Even Low Nitrate Levels in Drinking Water May Be Linked to Preterm Birth, Low Birth Weight: Study Reveals

Even minimal levels of nitrate contamination in drinking water far below the current regulatory threshold may pose significant risks to unborn children, according to a new study published in PLOS Water. The research, led by Jason Semprini of Des Moines University College of Health Sciences, suggests that existing safety standards may not adequately protect pregnant women and their babies.

Nitrate is a naturally occurring compound commonly used in fertilizers, often seeping into groundwater through agricultural runoff. While the U.S. Environmental Protection Agency (EPA) has capped the acceptable nitrate level in drinking water at 10 milligrams per liter (mg/L) since 1992, Semprini's analysis indicates potential health effects at levels well below that limit.

Using a dataset of 357,741 birth records in Iowa from 1970 to 1988, Semprini linked county-level nitrate measurements to early pregnancy periods specifically within 30 days of conception. During the study period, nitrate exposure in drinking water increased by an average of 8% annually, with a mean concentration of 4.2 mg/L.

After adjusting for parental and seasonal variables, the study found that nitrate exposure of just 0.1 mg/L a mere 1% of the EPA’s current limit was associated with an increased risk of preterm birth. Exposure above 5 mg/L was also linked to low birthweight. Interestingly, no additional risks were identified at levels exceeding 10 mg/L, the current regulatory threshold.

“Our work adds to the evidence base that the current regulatory threshold (>10mg/L) may be insufficient for protecting the in utero transmission of water-based nitrate during the first trimester of pregnancy,” said Semprini. He emphasized that “there is no safe level of prenatal nitrate exposure,” and drew a striking comparison: “The estimated impact from prenatal exposure to nitrates reflects 15% of the harm from prenatal exposure to smoking cigarettes.”

With rising nitrate levels in groundwater and outdated standards in place, the study underscores the urgent need to reevaluate national water quality regulations.

Reference: Semprini J (2025) Early prenatal nitrate exposure and birth outcomes: A study of Iowa’s public drinking water (1970–1988). PLOS Water 4(6): e0000329. https://doi.org/10.1371/journal.pwat.0000329