Study: Nitrate pollution disproportionately impacts Iowa’s vulnerable populations

About 1 in 20 of the state’s public water systems over the last decade have reported potentially harmful levels of nitrate in their drinking water, a new yet-unpublished Iowa State University study finds, and disadvantaged Iowans — people of color, low-income communities, children and older people — are more exposed to them.

Nitrate, a form of nitrogen, is a pervasive pollutant in Iowa’s waterways and groundwater that largely originates from agricultural runoff. It is linked to blue baby syndrome when its levels exceed 10 milligrams per liter in drinking water. Long-term exposure to lower nitrate levels, even for adults, could lead to cancer and other negative health impacts, some emerging research suggests.

Prior research has illuminated disproportionate impacts of water pollution at the county level for the United States, including Iowa, said Padmore Mantey, an ISU graduate student who led the new study. His work is the first to dive into data about individual water treatment facilities in Iowa and their surrounding demographics.

Last year, ISU received a $3.2 million grant from the U.S. Environmental Protection Agency to reduce barriers for water reclamation and address issues in water quality and availability in small, rural communities. Mantey’s project is an offshoot of that larger initiative, sparked by data on nitrate pollution in Iowa.

His results — which haven’t been peer-reviewed yet — show disproportionate impacts of nitrate pollution in disadvantaged communities in Iowa.

“It's an environmental justice problem,” said Lu Liu, an ISU assistant engineering professor and an adviser to Mantey’s study.

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Diving into data

The EPA currently sets the safe drinking water level for nitrate at 10 milligrams per liter, based on the link to blue baby syndrome. For his project, Mantey chose to label nitrate levels at 5 milligrams per liter or above as “elevated” based on literature connecting such levels to negative health impacts.

He characterized the size of Iowa public water systems based on the EPA’s Safe Drinking Water Information standards. About 96 percent of Iowa’s public water systems serve fewer than 10,000 people and are considered “small.”

Mantey then dove into nitrate concentration data that Iowa’s public water systems reported to the Iowa Department of Natural Resources between 2012 and 2022. There are 1,076 active public water systems in Iowa; the team received data for 871 of those systems. Mantey calculated each facility’s average nitrate concentration per year to map trends in nitrate levels within the time period.

To find the Iowa communities most exposed to elevated nitrate levels, he relied on the demographic and population data associated with each public water system within the EPA Enforcement and Compliance History Online database. That information is gleaned from U.S. census data and American Community Survey summaries.

Mantey specifically focused on four demographic groups: low-income communities, people of color, children 5 and younger, and people 65 and above.

“These are historically disadvantaged or marginalized populations,” Liu said. “Existing literature shows that they are disproportionately affected by environmental degradation or problems.”

Disparities detected

Mantey found that about 4 percent of Iowa’s public water systems have reported elevated nitrate levels in their drinking water over that time period, amounting to 192,267 customers served. Some of those systems are lumped in Northeast Iowa, and others are found along the state’s western border.

Just over 2 percent of those facilities reported nitrate levels consistently above 5 milligrams per liter, making them “high risk,” Mantey said.

From 2012 to 2022, average nitrate levels in publicly supplied drinking water show a slight upward trend — both for facilities with nitrate treatment capabilities and for those without. Only 4 percent of the state’s drinking water facilities have nitrate treatment technology. Facilities lacking that tech tend to have consistently high nitrate levels.

On average, 7.4 percent of Iowans are exposed to elevated nitrate levels. When Mantey examined which communities were most impacted, he found disparities across the state for certain demographic groups:

Northeast to east-central Iowa — stretching from Linn County up to the Minnesota border, and from Grundy County to the state’s eastern border — showed the most disparities across all studied demographics. There, more than a third of people of color, almost a third of low-income communities and 26 percent of older people and children are exposed to elevated nitrate levels.

The discovered disparities align with disparities mapped by the U.S. Centers for Disease Control and Prevention and the U.S. Toxic Substances and Disease Registry’s social vulnerability index, which determines the relative social vulnerability of every census tract.

“Disparities for these specific demographic groups are quite high, compared to the state average,” Mantey said. “We’re tying how this demographic disparity, in terms of nitrate concentration, can relate to what the CDC is seeing. There is some form of correlation in terms of some similar hotspots.”

Brittney J. Miller is the Energy & Environment Reporter for The Gazette and a corps member with Report for America, a national service program that places journalists in local newsrooms to report on under-covered issues.

Comments: (319) 398-8370; brittney.miller@thegazette.com