ES&T’s Best Papers of 2007
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n 2007, ES&T published more than 1200 papers on a wide range of topics. But which papers were the top papers—the best of the year? This year, our associate editors and editorial advisory board nominated papers
that they felt were of the highest caliber—these are papers expected to have a significant and long-lasting impact on the field. I chose a subcommittee from our editorial advisory board to pore over the nominations and narrow the list to 5–10 papers in each category: top papers in environmental science, technology, and policy. I had the difficult task of trying to choose the best of the best. We hope this brings special recognition to you, our authors, and focuses attention on our high-quality papers. The Best Paper Awards are an annual event announced online in February or March of the year after publication. Each author receives a certificate of award and our heartiest congratulations. —JERALD L. SCHNOOR
Courtesy of Wendelin Stark
ENVIRONMENTAL SCIENCE
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Top paper: Nanoparticle exposures “Exposure of Engineered Nanoparticles to Human Lung Epithelial Cells: Influence of Chemical Composition and Catalytic Activity on Oxidative Stress” by Ludwig K. Limbach, Robert N. Grass, and Wendelin J. Stark, Swiss Federal Institute of Technology Zurich (ETH Zurich); and Peter Wick, Pius Manser, and Arie Bruinink, Swiss Federal Laboratories for Materials Science and Technology (Empa), 2007, 41 (11), 4158–4163. A box in a lab at ETH Zurich may be one of the safer places to conduct experiments on nanomaterials. The 1 metric ton aluminum box, built by Wendelin Stark and his co-workers, protects its users from high exposures to tiny particles. Stark and his team, together with researchers at Empa, have good reason to be cautious. In one of ES&T’s top papers of 2007 they have identified some of the first mechanisms of toxicity for metal and oxide nanoparticles. In the winning paper the researchers describe their discovery as the “Trojan horse” behavior of nanoparticles, which can carry metals into cells. The work lays out how interactions between nanoparticles and cells’ interiors or tissues help create reactive oxygen species, including free radicals and peroxides, which at high levels can damage cell structures (e.g., during oxidative stress). The researchers com-
2212 ■ Environmental Science & Technology / April 1, 2008
Nanoparticles act as Trojan horses that can smuggle metal oxides into cells.
pared nanosized cobalt and manganese oxides with their molecular-sized cousins and found eight times more reactive oxygen species(ROS) generated with the nanoparticles than with aqueous solutions of the heavy metals. Stark is one of the younger scientists to be hired as head of a lab at ETH. He estimates that two-thirds of his work is product development and one-third is biomedical-related. Funding comes from both in© 2008 American Chemical Society
dustry and government, and Stark’s team includes biologists, chemists, and mechanical engineers. Stark started out as a chemist who got lured into nanomaterials during his graduate work as a mechanical engineer. “If somebody had asked me 5 years ago, ‘Are you going to be one of the guys doing nanotoxicity?’” his answer would have been “no,” he insists. But he quickly got interested in toxicity research, in part because of his knowledge of particulate matter and human health (both of his parents trained as medical doctors). One of his main goals is to avoid opening the Pandora’s box of nanomaterials ecotoxicity. “We can’t do product development without toxicology research; anything else would be irresponsible,” Stark says. In building prototypes for companies, “we don’t [continue] if we think it’s not safe,” he comments, and the researchers inform a
company as to why they think a new nanomaterial might be toxic, in support of the choice not to pursue it. “I never know if I made the right judgment call,” he says, adding that only time will tell if “we were overcautious. . . . We have to be very, very proactive and very, very precautious. One day we’re going to make a wrong decision.” His rules are simple, the first of which is to avoid nanomaterials that are “ultrapersistent”. “I think we’ll hear more from him,” says Peter Gehr, a particle–lung dynamics researcher at the University of Bern (Switzerland) and a collaborator with Stark’s group. The team “has an exposure system that’s unique,” Gehr comments, in that the experimental apparatus in the glove box “creates an atmosphere of nanoparticles [that is] much more natural than . . . other tricks to get nanoparticles to cells.” —NAOMI LUBICK
