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Van Uitert, L. G.; Johnson, L. F. J. Chem. Phys. 1966,44, 3514-3522. Tripathi, H. B.; Kandpal, H. C.; Agarwal, A. K.; Belwal, R. Chem. Phys. Lett. 1978,57, 50-53. Tripathi, H. B.; Kandpal, H. C.; Agarwal, A. K.; Belwal, R. Solid State Commun. 1978, 28, 807-810. Kandpal, H. C.; Tripathi, H. B. Solid State Commun. 1979, 29, 139-142.
(25) Kandpal, H. C.; Tripathi, H. B. Ind. J. Pure Appl. Phys. 1979,17, 587-589.
Received for review September 9, 1991. Accepted December 12, 1991. Financial support by the U.S. Department of Energy through the New Mexico Waste-Management Education and Research Consortium is gratefully acknowledged.
A Trace-Element Technique for Determining Nonpoint Sources of Contamination in Freshwaters Kenneth A. Rahn,” Steven B. Hemlngway, and Margaret W. Peacock Center for Atmospheric Chemistry Studies, Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882-1 197
An elemental tracer system has been developed for determining natural and pollution sources of contamination in freshwaters. A suite of eight soluble elements (Na, C1, Ca, Mg, K, Br, I, and S as sulfate) is used. The first seven of these are determined by short-lived instrumental neutron activation of 20 mL of the water directly; sulfate is measured by turbidimetry. Sampling and analytical procedures are well-established and highly reproducible. To date, 5-10 major types of background and nonpoint contaminants have been considered, plus several less-important sources. Except for the four versions of atmospheric deposition, signatures of the sources appear to be distinct from one another. Because compositions of sources derived from strong signals in streams agree well with the same sources measured in the laboratory, fractionation of elements during transport does not seem to present a problem. Contributions of multiple sources to freshwaters can be resolved visually from signature plots or mathematically by a progressive series of multiple-linear regressions. The next developmental steps for this technique seem well-defined and should pose no particular problems. W
Introduction Background to This Research. The Clean Water Act of 1972 has generally improved water quality in the United States by controlling emissions from point sources. Nonpoint emissions are proving much harder to evaluate, however, and represent the major challenge facing water-quality research in the near future ( I ) . Models of sources and transport of nonpoint pollutants are no better than the empirical source-receptor relationships on which they are based: we need to be able to determine sources of nonpoint pollutants in specific cases before we can model them generally. This work describes an elemental tracer system which can do that for several important soluble, conservative nonpoint pollutants such as road salt, septic effluent, and fertilizers. It also shows how these pollutants can be differentiated from geological and atmospheric backgrounds. This tracer technique was developed for acid rain purposes, to help us see whether streams in nonpristine watersheds of Rhode Island could be used to monitor dry deposition of sulfate and associated acidity. The dry component of deposited sulfate would be determined by subtracting the wet-deposited component (measured in precipitation) from the total deposited sulfate (measured in streams). The tracer system was intended to sense the presence of nonpoint signals in these streams and thereby 788
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provide an estimate of nonpoint sulfate which could be used to correct the total observed sulfate to total deposited sulfate. Requirements for a Nonpoint Tracer System. In order for a nonpoint tracer system for freshwaters to function satisfactorily, its elements and signatures must satisfy three general requirements: (1)Signatures must be well-defined, i.e., have reasonably consistent and reproducible elemental proportions. Because no firm guidelines yet exist on just how consistent the proportions need to be, uncertainties of elemental concentrations in signatures should always be included. (2) Signatures must be operationally distinguishable from one another. Although experience is still the best test for distinguishability, linear correlations between signatures can offer a rough objective guide to their degree of independence (lack of collinearity). (3) Signatures must be stable during transport. While they may change somewhat as they move through a watershed, they must still be recognizable by the eye or by the apportionment program. Stability of signatures is roughly equivalent to near-conservative transport of elements through soils and the watershed. A desirable property of elements is that they be measurable easily, sensitively, and with minimum preparation of samples for analysis. Rationale for Selecting Neutron Activation and the Particular Suite of Tracer Elements. Neutron activation was chosen as the basic analytical technique because it is rapid, reliable, precise, sensitive, free of matrix effects, instrumental, available to us, and it offers an excellent suite of cationic and anionic tracer elements. In addition, spectrophotometry was to be used for measuring sulfate. Because we had used these same two techniques extensively for aerosol and precipitation, those sets of elemental data could be compared directly with newer data for freshwaters from the same area. Data for sulfate and other anionic elements such as Br and I (from neutron activation) turned out to be critical in distinguishing some of the most-important sources, as described in later sections. This experience shows how critical certain anionic tracers can be for freshwaters. If other analytical techniques such as atomic absorption or inductively coupled plasma are considered as alternates to neutron activation, they should always be supplemented by anionic analysis, preferably for multiple anions. After some experimenting with neutron activation, seven soluble and near-conservative anionic and cationic elements were chosen as tracers (Na, K, Ca, Mg, C1, Br, and I), in addition to the sulfate mentioned above. Because
