In 2023, sewage plants in Maryland started to make a troubling discovery. Harmful “forever chemicals” were contaminating the state’s sewage, much of which is turned into fertilizer and spread on farmland.

To protect its food and drinking water, Maryland has started restricting the use of fertilizer made from sewage sludge. At the same time, a major sludge-fertilizer maker, Synagro, has been applying for permits to use more of it across the state border, on farms in Virginia.

A coalition of environmentalists, fishing groups and some farmers are fighting that effort. They say the contamination threatens to poison farmland and vulnerable waterways that feed the Potomac River.

These sewage sludge fertilizers “aren’t safe enough for farms in Maryland, so they’re coming to Virginia,” said Dean Naujoks of the Potomac Riverkeeper Network, which advocates for clean water. “That’s wrong.”

Virginia finds itself at the receiving end of a pattern that is emerging across the country as states scramble to address a growing farmland contamination crisis: States with weaker regulations are at risk of becoming dumping grounds for contaminated sludge.

In Virginia, Synagro, one of the nation’s leading providers of sludge for use as fertilizer, has sought permission to apply more sludge in rural Virginia, according to local filings. Synagro is controlled by a Goldman Sachs investment fund.

Kip Cleverley, the chief sustainability officer at Synagro, said in a statement that the fact that the fertilizer “may contain trace levels of PFAS does not mean that they are contaminated.” He said that Synagro continually adds new farms to its fertilizer program and that its decision to seek additional permits in Virginia was independent of any Maryland guidelines.

The fertilizer industry says more than 2 million dry tons of sewage sludge were used on 4.6 million acres of farmland in 2018. And it estimates that farmers have obtained permits to use sewage sludge on nearly 70 million acres, or about a fifth of all U.S. agricultural land.

But a growing body of research shows that this black sludge, also known as biosolids and made from sewage that flows from homes and factories, can contain heavy concentrations of harmful chemicals called per- and polyfluoroalkyl substances, or PFAS. Those chemicals are thought to increase the risk of some cancers and to cause birth defects and developmental delays in children.

For people in regions like Virginia’s Northern Neck, the “Garden of Virginia” that is the birthplace of George Washington, the threat feels doubly unfair: Much of the biosolids moving across state lines come from big industrial cities like Baltimore.

The contamination, locals fear, will wash off the farmland and into the region’s rivers and creeks, and will hurt the farmers and watermen who live side by side.

“The water just runs off from the farmland into the water,” said Lee Deihl, a seventh-generation waterman who owns the Northern Neck Oyster Company, as he maneuvered an oyster boat through a winding tributary of the Potomac. “And we get some pretty big rains this time of year.”

His concerns are not unfounded. New research published in the scientific journal Nature found that PFAS in sludge applied as fertilizer can contaminate both farms and surrounding rivers and streams.

“That stream might be the headwaters to your drinking water, further downstream, or the chemicals might be bioaccumulating in fish,” said Diana Oviedo Vargas, a researcher at the nonpartisan Stroud Water Research Center, who led the federally funded study. “There’s a lot we don’t know. But these contaminants are definitely reaching our surface water.”

It is a tricky problem. Fertilizer made from sewage sludge has benefits. The sludge is rich in nutrients. And spreading it on fields cuts down on the need to incinerate it or put it in landfills. It also reduces the use of synthetic fertilizers made from fossil fuels.

But the sludge can be contaminated with pathogens as well as chemicals like PFAS, research has shown. Synthetic PFAS chemicals are widely used in everyday items like nonstick cookware and stain-resistant carpets, and are linked to a range of illnesses.

The E.P.A. regulates some pathogens and heavy metals in sludge used as fertilizer, but it does not regulate PFAS. This year, for the first time, the E.P.A. warned of the health risks of PFAS in fertilizer made from sewage sludge. The Biden administration last year also set the first federal PFAS drinking water standards, saying there was virtually no safe level of the chemicals.

The lack of federal rules on PFAS in sludge has left states in charge, leading to a hodgepodge of regulations and the diversion of contaminated sludge to states with weaker regulations.

Maine banned the use of sludge fertilizer in 2022. Since then, some of its sewage sludge has been shipped out of state because local landfills can’t accommodate it, local officials have said.

Maryland temporarily halted new permits for the use of sludge as fertilizer. The Maryland Department of the Environment also ordered PFAS testing at sewage treatment plants across the state. It found contamination in the wastewater and sludge, even after the treatment process, and now has adopted guidelines, albeit voluntary, that say sludge with high levels of PFAS should be reported and disposed of.

In Virginia, the groups opposed to Maryland’s sewage imports are urging the state to start regulating PFAS in sludge.

