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Research Magazine > ARCHIVE > Fall 92 > Article

by Judy Purdy

In at least one way, radioactive waste actually may benefit the environment.

"The presence of radioactivity keeps people away from an area," said Dr. F. Ward Whicker. "It's a preservationist idea. If it weren't contaminated, people would want to exploit it.

"In that sense, radioactivity at sufficiently low levels is good for the environment," he said.

By that measure, the Savannah River Site is a well-protected environment.

The federal nuclear materials production facility on the Georgia-South Carolina border harbors 300 square miles of semiwilderness area largely surrounded by barbed wire fence. And because it is basically off-limits to the public, the site "provides a unique opportunity for research," Whicker said.

"The site is akin to a national park in some areas, absolutely pristine and beautiful. I can do things here that I can't do anywhere else because it's undisturbed," he said.

What Whicker does is research in radioecology, how radioactive contaminants move through the environment -- land and water, plants and animals.

Scientists like Whicker have been tackling environmental research at the Savannah River Site (SRS) for more than 40 years, even before the first of five nuclear reactors at the site was built.

Their work on the transport and effects of radioactive isotopes, or radionuclides, in the environment is now helping others understand and evaluate contaminated environments like those at Chernobyl and the Nevada Test Site.

"I care about the science of radioecology because it affects the ultimate result that the average person is concerned about -- the quality of the environment," said Whicker, a senior research ecologist at the University of Georgia's Savannah River Ecology Laboratory (SREL), which operates on the site.

"Ultimately, I want to develop computer simulation models that will predict the transport of radioactivity in aquatic ecosystems and project concentrations and potential hazards in a hundred or even a thousand years," he said.

The ecology lab, which is under contract with the U.S. Department of Energy, began its work in 1951 when Dr. Eugene P. Odum, director emeritus of the university's Institute of Ecology, started conducting ecological studies of the plants and animals on the site. That work provided a baseline for monitoring the effects of nuclear materials production on the environment.

SREL scientists continue to compare that baseline with the data they are compiling today. Their discoveries are pivotal to understanding how radioactivity moves through soil, water and food chains.

For example, Whicker traces radionuclide movement through aquatic environments; his colleagues analyze blood samples from bass, test muscle tissue from birds, and take "whole body counts" of radioactivity in various vertebrates, including snakes, alligators and turtles.

In fact, radioactive turtles on the site were found purely by accident.

"In the late '70s someone found a turtle in a nearby seepage basin and brought it to the ecology lab," said Dr. J. Whitfield Gibbons, senior research ecologist and head of the SREL environmental outreach and education division.

As the man walked into a "counting" lab, he set off a sensitive radioactivity counter. The lab technician suspected radioactive mud on the man's shoes. Tests showed the mud was clean; the turtle was radioactive.

With that chance discovery, nuclear waste became an accidental ally of ecological research. It gave scientists a new way to track turtles or other organisms in the wild- just as radioactive isotopes can be used to trace substances in the human body.

Turtles that swam in certain SRS seepage basins emerged permanently marked by low, apparently harmless, levels of radiation. Gibbons and his colleagues have captured the turtles, measured radioactivity and other data, then released them unharmed. Their research has shed light on turtle natural history, from how far they travel to lifestyle differences between the sexes.

Unfortunately, those contaminated seepage basins aren't the only source of radioactivity at the site. In the early '60s, when all five nuclear reactors were operational, some uranium fuel rods in the "R" reactor leaked and radioactive isotopes escaped. Although "R" reactor was permanently shut down, the radioactive isotopes contaminated water that was, by necessity, discharged to the environment. Consequently, cesium-137, strontium-90, tritium, plutonium-239 and other radioactive isotopes were flushed into aquatic ecosystems, including two ponds that are the subject of intensive ecological research: Pond B and Par Pond.

What happened to those isotopes -- where they are and where they are not -- is now the focus of numerous studies by Whicker and others at SREL.

Radionuclide Research

Through the years, Whicker has consulted on almost every major committee or panel convened in the United States to assess or trace radiation fallout through the environment. And yet Whicker, America's acknowledged father of radioecology, said he needs to understand a lot more than he does now to develop computer simulation models for aquatic ecosystems at the Savannah River Site.

