Environ. Sci. Technol. 2010, 44, 4400–4401
Authors’ Viewpoint RHONDA SAUNDERS
More of EPA’s SPARC Online Calculator-The Need for High-Quality Predictions of Chemical Properties HANS PETER H. ARP* Norwegian Geotechnical Institute, Oslo STEVEN T. J. DROGE* UFZ Helmholtz Centre for Environmental Research, Leipzig, Germany SATOSHI ENDO* UFZ Helmholtz Centre for Environmental Research, Leipzig, Germany WALTER GIGER Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Du ¨ bendorf, Switzerland Giger Research Consulting (GRC), Zurich, Switzerland KAI-UWE GOSS UFZ Helmholtz Centre for Environmental Research, Leipzig, Germany STEVEN B. HAWTHORNE Energy and Environmental Research Center, University of North Dakota, Grand Forks SCOTT A. MABURY University of Toronto, Canada PHILIPP MAYER Aarhus University, Roskilde, Denmark MICHAEL S. MCLACHLAN Stockholm University, Sweden JAMES F. PANKOW Portland State University, Oregon ´ P. SCHWARZENBACH RENE Swiss Federal Institute of Technology Zurich FRANK WANIA University of Toronto Scarborough, Canada BAOSHAN XING University of Massachusetts, Amherst
* Please address correspondence regarding this Viewpoint to
[email protected],
[email protected], and/or
[email protected]. 4400
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It has come to our attention that in November 2008 the U.S. EPA cut external funding for its SPARC online calculator (1) (http://ibmlc2.chem.uga.edu/sparc/). Although the University of Georgia still maintains and hosts the SPARC Web site for free access to the general public, funding for further developments by the U.S. EPA has become extremely reduced. This is unfortunate considering SPARC is increasingly being utilized by scientists and policy makers to estimate a vast array of chemical properties. We encourage the U.S. EPA to continue developing the SPARC online calculator, as SPARC provides a valuable national and international public service. An ever larger variety of mass produced organic compounds are emerging on the market and in the environment. For the vast majority of such compounds, little is known about their environmentally relevant chemical properties, such as partitioning constants and degradation rates. Experimental techniques to measure these properties are often very time-consuming or not yet available. Thus, to make preliminary assessments on the environmental behavior and ecological toxicity, industry, regulators and researchers turn toward chemical property estimation software. Currently, there are very few high-quality freeware programs available for predicting environmentally relevant chemical properties. However, such tools are needed in the public domain in order to (1) be accessible to researchers, students, and citizen scientists lacking funds; (2) form the basis of transparent and consistent decision making by policy makers; and (3) be open to discussion and evaluation by the scientific community at large. 10.1021/es100437g
2010 American Chemical Society
Published on Web 05/18/2010
The U.S. EPA’s EPISuite and SPARC are the only two freeware programs in major use for predicting environmentally relevant chemical properties, and remain so despite the fact funding appears to be severely cut to both. Of these two, SPARC is increasingly credited with being more robust and giving better predictions. Independent validations showing the predictive quality of SPARC have been performed for the subcooled-liquid vapor pressure (p*iL) (2), the acid-dissociation constant (pKa) (3), aqueous solubility (4), as well as other properties. Further, unlike EPIwin, SPARC is able to predict partitioning to almost any biological, industrial, or environmental organic phase, and accounts for chemical properties overlooked by EPIwin (e.g., tautomerization, hydration, etc.). This increases its range of applicability to a broader set of chemicals and applications both within and outside the field of environmental science (e.g., chemical engineering, drug development). As an example, SPARC was recently used to validate a multiphase, pH-dependent gas-particle partitioning model for a broad set of neutral and ionizable compounds (5). We do not argue that SPARC predictions are perfect, and would like to see its development continue on many fronts. SPARC would benefit by increasing its transparency (e.g., provision of specific information about the underlying theoretical model and the calibration data), chemical application domain (e.g., inclusion of 3D structures, organometallic-compounds and silicon-containing molecules), user-friendliness (e.g., increasing server capacity, allowing for batch processing), and adding a search function for experimental chemical property data. Further, a much discussed issue with SPARC is its inconsistency in predicting partitioning properties across various updates of the program, particularly for highly fluorinated compounds (5). However, despite these shortcomings, SPARC is considered by us to be currently the best performing and most robust publically available program for predicting chemical properties. With even a limited amount of funding, several of the mentioned shortcomings could readily be addressed. One strategy for low cost improvements would be if the U.S. EPA allowed SPARC, or a SPARC-like program, to be open source. This would allow the environmental research community (as well as others) to make improvements and
design new program applications for their needs. Potentially, an open-source program like this could serve as an “evolving standard” (when experimental data are not available) for use by scientists, companies and regulators. As such, this program could account for emerging chemical property data as it is published, as well as account for the latest advances in molecular modeling. We would encourage the U.S. EPA to push SPARC in this low-cost, fruitful direction. Alternatively, we would encourage other environmental or chemical standards agencies, such as the European Environmental Agency (EEA) or the National Institute of Standards and Technology (NIST), to host and administer such an initiative. As environmental scientists in various stages of our careers, we would like to be reassured that the U.S. EPA and other environmental agencies would want us and the public domain to work with the best available tools and to see their further development, thereby enabling scientific research and decision making of the highest possible quality. SPARC shows much potential, but we need much more of SPARC for full development of this potential.
Literature Cited (1) Hilal, S. H.; Karickhoff, S. W.; Carreira, L. A. Prediction of Chemical Reactivity Parameters and Physical Properties of Organic Compounds from Molecular Structure Using SPARC; publication no. EPA/600/R-03/030; U.S. Environmental Protection Agency: Athens, GA, 2003. (2) Asher, W. E.; Pankow, J. F.; Erdakos, G. B.; Seinfeld, J. H. Estimating the vapor pressures of multi-functional oxygen-containing organic compounds using group contribution methods. Atmos. Environ. 2002, 36 (9), 1483–1498. (3) Liao, C. Z.; Nicklaus, M. C. Comparison of Nine Programs Predicting pK(a) Values of Pharmaceutical Substances. J. Chem Inf. Model. 2009, 49 (12), 2801–2812. (4) Hewitt, M.; Cronin, M. T. D.; Enoch, S. J.; Madden, J. C.; Roberts, D. W.; Dearden, J. C. In Silico Prediction of Aqueous Solubility: The Solubility Challenge. J. Chem Inf. Model. 2009, 49 (11), 2572– 2587. (5) Arp, H. P. H.; Goss, K. U. Ambient Gas/Particle Partitioning. 3. Estimating Partition Coefficients of Apolar, Polar, and Ionizable Organic Compounds by Their Molecular Structure. Environ. Sci. Technol. 2009, 43 (6), 1923–1929.
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