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LETTERS Exposure assessment: author’s response Dear Sir: Andrew Klein’s letter (ES&I: April 1988, p. 349), which pertains to my citation of an EPA Special Review Technical Support Document as an example of an exposure assessment (ES&I: December 1987, pp. 1159-63), deserves response. EPA’s procedures for preparing scientific support documents include a much broader exchange of views than is usual for peer review of papers submitted for publication in the scientific literature. The “peer review” process used for such regulatory exposure assessments is the public comment period. Documents such as the Alachlor Technical Support Document (1)are announced in the Federal Register and made available to the public, formally sent to USDA, and reviewed at public meetings of the FIFRA Scientific Advisory Panel. In the case of alachlor, an earlier version of the exposure assessment (2) had been prepared and published for external comment. Many of the issues raised by Klein were discussed in the Technical Support Document in response to comments received from Monsanto and others regarding this earlier document. In particular, the dissipation half-life of alachlor was extensively discussed: For modeling potential transport to groundwater, EPA selected an intermediate value from an array of estimates contained in secondary sources because field measurements for this important parameter were not available. The resulting disagreement between EPA and Monsanto over the field dissipation half-life for alachlor is better characterized as a difference of opinion rather than an error of fact. The surface water data cited by Klein were from monitoring studies of community water systems (CWSs) carried out by Monsanto in 1985 and 1986 and submitted to EPA. The 1985 data were used by EPA in the Technical Support Document as part of the exposure information that led to the conclusion that estimates of 1-2 ppb for long-term exposure to alachlor from contamination of drinking water appeared realistic in some areas of the Corn Belt region. The 1986 data from additional CWSs were submitted to EPA in time for inclusion in the final regulatory position document (3). Based on the expanded 596 Environ. Sci. Technol., Vol. 22,
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data set, EPA concluded that, for areas of high alachlor use, residues that may occur in some sources of drinking water will generally be below 2 ppb on an annualized basis, and more likely will fall in the range of 0.5 to 1 ppb. Exposure assessment is an ongoing process that is always data-hungry. Regulators need exposure and risk assessments to form an understandable and defensible basis for regulatory decisions. The Alachlor Technical Support Document was based on all the information available at the time. The final regulatory decision incorporated more recent monitoring data to arrive at its final conclusion. Additional exposure data in the form of groundwatermonitoring surveys now being carried out by Monsanto and by EPA will no doubt contribute further exposure information in the future. References
streams in acid-vulnerable areas of northeastern North America have suffered substantial declines in acid-neutralizing capacity, the worst cases resulting in biological damage. , . , It is now clear that acid rain has already caused widespread acidification of many aquatic ecosystems in the northeastern United States, Canada, Norway, Sweden, and the United Kingdom” (1-4,However, the role of acid rain in forest decline is still unclear based on current scientific evidence, as has been covered by ES&T (5-7). Acid rain and its environmental effects are only one of many concerns motivating supporters of stronger and more comprehensive air pollution regulation. Not only sulfur oxides, but also nitrogen oxides, carbon monoxide, ozone, hydrocarbons, methane, and other air pollutants are known or suspected of contributing to forest and crop damage, acidification of ecosys(1) . . “Alachlor Special Review Technical SUDtems, depletion of stratospheric ozone, port Documenl“; U.S. Environmental Protection A enc . Washin ton, D.C 1986; decreased visibility, arctic haze (8), cliNTIS PB b - i l i 3 1 9 ; mate change, and poor public health (2) “Alachlor Special Review Position Docu(9).All environmental legislation pendment 1”: U.S. Environmental Protection Agency: Washington, D.C., 1984; NTIS PB ing in Congress targets reductions for 85-175503; EPA-540/09-85-001. the variety of air pollutants from many (3) “Alachlor: Notice of Intent to Cancel Registrations-Conclusion of Special Re- sources. Legislation specifically on view”; U . S . Environmental Protection acid rain requires reductions in SO2 and Agency: Washington, D.C., 1987; FR 52, NO, emissions from power plants, boil49480. David J. Severn ers, and mobile sources, not just SO2 ICF Clement, Inc. emissions from “coal-burning utilities Fairfax, VA 2203 1-1207 in the Ohio Valley, ” as Ray claims.
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References Acid rain What to do? Schindler, D. W. Science 1988,239, 149Dear Sir: In a guest editorial (ES&I: (1) 57. April 1988, p. 348), D. L. Ray claims (2) Brakke, D.; Henriksen, A. Environ. Sci. Technol. 1987,22, 8-14. that there is not enough scientific eviHavas, M.; Likens, G. Environ. Sci. dence on the environmental effects of (3) Technol. 1984, 18, 177A-184A. acid rain to warrant spending taxpay- (4) Driscoll, C.; Newton, R. Environ. Sci. Technol. 1985, 19, 1018-24. ers’ dollars to reduce the emissions of SO2. However, Ray’s views are the mi- (5) Cowling, E.; Woodman, J. Environ. Sci. Technol. 1987,21, 120-26. nority opinion in the scientific commu- (6) Johnson, A , ; Siccama, T. Environ. Sci. nity. Technol. 1983, 17, 294A-305A. I would like to refer the reader to a (7) Tomlinson 11, G . Environ. Sci. Technol. 1983,17, 246A-256A. recent review article by D . W. (8) Hileman, B.Environ. Sci. Technol. 1983, Schindler for a scientific evaluation of 17. 282A-286A. acid rain and its environmental ramifi- (9) ’Gaffney, J. et al. Environ. Sci. Technol. 1987,21, 520-23. cations (1). In direct contradiction to Ray’s views, Schindler comments: Dorene Bolze “Clearly, we know enough about the National Audubon Society New York, N.Y. 10022 effects of acid rain on aquatic ecosystems to make a strong case for regulating emissions of sulfur oxides. . . . Errata: Editorial Most scientists in fact now agree that The editorial in the April 1988 issue of reducing deposition of sulfuric acid will ES&T (p. 347) was written by William benefit aquatic ecosystems” (1). H. Glaze, editor of ES&T. The wrong According to Schindler, “lakes and signature appeared on this page. 0013-936X/88/0922-0596$01.50/0 C2 1988 American Chemical Society
