In the evening of April 13, 2006, my hometown, Iowa City, Iowa, got hit with a major tornado. It uprooted trees, overturned cars and semis, took the steeple off one of the city’s oldest Catholic Churches, and destroyed 35 commercial buildings and over 1,000 homes, many of them just a few blocks away from my parents’ house, which was spared. FEMA estimated $12 million in damages to the city.

It was Easter weekend, and I was home visiting from Italy, where I was living at the time. As the skies darkened to a hue resembling a deep bruise, I remember urging my parents to follow me to the basement. But they wouldn’t budge. As my dad stood on the porch, arms crossed, I thought, ‘Man defies nature.’ My mother stayed with him. Only the cats followed me downstairs.

Once the storm passed, I found my parents sitting in the candle-lit family room, since we’d lost electricity. My dad sat in his armchair, stroking the orange tabby cat, Samson, his beloved ‘farm cat.’ I lay on the ground, staring up at the ceiling, at the shadows on the wall cast by the candlelight. Later, this moment would remind me of Plato’s Allegory of the Cave—about mistaking shadows for reality—especially because of the conversation that ensued.

My dad asked me about my meeting earlier that day with Dave, one of the farmers who worked my dad’s land. I’d gone to Dave’s farm to see him apply pesticides and herbicides to his crops. We got inside his spreader with its huge arms that could span a small building. He also showed me barrels filled with pre-treated seeds the color of highlighter pink. I was curious about the effect of these chemicals on the human body. Dave’s crops, as with most crops on today’s commercial farms, head straight to the market, where they’re used as animal feed. So, people don’t directly ingest what grows in the ground. But still, I wondered about the spill-off into the water—given all the creeks that feed into the rivers; and the water in the underground wells that people in rural communities drank. I also wondered about the risk to people like Dave—who handled the chemicals directly.

As I told my dad about my day with Dave, it was my mother who was listening most intently. After all, she had inspired my questions. One year before, she’d been diagnosed with advanced breast cancer, which is incurable. I wanted to know what had caused her cancer, and specifically, if chemicals on the land were culpable. Ultimately, the question that went through my mind was a sobering one: had my father’s livelihood led to my mother’s demise?

My father, who grew up on a farm in Northwest Iowa, had a small business where he did land appraisals and managed farms. He also owned about a dozen of his own farms. My parents never lived on a farm, and most likely, the connection between my dad’s career and my mother’ illness was a tenuous one. But my provocative question would lead to many other questions and observations. On that same trip home, I talked to another Dave, a family friend and professor in the school of public health at the University of Iowa. Dave had lymphoma and was convinced it had something to do with the chemical spill-off in the water. Incidentally, I had remembered as a teenager, reading a jarring report in the newspaper about the elevated levels of nitrate, known to cause certain cancers like lymphoma. The finding led to the revamping of the city’s water plant.

I made other observations as well: I also couldn’t help but notice the abundance of cancer-related deaths in the obits section of our local newspaper. I had no way of comparing these to cancer deaths in Italy, but it seemed like cancer was much more visible in Iowa than Italy.

When a year later, I moved back to America to take care of my mother, at her oncology appointments, I noticed a disproportionate number of patients whom I presumed to be farmers, given their overalls and John Deere hats. Several years later, farmer Dave would get stomach cancer. My father would get prostate cancer. The potential associations between farm life and cancer risk continued to haunt me long after my mother died in 2008.

Last summer, I reconnected with Charles Lynch, the Iowa director of the Agricultural Health Study, a study of pesticide applicators and their wives in Iowa and North Carolina that started in 1993 and is sponsored by the National Cancer Institute. I’d first met with Lynch about the study on that same tornado visit home in 2006. Importantly, Lynch explained, the study is a prospective one—meaning, it enrolled some 89,000 people twenty-five years ago to follow throughout their lifetimes—to test who developed cancer. The study was done this way to prevent what pesticide companies call recall bias, when people diagnosed with cancer blame pesticide use for getting cancer. “Farmers usually think about exposure—many of them get sick in the application of the pesticide. They’re known to make you ill, with vomiting, nausea, headaches,” Lynch said. “They remember that, and they start thinking about what might have caused this.”

In November, 2017, the European Union approved Roundup for another five years, although certain countries within the EU, Italy included, banned it.

Usually, it’s only sick farmers who doubt the chemicals that otherwise help their yields, Lynch continued, adding that this has been the case with the common weed killer, Roundup.

“Farmers are on two side of this: Roundup has increased their yields. If you were to take it away, some farmers say it would impact their livelihood,” Lynch said. “Probably the majority of farmers feel that way; when they feel differently it’s when they develop a disease.”

Roundup, which is manufactured by Monsanto and is also known as glyphosate, its active ingredient, came into the spotlight in 2015, when the International Agency for Research on Cancer (IARC) classified the pesticide as “probably carcinogenic” to humans. According to the IARC website, this was based on “limited” evidence of cancer in humans; and “sufficient” evidence of cancer in lab animals. The fall-out of the IARC classification has been mixed, Lynch explained. While people with cancer have won individual lawsuits against Monsanto using IARC’s finding, other regulatory bodies have not endorsed it. In November, 2017, the European Union approved Roundup for another five years, although certain countries within the EU, Italy included, banned it.

In the U.S., last April the Environmental Protection Agency concluded that glyphosate is “not likely to be carcinogenic” to humans. In 2018, Lynch and his Ag Health Study colleagues re-evaluated their own findings on glyphosate usage and cancer, amongst their study cohort. “We looked hard for the association with lymphoma that IARC found. We just didn’t find it,” Lynch said. “Our public health message was that there was no risk of solid tumors or non-Hodgkin’s Lymphoma and Roundup.”

They did, however, find an association between Roundup and acute myelogenous leukemia, Lynch added. “We are the first group globally to find that association. We need more cases to develop within our cohort.” Their results were published in the Journal of the National Cancer Institute.

Other key findings of the Ag Health Study over the past twenty-six years include that farmers overall have lower rates of the pancreas, oral cavity, and lung, and higher rates of prostate, lip, thyroid, testicular and peritoneal cancers, and multiple myeloma in addition to acute myeloid leukemia.

“In terms of what we know about cancer today, the major causative factors are lifestyle: smoking, diet, alcohol, obesity,” Lynch said. “These are the major known risk factors.”

What about non-farmers, who live in proximity to farmland? And specifically, their risk of chemical exposure through drinking water? “Most of the pesticide concentrations in drinking water are fairly low,” Lynch said, explaining that public water supplies are regulated for standard pesticide levels, but that private wells in rural areas, which are unregulated, pose the biggest risk.

The study has found associations between pesticide usage and other diseases as well, including an elevated incidence of Parkinson’s disease, diabetes, macular degeneration and asthma. It’s added a study branch to include children and early life exposures. Lynch said the probing continues, and “the future looks bright.”

As for me, I continue to wonder if the shadows I once observed in my parents’ family room will be displaced by definitive answers in my own lifetime. Science moves slowly, and questions beget more questions, but I do feel better for the asking.