Cancer in Iowa: What role does agriculture play in Iowa’s high cancer rates?

Iowa is the No. 1 corn-producing state. We also lead the nation in production of pork, eggs and ethanol.

But another state ranking has gotten more attention in recent years: Iowa has the fastest-growing rate of new cancers in the nation and the second-highest cancer rate overall, behind Kentucky.

Iowa’s stubbornly-high cancer rate can’t be blamed on just one thing, but oncologists and public health researchers agree it’s time to look more closely at Iowa’s top industry to see how it might be contributing.

“If you did an aerial map of Iowa, we are — river to river and north to south — a bath of ag chemicals: herbicides, pesticides, fertilizers, nitrates,” Dr. Richard Deming, a Des Moines oncologist, said at The Gazette’s Iowa Ideas conference last fall.

“We’re not yet at the point where we can say what every single chemical that ultimately gets into our water supply (or) onto our skin causes, but when you look at the amount of ag chemicals Iowans are exposed to compared to other states, I suspect that we’ll find that might also be one of the contributing factors.”

In a state where college sports arenas blaze with fertilizer logos, the phrase “corn grows Iowa” is common on TV and radio and nearly 15 percent of lawmakers are farmers, there’s reluctance to pinpoint agriculture as a possible reason for Iowa’s rising cancer rate without conclusive evidence.

However, a growing body of evidence linking agricultural chemical exposure to cancer has caused cancer researchers, doctors and survivors to push for action to protect Iowans. Let’s consider some key studies and how Iowans may be more at risk.

Nitrate in drinking water linked to some adult cancers

• Nitrate, a key ingredient in much of the fertilizer sold in Iowa, not only can cause blue baby syndrome, but a 2018 review of 30 academic studies showed a link between ingesting nitrate from drinking water and adult diseases, including colorectal cancer.

• Other University of Iowa studies show nitrate consumption may cause bladder and ovarian cancer in older women.

• The Agricultural Health Study, a 30-year study of 89,000 pesticide applicators — mostly farmers — and their spouses in Iowa and North Carolina has provided data showing farmers have a higher rate of prostate cancers — one of the top four cancers contributing to Iowa’s No. 2 ranking.

• Applicators who used weedkiller dicamba had elevated risk of liver cancer and intrahepatic bile duct cancer, a 2020 review of Agricultural Health Study data showed. Among farmers in the Agricultural Health Study, a greater use of herbicide atrazine increased risk of lung and prostate cancer, a 2022 study showed.

Iowa’s ag risks may be higher than other states

• Nitrate is found at potentially harmful levels in 1-in-20 Iowa public drinking water systems and in more than 12,000 private wells in Iowa.

• Nitrate-attributable cancer in Iowa could range from 2.3 to 10.43 cases per 100,000 people, putting Iowa among four states with some of the highest risk, according to estimates from the Environmental Working Group using data from their 2019 peer-reviewed study.

• Iowa farmers used more fertilizer in 2022 than Illinois, Nebraska and Missouri — other big corn states.

• Iowa has more hogs than any other state — by a long shot — and the number of hogs in Iowa increased 76 percent between 2002 and 2022, Investigate Midwest reported. Because hog manure, dense with nitrate and phosphorus, must be applied to land near hog confinements, it can result in more nitrate in groundwater and waterways.

Farmers are the focus of 30-year health study

When Rob Faux was running a small-scale vegetable farm and raising poultry full time near Tripoli, he worked outside from sun up to sun down. He doesn’t use pesticide, but his neighbors with traditional corn and soybean farms do.

In 2020, doctors found a cancerous tumor in Faux’s kidney. They removed the kidney in 2021 and Faux, 58, has been in good health since. But he thinks about chemical exposures, including an incident in 2012 when he was doused by a crop duster.

“I got this cancer because there was a confluence of events,” he said. “Some of it might be genetic. Some of it situational. Some of it might be what I ate or how I live. It might be exposure to pesticides. Who knows which of those things provided the tipping point?”

Faux has been working since 2020 with the Pesticide Action Network, an international group critical of modern pesticide practices.

Farmers, in general, are healthier than the average public. Chalk it up to physical labor. Or early bedtime. Or a religious heritage that frowns on drinking too much alcohol.

They also have a lower rate of cancer overall, according to a 20-year follow-up of Iowa and North Carolina farmers enrolled in the Agricultural Health Study. But for some types of cancers — prostate, lip, acute myeloid leukemia, thyroid, testicular and peritoneal — farmers in the study had higher rates than the general public.

“Farmers generally have elevated rates of prostate cancer related to the general population,” said Laura Beane Freeman, National Cancer Institute principal investigator of the Agricultural Health Study.

Beane Freeman grew up on an Iowa farm before getting degrees from Iowa State University and the University of Iowa and moving to the Washington, D.C., area.

A 2023 study by Beane Freeman and others showed farmers in the ag health study with a genetic predisposition for prostate cancer may have an even higher risk when exposed to some pesticides.

Among about 53,000 male farmers in the ag health study, 85 men developed thyroid cancer between the mid-1990s and 2015. Researchers found those who used the fungicide metalaxyl developed thyroid cancer at a rate two times higher than those who did not. Those who used the insecticide lindane were 1.7 times as likely to be diagnosed with thyroid cancer, the 2021 study showed.

The Agricultural Health Study’s rich data have led to hundreds of publications, including some on non-cancer health effects, such as the links between pesticides and Parkinson’s disease, house dust bacteria and asthma, and raw milk consumption and lung function.

