In the Lab
Sticky Problems with Chemical Used in Making Teflon
The U.S. Environmental Protection Agency is releasing a preliminary risk assessment for the chemical perfluorooctanoic acid (PFOA), a chemical processing aid used in the manufacture of a wide variety of consumer and industrial products, including items coated with Teflon®., the tough, insoluble polymer used in making nonsticking coatings.
Studies recently evaluated by the agency have raised a number of potential toxicity concerns, and when combined with information that the general U.S. population may be exposed to very low levels of PFOA, has led the agency to conclude that additional scientific information is needed to determine if new regulatory actions are necessary, officials said on April 14.
"To ensure consumers are protected from any potential risks, the agency will be conducting its most extensive scientific assessment ever undertaken on this type of chemical," said Stephen L. Johnson, assistant administrator of EPA's Office of Prevention, Pesticides, and Toxic Substances. "This announcement puts in place rigorous regulatory and scientific steps that will lead to a better understanding of PFOA. This priority scientific review will guarantee that any future regulatory action on PFOA is protective of public health and supported by the best scientific information."
To initiate this process, the agency is releasing its preliminary risk assessment on PFOA for public review. A public docket has been established so interested parties can review the scientific information available to the agency. Similarly, through public meetings, the agency is inviting participation in the development of enforceable consent agreements, which will be used to direct the generation of new scientific information critical to understanding the sources and pathways of potential exposures to PFOA. By using enforceable consent agreements, the generation of new data can be accelerated so the data is available quickly.
The agency is interested in collecting additional information because a new laboratory studies recently evaluated by the agency shows that PFOA may cause developmental toxicity and other health effects. Further, the available data indicate that the general U.S. population may be exposed to PFOA at very low levels. The potential sources and exposure pathways of PFOA are not well understood at this time.
Given these considerable scientific uncertainties, EPA has not made a determination as to whether PFOA poses an unreasonable risk to the public.
For further information on EPA preliminary risk assessment of PFOA, including the Federal Register notice, see www.epa.gov/oppt.
Panda Power Has Great Potential
A Japanese scientist could soon become stinking rich with an invention to be ready by 2005 that would use panda excrement to create electricity, according to a report dated April 29, 2003, in The Australian, Australia's national daily newspaper.
Fumiaki Taguchi, emeritus professor of Kitasato University in Tokyo, embarked on the project five years ago when he asked Ueno Zoo for a bucketful of one of their most popular residents' feces. Bacteria inside the panda's belly must be pretty special to be able todigest tough bamboo leaves and shoots, he reasoned.
"If a panda can support such a big body by eating bamboo leaves, it's really different from other animals," Taguchi said. "There might not be any other living thing on the planet able to digest bamboo leaves or the skin of the shoots. They are made of such tough organic materials."
His research team then selected five microorganisms among the approximately 270 they discovered in the excrement - ones that were the most efficient at breaking down proteins, fats and could reproduce easily even under high heat. The team mixed the bacteria with 70 to 100 kilograms of raw garbage, such as vegetable stems, for 17 weeks in an industrial waste disposal machine. The result: only three kilograms of waste remained, while the rest had turned to water and carbon dioxide - way above the 80 per cent efficiency of most commercial disposal bacteria. The outcome is not just soggy gas.
Taguchi said the company of which he is a director, H2Japan, hopes to create a hydrogen fuel cell and waste disposal unit in one to sell to food processing companies across Japan. He aims to showcase his invention at the 2005 World Expo in Aichi, which will be held in March. Aichi is approximately 250 kilometers west of Tokyo.
"For every one kilogram of waste I can get about 100 litres of hydrogen," he said. "It won't amount to much electricity, maybe enough to power the exit lamps in an entire building."
"In the next year, we want to see if we can improve this," Taguchi said.
For more information, check out www.h2japan.com.
