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Fishing for Answers in the Willamette River

Fishing for Answers in the Willamette River header image
A team of OSU scientists explores one of the mysteries of the Newberg Pool.

It began more than a decade ago. Little fish with crooked backs were found living in a stretch of the Willamette River near the town of Newberg, just south of Portland. The little fish, relatives of minnows and most native to the river, got people worrying about what could cause such deformed skeletons in fish. Were they deformed by unseen poisons that could endanger human health as well? A brand new $47 million water treatment plant sat almost idle a little ways downstream on the Willamette River at Wilsonville. People refused to drink the water. What was in the Newberg Pool?

The Oregon Department of Environmental Quality had spent years searching for toxic chemicals that would explain the fish deformities. Their studies confirmed that more than half of some species sampled in the Newberg Pool had kinked or crooked backbones, a much higher frequency of deformities than they had found in fish living farther upstream. But the DEQ studies were not able to find any significant difference in chemical contamination between the Newberg Pool and sites they’d sampled farther upstream. The water quality was the same, but the fish were definitely different. What was going on in the Newberg Pool?

With more questions than answers, concern grew in the communities along the lower Willamette River. In 2001, state representative Mae Yih of Albany and legislators from the Portland Metro area called on Oregon State University to find out what was causing fish deformities in the Newberg Pool. “This was a researchable question, not a mystery of nature,” said Larry Curtis, head of OSU’s Department of Environmental and Molecular Toxicology, “and I knew we had the science and technology to find the answer.”

Skeletal deformities can be caused by many different things — toxic chemicals, infectious diseases, hybridization and more. So instead of focusing strictly on water quality, Curtis engaged OSU faculty from many different disciplines across the Agricultural Experiment Station to examine the question from several different angles.

“Each person came to the study with their own theories of what could be causing these skeletal deformities,” Curtis said. “The collaboration across disciplines made it possible to do a comprehensive study that cross-examined evidence from many different perspectives.”

Larry Curtis and laboratory zebrafish

OSU toxicologist Larry Curtis used laboratory zebrafish among other species to test the effect of highly concentrated river water on developing fish. Photo: Lynn Ketchum

With $500,000 from the Oregon Watershed Enhancement Board and two years to complete their report, the scientists went to work in 2002. Almost immediately, they discovered surprises and new challenges.

Doug Markle, a professor of fisheries and wildlife at OSU, had known about the Newberg Pool deformities for several years. He had searched the preserved specimen collections at OSU and beyond to see if such deformities had ever been observed in the past. They had. His search took him to the Smithsonian Institution in Washington, D.C., where he found three northern pikeminnows that had been collected from the Willamette River by a scientific expedition in 1855.

“We had x-rays taken of the three preserved fish,” Markle said, “and one of them had skeletal deformities exactly like what we’re seeing now in the Newberg Pool.”

OSU researchers sampling river water x-ray of fish with bent spine

OSU researchers designed sampling equipment that would absorb dissolved chemicals from the river water just like a fish or human would. Photo: Kim Anderson


When the OSU research team examined skeletal tissue in relation to x-rays, they found tiny parasites wedged into the bones of deformed fish. Photo: OSU Center for Fish Disease Research

Next, Markle’s team headed to the field to determine the distribution of deformed fish in the Willamette River. Sampling fish along the 150-mile stretch between Newberg and Corvallis, they confirmed DEQ findings that the Newberg Pool had twice the number of fish deformities than upstream near Corvallis. But by sampling in between, they found that the distribution of deformed fish was not a simple gradient.

“We found another hotspot about halfway between Newberg and Corvallis, near the Wheatland Ferry,” Markle said. “But between the two hotspots — Wheatland and Newberg — we found a very low incidence of deformed fish.”

Although they found no geographic pattern of distribution, they did find a biological pattern. “We found that fish species with the highest incidence of spinal deformities were broadcast spawners,” Markle explained. “That means they release their eggs into the water and let the current disperse them. The young, newly hatched fish swim into shallow water to avoid being eaten by larger predatory fish. Other fish species rear their young in nests further offshore, and we found that those species have a far lower rate of spinal deformities.”

