OREGON STATE UNIVERSITY

OSU researchers discover high rate of liver cancer in trout

03/30/2000

CORVALLIS, Ore. - Researchers at Oregon State University have discovered an unusually high cancer rate in hundreds of rainbow trout at a research facility near Corvallis. One out of every 10 fish was found to have liver cancer, a rate 100 times greater t han the "normal" background rate established in 35 years of research at the facility.

Many fish also are showing severe anemia.

The researchers are now focusing on various potential causes for the cancer outbreak. There are no known fish tumor viruses that could cause such tumors, and nothing is known to have changed in the trout's feed that would account for the sudden cancer inc rease, according to George Bailey, director of the OSU Freshwater/Marine Biomedical Sciences Center, which uses the research facility.

This leads the researchers to suspect the water supply as a possible - and perhaps likely - source. The facility receives its water from a series of wells drawing from a shallow aquifer in the area just east of Corvallis, across the Willamette River. Stan dardized chemical and metal tests on the water have not yet revealed any significant contaminants.

"A great deal more work is needed to identify the contaminant involved, and its source," Bailey said.

The trout showing cancers were spawned from brood stock reared at the research facility. An additional group of trout imported last year as fertilized eggs from the Mt. Shasta hatchery in California also showed the same cancer rate when reared in the faci lity.

"We don't yet know exactly what we are dealing with or the potential risks to people living in that area," Bailey said. "No animal species, including rainbow trout, is an exact predictor of effects on human health. Trout can be extremely sensitive to some carcinogens but, on the other hand, their susceptibility in some cases may be equal to or less than humans."

Tim White, interim provost and executive vice president at OSU, said that while more testing and analysis remains to be done on the nature and source of the carcinogen, "we feel compelled in fulfilling our commitment to the public trust to communicate th is information now.

"While we cannot conclude today that this discovery constitutes a significant human health hazard to people using water in that area, we also cannot rule this possibility out," White said.

"Because of this possibility, we decided upon the course of engaging the proper public agencies and notifying the public," White added. "Indeed, it is fortunate that we have a world class research facility at that site which was conducting studies that ha ve served to alert us of a possible environmental problem."

The university is working with the Oregon Department of Environmental Quality, the Oregon Health Division, and the Linn County Health Department to further assess the situation and determine next steps. The Oregon Health Division, 541-752-7394, oversees p ublic health in Oregon, and the Department of Environmental Quality, 503-229-5983, investigates toxic spills and other environmental contamination.

This is the second incident in 15 months where fish have died or otherwise been affected at the OSU laboratory. In December of 1998, several thousand rainbow trout at the facility died within a 48-hour period. Researchers concluded the 98-percent mortali ty rate was caused by an unknown contaminant passing through the system. The 1998 contaminant could not have come from the trout food, Bailey said, because trout of all ages died, including those too young to be fed. "Therefore, we think it can only have come through the water supply."

Water is supplied to the area by a shallow aquifer, which has never been mapped. Fortunately, Bailey said, another nearby OSU fish research facility has suffered no problems from its water supply. That facility gets its water from the same general aquifer a mile away.

Bailey says it is possible that the recently discovered cancerous tumors were caused by months of exposure to a lower dose of the same toxic agent in the water. These tumors could not be detected earlier, he pointed out, because they take about nine mont hs to develop. Tests just confirmed the tumors to be cancerous.

The trout with cancerous tumors were "control" fish from a study conducted by Bailey, a leading national expert in cancer and cancer prevention. Bailey said the fish received a pure, standard diet formula that has been unchanged for the past three decade s of research. The researchers were surprised to observe the declining health of some of these control fish. Many fish in this ongoing study were smaller than expected and in obvious poor condition. Follow-up examinations revealed abnormally low productio n of red blood cells, or anemia.

When the study was completed, the control trout were examined internally and 10 percent of them were found to have developed the cancerous tumors.

Bailey, who holds the title of "Distinguished Professor of Environmental and Molecular Toxicology," says his colleagues have never seen such conditions in control fish. While it is of concern and needs further study, "it is too early to conclude that the re is a human health hazard."

"Trout can be more susceptible to things than you and I are," he said. "There is a compound, for example, called aflatoxin that the Food and Drug Administration allows in foods such as peanut butter at 20 parts per billion. However, when you give aflatox in to rainbow trout at this rate, it causes cancer in 40 percent of them.

"The flip side," he said, "is that there are examples where trout are less susceptible than humans to certain contaminants. And since we don't know what we're dealing with, we need to keep an open mind."

The fish research facility - known as the Food Technology and Nutrition Lab - is located just east of Corvallis in Linn County.