Blue-Baby Syndrome

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Blue-baby syndrome

Blue-baby syndrome (or infant cyanosis) occurs in infants who drink water with a high concentration of nitrate or are fed formula prepared with water containing high nitrate levels. Excess nitrate can result in methemoglobinemia, a condition in which the oxygen-carrying capacity of the blood is impaired by an oxidizing agent such as nitrite, which can be reduced from nitrate by bacterial metabolism in the human mouth and stomach. Infants in the first three to six months of life, especially those with diarrhea, are particularly susceptible to nitrite-induced methemoglobinemia.

Adults convert about 10% of ingested nitrates into nitrites , and excess nitrate is excreted by the kidneys. In infants, however, nitrate is transformed to nitrite with almost 100% efficiency. The nitrite and remaining nitrate are absorbed into the body through the intestine. Nitrite in the blood reacts with hemoglobin to form methemoglobin, which does not transport oxygen to the tissues and body organs. The skin of the infant appears blue due to the lack of oxygen in the blood supply, which may lead to asphyxia, or suffocation.

Normal methemoglobin levels in humans range from 1 to 2%; levels greater than 3% are defined as methemoglobinemia. Methemoglobinemia is rarely fatal, readily diagnosed, and rapidly reversible with clinical treatment.

In adults, the major source of nitrate is dietary, with only about 13% of daily intake from drinking water. Nitrates occur naturally in many foods, especially vegetables, and are often added to meat products as preservatives. Only a few cases of methemoglobinemia have been associated with foods high in nitrate or nitrite. Nitrate is also found in air, but the daily respiratory intake of nitrate is small compared with other sources. Nearly all cases of the disease have resulted from ingestion by infants of nitrate in private well water that has been used to prepare infant formula. Levels of nitrate of three times the Maximum Contaminant Levels (MCLs) and above have been found in drinking water wells in agricultural areas. Federal MCL standards apply to all public water systems, though they are unenforceable recommendations. Insufficient data are available to determine whether subtle or chronic toxic effects may occur at levels of exposure below those that produce clinically obvious toxicity. If water has or is suspected to have high nitrate concentrations, it should not be used for infant feeding, nor should pregnant women or nursing mothers be allowed to drink it.

Domestic water supply wells may become contaminated with nitrate from mineralization of soil organic nitrogen , septic tank systems, and some agricultural practices, including the use of fertilizers and the disposal of animal wastes. Since there are many potential sources of nitrates in groundwater , the prevention of nitrate contamination is complex and often difficult.

Nitrates and nitrites can be removed from drinking water using several types of technologies. The Environmental Protection Agency (EPA) has designated reverse osmosis, anion exchange, and electrodialysis as the Best Available Control Technology (BAT) for the removal of nitrate, while recommending reverse osmosis and anion exchange as the BAT for nitrite. Other technologies can be used to meet MCLs for nitrate and nitrite if they receive approval from the appropriate state regulatory agency.

[Judith L. Sims ]