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596A
Environ. Soi. Technol., Vol. 16, No. 11, 1982
terms "tentative," "confident," and "confirmed" be allowed to describe degrees of confidence when other techniques are used or other nonG C / M S data are available? Will this lead to confusion? • Frequently, knowledge of the source of the sample, historical data, physical/chemical characteristics (acid-base solubility, volatility, etc.) of the compound, and other informa tion are available to the analyst to lend considerable credibility to "confir mation" by EI (electron ionization) only data. For example, I don't see any need for CI (chemical ionization) and accurate mass measurements to "confirm" that chloroform is the major peak on a purge-and-trap-generated chromatogram of a chlorine-disin fected drinking water sample when the EI spectrum matches a library refer ence and the retention time matches the standard. In fact "identification" is routinely accepted from a Hall de tector response only. • Singling out G C / M S (as opposed to other methods) for establishing standardized definitions of reliability of structural assignments may reduce the confidence of nonchemist profes sionals (lawyers or engineers) in G C / M S results reported and inter preted by competent analytical chemists. Will these individuals accept anything other than "confirmed" in the future? • The degree of confidence of as signment is related to the subject compound, not just the combination of analytical procedures used. For ex ample, I might have more confidence in an assignment for benzene from a purge-and-trap GC analysis with ac companying EI data only ("tentative") than I would for a specific alkyl-PAH isomer when given all of the data re quired for "confirmed" status. CI and accurate mass measurements do not necessarily give more structural in formation than EI spectra, especially when isomers are involved. I believe that ES& Τ should require complete documentation of procedures leading to data that support a struc tural assignment but should leave it to the author, reviewers, and the readers to decide upon the appropriateness of the adjective description of degree of confidence of structural assignment. This is consistent with good scientific reporting procedures, allowing for peer acceptance or rejection of conclusions derived from the data presented. A special nomenclature for G C / M S is not needed. Alan A. Stevens Cincinnati, Ohio
Note: See the editorial on page 594A of this issue for the editor's response to the preceding letters.
Air pollutant baselines from glacial studies Dear Sir: I appreciate the opportunity to comment on the excellent article by Julian Josephson entitled "Air pollu tant baselines from glacial studies," (ES&T, Vol. 16, No. 8, 1982, p. 437A). The article was well re searched, well written, and informa tive. I am particularly pleased that you published an article on the importance of baseline pollutant measurements. I feel these studies are extremely valu able, yet it can be difficult to get funding for them because of the per ceived long pay-back time. I have been doing research on pol lutant levels in remote wilderness areas (U.S. National Parks) for six years now. Dr. Cliff Davidson has collabo rated with me on these studies. Based on this experience, I have a few specific comments to make on the article: • W e feel baseline studies should also be carried out in nonglacial sites. • We also ran into the problem of melt/ freeze on glaciers in Olympic National Park. The problem precludes any significant coring. However, sur face snow samples seemed to indicate significant trace element contamina tion. But, enrichment factors—calcu lated from soil samples taken on the lateral moraine—indicate that vir tually all the detected "contamination" was merely resuspended material from the surrounding area. • I was particularly interested in the difficulties of obtaining uncontaminated samples from glacier ice. W e have faced this same problem in setting well points in remote valleys. We finally have had some success with a hand-powered, pneumatic drill rig. The drilling depth is, of course, limited to ~ 3 0 - 4 0 ft. • Finally, I found the discussion of Patterson's work very interesting. Our air data from Olympic National Park showed average lead concentrations of 2 n g / m 3 of air. Based on enrichment factor calculations, using both average crustal values or measured values from park soils, we estimated that this lead level, as low as it is, is 1 25 to 150 times higher than could be expected from natural crustal/soil sources. G. B. Wiersma, Manager Earth & Life Sciences EG&G Idaho Falls, Idaho 83415
