How can high nitrate levels in drinking water primarily affect infants?

High nitrate levels in drinking water are particularly concerning for infants due to the potential to induce methemoglobinemia, a condition that affects the body's ability to transport oxygen in the blood. Nitrates are converted into nitrites in the digestive system, and nitrites can interfere with the normal function of hemoglobin, the protein in red blood cells that carries oxygen.

In infants, especially those under six months of age, this condition is especially dangerous because their bodies are less able to handle the effects of nitrites. Methemoglobinemia can lead to a reduction in the amount of oxygen delivered to vital organs, resulting in symptoms such as bluish discoloration of the skin (often referred to as "blue baby syndrome"), lethargy, and difficulty breathing.

Addressing the specific conditions listed in the other options, while high nitrate levels can have serious health implications, they are not the direct cause of developmental disabilities, respiratory issues, or cutaneous (skin) reactions. The risk of methemoglobinemia is particularly acute in infants, making it the most relevant concern regarding high nitrate levels in their drinking water.