Am Fam Physician. 2005;72(12):2558
The American Academy of Pediatrics (AAP) recently released a clinical report on the risk factors of nitrate poisoning in infants. “Infant Methemoglobinemia: The Role of Dietary Nitrate in Food and Water” was published in the September 17, 2005, issue of Pediatrics and is available online at http://www.pediatrics.org.
Nitrate poisoning is a continuing problem among infants in the United States. Most reported cases have been linked to the use of contaminated well water for preparation of infant formula. Approximately 15 million families in the United States receive their drinking water from unregulated wells. A survey of 5,500 private water supplies from nine Midwestern states found that 13 percent had nitrate concentrations of more than 10 mg per L or 10 parts per million (ppm) nitrate nitrogen, the federal maximum contaminant level. Estimates are that 2 million families drink water from private wells that fail to meet the federal drinking-water standard for nitrate; 40,000 infants younger than six months live in homes with nitrate-contaminated water. The problem is aggravated in urban areas by municipal wastewater treatment discharges on surrounding farmland.
It is recommended that foods with naturally occurring nitrates (e.g., green beans, carrots, spinach, squash, beets) be avoided before three months of age because an infant's intake can be at least as high as that from well water. A target concentration of nitrate nitrogen for food of less than 100 ppm is desirable for infants, and some commercially prepared infant food vegetables are monitored voluntarily by manufacturers for nitrate content. Because the target concentration level often is exceeded in spinach, this product is commonly labeled not to be used in infants younger than three months.
There is no evidence of an increased risk of methemoglobinemia in breastfed infants from maternal ingestion of water with nitrate nitrogen concentrations as high as 100 ppm. These mothers do not produce milk with high nitrate concentrations. The predominant organism (Lactobacillus species) in the gastrointestinal tract of the breastfed infant does not reduce nitrate to nitrite.
Other than cyanosis, there are few clinical signs of methemoglobinemia. Although obvious cyanosis can occur with methemoglobin concentrations as low as 3 percent in infants with low hemoglobin concentrations, symptoms are usually minimal until methemoglobin concentrations exceed 20 percent. A diagnosis of methemoglobinemia should be considered in a child who becomes acutely cyanotic and does not respond to oxygen administration.
Health care professionals who suspect that an infant has methemoglobinemia should contact the local poison control center or a toxicologist to assist in guiding management. Identification and elimination of the source of exposure are the only treatments required in an asymptomatic infant with cyanosis who has a methemoglobin concentration of less than 20 percent.
Questions about the family residence, parental occupations, drinking water, foods ingested, topical medications, and folk remedies are included in an assessment of potential nitrate exposure. Testing well water for nitrate contamination is recommended for prenatal and newborn care of patients with private wells, and water found to have high nitrate concentrations should not be ingested by the infant or used for preparation of infant formulas or food. Although in-home systems for nitrate removal are effective, they also can be expensive. Nitrates are not removed by ordinary home water softeners. Most state health departments have listings of public health laboratories that have been certified by the U.S. Environmental Protection Agency for testing water for nitrate.