrate exposure in the same direct manner as methemoglobinemia is.