People living near clusters of animal factory farms in Iowa, Texas, and California appear to face higher cancer rates, according to new research from Yale University. The study examined county-level cancer data between 2000 and 2021, comparing areas with dense concentrations of animal feeding operations to similar counties with far fewer such facilities. Researchers found that overall cancer incidence was 4% higher in high‑factory‑farm counties in California, and 8% higher in both Iowa and Texas.
The scientists focused on concentrated animal feeding operations, where large numbers of cows, pigs, or birds are confined without vegetation for at least 45 days a year, generating huge volumes of excrement. In Iowa alone, pigs are estimated to produce 110 billion pounds of manure each year, vastly more than the excrement from the state’s human population. This waste is often stored in open-air lagoons, releasing ammonia, hydrogen sulfide, and particulate matter into the air, while run‑off can carry pathogens and nitrates into rivers and groundwater.
A previous report from the Iowa Environmental Council and the Harkin Institute has already linked widespread nitrate contamination and other pollutants to elevated cancer risk in the state, which has the second‑highest, fastest‑rising cancer rate in the US. Iowa oncologist Dr Richard Deming, who co‑authored that report, said to Sentient Media, “When you know the relationship between CAFOs and nitrates that get into the water, it doesn’t surprise me that it’s another study that supports the data.”
The Yale team reported positive associations between the density of animal feeding operations and almost all cancer types they studied, though some cancers showed stronger correlations than others. Anne Schechinger, senior director of agriculture and climate research at the Environmental Working Group, warned that rural residents often face overlapping vulnerabilities, including lower incomes, older populations, and reduced access to preventative healthcare. She said, “It’s especially tricky in rural counties to tie something specific to increased rates of cancer, because we know rural counties oftentimes have less preventative health care access, lower incomes, higher age.”
