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Successes and Discoveries in Environmental Chemical Science Progress in environmental science during the last several decades has de- pended heavily on contributions from chemistry and chemical engineering. These contributions range from understanding fundamental concepts of the behavior of materials in the environment to the development of procedures for protecting the environment and remediating environmentally contaminated sites. In the areas of fundamental science and engineering, the contributions fall into the categories of new or enhanced analytical capabilities, advances in fundamental science, and the development of new models and databases. Chemical contributions in the areas of environmental protection and remediation can be classified into tech- nologies for pollution control and remediation and for pollution prevention via synthesis, manufacturing, and process advances. ANALYTICAL CAPABILITIES Developments in analytical capabilities have allowed chemists and chemical engineers to detect ever smaller quantities of chemical substances. One hundred years ago, chemists were challenged by the task of carrying out analysis on samples smaller than a gram. But in some cases it is now possible to detect and measure the presence of substances at the level of single molecules, an improve- ment of some 20 orders of magnitude. Increases in time resolution have been similarly astonishing, from a situation in which it was difficult to measure events taking place at a time scale of less than a second to the investigation of processes that take place on the femtosecond (lo-~5 S) time scale. Often the measurements must be made remotely or must examine substances that are present in vanish- ingly small concentrations. 10
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SUCCESSES AND DISCOVERIES IN ENVIRONMENTAL CHEMICAL SCIENCE 1 1 Some of the improvements in detection, monitoring, and measurement science that have contributed to advances in environmental science include the development of the electron-capture detector (with its high sensitivity for haloge- nated organic compounds), the application of gas chromatography-mass spec- trometry (which combines separation of mixtures with reliable identification of their components), advances in sensor technology, and the availability of syn- chrotron-based methods for x-ray studies. Improved mass spectrometric methods have made it possible to characterize single aerosol particles in the atmosphere and have provided improved time resolution for atmospheric measurements. Sat- ellite-based technology and remote sensing have enabled monitoring and space- based measurements that are far more comprehensive than those that were pos- sible using aircraft and balloons. FUNDAMENTAL CHEMICAL SCIENCE Advances in the understanding of basic chemical science have been respon- sible for substantial progress in environmental science. Similarly, progress in environmental chemistry has driven fundamental science, as illustrated by the vastly improved understanding of the nature of complex bimolecular reactions brought about by investigations of important atmospheric chemical processes. Key contributions include the following: · advances in fundamental understanding of the chemistry of free radicals, which play key roles in a variety of atmospheric, aquatic, and terrestrial chemical processes; · advances in surface chemistry that have provided a better understanding of reactions on surfaces and in microporous regions; · better understanding of homogeneous gas-phase chemistry; · establishing structure-activity relationships for the activity and fate of chemical species in the environment; · advances in genetics at the molecular level that have made it possible to use bioremediation to clean up environmentally contaminated sites and to under- stand generic gene-environment relationships in the environment; · fundamental understanding of the internal combustion process, which has led to improved engine efficiency; and · advances in chemically based technologies (e.g., fuel cells, batteries, and photovoltaics) that have contributed to environmental improvements in the en- ergy and transportation sectors.) ~ Also see the related report in this series: Challenges for the Chemical Sciences in the 21st Cen- tury: Energy and Transportation, National Research Council, The National Academies Press, Wash- ington, D.C., 2003.
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2 THE ENVIRONMENT Some of the advances in fundamental science that have led to new attitudes and approaches to environmental problems include the use of correlated chemical measurements to investigate environmental processes, development of industrial ecology as a framework for studying issues, use of life-cycle analysis to evaluate the impact of substances in the environment, recognition of the importance of speciation (in contrast to total concentration) of chemical substances, and recog- nition that a systems approach is often necessary to address complex environ- mental issues. MODELS AND DATABASES By any criteria one might employ, the environment is a large and complex system. As a consequence, there are large barriers to developing predictive capa- bilities, even for localized portions of the environment. However, these barriers have been partially surmounted by the substantial progress that has been made in computing-related areas, enabled in large part by the tremendous growth over the last several decades in computing speed and capabilities. Specific areas of ac- complishment include the generation of databases of kinetic and thermodynamic data, new software and modeling techniques (at scales from molecular to global), development of computational models that permit the simulation of both funda- mental and complex systems with ever increasing fidelity, and to some extent, advances in predicting risk and taking risk-based corrective action. POLLUTION CONTROL, REMEDIATION, AND PURIFICATION Technical solutions have been developed to a number of important environ- mental problems. One of the most important contributions to human health has been the chemical purification of drinking water, which has nearly eliminated water-borne diseases in developed countries.2 Disinfection with chlorine and ozonation have been used to eliminate pathogens, and advances in membrane science have enabled removal of various substances from water. Many of the technical solutions have been developed in response to unexpected problems cre- ated by other technical advances. Solutions have not been limited to water, however. Atmospheric pollution from automobiles has decreased dramatically in the last 25 years since the devel- opment and deployment of the catalytic converter (Box 2-1~. Modern three-way catalysts can simultaneously reduce the concentrations of carbon monoxide, hy- drocarbons, and nitrogen oxides in the automobile's exhaust stream. Also, new methods for remediation of contaminated soils have been provided by the selec- tion of unique plants and microbes for this purpose. 2Greatest Engineering Achievements of the 20th Century; National Academy of Engineering: Washington, DC, 2000; http://www.greatachievements.org/.
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SUCCESSES AND DISCOVERIES IN ENVIRONMENTAL CHEMICAL SCIENCE 13
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4 THE ENVIRONMENT
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SUCCESSES AND DISCOVERIES IN ENVIRONMENTAL CHEMICAL SCIENCE 15 POLLUTION PREVENTION: SYNTHESIS, MANUFACTURING, AND PROCESS ADVANCES Environmental contributions from the chemical sciences have not been lim- ited to cleaning up existing problems. Major contributions have been also been made in pollution prevention, so that the undesired components are never gener- ated in the first place. Some of the contributions include · using life-cycle analysis to identify more clearly where and when envi- ronmental impacts occur in the cycle of raw material production and product manufacture, packaging, storage, use, and disposal; · improving existing processes, such as the development of cleaner-burning fuels, for which less exhaust-stream treatment is needed;
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16 THE ENVIRONMENT · using substitutes for example, replacing organic solvents with water or supercritical carbon dioxide to reduce emissions of organic solvents into the envi- ronment; other substitutes include replacement for heavy metals and chlorofluoro- carbon (CFC) replacements as discussed in Box 2-2; · enhancing energy efficiency and development of improved photovoltaic devices; · developing degradable materials such as pesticides and polymers to reduce potential problems associated with persistent chemicals and materials; · using biomass rather than petroleum as a feedstock for chemical processes; and · employing atom economy as a strategy in chemical processes, thereby minimizing the amounts of waste for disposal. Much of the contribution that has been made in these areas is encom- passed by the phrase green chemistry, which is an approach to doing chemistry and chemical engineering that minimizes negative impacts on the environment through pollution prevention. It has been defined as the "design of chemical prod- ucts and processes that reduce or eliminate the use and generation of hazardous substances."3 Such processes continue to be developed, and they demonstrate that such technologies can be both economically and environmentally viable. Sev- eral speakers at the workshop presented examples of green process technologies (see Appendix D): . · Development of new catalysts eliminates carbon tetrachloride as a by- product in the production of phosgene from carbon monoxide and chlorine (U. Chowdhry); · Manufacture of new high-solids enamel for automotive coatings reduces volatile organic compound emissions, reduces odor emissions by 86%, and reduces total raw materials use by 20% (U. Chowdhry); · The use of a big-based catalyst to make a key intermediate (5-cyano- valeramide) in the production of a new herbicide has increased the yield from 20% to 93% and greatly reduced the quantity of catalyst waste (U. Chowdhry); · Polymerization of fluoroolefins in liquid and supercritical carbon dioxide eliminates the use of water and C-8 surfactant that has been identified as a persis- tent organic pollutant (R. Carbonell); . The development of surfactants for CO2 has made possible the commer- cialization of a dry cleaning process replacing perchloroethylene (R. Carbonell); · The use of new catalyst in the process for manufacture of glyphosate (a herbicide with desirable environmental properties) results in the use of reduced waste, raw materials with lower toxicity and volatility, and lower energy con- sumption (M. Stern); and 3http://www. epa.gov/opptintr/greenchemistry/
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SUCCESSES AND DISCOVERIES IN ENVIRONMENTAL CHEMICAL SCIENCE 17 · Genetic modification of soybeans, corn, canola, and cotton has produced glyphosate-resistant crops that lead to lower pesticide use, yield improvement, and improved water quality (M. Stern). The Presidential Green Chemistry Challenge Awards Program4 has rec- ognized a wide range of accomplishments that include the following: · Cost-effective production of 1,3-propanediol, a new feedstock for polyes- ters, using a genetically engineered fermentation pathway (DuPont, 2003~; · Polylactic acid, a polymer for fibers and packaging that is derived from renewable resources (Cargill Dow LLC, 2002~; Waste-free manufacture of an environmentally friendly chelating agent (Bayer Corporation and Bayer AG, 2001~; . . Wong, 2000~; · A new catalyst for oxidation in pharmaceutical manufacturing that re- duces chromium waste and solvent usage (Lilly Research Laboratories, 1999~; · The concept of atom economy (Barry M. Trost, 1998~; Enzymes and processes for large-scale organic synthesis (Chi-Huey Surfactants for supercritical CO2 (Joseph M. DeSimone, 1997~; and Manufacturing of polystyrene foam with CO2 replacing CFCs as the blow- ing agent (Dow Chemical Company, 1996~. IDENTIFICATION OF PROBLEMS Environmental problems cannot