Mink in the Hudson: A Region’s Pollution
By: Ronald Smith
Tags: Environment, Pollution

By RJ Smith

A quick look at the Hudson River (photo taken by the author).

A mink in its natural habitat. Photo taken by Brady Dillsworth.

Mink are among many aquatic species that call the Hudson River their home. General Electric is responsible for dumping roughly 1.3 million pounds of PCBs into the Hudson between the years 1947 and 1977. Mink feast on fish and insects that exist in the river’s ecosystem, something that acts as the mink’s primary exposure to PCBs. According to a study published on mink’s dietary exposure to fish in the Hudson River, mink experience lesions in the jaw. They can’t reproduce as well as they normally can. Their babies also have a higher chance of dying. In 2005, GE signed a decree from the EPA to dredge the Hudson in an attempt to remove some of the PCBs in the water and sediment.

The sun starts to set on the horizon. A chill breeze sweeps across the area next to the Hudson River. Alex Wolf, a scientist that works with Scenic Hudson, watches the tranquil river. The surface of the water glitters beneath the setting sun.

“It all starts in the ecosystem,” Wolf says. “An insect gets a lot of PCBs from the contaminated environment. Then a fish comes and eats that insect. Then a bigger fish comes and eats the smaller fish. A mink comes along and eats the bigger fish, accumulating a lot of PCBs into its body.”

A mink observing its surroundings. Photo taken from Shutterstock.

By nature, mink are solitary animals. Males and females typically only associate with each other during the breeding season, which occurs during the winter. Female mink become sexually mature after one year of age. While pregnant, they tend to make den sites in the cavities of tree roots, rock piles, brush piles, and log jams or beaver lodges. A mink’s most used den sites are in the bank burrows of muskrats and other animals.

A new life is born after only 51 days of pregnancy. On average, a female mink will give birth to between 1–8 offspring, with 4 being the average. Their offspring are born mainly between April and June.

Mink cannot see when they are born. Their bodies lack hair. Baby mink are weaned at 6 to 10 weeks. During this time, they are completely dependent on their mothers. The mink that depend on the Hudson for survival grow independent anywhere from 6 to 10 months of life.

Furthermore, research has found that mink are more abundant in areas beyond the Hudson River.

Wolf says PCB exposure means mink populations don’t thrive as well on the Hudson as they do on the Mohawk River, which is the Hudson’s largest tributary. . “We know that mink in the Hudson River are less abundant than in the Mohawk River,” Wolf says. “The Mohawk River is similar to the Hudson River in a lot of ways, but has lower PCB contamination levels. There were 108 mink found in the Hudson River, while 208 mink were found in the Mohawk River. You can infer that the Mohawk River is less problematic for mink, since they exist in a greater quantity there.”

A data visualization comparing the number of mink in the Hudson to the number of mink in the Mohawk.

Mink live throughout New York, as well as most of the United States and Canada. They stick to streams, rivers, lakes, and freshwater and saltwater marshes and coastlines. Mink are nocturnal. A lot of their time is spent feeding on fish, birds, small mammals, amphibians. They are most commonly seen close to streams and creeks the day after light snowfall.

Nonetheless, the pollution present in the Hudson River has had various uses.

Polychlorinated biphenyls, also known as PCBs, are industrial products or chemicals. They build up in organisms through a process called bioaccumulation, which involves taking in PCBs from the environment over time. Biomagnification is a comparison between the concentration ratio in tissue present in a predator’s body and its prey. PCBs biomagnify along the food chain. This leads to higher amounts of PCBs in organisms that are higher up in the food chain. Accumulation of PCBs starts in soil. “PCBs from the Hudson River build up in invertebrates in river sediments,” said Margaret Byrne, an Assessment and Restoration Manager for U.S Fish and Wildlife Services. PCBs eventually end up contaminating insects and birds and mammals. When mink consume these mammals, they are directly exposed to PCBs.

For once, a mink stands still. Photo credits: John Reynolds

Furthermore, mink move around quite a bit. Their diet depends heavily on what is available to them in their current environment. Though they depend on aquatic environments, they will roam far from the closest stream in their quest for food. “Mink really are a bridge between the aquatic and terrestrial environment,” says Sean Madden, a researcher that works for the New York State Department of Conservation. “They like cover, both for denning and for finding prey, so things like downed logs, undercut banks, rock piles, and shrubs can be important parts of their habitat. One of the real drivers of mink on the landscape, which can be equally as important (really they are linked) is prey availability. When mink are on the move, they are pretty much constant foragers, and they will opportunistically eat a lot of different things. If they find an easy and reliable food source, they will exploit it.”

