UNIVERSITY PARK, Pa. -- Researchers in Penn State's College of Agricultural Sciences are using bullheads -- a type of catfish -- as an indicator of the levels of the pollutant dioxin in Lake Erie's Presque Isle Bay.

"About five to 10 years ago, people fishing in Lake Erie began to report catching bullheads with tumors on their mouths and skin," explains Daniel Weinstock, senior research associate in Penn State's Animal Diagnostic Laboratory. "Cornell University did the initial evaluations of why these fish showed tumors, followed by a second evaluation by Pennsylvania's Department of Agriculture. Now, Penn State, doing a third evaluation, used molecular detective work to establish bullheads as an animal that can be used to monitor the contamination levels of toxic compounds over time."

Sponsored by a 1997 grant from Pennsylvania's Department of Environmental Protection, Penn State's research team focused on determining levels of dioxin, an environmental contaminant produced in minuscule amounts as byproducts of industrial processing and combustion. The project was spearheaded by Eric Obert, associate director of the Sea Grant program at Penn State Erie, The Behrend College.

The term dioxin describes a family of 75 related chemical compounds that are extremely toxic. The jungle defoliant Agent Orange, used extensively during the Vietnan War, contained dioxins. The pollutants found in the Love Canal environmental crisis also were dioxin compounds. Almost every human being carries traces of dioxin in their fatty tissue, and quantities can build up over time because dioxins, with a half-life of 12 years, break down very slowly within the body.

Bullheads were chosen as the species to observe and monitor for pollutant levels because they are bottom-feeding fish, and dioxin compounds tend to settle into the sediments at the bottom of bodies of water.

Weinstock, Tom Drake and Arthur Hattel, all veterinary pathologists at Penn State's Animal Diagnostic Lab, evaluated 100 fish for evidence of tumors caused by exposure to dioxin. Sixteen tissues from each fish were examined microscopically. "Traditional toxicology studies use laboratory rodents with controlled exposure to toxicants to assess the harmful effects of that substance," Weinstock explains. "The novelty of this approach is the evaluation of a wild population of fish to gauge levels of environmental pollution."

Previous studies of Presque Isle Bay bullheads showed a high incidence of skin and mouth tumors. The Penn State study showed the number of tumors had drastically decreased. "The big question is why," Weinstock says.

In order to fathom how dioxin might be affecting Presque Isle bullhead populations, the research team compared levels of dioxin in bile in the liver of fish -- with and without tumors -- with the levels of dioxin found in sediments at each collection site.

Jack Vanden Heuvel, assistant professor of veterinary science and a molecular toxicologist, used genetic research techniques to determine the dioxin levels within the sediments at each collection site in Presque Isle Bay as well as Eaton Reservoir, a nearby collection site away from Lake Erie. He started by developing a test that would allow researchers to "see" whether fish tissues contained dioxin.

"I combine luciferase, the enzyme that makes fireflies' bodies glow with genetic material that interacts genetically with dioxin molecules," Vanden Heuvel explains. "The higher the levels of dioxin, the more light is emitted."

Vanden Heuvel is using even more sophisticated cellular sleuthing to determine if the incidence of tumors in Presque Isle bullhead have been reduced over time. "We didn't see as many tumors in the last sample collection," Vanden Heuvel says. "We don't know if the reason is fresh sedimentation covering up dioxin-laden sediments, remediation efforts in the bay, or evolution. Since the levels of dioxin are still quite high, I suspect the reason for decreased tumors is natural selection."

In the coming year Vanden Heuvel will use a polymerase chain reaction (PCR) test to identify the unique genetic material in bullhead that is activated by interaction with dioxin compounds. Using this "genetic fingerprint" for dioxin, Vanden Heuvel can trace dioxin levels not only for bullheads collected for the Penn State research project, but also for fish samples collected previously.

"The PCR test allows you to set up an experiment in evolution," Vanden Heuvel explains. "If we examine samples collected 10 years ago and move toward the present day, we can get an idea of how dioxin levels have affected this environment. For example, if I test more recently collected samples and see fish whose genetic material is not affected by dioxin, then that suggests the bullhead population is genetically adapting through natural selection in order to survive in that environment."

Vanden Heuvel says the same genetic detective work also is adaptable for other pollutants. "You can pick a gene that is activated by metals such as cadmium or mercury, or even a particular herbicide," he says.

He also points out that the tests are easily adapted to other fish species. "We had to design all new testing procedures because bullheads are not normal laboratory test animals, nor are they related to other test animals," he says. "Now scientists can use these same techniques to gauge pollutant levels in any type of fish, from trout to bluegills. All you have to do is go out and catch them."

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EDITORS: For more information, contact Jack Vanden Heuvel at 814-863-8532. Daniel Weinstock can be reached at 814-863-0837, ext. 7.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax