Environmental group warns of widespread health risks from unregulated livestock pollution

A new nationwide analysis by the Environmental Working Group (EWG) has found that cancer-linked chemical byproducts formed from livestock manure runoff have contaminated drinking water in thousands of communities across the United States, affecting an estimated 122 million people.

According to the report, manure from large-scale livestock operations is frequently sprayed on fields as fertilizer. Rainfall and irrigation then wash the manure into waterways, where it interacts with chlorine and other disinfectants used in water treatment plants to form trihalomethanes (TTHMs)—a group of chemical compounds known to pose serious health risks.

Between 2019 and 2023, nearly 6,000 community water systems in 49 states and Washington, D.C., recorded at least one instance of TTHM levels exceeding the federal legal threshold of 80 parts per billion. Some systems reported concentrations as high as 300 parts per billion. Health researchers argue that the current U.S. Environmental Protection Agency (EPA) standard is outdated and insufficiently protective, citing studies that link TTHM exposure to bladder and colorectal cancers, birth defects, low birth weight, and stillbirths.

Anne Schechinger, the EWG analyst who authored the report, emphasized that many of the worst-affected areas are located in states with high densities of cattle, hog, or poultry operations—including Texas, Oklahoma, California, Illinois, North Carolina, and Pennsylvania. While the Clean Water Act requires some of the largest livestock facilities to obtain discharge permits under the National Pollutant Discharge Elimination System (NPDES), many operations fall below the size thresholds and are exempt from federal oversight.

“If you have 955 cows, you don’t have to have a manure management plan,” Schechinger said. “And you still generate a lot of manure.”

EWG’s report argues that inadequate regulation has enabled both permitted and unregulated facilities to contribute to a growing pollution crisis. Nutrient runoff from manure not only leads to TTHM formation in treated drinking water but also degrades ecosystems by fueling algal blooms and harming aquatic life.

The group is calling for stricter manure management requirements for medium-sized farms, increased enforcement of existing pollution regulations, and the reinstatement of federal conservation funding. The Biden administration’s Inflation Reduction Act allocated $19.5 billion to conservation and climate programs, but much of that funding remains frozen. EWG warns that without restoring access to those funds, efforts to address manure-related pollution will fall short.

“Conservation programs that reduce runoff also support climate resilience,” said Schechinger. “It’s a win-win that deserves urgent attention.”

The EPA and U.S. Department of Agriculture did not respond to requests for comment on the findings.