rotecting the environment, cleaning up legacy wastes, reducing pollution, and providing renewable energythese are areas of concern addressed by ORNL's multidisciplinary expertise in environmental sciences and technology. We conduct applied research to help resolve environmental issues related to the development, production, and use of energy. This work is an extension of a long tradition of basic and applied research in diverse disciplines including biology, chemistry, engineering, physics, ecology, geology, hydrology, toxicology, computational sciences, and the social sciences.
Some ORNL scientists are determining the effects of pollutants on plants and are genetically engineering plants to create alternative sources of fuel; others are finding ways to use microbes as a cost-effective means of removing pollutants or cleaning up wastes. Interdisciplinary studies in ecology, biology, geology, and chemistry have yielded a greater understanding of the structure and function of ecosystems and the processes that determine the cycling of basic elements and the transport of contaminants through soil, water, and air. Such studies have led to advanced techniques for analyzing the effects of stresses on the environment and for assessing risks to ecological and human health.
Also, we have created complex computer models to predict effects of contaminant movement and of global environmental change. We have assessed environmental impacts of energy production, determined the value of environmental assets, performed life cycle analyses (including the environmental and energy costs of producing and maintaining various products), and evaluated the energy efficiency of ozone-safe substitutes for chlorofluorocarbons. We have pioneered techniques for avoiding pollution, for treating and storing hazardous and radioactive wastes, for monitoring contaminant migration, and for restoring the environment at contaminated sites.
Ozone, Climate Change May Slow Tree Growth
Without air, plants could not live. But air also carries pollutants from natural processes, fossil-fuel power plants, and highway vehicles that can endanger tree health. Among these pollutants are ground-level ozone, which forms when airborne hydrocarbons and nitrogen oxides react in sunlight, and greenhouse gases, which threaten to alter climate.
ORNL scientists have found that ground-level ozone in the environment can reduce the growth of the loblolly pine, a forest tree species of economic importance in the Southeast. Their findings, reported in March 1995 issues of the journal Nature and The New York Times, suggest that forest tree growth could significantly decline because of exposure to ozone combined with the higher temperatures and increased drought predicted as a part of our future global climate.
In the 1980s, reductions in growth of loblolly pine trees in the Southeast were observed. This decrease aroused concern because loblolly pine is an important component of southern pine forests. Logging of southern pine forests, which cover an estimated 60 million acres, contributes over $4.5 billion annually to the regional economy.
Studies of tree seedlings exposed to ozone in closed chambers at ORNL and elsewhere showed the pollutant stunted seedling growth. The new ORNL study, which precisely measured growth patterns of tree trunks of mature trees and used statistical techniques to separate ozone effects from other influences, is the first to determine that ozone retards mature tree growth in a real forest environment.
Under normal ozone levels in the eastern United States, we observed tree growth reductions of 5%, except during the wettest years. The decline was more pronounced under dryer conditions (up to 13%). When ozone levels were especially high, tree trunks actually contracted slightly during the driest periods.
Evidence from other studies suggests that ozone may impair a tree's ability to efficiently use available water. How? By increasing water losses through foliage and reducing root growth, thereby lowering water uptake. Thus, ozone can magnify effects of water stress on tree growth.
Sandy McLaughlin (left) and Darrell Downing precisely measure the growth of loblolly pine trees in a forest exposed to high ozone levels and hot, dry conditions. Inset: Growth of each tree was monitored by a dendrometer, a metal band positioned around the trunk that precisely measures fluctuations in its expansion rate. Photograph by Tom Cerniglio.
Some computer models predict that future climate change will be marked by increasing temperatures and drought. Our results suggest that trees exposed to ozone under these climatic conditions would experience significant reductions in growth. Even for trees, change is in the air.
Funding for this research was provided by the U.S. Forest Service Global Change Program.
Trees Emit Mercury
Like most people, some green plants like to give as well as receive. In the 1970s, we discovered that plants can take up mercury from soil and air. Now, 20 years later, we have scientific proof that plants emit mercury to the air.
This finding came from an ORNL-designed study in the laboratory and field. We sought to determine if the landscape mainly emits mercury to the air or if it stores mercury deposited on it from air. In this study, a high-precision sampling technique developed at ORNL measured exchanges of mercury between air and land to see if land is a mercury source or sink.
In laboratory experiments, maple, oak, and spruce saplings were grown in a chamber into which low-mercury air was introduced. The soil the saplings were planted in was isolated from the chamber. When a researcher sampled the air for mercury vapor, he was surprised that mercury was coming from the plants.
Further experiments showed that the plants take mercury from the air when the air's mercury level is above about 20 nanograms per cubic meter. When the mercury level in air is only 2 nanograms per cubic meter, the plants emit mercury. These different levels of mercury occur near pollution sources and at background sites respectively.
We also measured gradients in mercury concentrations over Tennessee forests. Meteorological tower data from Walker Branch Watershed in Oak Ridge showed significant emissions of mercury from oak, hickory, and maple trees below. Our studies of trees at a Christmas tree farm in Wartburg showed that mercury deposits from air to trees when they are wet. We also observed that trees there are a strong source of mercury to the air when they are dry, supporting data from our laboratory studies.