“Carbon and Chlorine Isotope Effects During Abiotic Reductive Dechlorination of Polychlorinated Ethanes” by Thomas B. Hofstetter and Christopher M. Reddy, Woods Hole Oceanographic Institution; Linnea J. Heraty and Neil C. Sturchio, University of Illinois Chicago; and Michael Berg, Swiss Federal Institute of Aquatic Science and Technology (Eawag), 2007, 41 (13), 4662–4668. In 2004, Thomas Hofstetter left his home in Switzerland to spend a year in the U.S. devoted almost entirely to one project. The end result is one of ES&T’s best papers of 2007, work that Dave Dzombak of Carnegie Mellon University’s department of civil and environmental engineering calls “broadly pathbreaking.” When Hofstetter began the project, he was affiliated with Eawag, the Swiss Federal Institute of Aquatic Science and Technology. He credits previous work on chlorine isotopes by coauthors Chris Reddy and Neil Sturchio with inspiring him to undertake this research at Woods Hole Oceanographic Institution (WHOI), where Reddy is a marine geochemist. The proposal was to use combined carbon and chlorine isotope analysis to elucidate chlorohydrocarbon degradation pathways in the environment. Hofstetter chose chromium(II) as a model reductant because it mimics one of the reductive transformation reactions of this contaminant class in anoxic soils and groundwater. As Reddy recalls, Hofstetter’s ambitious goal of determining the physical–chemical underpinnings of why the isotopic effects were happening made the proposal stand out. The Swiss
Thomas Hofste t ter
First runner-up: Chlorohydrocarbon degradation pathways
A key step in sample preparation for chlorine isotope analysis was conducted with this setup in Neil Sturchio’s laboratory at the University of Illinois Chicago.
National Science Foundation funded Hofstetter’s stay in the U.S. Compound-specific isotope analysis is rapidly gaining importance for assessing fate and degradation of organic contaminants in the environment, but it has been used mainly with hydrogen and carbon, and more recently nitrogen, Hofstetter explains. Chlorine isotope fractionation hasn’t been used much in environmental chemistry because of “a combination of analytical challenges,” Dzombak points out. The large natural abundance of 37Cl makes interpreting isotopic effects much more difficult than is the case for carbon, hydrogen, or nitrogen isotopes, Dzombak says. WHOI is known for its isotope analysis research (among other things), and some of the commercial equipment used in the field was developed there, Hofstetter notes. However, the institution does not April 1, 2008 / Environmental Science & Technology ■ 2213
have the equipment required to analyze chlorine isotopes. As a result, Sturchio’s group conducted all of the chlorine isotope analytical work at his laboratory in the University of Illinois Chicago’s department of earth and environmental sciences. Hofstetter made two visits to Chicago during his year in the U.S., although one of the trips was cut short by a snowstorm. Dzombak commends the paper for demonstrating “that chlorine isotope effects can be used to elucidate transformation products and alternative transformation pathways of such compounds. In addition to providing specific new insights into the
transformation of [polychlorinated ethanes], the paper provides a methodology that can be used for reaction pathway study with many other chlorinated compounds.” Hofstetter is now a senior researcher at the Swiss Federal Institute of Technology Zurich Institute of Biogeochemistry and Pollutant Dynamics. He says that “recent analytical developments regarding compound-specific analysis of chlorine isotopes seem to simplify such measurements and are likely to motivate further work on chlorine isotope effects in this area.” —KELLYN BETTS
“A Sensory System at the Interface between Urban Stormwater Runoff and Salmon Survival” by Jason F. Sandahl and Jeffrey J. Jenkins, Department of Molecular and Environmental Toxicology, Oregon State University; and David H. Baldwin and Nathaniel L. Scholz, NOAA Fisheries, Northwest Fisheries Science Center, Ecotoxicology and Environmental Fish Health Program, 2007, 41 (8), 2998–3004. When Jason Sandahl started learning about salmon noses as a doctoral student at Oregon State University, he didn’t know his research might help change the way toxicologists think about how contaminants affect animal health. Sandahl grew up on a pear and cherry farm in Oregon’s Hood River valley. “One concern in the Northwest is what contaminants may be doing to [declining] salmon populations,” he says. In graduate school at Oregon State University, he began studying the effects of pesticides on salmon by using traditional toxicological approaches, which rely heavily on determining the levels that kill an animal. His research soon took a different turn. He realized that fish noses are essentially bundles of nerves exposed directly to the water. That meant pesticides in the water, specifically the copper that many streams contain, might interfere with a fish’s sense of smell. Copper in streams comes not only from pesticides but also from the copper-containing brake pads that drop dust onto roadways. Stormwater later washes the copper dust into streams. In salmon, the sense of smell is especially keen— and important. They find food and mates, navigate, and avoid predators by using their finely tuned noses. Sandahl teamed up with ecotoxicologist Nathaniel Scholz of the National Oceanic and Atmospheric Administration (NOAA) to learn whether copper might damage salmon’s sense of smell enough to put them at risk. One important behavior for salmon is predator avoidance—when a salmon smells pheromones from torn fish skin, it knows that a comrade has been attacked. It then carries out a “stop and 2214 ■ Environmental Science & Technology / April 1, 2008
Nathaniel Schol z
Second runner-up: Copper changes salmon behavior
Jason Sandahl probed fish noses and found that nerve damage from copper can spell big trouble for little salmon.