But in the meantime, tens of thousands of tons of Maryland sludge are already heading to Virginia, according to data from Virginia. Biosolids from 22 wastewater treatment plants in Maryland have been approved for use as fertilizer in Virginia, and all 22 of those plants have reported PFAS contamination in their biosolids, according to an analysis by the Potomac Riverkeeper Network.

In Westmoreland, a rural county in the Northern Neck, Synagro has reported applying sludge from 16 wastewater treatment plants in Maryland, all from facilities that have reported PFAS contamination.

In December, Synagro applied for a permit expansion that would allow it to apply sludge on 2,000 additional acres of agricultural land in Westmoreland, more than doubling the total. After comments filed by local residents prompted a public hearing, Synagro withdrew its application, though it has told Virginia regulators it intends to reapply.

In neighboring Essex County, Synagro is seeking to apply sludge to an additional 6,000 acres, increasing the acreage by nearly a third, according to its permit application.

Mr. Cleverley of Synagro said the biosolids the company applied in Virginia met Maryland’s PFAS guidelines.

Irina Calos, spokeswoman for Virginia’s Department of Environmental Quality, said her state had yet to see a significant increase in the amount of Maryland biosolids being applied in Virginia. She said the state was still reviewing Synagro’s applications to increase its acreage in Virginia.

Ms. Calos also said Virginia was not aware of any Maryland biosolids with levels of PFAS higher than what was recommended in Maryland. Environmental groups have countered that it is difficult to verify.

Jay Apperson, a spokesman for Maryland, said the state’s guidelines and testing requirements aimed to protect public health while also supporting utilities and farmers.

Robb Hinton, a fourth-generation farmer, has grown corn, soy and other crops on Cedar Plains Farm in Heathsville, Va., southeast of Essex and Westmoreland counties, for 45 years. He fears farmers in the Northern Neck are being misled.

“When people are giving you something for free, or nearly free, it sounds attractive, and I don’t fault any farmer trying it,” he said. But they had to remember that “it’s these big cities that are bringing their waste to us,” he said.

“I didn’t know about PFAS until I was talking with my watermen friends,” he said. “I can’t understand how Virginia doesn’t test for this.”

Synagro has also been directly lobbying farmers and other local residents. At a presentation in March, a Synagro representative, together with a researcher from Virginia Tech, distributed data from a study that appeared to show that fields that had received sludge fertilizer had only a third of the PFAS levels of fields that had not, according to attendees as well as presentation slides reviewed by The New York Times.

Synagro said it could not provide the full study because the company was not involved in it. The Virginia Tech researcher named on the materials did not respond to requests for comment.

At a meeting of Virginia’s State Water Control Board in March, Bryant Thomas, the Virginia Department of Environmental Quality’s water division director, said the public had submitted 27 comments on Synagro’s plans to expand its use of sludge in Essex County. Of those comments, 26 expressed concerns over the effects of the sludge on public health and wildlife, including shellfish, he said.

The board subsequently requested that the agency study the issue further and report back.

“I think it’s interesting that Maryland is working on their rules and regulations, but then they’re sending their biosolids to us in Virginia,” Lou Ann Jessee-Wallace, the water board chairwoman, said in an interview. “We in Virginia are going to have to be on our toes to make sure that we are taking care of our water and our citizens.”

Experts say Maryland’s approach is a good first step. But even in Maryland, a bill that would have strengthened PFAS limits in biosolids failed at the last minute. And “we’re concerned about the patchwork of regulations among states,” said Jean Zhuang, a senior attorney at the Southern Environmental Law Center, an environmental nonprofit group. “The federal government needs to play a bigger role.”

President Biden had been set to propose a rule that would have limited how much PFAS industrial facilities could release in their wastewater. The Trump administration has pulled back that proposal, though recently said it could develop its own effluent limits.

Across the South, the center has already been pressing wastewater treatment plants to get local factories and other industrial facilities to clean up their wastewater before it reaches the treatment plant. That forces polluters to control pollution at the source, or even phase out the use of PFAS entirely, Ms. Zhuang said.

“If wastewater treatment plants acted, industries would be the ones paying for their own pollution,” she said, “and not the families and communities that rely on farms and pastures for their food, water, and livelihood.”

One recent evening, Michael Lightfoot, a waterman, went out to bring up a wire-mesh cage of oysters he cultivates in Jackson Creek, where he lives with his wife, Phyllis. After a nearly three-decade career with the federal government, he retired in 2012, and has been a full-time waterman since.

Mr. Lightfoot is part of an oyster cultivation boom in Virginia, which is now the East Coast’s biggest oyster producer and among the biggest producers in the nation. But his proximity to contaminated farms worries him, he said. “There is no farm field that doesn’t drain into our waterways,” he said.