ORNL researchers theorize that elemental mercury in soil gas is pulled into the plant when the plant's mercury level is low. The plant tries to achieve equilibrium with respect to mercury levels in the air. When the plant's mercury level rises and the air mercury level decreases, at some point the plant releases some of its mercury to the air. Some mercury-containing plants are waiting to exhale.
This research was sponsored by the Electric Power Research Institute, the research arm of the U.S. electric utility industry.
Newly Discovered Bacteria Produce Magnetic Material
In 1993, while Texaco engineers explored for oil and gas deposits near the Chesapeake Bay, ORNL microbiologists working in a trailer by the oil company's derrick discovered novel bacteria. Studying samples extracted by Texaco from a depth of 2800 meters (91,000 feet), the microbiologists observed that metallic compounds had been chemically altered by microbes at a temperature of 70°C (158°F), even though the subsurface samples had been geologically isolated for some 100 to 140 million years.
In 1994 ORNL researchers determined that these microbes from the Taylorsville Triassic Rift Basin near Fredericksburg, Virginia, have an interesting capability: they produce magnetic material. The researchers isolated micron-size bacteria and found that these microorganisms produced nanometer-scale magnetic iron precipitates. The researchers also found evidence that the microbes can remediate groundwater containing chlorocarbon compounds (trichloroethylene and tetrachloroethylene) and heavy metals.
The researchers found similar bacteria at the Naval Oil Shale Reserve at the Piceance Basin in Colorado. Both the Taylorsville and Piceance basins, although separated geographically and formed at different times, contain deep subsurface formations heated by compression to high temperatures. The thermophilic (heat-loving) bacteria feed on compounds containing carbon, hydrogen, and oxygen, such as acetate and lactate (an ingredient of sour milk). The Piceance Basin bacteria, which also metabolize hydrogen and pyruvate, were found in groundwater and drilling mud; the Taylorsville bacteria were present in subsurface shale and sandstones.
The anaerobic bacteria convert food to energy and waste through an electron transfer process typical of respiration, rather than fermentation. Just as humans get rid of electrons by forming and exhaling carbon dioxide, these bacteria dump electrons on nearby electron-accepting metals, such as iron. In the process, they reduce iron hydroxide [Fe(OH3)] to magnetic iron (Fe3O4). These magnetite particles can catalyze the degradation of chlorocarbon compounds. The bacteria can also reduce other electron-accepting heavy metals such as chromium, cobalt, and uranium, making the bacteria potentially useful for bioremediation of soil and groundwater contaminated with mixed waste, if the environment is sufficiently heated.
|Living on hydrogen in drilling mud, these newly discovered bacteria produce tiny particles of magnetic iron oxides, as shown under a scanning electron microscope.|
The research was supported by DOE, Office of Health and Environmental Research.
Electromagnetic Fields and Body Cells
Some people have a fear of fieldselectromagnetic fields (EMFs) from power lines and electric blankets. They are concerned about evidence suggesting that EMFs cause leukemia and brain cancers. Because of their health concerns and the associated economic impact (e.g., inability to site new lines, re-engineered appliances, and the expense of underground siting of power lines), the Energy Policy Act of 1992 has authorized government researchers to find out if these fears are grounded in science.
Guy Griffin (left) and Paul Gailey use a fluxgate magnetometer to perform a calibration check of ORNL's magnetic field exposure system, which exposes biological cell cultures to precise magnetic fields in an environment in which temperature, humidity, and carbon dioxide are controlled. Cell cultures are placed in two chambers, but the control electronics turn on exposure fields in only one (and the researchers don't know which one, ensuring that no inadvertent bias enters the experiments). Photograph by Tom Cerniglio.
Since 1990, ORNL has played a major role in the national EMF research effort, and in 1995, it became one of four government facilities charged with determining whether published results of several EMF experiments can be replicated under controlled conditions. Here are some recent scientific scenes at our Electromagnetic Fields Bioeffects Laboratory.
ORNL scientists obtain some genetically engineered breast cells from a researcher in France. When properly cultured, these cells are designed to give off faint but detectable light when exposed to estrogen or estrogenlike compounds such as DDT. Exposure of these cells to estrogen shows at least one gene expresses itself (causes itself to produce effects), as revealed by light emission. We are studying the effects of EMFs on these cells to see if the genetic region sensitive to estrogen also responds to EMFs of certain strengths by emitting light.
A technician removes cells from a 6-day-old fertilized egg that would eventually form a chick's heart. The beating rate of the throbbing heart cells is measured by an ultrasensitive pressure transducer, a sort of miniature stethoscope. The heartbeat is slightly irregular, which is normal. Scientists then expose the heart cells to electric fields like those induced in the body by exposure to moderately strong EMFs. They discover that certain electric fields perturb the heart cells, increasing or decreasing their beating rate in regular synchrony with the field's frequency. More experiments will help determine how low an electromagnetic field must be before the heart cells show no signs of perturbation.
