What contaminant in water is known to cause methemoglobinemia?

Nitrate is known to cause methemoglobinemia, commonly referred to as "blue baby syndrome." This condition occurs when nitrates are converted in the body to nitrites, which then react with hemoglobin to form methemoglobin. Methemoglobin cannot effectively carry oxygen, leading to reduced oxygen delivery to tissues and resulting in symptoms such as a bluish discoloration of the skin due to lack of oxygen.

Nitrate contamination is particularly a concern in drinking water supplied by wells, especially in agricultural areas where fertilizers are used, as these can leach into groundwater. Infants under six months old are particularly vulnerable to methemoglobinemia when exposed to elevated nitrate levels in drinking water, which is why monitoring and maintaining safe nitrate levels in water supplies is critical for public health.

Other contaminants listed, while harmful, do not specifically lead to methemoglobinemia and have different associated health effects.