There may be no safe level of nitrate in drinking water during pregnancy. That’s the takeaway from a new study linking even low-dose nitrate exposure to increased risks of preterm birth and low birthweight.
Published in PLOS Water, the study examined more than 350,000 Iowa birth records from 1970 to 1988 and connected them to county-level public water data. Researchers found that nitrate levels as low as 0.1 mg/L — just 1% of the current federal limit — were associated with an increase in preterm births. Exposure above 5 mg/L was tied to higher rates of low birthweight.
“There is no safe level of prenatal nitrate exposure,” said lead author Jason Semprini, PhD, of Des Moines University. “The estimated impact ... reflects 15% of the harm from prenatal exposure to smoking cigarettes.”
Nitrate is a common agricultural pollutant that enters drinking water through fertilizer runoff. Once consumed, it can reduce the blood’s ability to carry oxygen. The EPA’s maximum contaminant level, set in 1992, remains at 10 mg/L — a threshold the new study suggests may not account for risks during early pregnancy.
During the study period, average nitrate levels rose by 8% per year. While there was no added risk at exposures above the EPA limit, the data show concerning effects well below that level.
“The regulatory threshold for nitrates in public water does not consider prenatal exposure and has not been updated since established in 1992,” Semprini said. “Ignoring the potential harm from lower levels, … the current regulatory standards are not adequately protecting America's mothers or children.”
Though limited to Iowa and public water systems, the study adds to a growing body of evidence calling for a reassessment of national standards. The author received no external or specific funding for this research.