The significance of mink to the region dates back several centuries, during Henry Hudson’s life. Mink fur can be considered an exotic item, particularly due to being an indication of wealth. “Mink were a historically important fur species and part of a thriving trapping and fur trade,” says Madden. “If you think about it, European settlement in New York was inextricably linked to furs. Only a few years after Henry Hudson sailed up the Hudson, there was a Dutch fur-trading post around current Albany. Of course, beaver was the big draw, but there was a trade for all furs, including mink.”

Violence against mink is a problem that continues today. “At one time in this country, owning a mink coat was a symbol of luxury and wealth,” said Madden. “Mink are still trapped for their pelts, but trapping pressure really depends on fur market prices. Generally, mink prices have been down in recent years and there are plenty of farm-raised mink pelts to be had. Much of the fur market is now driven by overseas markets primarily Russia and China.”

PCBs exist in and affect food webs. It all begins with the sediment. However, PCBs don’t naturally exist there. The sediment present in the Hudson River is contaminated as a result of GE’s actions. “PCBs can be bound to organic material in the sediment, so organisms, like benthic macroinvertebrates, living and feeding in the sediment can have direct uptake of PCBs,” said Madden. “PCBs can also move into the water column through suspended sediment (like after high flow events) and some amount of dissolving. So, things living in the water column also take up PCBs.”

Fish are among the many organisms that take up PCBs. They’re often exposed to PCBs through their gills. “Fish can accumulate PCBs from the water column across their gills, but also will get PCBs from their diet,” said Sean Madden. What does this mean for the mink? Mink are carnivorous. They love to feast on things like muskrats, rabbits, mice, chipmunks, fish, snakes, frogs and birds. Their primary form of PCB exposure is through the consumption of fish. “Fish that eat at higher trophic levels will have higher PCB concentrations,” said Madden. “Since mink eat a lot of fish (in some cases nearly half their diet is fish) they have a lot of PCB exposure in the Hudson River.”

Between 1947 and 1977, General Electric dumped about 1.3 million pounds of PCBs into the Hudson River. The source of the PCBs was two manufacturing plants in Fort Edward and Hudson Falls. This is problematic because there are people who are part of communities that depend on the Hudson for their drinking water.

A look at the General Electric plant at Fort Edwards. Photo credits: Paul Buckowski

“When they take the sediment out of the river, it’s very wet,” said Manna Jo Greene. “It has to be filtered. The water has to be filtered before it can be discharged back into the river. It is fairly easy to filter PCBs out of water. Thank goodness, because there are people who take drinking water from the Hudson.” During the dredging of the Hudson, people had to find water elsewhere. “People had to be rerouted during the dredging,” said Greene. “They had to make use of a nearby reservoir. They couldn’t use the Hudson River’s water as a drinking source.”

Manna Jo Greene’s article dives into the origins of PCBs, which can be traced back to industrial use. PCBs were used industrially in mixtures that were trademarked Aroclors. They were first used in carbonless paper and in adhesives and caulking compounds. Because they are They are hydrophobic, meaning that they can be filtered out of water by sticking to sand and silt. They are also lipophilic, meaning that they are stored in fatty tissue and can be harbored in the body for a lifetime. Greene also wrote that PCBs are able to “bioaccumulate in the fatty tissue of top predators,” which is where they are found in orders of magnitude greater than in the blood.

Microorganisms are the members of an ecosystem that are responsible for breaking down PCBs in soil and sediment.

A quick look at the concept of bioaccumulation. Photo credit: Wisconsin Department of Natural Resources

Studies have determined the impact of PCBs on natural resources present in the region. “Natural resources continue to be exposed to the PCBs that remain unremediated in the river and on the floodplain, and will continue to be adversely affected as a result of that exposure,” said Meagan Racey, a spokesperson for the U.S. Fish and Wildlife Service, one of the trustees behind the mink research. “Trustees are looking closely at the PCBs remaining in the river and their effect on future injury to natural resources, as well as how they influence damages and restoration.”

