Available data are inadequate to support an association between nitrate and nitrite exposure from drinking water and any non-cancer effects other than methemoglobinemia in infants. That conclusion is based on the following observations:
No studies in humans have demonstrated adverse health effects that can be attributed to nitrate or nitrite toxicity other than methemoglobinemia in infants.
There is scant evidence from laboratory animals of developmental effects attributable to nitrate. One study reported deficits in neurobehavioral development when pregnant rats and their offspring received a low dosage of nitrate, 7.5 mg/kg-day. That is the lowest dosage at which adverse health effects of nitrate or nitrite have been reported in laboratory animals. The study had several limitations, and it is not known whether the neurobehavioral effects reported in rats can be extrapolated to humans; however, if so, converting the dosage to an adult human dosage yields 317 mg of nitrate per day, which is equivalent to the total dietary intake of a typical pregnant woman. That dosage is therefore unlikely to pose a threat to the fetus. The adverse effects reported in rats might have resulted from exposure after birth; the equivalent human infant nitrate dosage is about 23 mg/day. If an infant drinks 850 mL of formula prepared with water that contains nitrate at 44 mg/L each day, more than 23 mg of nitrate would be received each day. It would be inappropriate to classify nitrate as a developmental toxicant on the basis of this limited experimental evidence, although the results suggest that further studies of such effects should be conducted.
Methemoglobinemia in infants is the only adverse effect that has been associated with nitrate exposure. It can occur as a result