Whicker and other SREL researchers have been gathering data on how much radioactivity is still in Pond B and Par Pond -- and what, if any, effects it may have on the ponds and their inhabitants.

With UGA scientists Dr. John Pinder III, Mr. John Bowling, Dr. James Alberts and Dr. I. Lehr Brisbin, Whicker looked at the distribution and movement of radionuclides in Pond B, which received discharges of contaminated water from September 1961 to June 1964.

Surprisingly, their findings show that very little of the radioactive material released 30 years ago has escaped from local ponds and streams.

"The only radionuclides left now are longer-lived contaminants like cesium-137 and strontium-90, which have half-lives of about 30 years, and plutonium-239, which has a half-life of 24,000 years," Whicker said. In fact, the plutonium levels are so low they could not even be measured in the fish scientists collected. Releases of tritium at the site have far exceeded that of other radionuclides; however, tritium has a shorter half-life and disperses and becomes diluted with normal water. For the most part the isotopes that remain are locked up in the sediment of the ponds.

"Ninety-nine percent of the radioactivity is located at the bottom of the lake," Whicker said.

"If you have to put small amounts of radioactivity in the environment, a lake or reservoir is a pretty good place to do it," he said. "The escape of radioactive material through the pond food chain or by seepage is so low at the SRS that it is inconsequential."

Cesium-137, the predominant radionuclide in Pond B, accounts for 99 percent of the radioactivity in the pond. It is relatively easy to find and measure because it emits high-energy gamma rays that can be detected with sensitive instruments like scintillation counters. But other radionuclides -- like plutonium-239 and strontium-90 -- are much harder to find in the pond sediment. They emit alpha and beta particles that are hard to detect, and they occur in extremely low concentrations, said Dr. Sue Clark, an SREL research chemist.

In addition, these radionuclides "carry electron charges that influence how they behave in the environment," Clark said. For example, a positively charged isotope may stick to a negatively charged soil particle, such as clay. Some soil particulates are so fine they slip through the soil subsurface, carrying contaminants with them.

The alpha- and beta-emitting isotopes must be chemically separated, which was a labor-intensive and expensive process until recently, she said. Clark is among those who are trying to simplify the chemical separation process and to adapt new electronic technology to trace low-level radionuclide movement.

"Just because there is measurable contamination doesn't mean that it is dangerous or that it is having an impact on the wildlife or the plants or anything else," Whicker said. "At the concentrations in these lakes I don't believe there are any measurable physiological or ecological effects on vegetation and animals."

In fact, Whicker said he doesn't think there is any danger to populations of people living near American nuclear production sites.

"The thing about radioactivity that people don't quite realize is that we can measure levels that would convert to not very many atoms," he said. "In chemistry you can measure down to the parts-per-billion range. We can measure some radionuclides in concentrations that are a million times less than that.

"Even when doing dives in the lake [to collect samples], I never had a detectable personal dose reading," Whicker said.

Samples of pond sediment, which showed the highest levels of radioactivity in the pond, contained only minute amounts of radionuclides.

"Although the levels of radioactive material in the sediment are easily measurable with sensitive equipment, it is completely safe to be out there," said Whicker, who, quite naturally, tries to keep his radiation exposure as low as possible. "The radiation exposure that a person would get from these lakes is a very tiny fraction of what we get from the natural background radioactivity that occurs in the earth's crust and from cosmic radiation from space."

Researchers have examined all kinds of samples -- water, sediments, shoreline and submerged vegetation, invertebrates, fish and turtles -- for radioactivity. They've also examined coots, migratory birds that commonly feed in and around the pond, and "found no obvious impact that we can measure," Whicker said.

The pond is a "far healthier system than your typical fishing pond that people pollute," he said.

Among the vertebrates studied, fish contained the highest amounts of radioactive cesium, followed by the coots, which had slightly higher levels than the turtles.

Those results are partly explained by the fact that radioactive cesium tends to concentrate in the food web. Turtles and coots eat mostly plants, while the fish in the study eat mostly smaller fish and other animals.

Low concentrations of potassium and calcium in the water also are associated with the higher radioactive readings in fish. When potassium levels are low, organisms take up radioactive cesium as a substitute, and it ends up in their muscle tissue.

"The biggest radioactivity health risk at the SRS is radiocesium," Whicker said. "It builds up in the food chain, and that's why it's of concern. But if we were in the former Soviet Union, they would just chuckle at our problems. Ours are not even on the same scale as theirs."