One group is held responsible for the damage caused by the presence of PCBs in the Hudson River — GE. “Under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), GE is responsible for damages and the restoration of the natural resources that were injured or will continue to be injured by PCBs left in the environment,” said Meagan Racey. “At the Hudson River PCBs Superfund Site, damage assessment efforts are currently ongoing. The Trustees’ goal is to represent the interest of the public, by measuring how much harm has been caused by PCBs and determining how much restoration is necessary to address this harm.” The fact that the public is being represented by the Trustees should make people optimistic about the river’s future. It is clear that the Trustees are attempting to ensure the public that progress will be made, as well as show that efforts are being made to fix the issue.

A study has determined that women who have been exposed to PCBs have had trouble being able to conceive. The ability of sperm to move has been discovered to decrease as the presence of PCBs in men’s blood serum increased.

The presence of PCBs in the Hudson River is a huge issue for the mink. “Mink use both terrestrial and aquatic habitats, so they will use the river, the shoreline, the floodplains, the tributaries, and the wetlands near the river,” said Madden. “Mink are almost constantly foraging and very opportunistic predators. Some of our recent work confirmed that the major portions of their diet (fish, frogs, and small mammals) are all contaminated along the Hudson.”

According to Madden, the way forward is clear. “The dredging remedy was a good step. It removed a lot of PCBs from the Hudson River. But it also left a lot behind,” he said. “We need to continue to monitor PCBs in the sediment, fish, and other biota to figure how the river is responding to the clean-up and what else needs to be done.”

Madden said DEC officials are pushing for an investigation of PCBs in the lower river tidal estuary to better understand the nature and extent of contamination there. “We still need to work on a clean-up of the upper Hudson River floodplain,” he said. “PCBs are not the only contaminant out there. We need to pay attention to emerging contaminants, like PFOA/PFOS, and ones we may not even know of yet.”

Madden explained that humans in the Hudson Valley who eat fish from the Hudson River may face similar hazards from PCB exposure. “That’s a big question and a complicated one with varying perspectives. Some obvious impacts are the fish consumption advisories and regulations of the fisheries from the contamination,” said Madden. “The Hudson from Hudson Falls to the Federal Dam at Troy is take none/eat none fishery. You can fish there, but you can’t keep the fish.”

There is a process through which PCBs become harmful to mink. The effects of this process transfer to the mink’s offspring. “Toxicity to PCBs in mink is mediated through the aryl hydrocarbon receptor (AHR). For mink exposed to PCBs, the risk seems to be worse for their offspring,” said Madden. “For example, female mink exposed to PCBs in the lab have litters with severe kit mortality. Mink exposed to PCBs in the lab, develop these severe jaw lesions, which eventually cause the teeth to fall out and jaw bone, although this has rarely been observed in the wild. Also, there is evidence of organ abnormalities with PCB exposure.”

How has the General Electric Company (GE) responded to all of this? Greene said the relationship between GE and the PCB cleanup process involves quite a bit of flip-flopping. “Their tune has changed to say, ‘What a great job’ they did,” said Greene. “They’ve said that there was no problem. They then went on to say that they’ve done a great job with the clean-up.”

Madden said more research is needed to figure out what difference the GE cleanup has made on the mink population and whether more dredging is needed in the upper Hudson.

The presence of PCBs in the Hudson River has led to a disproportionate impact on people. “Clearwater made a connection with our 1993 Angler survey,” said Greene. “By interviewing people fishing at the waterfront, we determined that people were eating the fish despite the health advisories, and also doing so with disproportionate impact on communities of color and low income.”

In Wolf’s office, a shelf positioned against the wall is lined with books. Wolf takes a moment to speak.

“One way to make an impact is to contact state and federal officials,” says Wolf. “I know that most of the valley’s elected officials — state and federal — as well as Governor Cuomo have taken a stand. I think it would be helpful for them to hear from local citizens about this being an issue that really matters. Bringing political influence to bear on the EPA will help make sure that GE continues its cleanup of the Hudson.”

What does the future hold? Recently, the EPA decided to issue a certification to GE. This certification was awarded to GE to denote that the company has completed activities that were components of the remedy selected for the upper Hudson River. This has not been met without resistance, since the state has pushed back against this decision.