Early Prenatal Nitrate Exposure and Birth Outcomes: A Study of Iowa's Public Drinking Water

This guest blog comes from Jason Semprini, an Assistant Professor of Public Health at Des Moines University. His research uses novel data linkages and causal inference methods to evaluate the impact of public health policies or environmental exposures on health outcomes and equity.

Iowa is currently facing an unprecedented drinking water crisis. Recent reports indicate alarming nitrate levels in the Raccoon River; so high that city officials enacted emergency measures such as lawn water bans, to ensure water treatment facilities could comply with regulatory standards for safe drinking water. Unfortunately, at least for pregnant women, any level of nitrate in drinking water appears unsafe.

In my peer-reviewed study published by PLOS Water, I analyzed nearly 360,000 Iowa birth records from 1970 to 1988, linking births to nitrate measurements in public drinking water at the time of conception. During this time frame, nitrate levels in public water increased 8% annually. Although the data is old, the results still concern us all today.  

Figure 1: Nitrate levels in Iowa’s public water (1970-1988). SOURCE: Semprini 2025 in PLOS Water.

Consistent with evidence outside of Iowa, I found that prenatal nitrate exposure at levels far below the current EPA standard of 10 mg/L, significantly increases risks of adverse birth outcomes such preterm birth and low birth weight. Specifically, early prenatal exposure to nitrate levels as low as 0.1 mg/L increased the likelihood of preterm births. Exposure at levels of 5 mg/L, just half the EPA threshold, was linked with an elevated risk of low birth weight. These findings demonstrate that any amount of nitrate exposure during pregnancy may harm infant health.

Figure 2: Nitrate measures in Iowa’s public water (1970-1988). SOURCE: Semprini 2025 in PLOS Water.

The EPA established the current nitrate safety standard in 1992, without any reference to prenatal exposure. In the decades since, nitrate levels in Iowa's water have increased steadily. Today, many communities (especially in Iowa) regularly face nitrate concentrations far above historic averages, particularly populations who already shoulder poor health outcomes.

The water crisis today underscores the importance of municipal water utilities such as Des Moines Water Works, which operates the world’s largest nitrate removal facility. Yet, Des Moines’ nitrate removal facility cost millions of dollars to construct and over ten thousand dollars each day to operate. Other municipal or private activities to remove nitrate from water are also quite expensive. These costs are rarely paid by the people polluting our waters.

If you do not like paying these costs -- whether in the form of lawn watering bans, higher water bills, or consequences of adverse birth outcomes – reframe your thinking. Do not think of these costs as a tax on you, but rather as a subsidy paid directly to Big Ag. In our free market system, of which I am a big fan, these human and financial costs represent an externality. Since at least the 1970s, Iowans have been literally and figuratively subsidizing agricultural producers to continue polluting our. This status quo neither incentivizes better farming practices or implements any meaningful accountability on polluters.

The stakes are clear. No level of nitrate in drinking water appears safe during pregnancy. The EPA's decades-old standard does not reflect contemporary scientific evidence and is insufficient for protecting public health. In the absence of strong, updated federal regulations, we Iowans must rely on private and local efforts to deliver safe and clean water. Yet, nitrate pollution continues to rise Until we act upstream to slow or stop nitrate pollution into our water, we Iowans will continue paying excessive human and financial costs to mitigate the exposure of elevated nitrates. Whether our children continue paying will be up to us.

Jason Semprini is an Assistant Professor of Public Health at Des Moines University. He earned his PhD in Health Services & Policy at the University of Iowa and a Master's in Public Policy at the University of Chicago. Semprini has published his research in high-impact peer-reviewed journals and presented at national conferences. His research uses novel data linkages and causal inference methods to evaluate the impact of public health policies or environmental exposures on health outcomes and equity. A lifelong Iowan, Semprini is passionate about improving the wellbeing of everyone in our state.