Elevated Nitrate in Iowa's Public Water Systems Disproportionately Affects Vulnerable Populations

This guest blog comes from Dr. Lu Liu, Assistant Professor in Civil, Construction and Environmental Engineering at Iowa State University. It is based on their publication “Disparities in potential nitrate exposures within Iowa public water systems” from the journal of Environmental Science: Water Research & Technology.

Long-standing nitrate problems in Iowa affect drinking water quality

Iowa, a major agricultural producer of corn and swine in the US, has grappled with decades-long nitrate (NO3−) pollution in its rivers, lakes, and groundwater due to intensive farming practices and animal feeding operations. Nitrate originating from agricultural activities, industrial discharges, and wastewater treatment processes can contaminate drinking water sources such as groundwater and surface water bodies.

In the U.S., the Safe Drinking Water Act (SDWA) establishes a maximum contamination level (MCL) for nitrate at 10 mg/L NO3-N in drinking water. This regulation is implemented due to the adverse health effects of elevated nitrate exposure, including methemoglobinemia in infants, commonly known as “blue baby syndrome.” However, recent studies show that extended exposure to nitrate levels below the MCL (such as at 5 mg/L NO3-N) in drinking water can still have adverse effects on health, potentially increasing the risks of preterm birth, birth defects, and various types of cancer.

Average nitrate concentrations in Iowa's drinking water increased between 2003 and 2017, with a concentration averaged across 236 towns reaching as high as 5 mg/L NO3–N. Nearly half of the water samples from streams in heavily farmed areas in eastern Iowa had nitrate levels surpassing the MCL. However, only 4% of the public water systems (PWSs) across the state have some form of nitrate treatment, including anion exchange, reverse osmosis, and blending. These facilities require substantial capital investment and have high operational costs, making them inaccessible for many small and low-resourced communities across the state.

Disparities of potential exposure to elevated nitrate exist among different populations

Vulnerable populations can be exposed to the risks from high nitrate concentrations in public water supplies, turning what should be a basic human right—clean drinking water—into a hidden health hazard. Communities of color, families with low income, and residents of certain geographic regions disproportionately bear the brunt of inadequate water services, including exposure to contaminants. These issues often stem from systemic socio-economic inequalities and historical neglect.

In the Midwest, particularly in the agricultural regions of Iowa, Minnesota, and Wisconsin, areas where drinking water shows elevated levels of nitrate frequently align with communities whose median household incomes fall below the state's median. In our recent study, we delved into long-term nitrate levels in 871 Iowa PWSs between 2012 and 2022 and examined sociodemographic disparities in potential nitrate exposure in drinking water. On average, 7.4% of the state's population served by PWSs has been exposed to nitrate levels consistently exceeding 5 mg/L in the past decade. Disparities exist among various sociodemographic groups, with statistically significant higher exposure rates (10.1%, 9.6%, 9.2%, and 8.7%) observed for people whose incomes are below the federal poverty threshold ($26,496/year), older adults (65 years and above), people of color, and children (5 years and younger). These disparities are particularly concerning as these populations often lack the resources to address the consequences of water contamination.

Urgent nitrate remediation is needed in specific areas

Previous studies on Iowa’s private well water have shown that nitrate contamination in groundwater is particularly severe in these regions: Eastern Iowa (Floyd, Bremer, Tama, Jasper counties) with contamination in 11% of the wells, Western Iowa (Sioux, Cherokee, Ida, Cass counties) with contamination in 38.2% of the wells, and South-Central Iowa (Polk, Clarke, Wayne counties) with contamination in 28.1% of the wells. In our analysis, 2.5% of 871 PWSs are classified as ‘high-risk,’ with nitrate concentrations consistently exceeding 5 mg/L over the study period, primarily in eastern and western Iowa, where animal feeding operations are concentrated.

In particular, counties such as Black Hawk, Wapello, and Crawford, where percentages of people of color are relatively high, all have average nitrate concentrations exceeding 5 mg/L. The absence of nitrate removal processes in these counties contributes to the sustained elevated levels. According to the U.S. Centers for Disease Control and Prevention, Crawford County has the highest social vulnerability index score in the state. It also ranks among the twelve Iowa counties most at risk for drought. These factors exacerbate concerns for Crawford County communities, which are already struggling with limited resources to address nitrate contamination in their drinking water while grappling with ongoing water scarcity issues.

Policy recommendations and community support

On a policy level, there may be a need to revise regulatory standards and enforcement to ensure safer water for Iowans and the nation since epidemiological studies show that even lower levels could potentially harm human health. Public awareness campaigns and community support programs are also essential in mitigating the risks associated with nitrate exposure until more permanent solutions take hold. By addressing these issues comprehensively, there is an opportunity to improve health outcomes and advance environmental justice, ensuring all residents have access to safe drinking water.

Dr. Lu Liu (she/her) is an Assistant Professor in the Civil, Construction, and Environmental Engineering Department at Iowa State University. Her research focuses on the impact of climate change on water resources and adaptations in the water sector to climate change. Her research group seeks to facilitate sustainable water resource planning via robust decision-making tool development and active science-policy integration.