drop” maneuver, holding still near the streambed to avoid detection. In laboratory experiments, fish that had been exposed to low levels of copper seemed oblivious to torn salmon skin and kept swimming. This could make salmon, especially small juveniles, vulnerable to becoming a predator’s lunch. Sandahl used sensitive probes to measure nerve signals from the fish’s noses and detected nerve damage corresponding to the behavioral changes. “This research opens up the door to a greater array of ecological impacts than we’re accustomed to dealing with,” Sandahl says. The U.S. EPA sets waterquality standards for protecting threatened and endangered species, such as salmon, but Scholz notes that EPA does not take into account effects on behavior. If copper’s effects on behavior are shown to reduce population sizes, that might change one day. Scholz and colleagues have continued their experiments and recently published a paper in ES&T (2008, 42, 1352–1358) showing that organic matter
in natural waters could partially offset copper’s effects but that water hardness and alkalinity offer little protection. Scholz says, “I think a lot of the community has been waiting for this follow-up study, because they want to know if this [nerve damage from copper] happens under real-world conditions. This paper should reasonably put that question to rest.” Now,
his group is working to establish how copper affects whole salmon populations. He says it will be a long road to change federal environmental regulations, but in the meantime he is working with NOAA’s Coastal Storms Program to help community groups reduce contamination from stormwater in local watersheds. —ERIKA ENGELHAUPT
“A Graphical Systems Model to Facilitate Hypothesis-Driven Ecotoxicogenomics Research on the Teleost Brain-Pituitary-Gonadal Axis” by Daniel L. Villeneuve, Michael D. Kahl, Kathleen M. Jensen, Elizabeth A. Makynen, Elizabeth J. Durhan, and Gerald T. Ankley, U.S. EPA, Duluth, Minn.; Patrick Larkin and Barbara J. Carter, EcoArray; Iris Knoebl, U.S. EPA, Cincinnati, Ohio; Ann L. Miracle, Pacific Northwest National Laboratory; and Nancy D. Denslow, University of Florida, 2007, 41 (1), 321–330. So intricate it can only be displayed poster-sized. So involved it required a collaborative effort among molecular biologists, bioinformaticists, modelers, chemists, and toxicologists. The end product: a representation of an interactive set of molecular and biochemical pathways and controls related to fish reproduction. The work, which could eventually be applied to whole-organism effects relevant to ecological risk assessments, has been named one of ES&T’s best papers of 2007. Reproduction is complex, emphasizes lead author Daniel Villeneuve, a biologist at the U.S. EPA’s Mid-Continent Ecology Division in Duluth, Minn. Reproductive control requires interaction and communication among the brain (pituitary and hypothalamus), the gonads (testes or ovaries), and the liver. Genes are up- or down-regulated, RNA is translated into proteins (enzymes, protein hormones, egg yolk precursors, structural constituents, and more), and steroid hormones are synthesized. Hormones travel between organs—primarily via the bloodstream—where they trigger both physiological responses and multiple feedback loops. Scientists in systems biology are using relatively complex systems models to show what goes on in a single cell, notes Villeneuve. The EPA researchers apply similar concepts and tools to the study of fish reproduction. Their objective is to look at signals transmitted within this multiorgan system in response to chemical stressors and to understand both direct and indirect effects of chemicals such as endocrine disrupters. The approach enables researchers to look at where chemicals can impact signaling pathways and facilitates hypothesis-driven ecotoxicogenomics research, as opposed to a solely discovery-oriented approach, explains Villeneuve.
