Although persons at any age may be affected by methemoglobinemia, infants are particularly susceptible during the first four months of life.6 Newborn infants normally have a low concentration of methemoglobin reductase (erythrocyte cytochrome 5β-reductase), an enzyme that reduces methemoglobin. This concentration remains low until after 4 months of age.5
Infants who are breast-fed may possibly get some nitrite or nitrate in breast milk, but poisoning usually occurs when infant formula and other infant foods are prepared with contaminated water. Boiling the well water merely concentrates the nitrate. Nitrates do not directly reduce hemoglobin to methemoglobin but can be converted by intestinal microflora to nitrite, which can produce methemoglobinemia.6 Aniline dyes may be absorbed through the skin and also cause methemoglobinemia.6 Other chemical agents that cause methemoglobinemia include naphthalene and menadione (vitamin K3). Chronic effects of subclinical levels of methemoglobinemia on growth, development, and general health apparently have not been studied.
Diagnosis.—When an infant is severely cyanotic with a relative absence of distress, methemoglobinemia should be suspected. These infants have a peculiar lavender color.7 Blood from the heel stick is chocolate-brown and does not become pink when exposed to room air. Diagnosis can be confirmed by excluding other causes of cyanosis and by spectrophotometric analysis of blood for methemoglobin, which has a characteristic absorption peak at 634 µm. When methemoglobinemia levels reach 60% or greater, the patient will collapse and become comatose and may die.6
Treatment.—Patients who are only mildly affected do not require treatment, other than to avoid the contaminated source.6 The methemoglobin levels will be reduced spontaneously over a period of two or three days. A severely affected patient requires therapy with methylene blue.6,7 It may be sufficient to give 1 to 2 mg/kg of body weight of a 1% solution of methylene blue in saline intravenously over a ten-minute period. This converts the methemoglobin to hemoglobin and usually results in prompt relief of distress. If there is not an adequate response within an hour, a second dose can be administered. After the intravenous administration of methylene blue, it can be followed by 3 to 5 mg/kg of methylene blue orally or 200 to 500 mg of ascorbic acid orally.7
Prevention.—Because the consumption of well water with chemical or bacterial contamination may have serious consequences, especially for pregnant women and infants, physicians and community health nurses should be alert to this problem. Such wells should be tested annually to ensure their safety, especially before a new mother returns home with her infant. Further, the quality of well water may deteriorate overnight or change because of drought, a heavy rainstorm, flash flooding, spring thaw, or an application of pesticide or chemical fertilizer in a nearby cultivated field. Special precautions should be taken to ensure the safety of infants or persons in frail health. Public health nurses may make home visits to discuss infant feeding and preparation of formula and the use of well water. Alternative sources of water include water drawn from another well, which has tested safe; bottled water; a new deep well; water passed through a treatment device*; or connecting to a rural water system, if this is available.
Simple in-line filters are not effective for removing nitrates. Deionization, desalination, or reverse osmosis units are available, which do render water safe from nitrate contamination.
1. Rosenfield AB, Huston R: Infant methemoglobinemia in Minnesota, due to nitrates in well water. Bull Univ Minn Med Found 1950;21:315–338.
2. Nelson D, Siegel J, Pieterick C: The Big Sioux Aquifer Water Quality Study: Prevention of Contamination of Rural Domestic Wells by Proper Location and Construction. Brookings, SD, East Dakota Conservancy Subdistrict, 1984, pamphlet 3.
3. 1982 Census of Agriculture, Part 41, South Dakota, publication AC82-A-41. US Dept of Commerce, Bureau of the Census.
4. Meyer M: A Summary of Groundwater Pollution Problems in South Dakota, State/EPA Task 2–3.1–111B. Pierre, South Dakota Dept of Water and Natural Resources, Office of Water Quality, 1986.
5. The Big Sioux Aquifer Water Quality Study. Pierre, South Dakota Dept of Water and Natural Resources, Office of Water Quality, 1984.
6. Cecil R: Textbook of Medicine, ed 16, Wyngaarden JB, Smith LH Jr (eds). Philadelphia, WB Saunders Co, 1982, pp 894–896.
7. Conn HF (ed): Current Therapy. Philadelphia, WB Saunders Co, 1981, p 188.