Excess nitrate getting more scrutiny

While nitrogen, phosphorus and other nutrients are found naturally in soil, farmers over decades have added fertilizer, both synthetic and manure, to maximize crop yields.

Iowa and its five neighboring states, Illinois, Nebraska, Missouri, Minnesota and Wisconsin, together used more than 20 million tons of synthetic fertilizer in fiscal 2020, the most recent year data is available from all states, a Gazette review showed.

Illinois and Iowa — the nation’s top corn-producing states, which together produce about one-third the nation’s corn — are the biggest fertilizer users.

These states also have more excess nitrogen washing from farm fields into rivers and streams, the U.S. Environmental Protection Agency reported. Iowa’s estimated aggregated nitrate load is the highest of all U.S. states.

“Since 1950, human sources of nitrogen have increased substantially, creating a global surplus of nitrate/nitrite that supersedes natural sources by about 30 percent,” the EPA reported last fall when it restarted an assessment of how nitrate, consumed through food or water, affects human health.

About 43 million Americans — or about 13 percent of the population — relies on private wells for drinking water. This includes about 230,000 Iowans, ISU Extension and Outreach reported.

The EPA’s legal limit for nitrate in drinking water is 10 milligrams per liter, but many scientists believe much lower amounts can make people sick.

“There's been a number of epidemiological studies that have started to find potential associations between nitrate in drinking water and various forms of chronic disease, including certain forms of cancer,” said David Cwiertny, a UI engineering professor and director of the Center for Health Effects of Environmental Contamination.

Peter Weyer, a now-retired public health researcher from the UI, led many of those studies.

In one study, published in 2001, Weyer and co-investigators found nitrate in drinking water was linked to higher rates of bladder and ovarian cancer in postmenopausal Iowa women. In a 2010 study, Weyer found a higher risk of thyroid cancer with higher average nitrate levels in public water supplies and longer consumption of water with nitrate levels exceeding 5 mg/L — half the EPA’s legal limit.

“You’re hoping, if your study means anything, it’s eventually corroborated by somebody else’s study, which our bladder study was,” Weyer said.

Is more research — or action — needed?

With a growing body of evidence showing links between nitrate from drinking water and some types of cancer, why haven’t Iowa’s public health officials or Legislature taken steps to reduce nitrate risk?

“The agricultural industry is tough to deal with,” Weyer said. “They are very defensive and protective. I think most of the nitrate we see in the environment is, at least in agricultural areas, from excess nitrogen fertilizer application.”

Sen. Ken Rozenboom, an Oskaloosa Republican who has a family farm and has worked in agribusiness, said studies linking agricultural chemicals to cancer never express certainty.

“The fact there is no smoking gun, there is no definitive scientific finding that links cancer to nitrates in water,” he said. “Researchers say ‘more studies are needed,’ which is what I always hear.”

Rozenboom said he hasn’t heard first-person accounts from farmers who have gotten cancer from their exposures to ag chemicals. “I never hear an undercurrent of doubt or concern they've somehow been handling unsafe things over the years and haven't been told,” he said.

While scientists look for more studies to corroborate or disprove results, they also know when there’s enough evidence to take action, Cwiertny said.

“At some point, we need to move from just talking about it, and wanting to study it, to saying ‘OK, we've probably got enough evidence that we're uniquely vulnerable, and we should do something about it’,” he said.

Steps Iowa could take to reduce exposure to ag chemicals

So what could the state do to protect people from potential cancer-causing exposures? Below are steps other states are taking or suggestions by sources we interviewed for this story:

• Share more information: The Legislature could make it easier to study the volume of agricultural chemicals by allowing annual sales totals of pesticides and herbicides to be public information. Manure management plans — which say how much manure is applied on which farm fields — could be digitized so data experts could study these volumes holistically.

• Raise stakes on pesticide violations: Iowa fines few people for pesticide use violations and a bill passed in 2021 that would allow the state to fine farmers — not just commercial applicators — for pesticide drift hasn’t been implemented. “If you have a slap on the wrist, it's a signal you don't really think it's a problem,” Faux said.

• Set a lower standard for nitrate in public drinking water: The EPA, which set the 10 mg/L standard for nitrate in drinking water in 1991, has started a new review of research on how nitrate affects human health. It’s likely a long and political process, but could result in a lower protective standard.

• Provide cheap or free water filters: Reverse osmosis systems can remove nitrate and other chemicals, such as Per- and Polyfluorinated Substances (PFAS), from drinking water. Under-sink models can cost several hundred dollars, so the state or counties could set aside funds to defray the cost for residents with high nitrate levels in private wells.

• Fund local efforts: Minnesota lawmakers are considering a bill that would provide a 99-cent-per-ton nitrogen fertilizer tax that would raise $3 million a year to health departments in counties with private wells with high nitrate levels.

Free workshops for private well owners

Only about 10 percent of Iowans with private wells tested them for contaminants, according to a 2022 survey by ISU Extension, which is providing a series of free workshops this spring about well stewardship.

Jones — Thursday

Washington — April 2

Cerro Gordo — April 3

Webster — April 4

Jackson — April 9

Allamakee — April 10

Ringgold — April 17

Johnson — April 18

Linn — April 30

Wright — May 1

Warren — May 9

Click on the link above or call your local Extension office to register.

Gazette reporter Brittney J. Miller contributed to this report.

Comments: (319) 339-3157; erin.jordan@thegazette.com