Markle’s team also found that among the broadcast spawners, such as northern pikeminnow and chiselmouth chub, young fish had a higher incidence of spinal deformities than their older relatives. And they found that fish that hatched earlier in the season, from May to mid-July, also had higher rates of skeletal deformities.

“Because we know that skeletal deformities can be caused by many chemicals — organophosphates and heavy metals, for example — water chemistry was a large part of the study,” said Curtis, an expert in environmental toxicology. But characterizing water chemistry in a body as large as the Willamette River would be a challenge.

“The Willamette River is not an homogenous pool of unchanging water,” explained Kim Anderson, director of OSU’s Food Safety and Environmental Stewardship Program. “Its chemistry changes in pulses, currents and seasonal differences that can concentrate some chemicals and dilute others. If you take a sample in the afternoon you could miss a pulse of chemicals released in the middle of the night.”

To further complicate matters, the chemists needed precise measurements of only the dissolved contaminants that could be absorbed by fish or humans. Measurements of total contamination in the river would blur their results. So Anderson’s team designed and built sampling equipment that functioned like surrogate fish, simulating how a living creature would absorb dissolved contaminants from the river. Suspended in the water column, the model fish absorbed dissolved contaminants 24 hours a day, 7 days a week, from May through mid-July, when fish deformities were found to be most prevalent.

One surrogate fish, essentially a thin plastic tube filled with a kind of vegetable oil, absorbed organophosphates in the same way fatty tissues do in fish or humans. The other surrogate fish looked like a plastic milk jug lid and was filled with a resin that would absorb heavy metals.

The chemists knew that the contaminants they were trying to track could be so dilute as to be undetectable using laboratory methods specified by the U.S. Environmental Protection Agency (EPA). So, Anderson’s team developed new analytical methods that were 1,000 times more sensitive than the EPA methods, that could detect chemical compounds diluted to fractions of one part per trillion.

Anderson put that tiny fraction into perspective. “One part per trillion is one second in 32,500 years,” she explained. “Or, if you put one orange golf ball on the football field at OSU’s Reser Stadium and added one trillion white golf balls, then the stadium would need to be one mile tall.”

Even at this extraordinary level of laboratory precision, the chemists found that most of the target chemicals in the Willamette River were still below their limits of detection. They examined river sediments for persistent organic toxins, and the few they were able to detect were far below any minimum exposure levels set for human health. They even removed the ovaries from a sample of pikeminnows just before spawning to see if there were traces of toxins in the eggs that could disrupt bone development in young fish. They found nothing that would explain the high rates of fish deformities in the Newberg Pool.

OSU fish specimens collection

Preserved fish specimens, such as these in the OSU museum collection, helped researchers document that spinal deformities have been found in Willamette River fish since the pioneer days. Photo: Lynn Ketchum

Still, the researchers challenged themselves. Perhaps, they argued, there were other chemicals in the river that could contribute to fish deformities besides the target compounds they were monitoring. Or perhaps one chemical, that by itself was harmless, could become toxic in combination with trace amounts of other seemingly harmless chemicals.

OSU toxicologist Jeffrey Jenkins took up the challenge.

Because you can’t analyze river water for every possible chemical contaminant mixture, Jenkins designed a test to expose fish in the laboratory to organic contaminants concentrated from river water. Jenkins and his team collected water samples from the Newberg Pool and other locations in the Willamette, then concentrated the water into extracts that intensified the dose of existing contaminants. In the laboratory, they reared fish in these various water extracts and examined them for spinal deformities or other irregularities.

Jenkins’ team found that very few fish, two percent or less in each water extract, developed spinal deformities similar to those found in river fish. Finding no differences among the various water extracts, Jenkins found no evidence that unknown elements in the river water could be linked to fish deformities.

Examining every angle, the OSU researchers were not able to find a connection between water chemistry and fish deformities. But the concern expressed by people living along the lower Willamette was as much about their own health, and their doubts about the new water treatment plant, as it was about fish. Was Willamette River water safe to drink? Jenkins took his research further to consider how much risk to human health was posed by chemical pollutants in the Willamette River.

