Nitrates can change normal hemoglobin (the chemical in the blood responsible for oxygen transport) to methemoglobin. Normally, methemoglobin levels are less than 2.5 percent of the body’s total hemoglobin.
Nitrates act to increase the methemoglobin, which reduces the ability of the blood to transport oxygen to cells.

This oxygen starvation can lead to a bluish tint of the lips, ears and nose in slight cases (known as blue-baby syndrome in infants). In severe cases, it can lead to respiratory and heart problems, and death.

Infants are especially susceptible to the effects of nitrates in drinking water because of their low stomach potential of hydrogen (pH), which increases the conversion of nitrate to nitrite. This is doubly important if the drinking water is used to prepare their formula. Pregnant women are also at more risk from nitrate exposure as their methemoglobin levels are typically as high as 10 percent during pregnancy. This normal increase in methemoglobin means that they can tolerate less of an exposure to nitrate than when not pregnant.

How are nitrate and nitrite poisoning treated?

Most healthy people over 6 months of age have internal mechanisms efficient at removing nitrate from the body. Therefore, treatment of exposure to nitrates and nitrites is typically not required for mild and moderate
cases. Hospitals treat extreme cases of exposure by applying 100 percent oxygen and methylene blue. The most important step in treating persons with nitrate poisoning is to determine and remove the source of the nitrate.