|June 8, 2010 |
Environmental Effects of Tungsten: Damage Mitigation and Green Alternatives
For many years, lead and depleted uranium were commonly used as a functional, cost-effective, and reliable choice in the manufacturing of munitions. When first brought into use, scientists knew little about the environmental effects of these materials. Depleted uranium was typically seen as constituent of kinetic energy penetrators (which uses kinetic energy to penetrate the target) in medium to large caliber munitions. Lead, most frequently used in small arms ammunition, was at that time also found in a variety of household products such as gasoline, rubber, paint, and printing supplies.
It was only after decades of use that scientists revealed that these materials pose serious threats to the environment. The search was on for a "green" alternative in munitions components.
Extensive analysis resulted in the testing of tungsten (W), a naturally occurring element that exists in the form of minerals and other compounds, as a replacement for lead in small arms ammunition. Tungsten was considered to be environmentally benign, relatively insoluble in water, and nontoxic. Furthermore, tungsten-based munitions performed the same and were similar in costs to lead alternatives.
It seemed to be the ideal solution for greener munitions. Through the Department of Defense's (DoD) Green Ammunition Program, the lead core in military bullets was replaced with tungsten composites. The DoD hoped to save millions in remediating contamination while at the same time contributing towards advancements in green technology.
However, after years of tungsten use, the DoD chose to re-evaluate the material's potential environmental impact. Researchers from Stevens Institute of Technology identified a growing concern that tungsten was not as "green" as initially thought, and began investigating how a cooperative pursuit of improved environmental protection and DoD requirements may be beneficial.
In response to this concern, Professors Christos Christodoulatos and Washington Braida of the Center for Environmental Systems have undertaken a massive research effort aimed at identifying the specific nature of tungsten-based munitions and ultimately at minimizing the life-cycle environmental impacts and cost of munitions by researching the DoD's triple bottom line: mission, environment, and community.
In the Lab at the Center for Environmental Systems
Researchers at Stevens needed to determine whether dissolved forms of tungsten were released from munitions.
In 2004, Professors Christodoulatos, Braida, Dimitris Dermatas and Nikolay Strigul highlighted their initial results in an article appearing in Environmental Forensics, 5:5-13.
Toxic effects of heavy metals on ryegrass growth in meadow urban soil
(urban soil) after two weeks of germination
Toxic effects of different concentration of metallic tungsten
on ryegrass growth in forest soil after 4 weeks of germination
"This study found large amounts of dissolved tungsten when powder or alloy pieces were exposed to aqueous solutions, contradicting most of the scarcely available information regarding its solubility," they said. "This research represents one of the first systematic studies on environmental fate and transport of tungsten and adds information to the toolbox of environmental forensics regarding a heavy metal of potential environmental concern."
A 2009 article in the American Chemical Society's Chemical & Engineering News states: "...tungsten metal oxidizes to the tungstate anion. Previous toxicology studies indicate that tungsten would be stable in the environment. Although thermodynamically stable under most environmental conditions, the tungstate ion does have biological effects. For example, tungsten may substitute for molybdenum in certain enzymes, inactivating the enzymes."
Essentially this research had for the first time proven that tungsten may have a negative impact on the environment. Findings presented in these reports have led to growing discussion over its practical governance and the possibility of environmental regulations. This difficulty in predicting the behavior of tungsten is actually one of the primary reasons Ph.D. candidate Gulsah Sen entered into the field. Working with Professor Braida for the past three years, Gulsah's research focuses on the fate and transport of tungsten in the vadose, or unsaturated, zone.
According to Adebayo A. Ogundipe, a Research Engineer at Stevens during the tungsten investigation, "This research effectively showed that tungsten heavy alloys are not environmentally inert. We proved this by uncovering the various mechanisms involved in the environmental degradation of these alloys, the kinetics of release of tungsten and other alloy components and the subsequent effects on environmental conditions. Our research highlighted how the initial design and choice of alloying materials were essential factors in the patterns of chemical behavior. We developed morphological and spectroscopic analyses techniques for analyzing the manner and extent of the environmental degradation of various tungsten heavy alloy formulations."
Putting it all Together
Tungsten may not be as green as we once thought. But what can we make from this knowledge to drive innovation and improve technology?
Through their on-going collaborative efforts, the DoD is dramatically improving its assessment of the environmental impact and cost consequences of today's decision making. Governments are now factoring these green concerns directly into the research and development phase. This streamlines the development process, avoids costs that may arise if materials are later deemed hazardous, and highlights a paradigm shift in which the environmental concerns become an equal focus throughout.
This focus also creates tremendous opportunities for technology transfer efforts and the development of new procedures, methodologies, and companies that push the envelope of sustainable engineered products.
Ultimately, enhancements and discoveries made through the efforts of Stevens faculty are increasing the awareness of the issues, spurring discussion on alternatives, ensuring a more environmentally friendly future, and providing unique educational experiences through student participation.
To learn more about this innovative research or to inquire about joining us, please visit the Center for Environmental Systems and the Department of Civil, Environmental and Ocean Engineering.
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