The Sweet Smell of Success: Treating H2 Gas in Sewage Emissions
Scientists at the University of California at Riverside (UC Riverside) have pushed the current limit of a technique for biologically removing hydrogen sulfide from sewage emissions a step further. Dr. Marc Deshusses, associate professor in the Department of Chemical and Environmental Engineering, and his postdoctoral researcher, Dr. David Gabriel, report in the Proceedings of the National Academy of Sciences (PNAS) that they have modified an existing full-scale chemical scrubber at the Orange County Sanitation District (OCSD), California, to a biological trickling filter.
"Hydrogen sulfide odors, which have the smell of rotten eggs, can be treated in biological reactors called biotrickling filters at rates similar to those observed in chemical scrubbers," said Deshusses. "Biotreatment is cheaper, safer, and more environmentally friendly. In our paper, we also show that you can convert existing chemical scrubbers to biological trickling filters quite easily."
Chemical scrubbing suffers from important drawbacks, such as high operating costs, generation of halomethanes that are known air toxics, and the requirement for hazardous chemicals, which pose serious health and safety concerns.
In biological trickling filters or biotrickling filters, the waste air stream is passed through a packed bed on which pollutant-degrading bacteria are placed in the form of a biofilm. These bacteria absorb and degrade gaseous pollutants. After the bacteria begin to multiply, their efficiency at converting hydrogen sulfide to sulfate is nearly 100 percent. Moreover, the system removes more odorant chemicals, including other sulfur and nitrogen compounds.
"We did extensive research in the laboratory prior to and during the field demonstration at OCSD in an attempt to explain why we obtained such a high performance from the biotrickling filter," said Deshusses.
The UC Riverside researchers packed polyurethane foam cubes inoculated with hydrogen sulfide-degrading bacteria into the OCSD scrubber. They also replaced the existing liquid pump with a smaller one, disconnected the chemical supply system, and modified the control systems.
Emission of objectionable odors is a major problem for wastewater treatment plants and other processing facilities. For odor control, biological treatment is a promising alternative to conventional control methods, but so far biotreatment always required significantly larger reactor volumes than chemical scrubbers.
In the PNAS paper, the researchers report that effective treatment of hydrogen sulfide in the converted scrubber was possible even at gas contact times as low as 1.6 seconds, comparable to usual contact times in chemical scrubbers.
"Continuous operation of the converted scrubber for more than 8 months showed stable performances and robust behavior for hydrogen sulfide treatment, with pollutant removal performance comparable to that achieved using a chemical scrubber," said Deshusses. "Our study demonstrates that biotrickling filters can replace chemical scrubbers and be a safer, more economical technique for odor control."
An estimated 10,000 - 40,000 scrubbers for odor control operate at publicly owned treatment works in the United States and probably more than 100,000 scrubbers worldwide. "Many of those scrubbers treat hydrogen sulfide only," said Deshusses, "hence, based on the results of our study, they could potentially be converted to biotrickling filters."
An overall cost-benefit analysis of the scrubber that was converted at OCSD shows that total annual savings in operating costs (essentially chemicals and electricity) are about $30,000 per year for the biotrickling filter compared to chemical scrubbing. The estimated commercial cost of converting the chemical scrubber to a biotrickling filter was about $40,000 - 60,000, which compares well with the annual savings in operating costs.
"If one assumes that 25 to 40 percent of the chemical scrubbers worldwide could be converted to biotrickling filters," said Deshusses, "it would represent a total market of $1-3 billion and would result in net energy and chemical savings of approximately $0.25-2 billion per year."
The study was performed during 2001-2002 and is still on-going. Research was funded by OCSD. "OCSD has been wonderfully supportive of the project, not only financially, but also by providing us with an excellent staff at the site of the study," said Deshusses. "Indeed, they were enormously instrumental in the success of the project."
Change in Crop Fertilization Techniques Reduces Groundwater Contamination
Fine-tuning fertilizer and irrigation management requires farmers to carefully balance optimizing yield and protecting groundwater quality. Some states even require farmers to use crop production practices to minimize nitrate leaching to groundwater in environmentally sensitive areas.
