S. Hall and P. 0. Reichardt University of Alaska Fairbanks 99701
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DDE Leveb in Birds An environmentally oriented undergraduate experiment
As part of a n effort to develop a laboratory sequence for a iunior level environmental chemistw course. we have adapted a current method of pesticide residue a n a l y s i ~ l , ~ for use in the undereraduate chemistry laboratory. While somewhat similar t o a recently reporteb analytical experiment on pesticides in food,3 this investigation of DDE levels in birds can be easily modified for employment in a variety of laboratory courses. The experiment, as presented in our course, requires approximately three 4-hr laboratory periods. This investigation was chosen for our environmental chemistry course for a variety of reasons. The primary consideration was that the topic of pesticides in general seems to be an area of primary concern among today's students. Secondly, the experiment nicely demonstrates the fact that determinations of comparative and absolute levels of environmental pollutants are often two separate problems. Thirdly, the determination requires a reasonable amount of attention to experimental technique. Finally, road kills and unused portions of game birds provide a ready supply of raw material. Experimental Reaoents Anhydrous sodium sulfate, fuming sulfuric acid (20?&), concentrated sulfuric acid, reagent grade hexaue, reagent grade acetone. Procedure The laboratory manipulations can he divided into the three traditional steps of residue analysis: extraction, cleanup, and detection. Each step can be accomplished in a single laboratory period. Extraction: A 5-25-g sample of tissue (depending upon expected lipid content) is weighed, cut into small pieces, and ground in a mortar and pestle with an equal weight of anhydrous sodium sulfate. The resulting powder is quantitatively transferred to a Soxhlet extractor and extracted with a 2:l mixture of hexane-acetone overnight. (Note that this does require the student to come in the following morning, but merely to turn off the heat source.) Cleanup: The lipid extract is concentrated to a few ml and transferred to a tared beaker for oven drying (ffi°C for at least 30 mid. A chromatographic adsorbent is prepared by thoroughly mixing (fume hood) 10 g of Celite, 3 ml of fuming sulfuric acid, and 3 ml of concentrated sulfuric acid for each gram of extracted lipid (maximum of 5 g). This paste is transferred to a sintered glass Buchner funnel (€0or 125 ml) and packed by application of gentle air pressure until the Celite is dry. The column is rinsed with hexane (40 m1/10 g of Celite) and allowed to drain. The lipid extract in hexane (10 ml/g of lipid) is applied to the column and the eluate collected in a 125-ml Erlenmeyer flask. The original lipid containing beaker is rinsed with 5 rnl of hexane and the solution applied to the column, combining the eluate with that previouslv obtained. The column is eluted with hevane (40 ml for ~, each par,, of .tpidl; and, afrer dramnc. the lasr rrares ut snhenr are forced rhmugh w~thalr prerrure The cumbinrd rluarr i, coneentrntedand rransferrrd tod 1 - ur 2-ml volunwtriv flask. Detection: Detection is accomplished using a gas chromatograph equipped with a flame ionization detector. A suggested set of conditions is: column, %-in. X 6-ft glass column of 3% QF-l on Chromosorb W; injector, 2M)'C; column, 180°C; detector, 215'C; flaw rate adjusted for optimum combination of sensitivity and convenient retention time (about 5 min for DDE). Quantification
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Journal of Chemical Educafion
is achieved by either a calibration curve or the method of standard additions. Discussion This procedure allows detection of DDE a t levels down to 1 ppm in the raw material. Although traces of lipid which survive the cleanup procedure do appear in the gas chromatography trace, they cause no real difficulty in the analysis of a properly handled sample. Our results showed DDE concentrations in the range of 0-10 ppm in various organs of local birds. To set the experiment in its chemical and environmental contexts, we introduced it with a lecture on the environmental fate of chlorinated hydrocarbons. Included in this lecture was a discussion of chemical and biochemical aspects of the in uiuo conversion of p,p'-DDT to DDE.'
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cl/c'cl DDE Immediately following the conclusion of the experiment a biologist was invited to address the class on the application of this analysis in his studies of the peregrine falcon. Following this meeting student interest in the experiment was a t a level such that the initial investigation was turned into .an "open-ended" experiment in which the students investigated the net effects of varying experimental conditions (e.g., simple extraction versus Soxhlet extraction, duration of sulfuric acid digestion in cleanup). While this experiment is described herein a s a n exercise in environmental chemistry it seems adaptable to other types of courses. Qualitative analysis of other components indicated by the gas chromatography trace could provide a n interesting experiment in an advanced organic chemistry laboratory. An analysis of the efficiency of recovery of DDE by this general method could be included in an analytical course. In short, this experiment provides students the opportunity to investigate a practical analytical method in terms of the chemical principals upon which it is based. 'Biras, F., Burke, J. A., and Gaul, J. A. (Editors), "Pesticide Analytical Manual," Vol. I, 2nd Ed., US. Food and Drug Administration, Washington, D.C., 1970. 2Risebrough, R. W., Florant, G. L., and Berger, D. D., Can. Field-Not., 84,247 (1970). %ubach, D. J., and Butwill Bell, M. E., J. CHEM., EDUC., 50,855 (1973). 'For a brief discussion and leading references see, (a) Metcalf, in "Pesticides in the Environment," Vol. 1, (Editor: White-Stevens, R.), Marcel Dekker, New York, 1971, Chap. 1; (b) Brown, A. W. A,, "Pesticides in the Environment," Vol. 1, (Editor: White-Stevens, R.), Marcel Dekker, New York, 1971, Chap. 7.