Roger LePage
Third runner-up: A step toward predictive toxicology
The Duluth-based researchers and their complex graphical systems model. From left: Michael D. Kahl, Elizabeth A. Makynen, Daniel L. Villeneuve, Elizabeth J. Durhan, Gerald T. Ankley, and Kathleen M. Jensen. Coauthors from other locales are not pictured.
Endocrine disrupters have been an important area of research at the Duluth EPA lab for a decade, says team leader Gerald Ankley. By providing an approach to determine where impacts and adverse effects might occur, the authors aspire to link molecular initiating events to ecologically relevant outcomes. They hope that the model will help EPA make regulatory decisions and that it can serve as a guide for EPA and other regulatory organizations to understand and conduct the kind of research needed to support predictive risk assessment, notes Ankley. “There are way too many chemicals out there to test in terms of collecting empirical data, so the agency and the other regulatory agencies throughout the world are trying to develop better predictive models in terms of understanding possible consequences of exposure and effects of chemicals,” he says. The researchers applied their model to fadrozole, which inhibits aromatization, a specific point in estrogen biosynthesis. They hypothesized which genes fadrozole would affect and what the physiological consequences would be. When they subsequently tested fadrozole on fish, results showed that the model accurately predicted molecular responses in many, but not all, cases. The group is currently testing a dozen other hypothetically relevant chemicals. Knowing where their predictions are incorrect will help refine the model, says Villeneuve. The model is the first of its kind in ecotoxicology, says biologist John Sumpter of Brunel University (U.K.). “This model allows someone to predict all the known genetic and biochemical effects of a chemical that affects reproduction in fish, even if only one effect is known or has been measured,” he says. —BARBARA BOOTH April 1, 2008 / Environmental Science & Technology ■ 2215
ENVIRONMENTAL POLICY Top paper: A low-emissions future
Christian Solli
“China’s Growing CO2 Emissions—A Race between Increasing Consumption and Efficiency Gains” by Glen P. Peters, Norwegian University of Science and Technology; Christopher L. Weber, Carnegie Mellon University; and Dabo Guan and Klaus Hubacek, School of Earth and Environment, University of Leeds (U.K.), 2007, 41 (17), 5939–5944.
Glen Peters and coauthors find that the Chinese have taken steps to improve their energy efficiency and still travel mainly on bicycles, a sustainable, zero-emissions mode of transport.
Many people get emails that they would rather just ignore, either requesting information or asking for help. The top ES&T environmental policy paper of 2007 is a collaboration that sprang from just such a request. Carnegie Mellon University graduate student Christopher Weber was looking for energy-related emissions data from China to use in his model analyzing the impact of U.S. trade on global CO2 emissions. Weber, who had just finished reading an article by Glen Peters, an Australian-born researcher working in Norway, sent Peters an email about the paper’s data from China. Peters opened the email, and a few exchanges later, the two agreed to cooperate on a further analysis of the emissions impact of China’s rapidly growing economy. Peters had visited China several times before he decided to investigate the data located at the National Bureau of Statistics of China in Beijing. Once inside the stacks, he stumbled “by sheer coincidence”
First runner-up: Targeting agri culture to reduce fine particles “Ammonia Emission Controls as a Cost-Effective Strategy for Reducing Atmospheric Particulate Matter in the Eastern United States” by Robert W. Pinder and Peter J. Adams, Department of Engineering and Public Policy and Department of 2216 ■ Environmental Science & Technology / April 1, 2008
upon a report, written in English, detailing a project between Norway and China that analyzed China’s emissions of CO2, SO2, and nitrogen oxides (NOx). “For some reason, this report never made it into the literature. Unless you had walked into the statistical bureau, you wouldn’t know it was there,” Peters says. China is a huge player on the world stage today, and its growing economy and energy consumption are creating environmental problems on both local and global scales. The coauthors set out to examine the key drivers behind China’s growing energy consumption. Using data compiled by the Chinese government to examine the country’s economic development, the authors analyzed 95 different economic sectors, such as manufacturing, electricity, and transportation. They found that from 1992 to 2002, CO2 emissions in China rose by 59%, or from 2163 million metric tons (MMT) to 3440 MMT. But recent satellite data suggest that China may have underreported its coal consumption from 1996 to 2003. When the calculation is adjusted with modified data on coal consumption, CO2 emissions are found to have risen by even more (76%) over the 10-year period. Production processes related to increased consumption by the Chinese were the biggest driver for the rise, the researchers found. Yet efficiency processes related to improved technology offset that increase by –62% (or –50% with the modified data). “We see that the Chinese have increased their energy efficiency over the last 15 to 20 years, and they are trying to reduce their CO2 emissions,” Weber says. Key to this paper was a desire to provide insight into how other developing countries can develop a low-emissions future, the authors note. China is engaged in a high-speed industrial revolution, but the country has a clear opportunity to invest in a less-carbon-intensive economy. For example, rather than spend on a fixed telephone infrastructure, the government can invest in “leapfrogging straight to mobile technologies,” says Weber. It can develop natural-gas resources for transportation, instead of focusing on limited efficiency improvements in gasoline or other liquid fuels. China and India, in particular, will have to build vast amounts of infrastructure to care for their burgeoning urban populations, Peters says. “Our paper might show them where the opportunities are for innovation,” he adds. —CATHERINE M. COONEY
Civil and Environmental Engineering, Carnegie Mellon University; and Spyros N. Pandis, Department of Chemical Engineering, University of Patras (Greece), 2007, 41 (2), 380–386. When Rob Pinder came to Carnegie Mellon University (CMU) in 2001 to begin a graduate career that melded engineering with economics and policy, he planned to model global particulate matter.
Rob Pinder has found that reducing barnyard emissions of ammonia could be an inexpensive way to cut wintertime particulate matter.
Pinder found that cutting NH3 by 50% can diminish wintertime inorganic PM2.5 by up to 50%, and it is cheaper than putting controls on smokestacks. The study opens the door to begin regulating farms as significant sources of air pollution. Pinder’s advisers, Peter Adams, Spyros Pandis, and Cliff Davidson, had been studying the role of NH3 in forming haze—the mix of large and small particles of dust, gas from trees, and emissions from burning fossil fuels. Half of the PM2.5 was derived from SO2 and nitrogen oxides (NOx) emitted from power plants and cars and NH3 evaporating from farm-animal urine. These tiny particles cause tens of thousands of deaths in the U.S. each year. The U.S. EPA has regulated PM2.5 by tightening controls on smokestacks and vehicles, but most of the cheap and effective cuts—the “low-hanging
COURTESY OF ROB PINDER
But serendipity nudged him over to a project that many said could not be done—estimating the relative ease of reducing fine particulate matter (PM2.5) pollution by cutting ammonia (NH3) emissions on farms. His work went on to become one of ES&T’s best papers of 2007.
fruit”—have been made, Pinder says. That leaves NH3 as an ideal candidate to further ratchet down PM2.5, he says. “But everyone said there was too much uncertainty about NH3 —its chemical interactions and the amount of emissions—to do anything about it,” Pinder adds. When Pandis was working on the thermodynamics of NH3 in the atmosphere, Adams, Davidson, and Pinder were perfecting NH3 emissions inventories. The next step was to combine their knowledge to determine whether it would be cost-effective to regulate NH3 emissions on farms, Adams says. Pinder says the biggest challenge was the absence of detailed NH3 cost data—the price of reducing nationwide emissions of NH3 by a certain percentage. His solution was to create the NH3 savings potential, which is the cost of cutting SO2 and NOx to achieve the same reduction in PM2.5 that you would get from cutting NH3 by 1 ton (t). “I struggled a lot with how to present that idea,” he says. The payoff was big. Pinder found that the SO2 and NOx cuts cost $8000–28,000/t. “Even at the lower end, there are a lot of ways to reduce NH3 that cost less than $8000/t,” he says. These techniques include covering animal-waste storage areas and adapting poultry housing. “I thought we would see an effective reduction in NH3 emissions and PM2.5, but how robust both were was surprising,” Pinder says. Cutting NH3 by 50% in winter reduces inorganic PM2.5 by 5–50%, depending on the region of the country. In 2005, Pinder moved to EPA’s Office of Research and Development, where he is looking at the ecosystem impacts of NH3 deposition. —JANET PELLEY
“A Global Comparison of National Biodiesel Production Potentials” by Matt Johnston and Tracey Holloway, University of Wisconsin, 2007, 41 (23), 7967–7973. For Matt Johnston, a honeymoon in Fiji served as inspiration for a novel research project and an award-winning paper in ES&T. The paper sets forth an analysis of countries positioned to jump into the growing biodiesel market, and it reveals some surprising future leaders. When Johnston started thinking about thesis projects for his M.S. at the University of Wisconsin Madison, he knew he was interested in international development. His adviser, Tracey Holloway of the university’s Center for Sustainability and the Global Environment, studies the environmental impacts of energy use. As the pair brainstormed research ideas, Johnston kept coming back to his recent trip to one of the islands of Fiji. “They used diesel exclusively on the island, mainly in generators for electricity,” Johnston says. “On
Tr ace y Holloway
Second runner-up: Future world leaders in biodiesel production
Matt Johnston (right) and Tracey Holloway compared 119 countries and identified the nations best suited to ramp up biodiesel production.
an island with only two vehicles, they were paying over $20 per gallon for diesel brought in by boat. Transport to the mainland was nearly impossible, and they hadn’t been able to afford to run the lights at their school since the Iraq war drove [diesel] prices up.” In contrast to the scarcity of fuel, the island was lush with natural resources. With all those tropical plants, Johnston started to imagine the islanders April 1, 2008 / Environmental Science & Technology ■ 2217
making homegrown biodiesel from vegetable oils, something he had tinkered with himself at home. “From an environmental standpoint, there’s a lot of potential for places like Fiji with no fossil resources but massive biological resources,” he says. Johnston and Holloway analyzed data from the UN Food and Agriculture Organization and ranked countries according to their potential to produce more biodiesel in the near future. The biodiesel industry has been doubling annually in some industrialized countries, but little analysis had been done of production potential around the globe. In terms of volume, the U.S. and Brazil topped the list because of their massive soy oil production. But the study also revealed that countries like Malaysia, Colombia, Thailand, Uruguay, and Ghana are well positioned to expand production. These countries already grow and export oil-rich crops such as coconut, sunflower, and rapeseed. Thanks to their stable governments and space to expand agriculture, these countries could convert such crops to biodiesel instead of exporting them.
“Our goal was certainly not to say that these countries should convert all of these resources to fuel oil. But some countries may be exporting commodities that could be converted to higher-value fuels or could be used domestically to meet their own energy needs,” Holloway says. The research was such a positive experience that Johnston decided to pursue a Ph.D. with Holloway as his adviser. He is now studying the environmental impacts of biofuel production, such as the effects of clearing tropical forests to grow biofuel crops—a practice that destroys stores of carbon that can take hundreds or thousands of years to replenish, Johnston says. To avoid losing forests, countries could use existing agricultural land more efficiently by increasing crop yields—the amount of oil produced on each hectare of land. Johnston and Holloway are now assessing the potential for raising yields around the world. “There is a place for biofuels,” Johnston says, “and we’re looking for how to [produce them] in the most sustainable way.” —ERIKA ENGELHAUPT
susan rosser
ENVIRONMENTAL TECHNOLOGY “Impact of Transgenic Tobacco on Trinitrotoluene (TNT) Contaminated Soil Community” by Emma R. Travis and Susan J. Rosser of the University of Cambridge and the University of Glasgow (U.K.); Christopher J. van der Gast and Ian P. Thompson of the Natural Environment Research Council Centre for Ecology & Hydrology, Oxford (U.K.); and Nerissa K. Hannink and Neil C. Bruce of the University of Cambridge (U.K.), 2007, 41 (16), 5854–5861. A barren patch of ground, devoid of microbes or plants. That’s what you’ll find in the middle of a military training field or at TNT manufacturing sites. Microbes that can break down the explosive often get overwhelmed by the task, and plants don’t make a dent because TNT is so toxic. By putting genetically modified plants and microbes together, you get a very different story, say Neil Bruce and colleagues in one of ES&T’s top environmental technology papers of 2007. The team showed that the transgenic plants not only clean up TNT; they can also buttress the microbial community in their roots, furthering the remediation process. TNT is one of the “most recalcitrant organic compounds; that’s why it persists so long,” says Bruce, now at the University of York (U.K.). “Bacteria will break it down, but they don’t like it.” The phytoremediation method “promotes a ‘rhizosphere effect’,” he continues, with roots pumping nutrients into the soil and performing a kind of “rhizoremediation” 2218 ■ Environmental Science & Technology / April 1, 2008
EMMA TRAVIS
Top paper: Microbes thrive with tobacco’s TNT cleanup
Emma Travis (left) and Neil Bruce visited a barren, TNTtainted site in western Scotland on one of the stormiest days of the year to collect soil samples. Inset: Transgenic tobacco plants in a growth room at the University of Cambridge.