One such practice is using a nitrification inhibitor when applying nitrogen fertilizer, which helps protect nitrogen from leaching below the root zone until the crop can use it. Farmers are often reluctant to use nitrification inhibitors since they add to the cost of production, and only increase yield or protect from nitrate loss with specific combinations of soil type and climate - such as a warm, wet spring and sandy soils.
Recent research in the central Platte river valley of Nebraska investigated a promising new option for producers growing irrigated corn in environmentally sensitive areas, according to Richard Ferguson, professor of agronomy, University of Nebraska.
The study, conducted from 1995 - 1998, explored ways to reduce nitrate leaching to groundwater. Results from the study are published in the May/June 2003 issue of the Soil Science Society of America Journal, published by the Soil Science Society of America. Co-authors are Murray Lark, Silsoe Research Institute, Great Britain; and Glen Slater, University of Nebraska. Soil Science Society of America Journal is a peer-reviewed, international journal of soil science published six times a year by the Soil Science Society of America. It contains contains soil research relating to physics; chemistry; biology and biochemistry; fertility and plant nutrition; genesis, morphology, and classification; water management and conservation; forest and range soils; nutrient management and soil and plant analysis; mineralogy; and wetland soils.
Using information about soil properties obtained from grid soil sampling, along with maps of crop yield and soil electrical conductivity, these researchers developed management zones to direct the application of nitrification inhibitors.
In relatively dry-to-normal growing seasons, the use of a nitrification inhibitor had no effect on grain yield or nitrate leaching. However, in a growing season with a very wet spring, the use of a nitrification inhibitor increased yield. Patterns of higher and lower yield in the wet growing season corresponded closely to patterns of soil electrical conductivity.
According to Ferguson, producing soil electrical conductivity or yield maps is much easier and cheaper for producers than grid soil sampling.
"If we can develop an approach to allow farmers to prioritize areas within fields where nitrification inhibitors will be most beneficial, we believe that will encourage more farmers to use the practice. This approach could help protect groundwater quality while significantly reducing the cost and time required for the farmer," he says.
While it's premature to say that maps of soil electrical conductivity or grain yield can be used to predict where nitrification inhibitors should be used, the researchers have seen enough similar results in other studies to warrant continued study.
For more information, check out the Soil Science Society of America's Web site at www.soils.org. and The American Society of Agronomy at www.agronomy.org.
Scientists Develop Lead Sensor Similar to Litmus Paper
A new biosensor developed by scientists at the University of Illinois at Urbana-Champaign could make it much easier to test houses for leaded paint.
Chemistry professor Yi Lu and graduate student Juewen Liu have developed a highly sensitive and selective biosensor that functions much like a strip of litmus paper. The colorimetric sensor is based on DNA-gold nanoparticle chemistry and could be used for sensing a variety of environmental contaminants. A paper discussing the researchers' work has been accepted for publication in the Journal of the American Chemical Society.
Using gold nanoparticles laced with DNA, Lu and Liu were able to hybridize the nanoparticles into aggregate clusters that have a characteristic blue color. In the presence of a specific metal ion, the catalytic DNA will break off individual gold nanoparticles, resulting in a dramatic color shift to red. The intensity of the color depends on the initial concentration of contaminant metal ions.
By applying the DNA-gold nanoparticle solution to a substrate, the researchers created a biosensor that functions in the same manner as litmus paper. "These simple colorimetric sensors eliminate the need for additional instrumentation and are well-suited for on-site, real-time detection and quantification," Lu said.
According to Lu, the DNA selection process used to obtain DNA for the biosensor can be customized to select catalytic DNA that would be active for lead or for other metal ions such as mercury, cadmium and zinc. "There are many old houses around the world that still contain leaded paint," Lu said. "According to EPA, leaded paint test kits that are currently available have shown high rates of both false positive and false negative results when compared to laboratory results. Our catalytic DNA-gold nanoparticle sensor can overcome these shortcomings."