An ORNL scientist uses this information in his mathematical models to predict the weakest electromagnetic fields that cause perturbations and other bioeffects in specific cells. These fields will then be compared with EMFs to which the public is exposed. For some scientists, the study of EMF bioeffects could be a field of dreams.
EMF bioeffects studies at ORNL were initiated through a grant from the Laboratory Directed Research and Development Program and are now supported by DOE's Office of Energy Management.
Helping the Army Assess Disposal of Chemical Weapons
Chemical weapons were made to kill, so few Americans want to keep them around. Taking orders from Congress and heeding international disarmament treaties, the U.S. Army has been seeking the safest way to destroy our nation's stockpile of toxic munitions. Stored in reinforced concrete igloos, these weapons comprise 3.3 million rockets, artillery shells, bombs, and land mines filled with nerve gas and blister agents.
In the mid-1980s, the Army faced a dilemma. It had decided to destroy the obsolete chemical weapons stored at eight depots, but it wanted to minimize the risks. Should it ship the weapons to one central disposal location or dispose of them at each of the storage sites? The Army turned to ORNL to assess the environmental impacts of the disposal options. Our team of environmental, health, and transportation specialists showed the Army that it would be far safer and environmentally preferable to destroy the weapons on-site than risk transportation accidents.
Obsolete chemical weapons in storage at a U.S. Army depot.
In the early 1990s, after deciding to destroy the munitions by incineration, the Army asked our help in preparing a site-specific environmental impact statement for a proposed chemical weapons incineration facility at the Pine Bluff Arsenal in Arkansas. So, using a variety of computer techniques, we determined the potential environmental and socioeconomic impacts of constructing and operating a facility for destroying the arsenal's inventory of chemical weapons. We used geographic information system software for evaluating issues of environmental justicefor example, are minority and low-income populations in the vicinity of the depot more likely to be affected by potential incineration emissions? The potential consequences of an unlikely hypothetical accident were found to be up to 4200 deaths for the worst-case scenario.
For comparison, we assessed the potential impacts of continued storage of the arsenal's inventory (one problem is that chemicals could corrode casings and leak out into the igloos). The Army released our draft document for comment on June 9, 1995; the final impact statement is being completed, taking into account the comments received.
Construction of the disposal facility is scheduled to begin in late 1996. During operations, the munitions containing the chemicals will be loaded onto conveyor belts and disassembled by remote-controlled machines. Then the chemical agents, munition parts, and explosive components will be incinerated. Destruction of the arsenal's inventory of 3850 tons, or 12% of the total U.S. chemical weapons stockpile, is expected to begin in late 1999. After an estimated 38 months of operation, the disposal facility will be dismantled and closed. And by 2004 it is hoped the Army's book on U.S. chemical weapons will also be closed.
Applying Inverse Electrostatic Spraying
In 1750, French cleric and physicist Jean-Antoine Nollet demonstrated that water dripping or flowing from a vessel would form an aerosol if the vessel were electrified and placed near a ground. Nollet noted that any electrically conductive fluid would behave the same way when passing into a nonconductive medium under similar conditions. He pointed out that, for example, "a person, electrified by connection to a high-voltage generator, would not bleed normally if he were to cut himself; blood would spray from the wound." A woodcut portrayal of a man in such a ghastly predicament appears in Diderot's encyclopedia.
Since Nollet first observed electrostatic spraying, it has become a useful tool for consumers and for industry. Electrostatic spraying is the principle behind inkjet printing. It also makes car spray-painting and crop spraying more efficient in two ways. Large drops are broken into a fine mist, providing a more uniform coating, and the particles are attracted to a grounded auto body (or a fruit tree grounded by its roots), resulting in less waste and less pollution.
Recently, researchers at ORNL have applied the same principles to mixing liquids that would otherwise not combine, permitting efficient chemical processes that would otherwise be difficult or impossible. Examples are the emulsion-phase contactor for liquid extraction and the electric dispersion reactor for materials synthesis.
|ORNL has demonstrated electrostatic dispersion of nonconductive fluids into conductive fluids, as shown here. Results could lead to effective nozzle design for cleansing polluted liquids.|
It was long thought that reversing this process, spraying a nonconducting fluid into a conductor, was impossible. Recently, however, inverse electrostatic spraying has been demonstrated and its mechanism has been explained at ORNL. This phenomenon may prove useful for waste management and environmental restoration.
For example, a gas pumped into polluted water can collect and remove harmful chemicals, or "scrub" the water. By breaking large bubbles into many small bubbles, inverse electrostatic spraying boosts the efficiency of this process in two ways. It increases the contact time of the gas in the fluid (small bubbles move slower than large bubbles), and it increases the surface area, creating more opportunity for the pollutants to migrate to the gas. In a similar way, a reactive gas, such as ozone, can break down harmful chemicals into harmless components while killing bacteria. In nearly 250 years, the world has come a long way in learning how to spray.
Funding for this research has been provided by DOE, Office of Energy Research, Basic Energy Sciences, Division of Chemical Sciences.