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Table I. Reproducibility of Sampling and Analysis for Freshwaters"
element Na
est anal. uncert, %
dup anal.* diff, % overlap, % 7 7
c1
7 7
Ca Mg
15
14
70
K
60
60 42
Br
13 30
16
I
8e
100 80 80 100 100
80 80
dup samplesC diff, % overlap, %
samples of same stream t
source
coefficient
prob > t
winter precipitation coarse aerosol sulfate
1.03 f 0.57 0.88 f 0.79 9.33 f 3.89
0.12 0.31 0.05
geol weathering road salt CaC1,
1.30 f 0.12 0.59 f 0.49 0.02 f 0.01
0.00 0.27 0.23
Na
c1
Ca Mg K Br I sulfate
precip
C. aer
29 36 4 21 12 44 70 13
25 30 2 15 10 55 30 9
% contribution sulfate geol
0 0 0 0 0 0 0
78
rd salt
CaC1,
17 21 2 0 0 1 0 0
1 13 17
29 0
74 64 78 0 0 0
only correlation of >0.90 is EG tapwater with CaCl,, at 0.91. Thus, except for atmospheric deposition, the principal sources are essentially uncorrelated and should not be confused with one another in regressions. (c) Protocol for Apportioning Elements in Freshwaters. Because only 6 of the 11 signatures can be used simultaneously in apportioning stream samples (if one degree of freedom is to be preserved), the optimum suite must be chosen systematically. The selection scheme which we have developed is orderly, efficient, and selfcorrecting. It begins with precipitation and alternately adds background and nonpoint (pollution) signatures if they improve the fit. At each step, the previous suite of signatures is modified as needed. When no more signatures improve the fit, or when six signatures are reached, the procedure is terminated. The exact series of steps is as follows: (1)Choose the best preliminary precipitation signature by fitting each of the three separately to the freshwater sample and retaining the one which fits it best. (The procedure begins with precipitation because experience shows that precipitation is retained for practically all freshwater samples. Precipitation from different seasons is considered because months may be required for it to reach streams.) (2) See if another background signature (dry deposition of aerosol, dry deposition of SOz, geological weathering) can be added to (l),by reapportioning the sample with the precipitation signature plus each other background signature singly. If more than one additional signature improves the fit, retain the one which improves it the most. If no signature improves the fit, retain none and proceed to the next step with precipitation alone. (3) See whether any nonpoint signatures can be added to (2), by adding each nonpoint signature in turn and reapportioning the sample. If more than one nonpoint signature improves the fit, choose the one which improves it the most. If none improves the fit, continue with the suite from (2). (4) See whether any other background signatures can be added to the suite from (3), by adding each remaining signature and reapportioning. As the first step, try other precipitation signatures. If the fit improves, replace the original with the new one and proceed through the other background signatures. (5) Repeat steps 3 and 4 alternately until six signatures are reached or no more signatures improve the fit. As appropriate, try other combinations of signatures at critical points. As a practical example, when the full apportionment procedure was applied to the average clean streams in the 796
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0 0 0 0 0
total, mg L-' apport obsd 3.57 5.16 2.81 0.61 0.5 12.9 x 10-3 2.0 x 10-3 12.0
3.8 5.0 3.0 0.6 0.5 14.0 x 10-3 2.1 x 10-3 12.0
apportjobsd 0.94 1.03 0.94 1.02 1.00 0.92 0.95 1.00
Hunt/Potowomut Watershed on 2 January 1990,17 successive apportionments were required to reach the following list of best signatures: winter precipitation, coarse aerosol, sulfate, geological background, road salt, CaC1,. The final apportionment is shown in Table VII.
Summary A suite of eight soluble elements (Na, C1, Ca, Mg, K, Br, I, and S as sulfate) appears to be capable of tracing at least 5-10 major types of background and nonpoint contaminants in freshwaters. The first seven of the elements are determined by instrumental neutron activation, sulfate, by turbidimetry. Sampling and analytical procedures are well-established and reproducible. Except for the four versions of atmospheric deposition, signatures appear to be distinct from one another. Signatures derived from clear appearances in freshwaters agree well with those determined in the laboratory. Contributions of multiple sources to freshwater samples can be resolved visually from signature plots or mathematically by a progressive series of multiple-linear regressions. Acknowledgments Samples were analyzed using facilities of the Rhode Island Nuclear Science Center, Narragansett. T. Jackvony of the Rhode Island Department of Transportation provided samples of road salt for analysis. R. Viens assisted in preparing and analyzing samples of sources and streams. M. Eldridge and S. Larimer also analyzed samples. We thank D. H. Lowenthal for many helpful discussions during the early stages of development. Registry No. Na, 7440-23-5; Ca, 7440-70-2; Mg, 7439-95-4;
K, 7440-09-7; CaC12, 10043-52-4.
