Mink dive deep into the depths of New York’s Hudson River to hunt frogs and fish. Scurrying along the river shore, they nose around in the dirt, building dens.

But their food and shelter are giving them heavy doses of industrial chemicals, which could be killing their babies and jeopardizing their populations.

In a new study, farm-raised mink were fed fish caught in the upper Hudson River, which is highly contaminated with polychlorinated biphenyls (PCBs). Kits born to the parents that ate the compounds were much more likely to die than the kits of those that ate less-contaminated food.

“Based on the kit mortality, we believe PCB contamination is causing decreased abundance and density of mink in the upper Hudson River,” said Kathryn Jahn, a U.S. Fish and Wildlife Service biologist who worked closely with Michigan State University researchers on the study.

All of the kits from 15 mothers that ate no PCBs survived, along with 96 percent of those from the 10 mothers that ate the lowest amounts. But in the four groups fed increasing amounts of the chemicals, all 50 kits died – most within 10 weeks.

The region’s wild mink consume similar amounts of PCBs. As a result, it’s likely that large numbers are stillborn or dying young in the wild, too, the scientists said. “A diet comprised of less than 10 percent fish with these environmentally relevant PCB concentrations could be expected to result in kit mortality,” the study authors wrote.

For decades, scientists have known that mink are more sensitive than other animals to reproductive and immune damage from PCBs, but it remains a mystery as to why.

About two feet long with luxurious fur, mink are found throughout much of the United States and Canada in places with abundant marshes and other wetlands. Dependent on water for food, they dive into rivers and lakes to eat muskrats, chipmunks, fish, frogs and birds. They are trapped and farmed for their soft pelts.

Mink numbers appear stable, according to the New York Department of Environmental Conservation. However, trapping data suggest that the Hudson River populations are smaller than elsewhere in the state.

The new study builds on two similar studies in which mink fed PCB-tainted fish from Michigan’s Saginaw Bay and Massachusetts’ Housatonic River also had large numbers of kits die.

Since they’re near the top of the food chain – rarely falling victim to predators – mink accumulate large quantities of chemicals, said Niladri Basu, a University of Michigan professor who studies fish and wildlife as indicators of health hazards.

As a sentinel species, their health is indicative of the surrounding ecosystem’s health.

“At a regional or local level, these chemicals’ affect on populations should be a concern,” Basu said. “These isolated areas like the Hudson River and the South River in Virginia, where there used to be a Dow facility, show [mink] are really struggling with PCBs and mercury.”

The Hudson River is one of the largest, most contaminated Superfund sites in the country. From the 1940s to about 1976, two General Electric plants released an estimated 1.3 million pounds of PCBs into the 315-mile river. Now banned, the chemicals, which were used largely as insulators in large electrical equipment, have plagued the river since because they linger in the environment.

People have been warned for four decades to avoid eating most fish from the river. PCBs are linked to many human health effects, including cancer and reduced IQs in children from Great Lakes states.

As early as 1982, scientists began documenting elevated PCBs in mink along the river. Within three miles of the river, about half of them have levels in their liver above the threshold for health problems, according to a report from the National Oceanic and Atmospheric Administration.

And the problem isn’t going away; their PCB levels have stayed the same for about three decades. Similarly, average PCB levels in the fish of the Upper Hudson have not changed significantly in recent years, according to the Environmental Protection Agency.

“There are just a lot of PCBs here and they don’t break down,” Jahn said. “Sediments, water, fish, birds, bats, shrews, insects, mink, everything we study in the Hudson River is contaminated with PCBs.”

The contamination is a concern for the mink farms scattered throughout the region.

Michael Whelan, executive director of Fur Commission USA, a trade association for fur farmers, said chemical concerns are one reason that mink farmers in upstate New York don’t feed much fish to their animals.

“The food is localized in most cases. In some Great Lakes states and the Pacific Northwest farmers may use some wild fish in the feed,” Whelan said. “But in places like upstate New York, they mix in more cheese, beef and poultry now.”

However, domestic mink that escaped farms had higher PCB loads than their wild counterparts along Lake Erie, in a 2012 study from researchers in Canada. While they could have been fed tainted food at the farms, it’s possible that escaped mink aren’t good hunters and eat things more likely to be contaminated, said Jeff Bowman, a research scientist at Trent University and the lead author of the study.

“We watched one mink – an escaped mink that had some of the highest PCB levels – walk up and down the beaches at Lake Erie eating zebra mussels, which filter sediment” that is highly contaminated, Bowman said.

Adult mink also may be at risk. In addition to the kit deaths, researchers linked the PCBs-tainted Hudson River fish to jaw lesions and altered organ sizes in adults.

The mink research will be used to help determine if cleanup efforts at the river should include specific provisions to help the animals recover. Increased dredging of sediment, dam removal and adding more plant cover are all possible remedies, Jahn said. Dredging, funded by General Electric under a Superfund cleanup, already has begun on sections of the upper river.

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.