Lu is working with colleagues at the National Science Foundation's Nanoscale Science and Engineering Center for the Directed Assembly of Nanostructures to further develop the technology.
"Our ultimate goal is to develop a microchip array with different color schemes for simultaneously detecting many different metal ions," Lu said.
For more information, see the University of Illinois at Urbana-Champaign's Web site at www.scs.uiuc.edu.
Enzyme could overcome industrial bleaching waste problems
Taken from a microbe that thrives in the depths of a Yellowstone National Park hot springs pool, a newly discovered enzyme may be the key to transforming industrial bleaching from environmentally problematic to environmentally green.
Chemical engineer Vicki Thompson and biologists William Apel and Kastli Schaller from the U.S. Department of Energy's Idaho National Engineering and Environmental Laboratory discovered that the catalase enzyme from a Thermus brockianus microbe flourishes in both a high temperature and high pH (basic or alkaline) environment.
Catalase enzymes chemically alter hydrogen peroxide into natural products - water and oxygen. Industry is increasingly using peroxide in industrial bleaching processes and needs an environmentally friendly process to handle process wastes. The T. brockianus catalase works well in the hot, alkaline process wastewater where commercially available catalase enzymes do not, so it could be an answer.
Thompson presented this work at the American Society of Microbiologists annual meeting in Washington, D.C. on May 20, 2003. A paper on this research was recently accepted for publication in Biotechnology Progress and will appear in print this summer. The work is part of the INEEL's efforts to support the DOE mission in environmental research and development.
Industries such as textile and pulp and paper have started shifting away from toxic, carcinogenic chemical bleaching processes to more environmentally friendly hydrogen peroxide-based bleaching. Until INEEL discovered the T. brockianus enzyme, there were only a few options for dealing with the wastewater.
Industry can chemically treat the water to break hydrogen peroxide down, but that practically cancels out the environmental benefit. Or they can heavily dilute wastewater with even more water, but that increases the volume of waste water. Using catalase to break down hydrogen peroxide is a good alternative, but commercially available catalase enzymes require much cooler wastewater temperatures and lower pH conditions. This costs industry significant energy, time and money.
But the T. brockianus catalase likes these extreme conditions-performing best at temperatures around 90 degrees Celsius (194 degrees Fahrenheit) and in highly alkaline pH of more than 9. In laboratory tests, it functioned well for as long as 360 hours under these conditions compared to a mere 15 to 20 minutes for other, commercially available catalases. Thus, the INEEL research will provide a chance for textile and pulp and paper companies to save significant energy and reduce environmental impacts.
"We didn't anticipate such extreme stability from the catalase, even though it's a thermophilic enzyme," said Thompson, noting that it was both unusual and a surprise. Thermophiles are heat-tolerant microorganisms.
"High-temperature stability makes this enzyme potentially viable and economically attractive for industrial applications," said biologist William Apel. "This new catalase is lasting for days where the typical performance limit for many industrial-use enzymes is a mere 10 hours."
For the T. brockianus catalase, breaking down hydrogen peroxide in an industrial setting is just another day at the office. Within a microorganism, the enzyme's normal role is to break down hydrogen peroxide that is naturally produced by cellular activity. This protects cells from oxidative stress-the biological equivalent of rust.
The next step to commercial development of T.brockianus catalase is to establish enzyme production at industrially relevant volumes. That means identifying the gene that encodes the T. brockianus catalase, and inserting it into a microbe that is easily grown in large quantities.
Then researchers can use already established technology to attach the enzyme to tiny polymer beads and pack them into columns that will filter industrial wastewater.
The team is currently discussing the industrial possibilities of this catalase with a major hydrogen peroxide manufacturer. This research was supported by the INEEL's Laboratory Directed Research and Development program.
For more information, see the Idaho National Engineering and Environmental Laboratory's Web site at www.inel.gov.
This article originally appeared in the June 2003 issue of Environmental Protection, Vol. 14, No. 5.
This article originally appeared in the 06/01/2003 issue of Environmental Protection.