What effect can a high concentration of nitrogen in groundwater have on infants?

A high concentration of nitrogen in groundwater, particularly in the form of nitrate, can lead to a serious health condition known as methemoglobinemia, often referred to as "blue baby syndrome." This condition occurs when nitrates are reduced to nitrites in the body, which can then bind to hemoglobin in the blood. This binding reduces the blood's ability to carry oxygen, leading to symptoms such as a bluish coloration of the skin, particularly around the lips and fingertips, and can result in serious health complications if untreated.

Infants are especially vulnerable to methemoglobinemia because their digestive systems are less mature, allowing for more nitrite absorption. This makes high nitrate concentrations in drinking water particularly dangerous for this age group. By contrast, the other options presented do not relate to the effects of nitrogen on infants' health; for instance, dental fluorosis and staining of teeth are associated with excessive fluoride consumption, while skin irritation is not linked to nitrogen levels in groundwater. Therefore, the correct answer highlights a specific and significant health risk posed by high nitrogen levels, particularly for vulnerable populations like infants.