be solved if they have not first been de- tected. Many environmental problems have been chemical in nature, but they have occurred as unexpected consequences of other processes or developments. Discovering such problems including identification of their underlying causes and elucidation of the details of the chemical processes involved has relied heavily on the work of chemists and chemical engineers. Atmosphere Chemically related atmospheric problems have had high visibility in recent years. No matter how cautious one may be on the topic of global warming, it is clear that the greenhouse effect of carbon dioxide, methane, ozone, nitrous oxide, and the CFCs must be considered as a factor in global climate change. The mo- lecular behavior of the greenhouse gases explain their ability to absorb infrared radiation from the earth and convert it to heat. Similarly, the photochemistry of chlorofluorocarbons (CFCs) molecules originally believed to be completely benign provided the explanation for stratospheric ozone depletion. 4 ht~p://www. epa.gov/opptintr/greenchemistry/docs/award_recipients_1996_2002.pdf
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18 THE ENVIRONMENT
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SUCCESSES AND DISCOVERIES IN ENVIRONMENTAL CHEMICAL SCIENCE 19
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20 THE ENVIRONMENT Chemists and chemical engineers have also contributed to the recognition of the importance of particulate matter in the atmosphere and the heterogeneous atmospheric chemistry that the particulate matter enables. Similarly, chemists and chemical engineers have provided the basic science that led to an understand- ing of photochemical smog formation and acid rain. This further helped to estab- lish the role of biogenic emissions in the formation of smog. Water Many environmental problems in water result from chemical species that are present in only trace quantities. Consequently, chemical analysis and detection have made major contributions to discovering and understanding these problems. Examples include the problems of bioaccumulation of certain chemicals, persis- tent organic pollutants, pesticide residues, and the health effects of arsenic and lead as well as other trace metals. Soil Soil contamination also can be very difficult to detect. New analytical meth- ods have made it possible to detect and analyze dioxins, polyaromatic hydrocar- bons (PAHs), and polychlorinated biphenyls (PCBs). Analytical techniques have made it possible to detect the presence of these substances, determine whether remediation is needed, and evaluate the extent to which it has been carried out. Chemistry has provided or contributed to the remediation technologies that have been developed, Chemists and chemical engineers have helped to develop a better under- standing of interracial processes. These govern the behavior of pollutants at the soil-water interface, and understanding them is essential to any remediation ef- fort. Such interracial processes can be of particular importance for the radioac- tively contaminated sites that were created over many years in the nation's nuclear weapons program. INTERDISCIPLINARY DISCOVERIES Chemists and chemical engineers do not work in isolation, and much of the work described here has involved collaboration with scientists and engineers in other disciplines. In many cases these collaborations have enabled particularly important advances in environmental science, as illustrated by the examples in the following list:
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SUCCESSES AND DISCOVERIES IN ENVIRONMENTAL CHEMICAL SCIENCE 21 Biology · Microbial in situ bioremediation and microbial community genomics · Proteomics and metabolomics · Polymerase chain reaction (PCR) and revolutions in molecular biology Physics and Engineering · Tools: new instrumentation; sensors, measurement systems and platforms Materials Science · New catalysts Mathematics and Computer Science datasets · Multiscale computing (time and space) · Bioinformatics (handling huge databases); analysis of high-throughput · Development and implementation of efficient molecular modeling soft- ware on advanced computers Atmospheric Science, Meteorology, and Geology · Biogeochemical cycles (carbon, nitrogen, etc.) · Mechanisms and impact of contaminants Many additional examples of collaborative work were brought up during the workshop, and these are summarized in Appendix G (Interfaces). It is frequently difficult to identify the particular scientific accomplishment that have led to envi- ronmental improvements or enhanced environmental understanding, in large part because environmental studies are inherently multidisciplinary. Consequently, cooperation across disciplines as described above and in Appendix G will continue to be necessary to fully understand and solve environmental problems, so the list also represents research opportunities for the future.
Representative terms from entire chapter: