Iowa’s cancer crisis — facts and its future

The most recent National Cancer Institute State Cancer Profiles (2018-2022) reported that Kentucky had the highest age-adjusted cancer rate (519.0/100,000) and that Iowa had the second highest cancer equivalent cancer rate (498.8). However, Kentucky’s most recent five-year trend rate was decreasing 0.6%/year while Iowa’s equivalent cancer rate was increasing 0.7%/year. If these same trends continue for the next five-year period, which is likely, Iowa’s 2025 cancer rate would have exceeded Kentucky’s declining cancer rate, thereby making Iowa America’s cancer capitol.

Why is this likely? Because environmental cancers do not manifest until after 10 to 20 years of exposure (called latency), it is necessary to look at risk factors that changed 10-20 years before Iowa’s cancer rate clearly began to increase by 2013, and we know what they were. Kentucky’s trend will likely continue downward, like almost all other states, because of declining smoking and air pollution. What changed in Iowa in the 1990s was industrialization of animal agriculture with national/multinational corporations — which own the animals, the stink and the pollution — forcing out nearly all independent producers and beginning aggressive increases in production — a doubling of both pork, to 25 million animals by 2020 and egg production, to over 15 billion by 2015. This resulted in the already very substantial increase in Iowa fine particulate and ammonia emissions that began in the 1960s when animals were moved indoors to thousands of small animal feeding operations (AFOs). Instead of ammonia emissions being largely neutralized on pasture, ammonia was then emitted 24/7 from manure pits, the contents which were then spread as fertilizer. That was farming until industrial domination in the 1990s with massive, concentrated animal feeding operations (CAFOs) housing several hundred to thousands of animals. That is not farming. Rather it is industrial production with Iowa’s CAFO waste, as documented by scientist Chris Jones in Swine Republic, rising to the fecal equivalent of 168 million people. CAFO pollution is driving Iowa’s water pollution problem, its air pollution problem and its cancer crisis.

Together with co-editor Bob Martin of the Johns Hopkins University, I wrote with co-authors two air pollution chapters and co-edited Industrial Farm Animal Production, the Environment, and Public Health, a 2024 12 chapter Johns Hopkins University Press book written by national experts. This 2024 publication was followed by a conference, by the same name, at Drake Sept. 25-26, 2024, sponsored by the Harkin Institute, and still available on its website, and the Hopkins’ Center for a Livable Future. In chapter 2, Chris Jones reviewed the world’s literature on the substantial impact of CAFO’s on water pollution. In chapters 3 and 4, I reviewed the world’s literature on the impact of CAFO air emission documenting occupational and nearby community behavioral impacts and diseases: childhood and adult asthma, bronchitis, impaired lung function and pneumonia, together with dose-related increased mortality from respiratory and cardiovascular disease, and from lung cancer. These adverse health effects arise from several harmful air pollutants including ammonia, hydrogen sulfide, volatile organic compounds (VOCs), methane, nitrous oxide, bioaerosols and fine particulate matter (PM 10  and PM 2.5). Importantly, and described by Professor Viney Aneja and colleagues, in Chapter 10 and at the conference, PM 10  and PM 2.5 arise as primary pollutants directly from animal production, but also secondarily in the atmosphere as ultrafine and 2.5micron diameter ammonium nitrate and ammonium sulfate salts. Also, both methane (27.9 times the radiative effect of CO₂) and nitrous oxide (273 times the effect of CO₂) are potent global warming gases and also arise from CAFOs. Of total anthropogenic emissions, about 37% of methane and 65% of nitrous oxide emanate from animal production.

Agriculture leads the world in ammonia pollution with about 60% of total emissions, with livestock production responsible for about 80% of total emissions. In Iowa, animal agriculture has accounted for over 80% of total ammonia emissions from 2000 to 2020. Fine air pollution particulates (PM 2.5 and PM 10) were declared to be “carcinogenic to humans” (Group 1A) by the International Agency for Research on Cancer (IARC) in 2015. Since then, the literature on the adverse health effects of PM 2.5 has grown substantially. I just did a PubMed search of the National Institute of Health’s electronic library to document the extent of PM 2.5 linked diseases that appear in the literature — PM 2.5 and cancer (829 citations), heart disease (763 citations), lung disease (1,816 citations), cerebrovascular disease (204 citations), cognitive impairment (96 citations), adverse reproductive outcomes (242), lung cancer (483 citations), breast cancer (52 citations), esophageal cancer (11 citations), liver cancer (35 citations), kidney cancer (13 citations), non-Hodgkin’s lymphoma (16 citations), and formation from ammonia air emissions (31 citations). PM 2.5 arising from ammonia emissions and PM 2.5 as a cause of cancer is settled science. PM 2.5 has been regulated by EPA since 1997 and has been sampled extensively and reported annually in several locations in Iowa since 1999.

