Expanw assessment Dear Sir: In an otherwise excellent article, “Exposure Assessment,” in your timelv series on cancer risk assessment. Davih Severn uses the recent speci2 review of alachlor as an example of a current risk assessment (ES&1:December 1987, pp. 1159-63). As support for his summary of the exposure assessment, Severn uses the unpublished document, properly entitled: “Alachlor Special Review Technical Support Document,” September 1986 (1). This document was not subject to external review and contains numerous errors of fact as well as faultv intcmnttations of data. For example, ‘the groundwater modeling simulations, which “confirmed the potential for alachlor to leach through soil,” were apparently generated using a time to 90%dissipation (2) instead of a dissipation half-life for alachlor (3). The transport model used, PRZM, is extraordinarily sensitive to this parameter, thus the use of realistic values is essential (4). Extensive monitoring data do not support the statement: “Researchers concluded that concentrations of 1-2 ppb represented a realistic assessment of long-term drinking-water exposure in some areas where alachlor is extensively used.” Long-term drinking-water levels for alachlor will rarely exceed 1 ppb, even in high-use regions. Figure 1 shows the probability distribution of annualized mean concentrations (AMC) predicted for surface water systems located in small and moderately sized watersheds in the alachlor-use region. Large watersheds such as the continental rivers and the Great Lakes have very low to undetectable levels of alachlor and other herbicides (5).Figure 1 was derived from a two-year study involving some 52 community water systems in the region where Lasso (Monsanto’s commercial alachlor) is used. The analytical results from this study were used to show that the “overland transport and in-stream distribution model” used in the technical support document (6)grossly overpredicted long-term exposures, probably due to oversimplified assumptions concerning pesticide use patterns (7,
8.
In a more recent review of watermonitoring studies, EPA concluded: “it is relatively unlikely that public water supplies will be out of compliance with an MCL (maximum contaminant level)
’O01
Distribution curve for AMCs
0.5
1
1.5
2
Ualied ‘Anndatu& Mean C m m ~ r m a n *Esbrna!sd I r a n mo ,885 ana ,986 S J W ~
for alachlor in the low parts per billion” (9)-a different conclusion from %vernk realistic of 1-2 PPb. The EpA Writes m Y documem for Comment, and Efemng to an inbe misleading, For terim position any substance Under evaluation the EPA. the final redatorv, decision document-including public comments-is crucial to understanding the entire bazard identification, risk evaluation, and exposure assessment process. References ~~~~~
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( I ) Federal Rcgisrer 51. 36166, October 6, 1986. (2) Stewart, B. A. et al. Confrol of Water Polfurion from Cropland: ARS USDA: Washington, D.C., 1975; EPA-6W2-75M61; Vol. 1. (3) Knisel, W. G., Ir. “CREAMS: A Field Scale Model for Chemicals, Runoff, and Erosion from Agricultural Management Systems”; Conservation Research Report 26, USDA: Washington, D.C.. 1980.
(4) Dean, J. D.; lowise, F! F!; Donigian, A. S. “Leaching Evaluation of AgriculNral Chemicals (LEACH) Handboor; U.S.Environmental Protection Agency: Athens, Ga., 1984; EPA-60013-84468. (5) Klein, A. 1. et al. Defermination of Herbicides in Surface M c r from Agrieuffwal Mersheds. 193rd National Meeting of the American Chemical Society, Denver, Colo., ~ “ ~ 10x7 i i --r---
(6) Donigian, A. S.; Imhoff, J. C.; Bickness, 8. R.; Kittle, 1. L. “Application Guide for Hydrologic Simulation Program-FORTRAN (HSPF)”; U.S. Environmental Protection Agency: Athens, Ga., 1984, EPA60013-82-069. (7) Gustafson, D. 1. J . Environ. Sci. Hcolrh.
Andrew J. Klein Manaeer. Reedaton, Affairs Monsant0kgric;itural eompany St. Louis, Mo. 63167 ~~
Hazardous organic compound analysis
both the regulatory agencies (state and federal) and the private sector. MisreDear Sir: I applaud your article on haz- porting and misinformation were obardous organic compound analysis” served in an equally alarniing number and misinformation associated with of cases for the priority pollutant analythese analyses (ES&T, February 1988, ses. Furthermore, it has been interestpp. 136-42.). Data review (quality as- ing to note how many sites have been surance) is definitely an important issue inappropriately placed on the National for nonpriority pollutants, because Priority List (NPL) based laboratory valuable information can be gained misinformation. An independent refrom careful interpretation of mass view of all analytical data is an essential spectra reported as unknowns. How- part of every environmental investigaever, the article tended to convey the tion, and I am happy to see that this idea that priority pollutant analysis is subject is finally a topic for discussion. much more reliable. An equally important issue is the validation of priority Rock J. Vitale pollutant data. Quality Assurance Specialist I have been reviewing organic and Environmental Standards, Inc. inorganic data for about five years, for Valley Forge, Pa. 19481 Envimn. Sci. Technol., Vol. 22, No. 4. 1988 2-49
