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The mission of the United States Environmental Protection Agency is to protect human health and the environment by ensuring a clean and healthy environment for the American people. EPA’s Office of Research and Development conducts research relevant to the regulatory mandate of the Agency. Transcript: ORD's National Exposure Research Laboratory conducts high priority research leading to improved methods, measurements and models to assess and predict exposures of humans and ecosystems to stressors in air, water, soil, and food. The goal is to apply strategic, integrated, and multi-disciplinary approaches to inform and implement regulatory programs. As one of six research divisions of NERL, the mission of the Ecosystems Research Division, located in Athens, Georgia, is to study the behavior of stressors, including contaminants, pathogens and nutrients in environmental systems. Once stressor behavior is known, mathematical models are developed to evaluate the response of aquatic systems, watersheds and landscapes to these stressors. To support this mission, ERD employs a staff of dedicated scientific and administrative professionals whose work results in high-quality and timely research. ERD develops tools, products and applications that address four critical areas of the exposure source to outcome continuum. ERD research focuses on determining and characterizing stressor origins and sources; developing laboratory, field and computational methods for deriving data used for fate and transport modeling; predicting and verifying resultant ambient environmental concentrations and distributions, which can lead to exposure, or the co-occurrence in time and space of a stressor and a receptor. Process chemistry is targeted to meet current research and modeling needs locally, across the Agency and federal government, and the academic community. ERD conducts process research in support of regulations such as the Safe Drinking Water Act, by identifying emerging chemical stressors, and FIFRA, by investigating the impact of chirality on pesticide fate and transport. Few Americans know what fluorotelomer-based polymers are, but most of us enjoy their benefits daily because these polymers are used in a wide variety of consumer products. Recent research has shown that by-products of these polymers are globally distributed in ecosystems, biota and humans. ERD research is focused on determining the degradation rates of these polymers, as well as the molecular-transformation pathways and environmental distribution of the by-products. In 2006, ERD opened a new state of the art Nuclear Magnetic Resonance, or NMR, Research Facility, housing two 600 megahertz spectrometers. These are being used to collect data for several high-priority research projects, including metabolomic studies on fathead minnows that seek to understand the linkage between formation of a chemical stressor, its level of concentration in the environment, and its dosage inside the organism. Overall, the NMR is a powerful tool for assessing the impacts of exposure to environmental contaminants in many different organisms. More capabilities -- which will expand the range of sophisticated experiments to be conducted – will continue to be added to the system. Recent trends in environmental regulation indicates that the Agency will have to rely more heavily on predictive modeling to carry out the increasingly complex array of exposure and risk assessments necessary to develop scientifically defensible regulations. Such assessments are dependent on tools and models capable of predicting ambient concentrations to inform potential exposure. However, as the Agency’s predictive capability increases, so must the requirements for data inputs. Chemical specific data, much of which is not currently available, will be needed. An ERD vision identified as a critical need is the development of an environmental fate simulator, which when complete, would encompass all the technical components needed to perform reaction pathway simulation and consensus and spatially-explicit modeling, as well as provide access to a wide range of national databases and expressions of uncertainty. Successful development of such a comprehensive tool will require integration of the technologies discussed in the rest of this tour. Chemical reactivity parameters and physical properties are being calculated from molecular structure for a broad range of organic compounds using the SPARC computer program developed at ERD, in cooperation with the University of Georgia. Current development involves refining, testing and extending SPARC to provide the additional physical and chemical properties needed. To that end, data gaps for important chemical reactions that are not current in SPARC, such as hydrolysis and reductive transformations, are being determined. Incorporating the process chemistry and data being developed at ERD, researchers are using mathematical models to assess the response of aquatic systems, watersheds, and landscapes to natural and anthropogenic stressors. ERD has a long and rich history in model development and support. The goal is to understand the behavior of chemical and pathogen stressors -- including organic contaminants, nutrients, mercury, petroleum hydrocarbons, fuel oxygenates and solvents through surface water, ground water and reactive transport. This and other models are available on the ERD Center for Ecosystem Assessment Modeling website and the Watershed and Water Quality Technical Support Center website, co-supported with Region 4. Spurred by Clean Water Act regulations and the Beach Act of 2000, ERD is conducting Microbial Source Tracking research to evaluate bacterial transport and fate in surface waters. Additionally, a new tool, Virtual Beach, uses forecasted meteorological data to forecast beach bacterial conditions. As the regulatory needs of the Agency have become more sophisticated, there is need to utilize “systems” of environmental models that attempt to mathematically describe stressor fate and transport within single media such as air, water or soil, as well as look across environmental media boundaries at multiple spatial and temporal scales. In an effort to provide the Agency with robust modeling systems for determining the potential environmental fate pathways of chemical stressors, the FRAMES modeling technology was developed at ERD. FRAMES provides the software architecture necessary for integrating environmental fate calculators, chemical property and environmental characterization databases, uncertainty analysis tools and expert systems for conducting spatially-explicit chemical exposure assessments. FRAMES is a flexible tool for all spatial and temporal scales for simple-to-complex modeling and evaluation. Another critical element in the development and evaluation of mathematical models, particularly for higher order complex models, is the analysis of the uncertainty and sensitivity of model output. Uncertainty analysis in model predictions is called for when there is a lack of knowledge or data and inaccuracies in model input data. Sensitivity analysis leads to a better understanding of how models respond to their inputs, which in turn can be used to better focus laboratory and field-based data collection efforts on processes and parameters that contribute most to resolving uncertainty in model outputs. The use of FRAMES would not be feasible without the computational hardware to support it. The computationally intensive analysis of uncertainty and sensitivity. ERD's state of the art supercomputer, SuperMUSE, is constructed from a collection of network switches and PCs supporting both Linux and Windows operating systems and provides the equivalent of roughly 1000 GHz computing capacity.