At the 2024 conference, I presented preliminary results of 45 years of National Cancer Institute SEER cancer incidence from the UI College of Public Health’s Iowa Cancer Registry, data from 1975, when the registry began, to 2020. We assessed cancer incidence among men and women and split Iowa into the nine most urban counties and three to five county clusters of Iowa’s 90 rural counties. What immediately became clear is that lung cancer incidence began to increase among men and women across the entire state beginning in 1975. Smoking in the 1960s was still prevalent among U.S. men (about 50%) and among women (about 35%). Pollution, including PM 2.5, from vehicles and Iowa’s coal-fired power plants had not yet declined and Iowa’s nationally leading radon exposure was stable. What was increasing from the thousands of AFOs were primary PM 10, 2.5 and ammonia emissions. All-site cancer incidence rose sharply among urban and rural men and women until 1992 when urban rates among men began to decline, but all-site cancer among both urban and rural women continued to rise until 2020 (See Figure 1).  As cigarette smoking among men sharply declined beginning in the 1960s, lung cancer among urban and rural men began to decline beginning in 1987, but lung cancer among women — in the face of declining smoking — continued to rise until 2010 when urban women’s lung cancer began to decline — but not rural women’s lung cancer that continued to increase until 2020. We hypothesize that PM 2.5 with radon exposure, especially in rural basements where washing machines are typically located, interact to greatly increase lung cancer risk especially among women. Lung cancer, which tripled in incidence among both urban and rural women, followed by breast cancer that continued to rise until 2020 and increased by over 40% from 1975-2020, are major drivers of Iowa’s cancer crisis (See Figure 2).

To determine what other cancers were increasing over time, we initially looked at several cancers mentioned in the literature and then analyzed those cancers that had at least doubled (lung, breast, esophageal, liver, kidney) and in the case of non-Hodgkin’s lymphoma, nearly doubled between 1975 and 2020. Most striking was the near parallel increase, from 1975 to 2020, in lung and breast cancer among urban, but especially, among rural women (See Figure 2). This suggests a common etiology. Also, doubling or nearly doubling among rural men and women were the much less common cancers of the esophagus, liver and kidney. As summarized above, these same cancers are now the subject an expanding PM 2.5 cancer literature. The minute PM 2.5 and smaller carcinogenic particles translocate from terminal airways to lung capillaries, are taken up by macrophages and are then distributed to distal organs where they are deposited. A 2026 Yale study of CAFO exposure and cancer incidence (2000-2020) in three states (California, Texas and Iowa) confirmed significant associations between CAFO densities and all-site Iowa cancers, lung cancer, breast cancer, lymphoma, non-Hodgkin’s lymphoma, colon cancer and all incident cases of the respiratory system. Also covered in my presentation were the marked decreases in smoking, and the modest increases in heavy drinking and estimated body mass index among Iowa men and women based on CDC surveys. All are well known to increase some specific cancers risk, as does water pollution, but not lung cancer together with the suite of other cited PM 2.5 linked cancers. 

Glyphosate, which travels with other carcinogenic pesticides (arsenic compounds, lindane, pentachlorophenol, atrazine, DDT, diazinon, malathion) with water nitrate pollution, IARC has found to be carcinogenic (Category 1) for non-Hodgkin’s lymphoma. Roundup (glyphosate) is the most widely distributed pesticide in the world resulting in extremely high prevalences of glyphosate in urine samples in national population surveys — 80% from a 2018 CDC U.S. survey and 99% from a 2022 French survey. We found, from 1975 to 2020, that non-Hodgkin’s lymphoma increased over 80% among rural men, 60% among rural women and over 50% among urban men and women. This suggests occupational exposures to glyphosate and other pesticides likely increase rural men’s risk to non-Hodgkin’s lymphoma, but that the entire population of Iowa is also likely to be at increased risk from low levels of carcinogenic pesticides in polluted drinking water.

Industrial animal agriculture corporations, and their collaborators, have been and continue to be aggressive, as summarized in the preface to our book, in denying and suppressing research on the very substantial environmental, health and rural community impacts of their industrial pollution. The political influence of this industry is potent and has been effective in shaping information about Iowa’s cancer crisis. Much has been written and proclaimed about water pollution and cancer, but very little has been about CAFO-linked air pollution that is driving Iowa’s cancer crisis.

Wake up Iowans! We are in a fight with these mainly out-of-state and foreign livestock corporations for our environment, for our health and, for some, our very lives. Vote for candidates who are serious about confronting Iowa’s cancer crisis, not those fronting for or supported by polluting CAFO corporations. As Senator Harkin stated in his very strong introductory comments for the 2024 conference, it is high time for a “course correction.” Corrective policy initiatives have never been more urgent: 1) further decrease smoking by increasing the cigarette tax by $2/pack, 2) phase out coal energy generation and oppose coal and gas powered data centers while increasing wind and solar, 3) redouble radon mitigation programs, 4) promote the return of animals to pasture by incentivizing contract growers to phase-out CAFOs, and 5) for industrial CAFOs that remain, regulate them as industries and require installation of USDA developed, and proven over three generations, super soil control technology that eliminates odor, water and air pollution, kills pathogens, enhances animal health, increases production and retains nutrients in solids for fertilizer and composting. Without attention to these policies, Iowa’s cancer crisis will deepen together with the severe illnesses, deaths and their attendant health care costs.

James A. Merchant, MD, DrPH

Professor Emeritus, Colleges of Public Health and Medicine

Founding Dean, College of Public Health

Emeritus Director, Division of Research on Respiratory Disease Studies, NIOSH/CDC

Emeritus Chair, Health Effects Institute Review Committee