Probes of Par Pond

Now that Whicker et al. have a handle on how cesium and other radionuclides move through Pond B and are absorbed by plants and animals, they have moved on to study Par Pond, a 2,600-acre reservoir 10 times bigger than Pond B.

Par Pond provides habitat and shelter for all kinds of organisms, from small fish and turtles to alligators and water fowl -- even the endangered bald eagle and wood stork. Because of its rich diversity of wildlife, Whicker calls Par Pond the site's "crown jewel" of wetland habitat.

Although it will take longer to study because it is so much larger, research results already are showing similarities between Par Pond and Pond B. For example, radiocesium is the main radioactive contaminant in both.

From their cesium studies, SREL ecologists are sure about one thing: Water is a good buffer for some types of nuclear contamination. It shields the surroundings from radioactive isotopes embedded in sediments and prevents sediments from drying out and blowing around, Whicker said. The presence of water also reduces contamination of the food chain.

But part of that buffer was removed from Par Pond more than a year ago when water levels were lowered to repair internal erosion of the dam. Now those sediments are exposed to wind, runoff, plant roots and even animals.

Because of dam safety and government regulations, officials are exploring alternatives concerning Par Pond. While many prefer to repair the dam, officials also are considering other solutions, including an expensive-- and potentially more damaging-- one: remediation of the exposed 1,300 acres.

Vegetation Invites Wildlife

Those contaminated sediments support vegetation that is a magnet for deer, wild turkeys and ducks, said Brisbin, a senior research ecologist who studies how animals transport radionuclides.

"Animals are coming in and grazing on the seeds and plants growing on those sediments," he said. "And they have the potential to leave the site and become food for hunters. Birds, especially, can move rapidly."

Limited harvesting of game also is permitted on the site. And although Brisbin said his findings so far show that ducks are "safe" to eat, safe is a relative term. It depends on many factors: a person's age, how much a person eats and how contaminated the duck meat is. Then there's the additional problem that other toxins, such as mercury, have been found in the lake and have worked their way into the food chain.

"We need to know as much about the food habits of hunters as we do about the behavior of [animals]," Brisbin said. "There's a big difference between a person who eats 50 ducks a year and one who eats two." And when it comes to larger animals like deer, "a hunter is likely to put the whole thing in the freezer. The unfortunate thing is that cesium accumulates and concentrates in the skeletal muscles that a man eats."

Brisbin also tracks cesium levels in feces of feral pigs found near Par Pond; those levels have risen since engineers lowered the pond's water level. Using a mathematical equation, he can predict the amount of contamination in pork muscle from the amount found in the feces.

His research shows the amount of radioactivity in an animal depends on such things as how much time the animal spends at the contaminated area, how recently it has been there and the level of soil contamination.

He also studies individual animals to determine if they reach a contamination equilibrium -- a stable level of radioactive contamination that won't rise despite continued exposure.

Using the old canary-in-the-mine ploy, he releases "sentinel animals" -- animals that are tamed or recapturable -- at contaminated areas and then measures their radiocesium intake through time.

"We've developed a special strain of bantam chicken that scratches in the dirt, picks up contamination, comes back and is put into a lead-lined, whole-body counting chamber," he said. Contamination levels are measured and the chickens are released unharmed.

Researchers use a number of creative ways to recapture sentinel animals, including clipping birds' wings or tracking them with special radios. Some are even trained to come to back to their handlers.

These experiments also have confirmed that some contaminants cause more problems than others. "The bottom line is that it depends on the contaminant," Brisbin said. For example, "chickens don't pick up plutonium because it is insoluble. You can't count it in their bodies. We ended up getting a lot of big `zero' data, which is comforting."

Small Genetic Changes

Recently another SREL group began looking for detectable genetic changes in organisms exposed to contaminants. "Changes in DNA are one of a series of biological changes that can be measured," said Dr. Michael H. Smith, SREL director.

The group found differences in DNA patterns between control animals and those that live in and around ponds contaminated both by radioactive and non-radioactive substances. But so far those differences are small.

"The appearance of altered DNA patterns is relatively low -- 6 percent in Pond B," Smith said. "And the genetically different organisms look externally just like their uncontaminated counterparts."

