What limitation does blue baby syndrome impose on unborn children?

Blue baby syndrome, or methemoglobinemia, primarily occurs when newborns consume water containing high levels of nitrates, often from contaminated drinking water. Nitrates interfere with the blood's ability to carry oxygen. In this condition, the nitrates are converted in the body to nitrites, which then oxidize hemoglobin into methemoglobin. This altered form of hemoglobin cannot effectively bind and transport oxygen.

As a result, infants, especially those under six months of age, may exhibit symptoms like a bluish tint to the skin due to reduced oxygen levels in their blood. This is particularly critical for unborn children as the adverse effects can impact fetal development. The oxygen deprivation can lead to serious health issues, emphasizing the significance of monitoring nitrate levels in water supplies, especially in areas where agricultural runoff is prevalent.

The other choices do touch on important health concerns but are not directly linked to blue baby syndrome. Excessive chlorine exposure does not relate to this syndrome, nor do heavy metals or fluoride; while they pose their own health risks, they do not cause the oxygen transport issues associated with nitrates that specifically lead to blue baby syndrome.