At what level of nitrates is Blue Baby Syndrome most commonly associated?

Blue Baby Syndrome, also known as methemoglobinemia, is a condition that primarily affects infants and is associated with high levels of nitrates in drinking water. The syndrome occurs when nitrates convert hemoglobin into methemoglobin, which cannot effectively carry oxygen, leading to a bluish discoloration of the skin, particularly around the lips and nails.

The threshold level of nitrates considered to pose a significant health risk, particularly for infants under six months old, is generally recognized to be around 10 mg/l. At this concentration, exposure to nitrates through drinking water can lead to the development of Blue Baby Syndrome. While levels above this threshold can further increase the risk, it is specifically the level of 10 mg/l that is crucial for identifying the potential onset of this condition in vulnerable populations, especially infants who may be consuming formula mixed with nitrate-contaminated water.

In the context of the options provided, selecting a level such as 50 mg/l, while certainly harmful, diverges from the specific threshold directly tied to the syndrome's onset in most documented cases. Therefore, identifying the association with the correct level of 10 mg/l highlights the importance of monitoring and managing nitrate levels in water supplies to protect infant health.