Source: Children’s Health Defense

By Pamela Ferdinand

Even very low levels of nitrate in drinking water — far below the federal government’s safety threshold — may significantly increase the risk of premature birth and low birth weight, according to a new study.

Nitrate, a pervasive chemical that enters drinking water mainly through chemical fertilizer runoff and animal manure from farms, is invisible, odorless, and tasteless — leaving many people unaware they’re consuming it.

Researchers analyzed more than 350,000 birth records in Iowa from 1970 to 1988 and found that even 0.1 milligrams of nitrate per liter (mg/L) — a mere 1% of the level the U.S. Environmental Protection Agency (EPA) currently considers “safe”— was linked to higher risks of babies being born too early or too small.

Prematurity and low birth weight is the leading cause of death in newborns and children under age 5. It also raises the risk of developmental disorders like cerebral palsy and the odds of chronic diseases like obesity and diabetes later in life.

“The stakes are clear. No level of nitrate in drinking water appears safe during pregnancy,” said Jason Semprini, assistant professor of public health economics at Des Moines University and lead author of the study, published June 25 in PLOS Water.

“For decades, we’ve known about the biological mechanisms suggesting potential harm from exposure to nitrates in utero. Now, we have consistent evidence from rigorous research across multiple studies showing this potential harm in live births.”

EPA limits fail to address key pregnancy health risks

The study’s findings come as Iowa faces an unprecedented drinking water crisis due to nitrate contamination.

They also add to growing concerns about the health effects of agricultural pollution by industry — in rural and agricultural regions throughout states like Kansas, Nebraska, Minnesota, California, and Pennsylvania, and even in major cities like Los Angeles and Chicago.

The EPA set the current limit for nitrate in drinking water at 10 mg/L, or 10 parts per million, to prevent methemoglobinemia or “blue baby syndrome,” a potentially fatal blood condition that starves the body of oxygen.

Semprini and others say that the standard — established in 1992 — does not reflect current science and fails to reflect birth outcomes and other potential health risks.

While a long-awaited EPA assessment remains stalled, nitrate has been linked to colorectal cancer, thyroid disease, and severe birth defects of the brain and spinal cord.

The International Agency for Research on Cancer classifies nitrate in food and water as “probably carcinogenic” to humans, while a report published last year suggests the risk of dying is higher by 73% compared to water without nitrates, even at low levels.

Iowa, where the new study took place, has some of the highest groundwater nitrate concentrations in the U.S., the study shows. It also ranks second nationwide for new cancer diagnoses.

Early pregnancy exposure found most harmful

To estimate nitrate exposure, Semprini matched drinking water data to birth records within 30 days of conception, when a fetus is especially vulnerable. He also tested for exposure more than 90 days before conception and found no link to poor outcomes — suggesting that early pregnancy exposure is what matters most.

The study found nitrate levels in the state’s public drinking water rose by 8% each year during the study period, averaging 4.2 mg/L across all births.

More than 80% of the babies studied were exposed to some level of nitrate, and 1 in 10 were exposed to levels above the federal limit. Overall, 5% were born underweight, and 7.5% were born preterm.

Key findings include:

• Exposure to more than 0.1 mg/L of nitrate was linked to a 0.66 percentage point increase in preterm birth risk — a 9% rise compared to the average.
• Exposure to more than 5 mg/L was associated with a 0.33 percentage point increase in the risk of low birth weight (under 5.8 pounds, or 2,500 grams).
• Pregnancies exposed to low nitrate levels were also slightly shorter — by about 0.25 to 0.5 days on average.
• Higher exposures above the EPA limit did not show stronger effects, suggesting the current threshold may not be protective enough.

The study calls on the agency to act and urges updates to the federal nitrate limit. It also recommends that states adopt stronger oversight, including frequent testing, transparent public reporting, and policies to reduce nitrate runoff through agricultural reform.

“This isn’t just about environmental regulations — it’s about the health of babies and mothers,” Semprini said. “If we don’t update our standards to match current science, we could be silently harming thousands of pregnancies every year.”

Originally published by U.S. Right to Know. 

Pamela Ferdinand is an award-winning journalist and former Massachusetts Institute of Technology Knight Science Journalism fellow who covers the commercial determinants of public health.