A more complete report on studies of the movement and interaction of polydimethylsiloxane fluids with soils will be published elsewhere. Conclusions Polydimethylsiloxane fluids in spill situations behave much the same as motor or mineral oil of comparable viscosity. The same cleanup procedures are applicable. Literature Cited
O W , alter I P # l l
(1) Rowe, V. K., Spencer, H. C., Bass, S. L., J . I n d H l g . Towicol, 30 (6). 332-52 (1948). (2) Hobbs, E. J., Fancher, 0. E., Calandra, J. C., Tox A p p i Pharm , 21, 4,5-54 (1972). ( 3 ) Hobbs, E. J., Keplinger, M. L., Calandra, d. C., Enciron. Res., 10
(in press). Noll, W., “Chemistry and Technology of Silicones”. p p 251,458, .4cademic Press, New York, N.Y. (1968). (.i) Dow Corning Corp., Ruli. 22-053 (Nov. 1972). (6) Shell Oil Co.. One Shell Plaza, P.O. Box 2463. Houston, Tex. 77001 (1972). ( 7 ) Parker Systems. Inc., P.O. Box 165%.Norfolk. Va. 23501. (8)Wyandotte Chemical Co. of Canada, Ltd., 41 Metropolitan Road, Scarborough, Ont. (9)Smith, A. L.. Ed.. “Analysis of Silicones”, p 352. CViley, New York, N.Y.(1974). (101 Lewicke, C. K., Enciron. Technoi., 7 ( 5 ) ,398 (1973). (11) Noll, W,, Sucker, C.. Fortschrittsber. Koiioide Poiym., 5 5 , 131 ( 19711. ( 1 2 ) Hull. No. 1103. Oil Mop, Inc., 1101 Edwards Ave.. S e w Orleans, La. 70123 (1972). (13) .Johnson. R. F., Manjrekar. T. G., Halligan. J. E.. EnL>iron.Sci. Trchnoi.. 7 ( 5 ) , 439 (1973).
Figure 3. Depth profile of 100-cS polydimethylsiloxane on soil as a function of time after spill
(4)
Results show a gradual downward migration to a depth of 50 cm during this time period (Figure 3). No significant lateral movement of the fluid was found. Vegetation within the spill area is sparse. Laboratory experiments with columns of soil showed that migration rates are dependent in a complex way on the kind of soil (sand, clay, or loam), its moisture content, and the amount of watering. In general, dry soils seem to have a greater absorptive capacity and hold silicone fluids more tenaciously than wet soils. The soil thus appears to act as its own absorbent, and if the presence of fluid is objectionable, the soil can be removed to a landfill area and replaced with fresh soil.
Rewired for recieic. Noi>emher14, 1974. Accepted Januar? 19, 1976.
CORRESPONDENCE SIR: Dr. Holland and I were much disappointed to see the publication of the article “Determination of Nitrate in Water Samples Using a Portable Polarographic Instrument”, E n vironmental Science and Technology, 9,1075 (1975), without reference to our own earlier paper. Since this paper was received November 6, 1954 and our paper, “Development of a Portable Polarograph for Determination of Aldehydes in Automotive Exhaust and Production Plant Samples”, ibid., 9,127 (1975), was received on April 18, 1974, and accepted on October 21, 1974, it is extremely difficult to understand why you did not call our paper to the attention of the authors of the nitrate paper. By way of explanation, you should understand that the phrase “peak-seeking circuit” has different meanings in the respective papers. In our paper we are referring to the capture, during each scan, of the maximum current flow value as a potential. In contrast, Young et al. are smoothing out the output of the dropping mercury electrode. Please note that our paper makes reference to our patent application. That application has since issued as U.S. Patent No. 3 922 205. Since the authors of the nitrate paper were not alerted by your office and no attempt made to cross reference our papers, we fear your readers have been misled into believing they are free to build and use a portable polarograph with our peak-seeking circuit. However, the commercial model is being supplied to the trade by a licensee of The Dow Chemical Co. James D. McLean
SIR: The paper “Development of a Portable Polarograph for Determination of Aldehydes in Automotive Exhaust and Production Plant Samples” appeared after our paper was submitted and while it was in review. Our failure to insert a reference to the above paper in our revision is an oversight for which we apologize. The emphasis of our paper should not be taken as the instrument (which is pretty standard OA circuitry), but as the demonstration of the utility of the ZrOC12 catalytic method coupled with background compensation for the determination of nitrate in complex samples. The clear message of both papers would seem to be that with the widespread availability of inexpensive, lightweight, and reliable circuits, the polarographic methods for a number of species of environmental interest should be re-examined.
Robert H. Philp, Jr University of South Carolina Columbia, S.C. 29208
Analytical Laboratories 5 7 4 Building The Dow Chemical Co. Midland, Mich. 48640
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