Tens of millions of Americans have likely consumed drinking water containing cancer-causing chemicals that form when livestock manure and other organic substances end up in public water sources, according to a new analysis.
Thousands of industrial-scale farms across the country spray manure from livestock onto farm or other lands, which then runs off into waterways. When water utilities disinfect water using chlorine and other chemicals, the process interacts with manure runoff to create a byproduct known as trihalomethanes, or TTHMs, which have been found to cause birth defects and cancers.
A new analysis by the environmental watchdog organization Environmental Working Group (EWG) found that, between 2019 and 2023, unsafe levels of TTHMs ended up at least once in each of nearly 6,000 community water systems across 49 states and Washington, DC affecting an estimated 122 million people.
“This was the first time we did a five-year look across all the public drinking water systems in the country,” said Anne Schechinger, an analyst for EWG and author of the new report. “The sheer number was surprising.”
The Environmental Protection Agency’s legal limit for TTHMs is 80 parts per billion, but research has shown that the limit should be much more stringent—around .15 parts per billion or lower. When the agency set the limit in 2004, it factored in the cost that water utilities would have to spend to meet a lower threshold.
“Eighty parts per billion, set by the EPA, is not fully health protective because they set it based on health, but also the cost of utilities removing the contaminant from drinking water,” Schechinger said. “When you actually look at the health studies, much lower limits are what you need to actually protect health.”
Schechinger’s analysis found that water systems in 49 states and the District of Columbia tested above the EPA’s limit for TTHMs and some tested higher—229 systems tested at 200 parts per billion and 69 tested at 300. The analysis looked at 40,000 community water systems across the country that test for TTHMs.
Researchers have linked bladder and colorectal cancers to prolonged consumption of TTHMs, and birth defects, low birth weights and stillbirths to TTHMs at shorter exposure times, even at levels below the EPA’s limit, Schechinger said.
Schechinger explained that her analysis, which was based on EWG’s database of drinking water contaminants, found that TTHMs were found in areas with higher percentages of livestock and livestock facilities.
“We can’t say for sure livestock manure is causing this problem everywhere,” Schechinger said. “But it seems like more than just a coincidence that some of the states that are the most affected are also the top livestock states.”
The analysis found that states with the highest number of water systems that tested at or above 80 parts per billion for TTHMs were in the top 10 cattle, poultry or hog-producing states: Texas, Oklahoma, California, Illinois, North Carolina and Pennsylvania.
Larger livestock operations are required to get water pollution permits under the Clean Water Act’s National Pollutant Discharge Elimination System (NPDES). Cattle facilities with more than 1,000 animals, or hog facilities with more than 2,500 animals, fall into this category. Though critics say the NPDES system is poorly enforced, in theory it requires huge farms to report how they manage the manure they produce. Farmers apply the manure as fertilizer, and also use the practice to dispose of excess excrement.
But thousands of farms fall just under this threshold, meaning that manure from tens of thousands—or even hundreds of thousands—of animals isn’t regulated under the EPA’s requirements.
“If you have 955 cows, you don’t have to have a manure management plan, and you still generate a lot of manure,.
— Anne Schechinger, EWG analyst
Manure from all of these facilities has inundated waterways across the country, causing what EWG and other advocacy and farm groups say is a nationwide crisis of manure pollution. Much of this manure—both regulated and unregulated—flows into waterways, supercharging them with nitrogen and phosphorus. This stokes algae growth that chokes aquatic species, poisons drinking water and makes waterways unusable for recreation.
The new findings on TTHMs, Schechinger argues, should prompt regulators to more closely examine these less massive farms that have flown under the radar.
“If you have 955 cows, you don’t have to have a manure management plan, and you still generate a lot of manure,” Schechinger said.
EWG is advocating not only for more, and more strictly enforced, management plans, but also for government support for conservation programs. The Trump administration has frozen tens of millions of dollars in funding that was allocated under the Biden administration’s Inflation Reduction Act that directed $19.5 billion for conservation and climate programs, including those that would boost the health of farmland.
“More conservation programs on the farm fields could help with runoff, too,” Schechinger said. “What absolutely needs to be done today is unfreezing all the funds.”
“Those conservation practices that are good for the climate are also good at reducing runoff of manure and nitrogen from farm fields,” she added. “That’s a no-brainer.”
Representatives for the EPA and the U.S. Department of Agriculture did not immediately respond to requests for comment Thursday.
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