at the same time. “There’s a huge amount of work with transgenic plants above ground,” says Bruce. “We wanted to answer what would happen to the microbial community” living with the plants. Building on tobacco plants created several years ago, Emma Travis, a graduate student at the time who is now at the University of Warwick (U.K.), set up rows of both wild-type and genetically modified plants in clean and TNT-spiked soils in growth rooms at the University of Cambridge (U.K.). Bruce’s lab, led by coauthors Nerissa Hannink and Susan Rosser (now of the University of Glasgow), had constructed the new tobacco plants by modifying them with genes from Enterobacter cloacae. The bacteria use two enzymes to catalyze the breakdown of TNT by a two-electron reduction. The transgenic tobacco plants take the resulting metabolites and make them
into harmless glycosylated compounds, sequestered away in the plants’ tissues. Months of monitoring showed that the genetically modified tobacco plants thrived in highly TNT-contaminated soils, compared with wild-type plants, which grew roots only half the length at concentrations of 4000 milligrams of TNT per kilogram of soil. The team reported that the transgenic plants had no effect on microbial communities living in uncontaminated soils. But microbes living with the modified tobacco plants in TNT-contaminated soils not only thrived; they also seemed to maintain diverse community structures. Bruce et al.’s paper presents “the first direct evidence that phytoremediation really is restoring the microbial community,” says Jim Spain, a microbi-
ologist at the Georgia Institute of Technology. After pioneering work on transgenic plants for breaking down TNT in soil, Bruce and his colleagues have “advanced the state of the art” with microbial experiments that are seldom conducted, he adds. “The results set the standard for examination of the effects of transgenic plants designed not only for destruction of contaminants, but also those designed for modification of other soil properties or functions.” Bruce’s lab recently joined with Stuart Strand of the University of Washington to explore the feasibility of transgenic poplars and grass for cleaning up military ranges and other contaminated sites. They will also look at disposal options for plants that contain transformed TNT or other explosives. —NAOMI LUBICK
Woods Hole Oce anogr aphic Institution
“Polyethylene Devices: Passive Samplers for Measuring Dissolved Hydrophobic Organic Com pounds in Aquatic Environments” by Rachel G. Adams, Massachusetts Institute of Technology (MIT) and Loyola Marymount University; Rainer Lohmann, MIT (now at the University of Rhode Island); and Loretta A. Fernandez, John K. MacFarlane, and Philip M. Gschwend, MIT, 2007, 41 (4), 1317–1323. Imagine being able to buy an efficient and accurate passive sampler that’s easy to deploy in aquatic environments and costs less than a dollar at the nearest hardware store. Rachel Adams of Loyola Marymount University and her co-workers say you can do just that. Those thin sheets of polyethylene plastic, often sold as painting drop cloths as well as for other purposes, serve well in the field as passive monitors for contaminants like PAHs, PCBs, and dioxins, they report. The team, led by Adams while she was a graduate student at MIT, published their findings in one of ES&T’s best environmental technology papers of 2007. The researchers “demonstrated how an inexpensive and simple device could be used to monitor hydrophobic contaminants in estuaries,” with “the potential to provide a new and better understanding of pollutant dynamics in these systems,” says David Sedlak of the University of California Berkeley. With this paper, comments Sedlak, the team has taken a method that until now has been qualitative and less reliable and done “an excellent job” of turning it into a quantitative one. Adams and her co-workers examined the polyethylene sheets’ partitioning coefficients, equilibrium absorption times, and other characteristics. Coauthor Rainer Lohmann, who also worked on the device at MIT and is now at the University of Rhode Island, says that the polyethylene monitors had never before been “investigated in such detail, with such physical chemistry background.” Lohmann and Ad-
RACHEL ADAMS
First runner-up: Simple sampler
Rachel Adams (right) and Linda Kalnejais prepare a buoy aboard the R/V Samantha Miller for deploying polyethylene passive samplers in the Hudson River estuary.
