A Texas county is taking steps to declare a state of emergency and seek federal assistance over farmland contaminated with harmful “forever chemicals,” as concerns grow over the safety of fertilizer made from sewage.

Johnson County, south of Fort Worth, has been roiled since county investigators found high levels of chemicals called PFAS, or per- and polyfluoroalkyl substances, at two cattle ranches in the county in 2023.

The county says the PFAS, also known as forever chemicals because they don’t break down in the environment, came from contaminated fertilizer used on a neighboring farm. That fertilizer was made out of treated sewage from Fort Worth’s wastewater treatment plant. A New York Times investigation into the use of contaminated sewage sludge as fertilizer focused in part on the experience of ranchers in Johnson County.

PFAS, which is used in everyday items like nonstick cookware and stain-resistant carpets, has been found to increase the risk of certain types of cancer, and can cause birth defects, developmental delays in children, and other health harms.

County commissioners passed a resolution this week calling on Texas governor Greg Abbott to join the declaration, and seek federal disaster assistance.

“This is uncharted territory,” said Larry Woolley, one of the county’s four commissioners, in an interview. The funds, he said, would be put toward testing and monitoring of drinking water, cleanup, as well as euthanization of cattle contaminated from the soil, crops and water.

Johnson county is also pressing the state of Texas to block the use of sewage sludge to fertilize local farmland. “Ultimately, our goal is to stop the flow of contaminants into the county,” said Christopher Boedeker, a county Judge.

For decades, farmers nationwide have been encouraged by the federal government to use treated sewage sludge as fertilizer for its rich nutrients, and to reduce the amount of sludge that must be buried in landfills or incinerated. Spreading sewage on farmland also cuts down on the use of fertilizers made from fossil fuels.

But a growing body of research shows that the black sludge, made from the sewage that flows from homes and factories, can contain heavy concentrations of PFAS as well as other harmful contaminants.

Last month, under the Biden administration, the Environmental Protection Agency for the first time warned that PFAS-tainted sewage sludge used as fertilizer can contaminate the soil, groundwater, crops and livestock, posing human health risks.

The Biden administration also set drinking-water standards for certain kinds of PFAS and designated two of the chemicals as hazardous substances that must be cleaned up under the nation’s Superfund law. The future of those measures is uncertain under the Trump administration. The E.P.A. says there is no safe level of exposure to those two PFAS.

There has been little testing on farms. Maine is the only state that has started to systematically test farmland for PFAS, and has shuttered dozens of dairy farms found with contamination.

Johnson County is the first to directly seek federal assistance. It remained unclear, however, exactly how the county could tap federal funds, particularly amid the Trump administration’s freeze on federal spending.

President Biden’s Bipartisan Infrastructure Law had provided $2 billion in funding to address PFAS and other contaminants in drinking water. It is the future of funds like these, which must be requested at the state level, that remain uncertain in the new administration.

The Federal Emergency Management Agency also has funds available for well testing, which must be requested by states, though that money is typically distributed after natural disasters. President Trump has also targeted FEMA funding, saying he wants states to handle disasters without the federal agency’s help. The Department of Agriculture also offers assistance to farmers affected by PFAS contamination, but that program is currently limited to dairy farmers.

That leaves Johnson County in a bind.

While President Trump has been hostile to regulations, he also spoke on the campaign trail of “getting dangerous chemicals out of our environment.” And concerns about PFAS contamination have reached some deeply red states and counties, like Johnson County, which voted overwhelmingly for Mr. Trump.

The E.P.A. and FEMA did not provide comment.

In December, Texas attorney general Ken Paxton sued the largest PFAS makers, saying they knew about the dangers of these chemicals, but continued to market their use. The G.O.P.-controlled Texas state legislature is considering bills that set limits on PFAS in sludge fertilizer and require producers to test for the chemicals.

The state of Texas has not indicated whether they will back Johnson County’s declaration and support its request for federal assistance. The governor’s office did not respond to requests for comment.

Ricky Richter, a spokesman at the state’s environmental regulator, the Texas Commission of Environmental Quality, said the agency’s own analysis of PFAS levels discovered by Johnson County investigators did not suggest any harm to human health or the environment.

The agency did not immediately provide details of its analysis.

Johnson county officials said they stood behind their findings. The ranchers are suing the fertilizer provider, alleging that the contamination on their land was slowly sickening and killing their livestock. They are still caring for the surviving cattle, but are no longer sending them to market.