Decline in Catfish Tumors Poses Pennsylvania Puzzle

It’s a decade-long scientific whodunit.

For years, researchers tried to figure out why so many bullhead in Presque Isle Bay had tumors. Now they’re trying to unravel a twist that is just as mysterious: Why has that cancer rate dropped so precipitously since the late 1980s?

It might be the millions of dollars Erie has spent to cut sewage overflows. Or maybe it’s that some of the big industrial polluters have closed. Or it could just be evolution: The catfish are adapting naturally to cope with the pollution.

The bay is formed by a thin sand spit reaching into Lake Erie from the industrial city. Long polluted by direct discharge of industrial sewage and municipal sewer overflows, the bay is in the process of being cleaned up. The city has spent millions to upgrade a wastewater treatment plant and millions more to stop the overflows that sent untreated sewage into the bay during heavy rains.

The city was up for a national anti-pollution award, and Erie might be able to take credit for the improved health of the resident bullheads too--if, that is, anyone knew what caused the tumors in the first place.

“We don’t really have a clue why,” said Eric Obert, who runs the region’s Sea Grant program, an arm of the National Oceanic and Atmospheric Administration.

The catfish, researchers have found, are a good tool for tracking pollution. If the water isn’t safe for the bottom-feeding bullheads, it might be a warning for humans.

“Bullheads are probably kind of a canary in a coal mine,” said Jack Vanden Heuvel, a Penn State molecular toxicologist. “They’re a sentinel kind of animal to tell us if there is a problem.”

The latest research on the cancerous catfish suggests what was assumed from the start: Polluted sediment is to blame.

Vanden Heuvel examined 40 sediment samples collected last year and found “dioxin-like activity” from any number of thousands of industrial pollutants.

But if the pollution is still there, why is the tumor rate down? Vanden Heuvel doesn’t know. He still needs to test the samples from the early 1990s to determine whether toxin levels have decreased.

“We could see if the dioxin-like response is stronger in the past than it is now, which would be a sign that the area is cleaning up.

“The other possibility,” he added, “is that the area is not cleaning up, but the fish have evolved. It’s not necessarily that the bay is getting better, but the fish are getting better at dealing with it.”

It was the 1980s when anglers first started noticing the tumors. In cancerous fish, red bumps clung to their whiskers, their lips turned puffy and red, and black spots dotted their bodies.

In 1990, Obert looked at 50 fish from the bay. An astounding 80% had skin tumors. Ten of the worst-looking fish were sent off to a lab in Maryland; four of them had liver tumors too. Two years later, a study of 110 bullheads found that 61% had skin cancer and 22% had liver tumors.

Then, in 1995, a new study found that just 10% of bullheads had liver tumors. In 1997 the rate fell to the single digits.

Researchers are still grasping for a way to explain that decline.

The first chemical to be investigated was a cancer-causing compound called nitrosamine. The bay had high levels of nitrogen after hot effluent from a power plant killed thousands of gizzard shad. That plant has closed.

Then they looked at PAHs, or polycyclic aromatic hydrocarbons, produced by burning fossil fuels. But catfish with high PAH rates didn’t necessarily have tumors.

Next they considered a virus.

No perfect answer popped up.

Paul Baumann, an Ohio State professor, related a story about how clams off a pristine Maine coast developed tumors. Nobody knew why, until they discovered a nearby blueberry farmer who sprayed his fields with pesticides, then washed his trucks in the bay.

“There is a cause,” Baumann said. “They just don’t know what it is.”

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On the Net:

Pennsylvania’s Sea Grant program:

https://www.pserie.psu.edu/seagrant/ seagindex.htm