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Happy Friday. And welcome to Cornhole Champions. I’m Zachary Oren Smith. Over at Iowa Starting Line, our team is laser-focused on our ongoing cancer investigation, The Host Spot. Some data needs parsing. Sources who need calling. And conversations—like this one—that I’m excited to share with you.
If you’ve been following the series—signing up for ISL’s flagship newsletter is the best way to do that—you know we’ve been looking at pesticides this week. And while I’m pretty happy with how we dug into it, I think about this series as a first step. An inception point. A place where you can get some good information about the causes and realities of Iowa’s cancer problem. But it’s not an endpoint.
To that end, I sat down with Dr. David Cwiertny to expand on the conversation on environmental contamination and its impact on our health. Cwiertny is a professor of civil and environmental engineering at the University of Iowa. He studies how agricultural chemicals move through our water, our air, and even the dust that blows around our homes. What emerged was a conversation about the messy reality of living in the gap between what science suggests and what policy actually does about it.
You can catch the full interview at our home on YouTube. Here are some interesting moments from the interview.
But first…
I said what I said - I had some folks in the comments saying I was using the word pesticide incorrectly… Here’s a teachable moment just for them.
Chemicals don’t just disappear
An idea Cwiertny hit on was “mass balance.” It’s the application of the law of conservation of mass: that mass is neither created nor destroyed. That we should be able to account for material entering and leaving a system.
"When you add something to the environment, it doesn't go away. It might transform, it might take on a new shape. It certainly can move, but it's still there,” Cwiertny said.
His team measures pesticide concentrations throughout agricultural regions. And he said they rarely find a water sample that does not contain one or two major chemicals—even in remote areas. That “ubiquity,” as he calls it, reflects decades of sustained use.
Take neonicotinoids, a class of insecticides you might have heard about because of their connection to bee colony collapse. Many farmers told Cwiertny it's hard to even find seeds that don't come pre-treated with these chemicals. The result? Background levels show up everywhere, even before anyone sprays anything.
The science-policy gap
Easily the most striking thought from this interview was what he termed the “grey area:” how scientific understanding evolves and how slowly policy follows.
The evidence around what chemicals are safe and which ones aren’t changes. In 2011, researchers published findings from the Agricultural Health Study showing no strong associations between atrazine use and cancer. But that same study, with more years of data, recently published updated findings in 2024 showing atrazine use is now associated with different forms of cancer.
"It's the same study, the same authors, and a completely different takeaway," Cwiertny said.
This isn't unusual. He pointed to forever chemicals (PFAS), where researchers have known about problems since 2000, but we're just now getting drinking water standards in 2025. That decade-to-two-decade lag between scientific discovery and policy change creates a "gray area"—where policy still considers something safe while emerging science suggests it may not be.
"That's really hard when you live in a place like Iowa where a lot of these chemicals get used," he said. "We could be in this gray area of, well, the legislation or the policy still says it's safe, but there's all this emerging science that says it may not be. What do we actually do?"
Reality > simple answers
If there’s a good come-away from the interview, one might be Cwiertny’s sober assessment that a clear cause for Iowa’s cancer rates isn't going to happen. Unlike toxic burn pits for veterans or chemical exposures in a factory, this kind of chronic, low-level exposure makes definitive connections nearly impossible to establish.
"Here in Iowa, the challenge is there's a variety of risk factors and it's not any one thing," he said. "It's diet, it's physical activity, it's our genetic history and family history. There are behavioral choices like do we smoke, do we drink? And then you throw in the environment."
If you remember last week’s conversation with Mary Charlton of the Iowa Cancer Registry, you’ll remember her remarks on the kinds of cancers differing across the state. There are different environmental risks associated with different areas. And we move from one to another, meaning we’re exposed to different environments at different times.
“If we’re waiting around for like, ‘Oh yeah, in Iowa, it’s this thing causing our main problem,’ we’re going to be waiting a long time,” Cwiertny said.
So what do we do?
Just because information is imperfect doesn’t mean we should wait to act.
“We know plenty to know where there are folks that deserve better protections,” Cwiertny said.
He pointed to research showing different models of agriculture—less chemically intensive approaches that might not get the same yields but don't require buying as much product, potentially maintaining profitability.
"I just wish we could have a more forward-looking conversation that it doesn't have to be either or," he said. "There are ways we could do this that could be productive and start to say that we don't necessarily have to do it this way, particularly if we're concerned there might be problems resulting from it."
Cwiertny's perspective stuck with me because it reframes how we think about uncertainty. Instead of using incomplete information as a reason to maintain the status quo, he said we could use it as a reason to be more proactive, to think about what options are at our disposal.
You wrote in
This week, I asked you how we bridge the conversational gap between farming interests and public health concerns. Your responses showed the complexity of the challenge:
Sophia from Ames: “My dad farmed for 40 years. He used what the extension office told him to use. What kept the farm profitable. He wasn’t trying to hurt anyone. But when he got diagnosed with lymphoma at 68, you can’t help but wonder. How do we have this conversation without making farmers the bad guys?”
ZOS: We are destined to enact those things we incentivize as a society and to avoid those things we disincentivize. We’ll get into this with next week’s interview with Chris Jones, so stay tuned. But I like your point that many folks involved in our ag system are doing what they are told is the right thing. There’s not malevolence here. It’s people working within the system that we created for them.
Bill from Iowa City: “Every chemical we sell is EPA approved. If there’s an issue, why is the EPA taking so long to change course?”
ZOS: Some argue it’s regulatory capture. Some argue its the slow process good science demands. Whatever the reason, it is frustrating.
To everyone who shared their two cents, thanks. I hope you’ll keep engaging with me about these stories.
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Your friendly neighborhood reporter,
Zachary Oren Smith
Political correspondent
Iowa Starting Line