ams have continued their use of the monitors on research in the Hudson River, Narragansett Bay, and Los Angeles’s Ballona Creek estuaries. The simplicity of the approach could prove irresistible, but the method is not necessarily appropriate for every situation. “Passive samplers out there have different pros and cons,” says Adams, and scientists “can pick and choose depending on the application.” Polyethylene monitors may be better for substances with very low detection limits, because the larger the piece of plastic, the more of a chemical can be collected. But polyethylene devices require solvent extraction that is not necessary for more elaborate passive April 1, 2008 / Environmental Science & Technology ■ 2219
samplers, for example, solid-phase microextraction devices. These monitors, created for easy use with GC/MS, allow for more rapid analysis because their preparation and processing times are shorter; however, they are more expensive and have higher detection limits, Adams points out. Polyethylene’s drawbacks might include differences among brands of plastic sheets, from their thickness to the proportions of amorphous and crystalline structures in the plastic, which depend on the temperatures and methods used in the manu-
facturing process. Nonetheless, polyethylene monitors are much faster and more reliable than the original passive monitors scientists once used: mussels, or the “living samplers” that eventually led to plastic ones (Environ. Sci. Technol. 1983, 17, 490–496). Phil Gschwend, who oversaw the initial research at MIT, continues to tell his students that he wants a passive sampling device that will be easily deployed and ready for pickup after a leisurely cup of coffee. —NAOMI LUBICK
“High-Throughput Determination of Biochemical Oxygen Demand (BOD) by a Microplate-Based Biosensor” by Hei-Leung Pang, Nga-Yan Kwok, Pak-Ho Chan, Chi-Hung Yeung, Waihung Lo, and Kwok-Yin Wong, Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, 2007, 41, 4038–4044. Biochemical oxygen demand (BOD) is one of the most widely used and important tests for measuring organic pollution. But the conventional BOD test requires a 5-day incubation period and the skills of a well-trained technician. So it’s no wonder that several analytical research groups have been trying to develop a rapid, reproducible method—ideally one that can simultaneously handle a large number of samples. Kwok-Yin Wong and colleagues at Hong Kong Polytechnic University cracked the problem. In one of ES&T’s best papers of 2007, they describe a new optical BOD biosensor with analysis times of just 20 minutes. The principle of optical oxygen sensing is based on monitoring the luminescence intensity of an oxygen-sensing dye immobilized in a solid material. One of the advantages of an optical oxygen sensor over a dissolved-oxygen electrode is that the optical fiber allows for simultaneous measurements. “It was logical to develop an optical BOD biosensor by immobilizing a microbial film onto the optical oxygen-sensing film,” says Wong. In the late 1990s, the scientists had a machine that worked, but “it was rather clumsy,” says Wong. At that time, biologists were using microwell plates with readers for high-throughput screening and measurements. Wong and colleagues wondered whether they could modify a microwell plate for high-throughput determination of BOD. The search for the right materials to make the oxygen-sensing film and the microbial film was painstaking and took more than 5 years. In the beginning, graduate student Nga-Yan (Bernice) Kwok focused on silicone materials for the oxygen-sensing film, because of silicone’s good performance. The problem was that the microbial film, which is hydrophilic to enable the bacteria to survive, simply did not stick to the silicone film. Kwok tried many compositions for more than 2 years, but nothing 2220 ■ Environmental Science & Technology / April 1, 2008
K WOK-YIN WONG
Second runner-up: BOD biosensor
After more than 5 years of searching for the right materials, Kwok-Yin Wong’s group developed a fast microplate-based biosensor. Front, from left to right: Joseph Hei-Leung Pang, Bernice Nga-Yan Kwok, Chi-Hung Yeung; back, from left to right: Kwok-Yin Wong, Thomas Waihung Lo, Pak-Ho Chan.
worked very well. Then her luck changed. “One day we asked an undergraduate student to help Bernice try organically modified silicate for the oxygen-sensing film, and she found that the microbial film immediately stuck onto the oxygen sensor,” recalls Wong. “Bernice had mixed feelings at that time. On [the] one hand we found the right material, but on the other hand, she regretted [that] she did not start testing the silicate materials much earlier,” he says. Graduate student Hei-Leung (Joseph) Pang took up the challenge of getting the organically modified silicate oxygen-sensing film to stick to the wells on the microwell plate. He tested various organic and inorganic compositions for the film and tried microwell plates with different surface treatments. Eventually he found that only microwell plates that had been treated by corona discharge or gas plasma work because the treated polystyrene surface has oxygen-containing functional groups that interact with the silicate. Now Wong and his team are carrying on their search for the right materials to further improve the biosensor’s performance. —REBECCA RENNER