"DNA mutations are there, but just looking at the organisms, you wouldn't see anything different about them," said Dr. Ronald K. Chesser, associate research ecologist and head of the division of wildlife ecology and toxicology.

A mutation may occur when radiation energy hits a strand of DNA in a cell and causes the DNA to break.

"Chances are that a break will repair itself properly, but it is possible for that break to be translated into a mutation," Chesser said. "The frequency of producing these abnormal chromosomes depends upon how much exposure there has been and the rate at which these abnormal chromosomes can be repaired."

"And even though there may be chromosome abnormalities, it does not necessarily mean they are harmful to the organism or even harmful to the long-term survival and maintenance of the population," Whicker said.

To document any genetic effects, Chesser, Smith and others have to look at thousands of cells from each organism.

Using technology borrowed from the medical field, SREL researchers have analyzed thousands of DNA samples from large-mouth bass and have completed studies of a smaller scope on turtles and waterfowl.

"This new laser-based technology allows us to look at 10,000 to 50,000 cells from a single individual within a few minutes," Smith said. "In the past it would have been impossible to do this kind of research."

The technology was first used for wildlife studies in the mid 1980s by scientists at Texas A&M University. They analyzed blood samples from animals that lived in an area chemically contaminated by repeated fire fighter training. Working with some of those same researchers, SREL ecologists initiated similar studies at the Savannah River Site.

Because such research is still in its infancy, no one knows what causes genetic differences found in organisms at the site. Nor do they have answers on whether the mutations affect an organism, much less what it could mean for humans, Chesser said.

They suspect that most mutations are related to one or a combination of several substances found in contaminated pond sediments.

"We don't know what's causing it and what's not, but it appears to be an effect of living in a contaminated area," Chesser said. "Your first conclusion would be it must be radiocesium, but that would be jumping the gun. Attributing those variations specifically to radiocesium isn't possible."

Finding the cause will take years of painstaking research.

"It takes a long time to see effects from some of these substances," Smith said. "Pond B has had 30 years for these effects to build up. Short-term experiments may not show anything."

Although Pond B sediments are more contaminated than those at Par Pond, radiation risks at Par Pond will continue to be higher as long as its contaminated mudflats remain exposed. A prescribed evaluation and decision-making procedure is underway now that the U.S. Environmental Protection Agency has declared Par Pond an operable site under the terms of the Comprehensive Environmental Response, Compensation, and Liability Act. Because of the need to complete this process and the requirement to repair the dam, Par Pond will likely remain as is for at least two more years, Whicker said.

"The baseline risk assessment involves doing extensive calculations to evaluate the risk to workers out there or to some person who might live out there," he said. "If the Energy Department should lose institutional control of the site, if it should ever revert to the public, it would be theoretically possible for the land to end up in the hands of a few farm families who are going to live off the land. If you have somebody living out there on the mud flats full time and growing crops and raising cattle, what would their health risks be?"

The information the SREL scientists are collecting is crucial to calculating those risks. Their research will help determine the amount of radioactivity in the food chain and its potential for contaminating humans. Once that's done they will use those figures to determine the possible radiation dose and calculate the risk of radiation-induced cancer.

The EPA radiation exposure risk limit ranges from one death in a million to one in 10,000, Whicker said. "We could argue until the cows come home about how ridiculously low and conservative that risk is when our risk of dying is 100 percent and our risk of dying of a fatal cancer [unrelated to radiation] is one in four or five," he said.

"Our calculations so far indicate that if you have a person or family living out there on the lake bed, their risk of dying of cancer [from radiation exposure] could be, under the worst possible circumstances, greater than one in 10,000," he said. "It's more like one in 1,000, which is still an extremely small risk, but it exceeds EPA's criterion. We have already flunked that test."

No matter what the future holds, one thing is clear: Radioactive contamination respects no political boundaries, peace treaties or agreements. It crosses state and national lines as easily and effortlessly as a contaminated stream or breeze.

With a history of research at the Savannah River Site that predates the nuclear reactors, the team of SREL scientists will keep giving us the information we need to solve nuclear waste problems.

"We are interested in this research because we think we can make a difference," Whicker said. "And we feel a social responsibility to keep this field going and provide factual information."

Research Communications, Office of the VP for Research, UGA
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