It’s impossible to calculate the risk from chemicals you can’t even detect. So Jenkins examined data from water samples collected by the U.S. Geological Survey from upstream tributaries of the Willamette. He hoped to find measurable amounts of pesticides before they were diluted by the water in the main stem river. Testing for the occurrence of nearly 100 different components of pesticides, he detected the presence of fewer than half, all at extremely low concentrations. Assuming these chemicals could make their way to the main stem, Jenkins calculated what the concentration of those pesticides would be in the Willamette at the point where river water entered the disputed water treatment plant at Wilsonville. Jenkins compared his calculations with drinking water standards from EPA and the World Health Organization. The calculated pesticide levels fell far below the allowable limits, a thousand to a million times — in one case a billion times — below the accepted limits for drinking water.

The Willamette River water quality was passing every test. So what was causing the fish deformities?

Michael Kent, director of the Center for Fish Disease Research at OSU, had cultured tissues from the deformed fish, searching for evidence of bacteria or viruses. He had found nothing. But when he examined the skeletal tissue of deformed fish in relation to x-rays that Markle provided, he found tiny parasites wedged into the bones of the little fish.

Parasites live complicated lives. The most prevalent parasite Kent’s team found was a kind of fluke that begins its life inside a snail. Later it’s released into the water where it infects young minnows taking shelter in the shallows. The fluke parasite drills into the bones of newly hatched fish, then encases itself in a cyst that disrupts normal bone development. Minnows with deformed backs swim slowly and awkwardly. They’re more visible and therefore more likely to be eaten by birds, the ultimate host for the reproductive stage of the parasite’s life cycle. Inside the bird, the parasite reproduces and its offspring are excreted, finding their way back into snails, beginning the cycle again.

The biologists confirmed the presence of snails in the shallow water where young broadcast-spawning minnows seek shelter.

Kent examined the tissues of hundreds of deformed fish collected from four sites between the Newberg Pool and Corvallis. In more than 80 percent of the fish he found two kinds of parasites attached to the bone deformities.

One question lingered: were parasites actually causing the deformities, or were deformed fish simply more vulnerable to parasitic infection? Kent tested the question in the lab, exposing healthy laboratory-born minnows to infected snails. The laboratory fish developed curved spines, split vertebrae and other skeletal deformities to the same degree as those found in the Newberg Pool. Kent demonstrated that it was the presence of parasites when and where a fish was born that was the strongest predictor of skeletal deformities.

The evidence undeniably pointed to parasites. Other possibilities, such as water chemistry, infectious disease and toxic contamination, had been carefully examined but could not explain the deformities.

snail parasite snail pikeminnow

More than 80 percent of the deformed fish were found to have tiny parasites drilled into their spines. Photo: OSU Center for Fish Disease Research


Fluke parasites live part of their lives inside snails before moving on to infect small fish in the shallow edges of the river. Photo: Lynn Ketchum


An infected pikeminnow, less than an inch-and-a-half long, has a crooked spine characteristic of many minnow-like fish from the Newberg Pool. Photo: OSU Center for Fish Disease Research

“Such lack of evidence from any single investigation would seem to have little significance,” Kent said, “but the negative results from so many lines of investigations served to strengthen the positive results we found with parasites.”

Discovering the link between parasites and fish deformities answered some questions and prompted more. Why, for example, is there a higher incidence of parasitic infections in the Newberg Pool than elsewhere in the Willamette basin? Doug Markle speculated that perhaps there are more snails in the Newberg Pool or fish with a greater susceptibility to parasites. In any case, unlike toxic chemicals, the parasites pose little or no risk to human health. Cooking or freezing will kill the parasites in infected fish.

On time and on budget, the OSU scientists delivered their report in July, 2004, with a public hearing in Wilsonville to explain to the community what they had found. Both the supporters and the detractors of the new water-treatment plant were pleased with the report’s results.

“That’s a sign we’ve been an honest broker of information and produced a balanced report,” Curtis said. “There are new questions that would be interesting to pursue, but this wasn’t an invitation for open-ended research. We were called on to answer one question — what’s causing fish deformities in the Newberg Pool? — and we answered it.”

Published in: Ecosystems