Literature Cited (1) Humenik, F. J.; Smolen, M. D.; Dressing, S. A. Enuiron. Sci. Technol. 1987, 21, 737. (2) Tabatabai, M. A. Enuiron. Lett. 1974, 7, 237. (3) Bormann, F. H.; Likens, G. E. Pattern and Process in a Forested Ecosystem; Springer-Verlag: New York, 1979; p 66. (4) Heaton, R. W.; Rahn, K. A.; Lowenthal, D. H. Atmos. Enuiron. 1990, 24A, 147. (5) NADPINTN Annual Data Summary. Precipitation Chemistry in the United States. 1989; NADPINTN COordination Office, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, 1990. (6) Davidson, C. I.; Wu, Y.-L. In Acidic Precipitation, Volume 3. Sources, Deposition, and Canopy Interactions;Lindberg, S. E., Page, A. C., Norton, S. A,, Eds.; Advances in Environmental Science Series: Springer-Verlag: New York, 1990; Chapter 5.
Environ. Sci. Technol. 1992, 26, 797-802
( 7 ) Rahn, K. A,; Lowenthal, D. H.; Heaton, R. In Control and Fate of Atmospheric Trace Metals; Pacyna, J. M., Ottar, B., Eds. N A T O A S I Ser. C 1989,268, 85. (8) Lowenthal, D. H.; Wunschel, K. R.; Rahn, K. A. Environ. Sei. Technol. 1988, 22, 413. (9) Mason, B. Principles of Geochemistry, 3rd ed.; Wiley & Sons: New York, 1966. (10) Metcalf and Eddy, Wastewater Engineering: Treatment, Disposal, Reuse; McGraw-Hill, Inc.: New York, 1979.
(11) Capar, S. G.; Tanner, J. T.; Friedman, M. H.; Boyer, K. W. Environ. Sei. Technol. 1978, 12, 785. (12) Gordon, G. E. Enuiron. Sei. Technol. 1980, 14, 792.
Received for review September 11, 1991. Revised manuscript received December 12,1991. Accepted December 18,1991. This work was supported i n part by a research contract from the Rhode Island Department of Environmental Management, Division of Water Resources.
Thermodynamic Study on the Reduction of the Polychlorinated Dibenzo-p -dioxins and Dibenzofurans in Incinerator Exhausts Masayuki Murabayashi" and Hasso Moesta Institute for Physical Chemistry, University of Saarland, 6600 Saarbrucken, Germany
Reactions for the dechlorination or decomposition of polychlorinated dibenzo-p-dioxin (PCDD) and/or polychlorinated dibenzofuran (PCDF) were investigated thermodynamically, in order to develop techniques to prevent the release of PCDDs and PCDFs from municipal incinerators. The Gibbs energy of formation of PCDDs, PCDFs, and some organic compounds was calculated by using a computer program, which was based on statistical thermodynamics. I t was found that CaO, Naz0.Si02, or 2Naz0.SiO2would promote the dechlorination reaction of PCDDs and PCDFs by receiving chlorine atoms and that such organic materials as butane or butene would help the reaction by giving hydrogen in the reactions. The calculation showed that thermal decomposition of PCDDs or PCDFs would not proceed at temperatures below 1100 K. Some ways to prevent the release of PCDDs and PCDFs from municipal incinerators were discussed. Introduction Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), including 2,3,7,8tetrachlorodibenzo-p-dioxin,one of the most potent chemical carcinogens to exist, have been the subject of acute public concern. They exist more widely, for instance, in air, soil, meat, milk, fish, and vegetation than ever considered. To further worsen the problem is the possibility that they would be concentrated by food chains (1). The main environmental sources of these chemicals are thought to be industrial sources, such as the metal refinery and steel industry. Other sources include the exhaust of cars, incinerators (including industrial hazardous waste, hospital, and municipal solid-waste incinerators), and some organic chemical manufacturing processes (1). Another report (2) indicated that the municipal solid-waste incinerator was the main source in some cities. In this paper we have dealt only with municipal waste incinerators. Vogg and Stieglitz (3) and Hagenmaier et al. (4) reported the experimental results of the heat treatments of PCDDs and PCDFs with fly ash from the municipal solid-waste incinerator. They heated a small amount of PCDDs and PCDFs with fly ash in the air for 2 h and measured the concentration change of the PCDDs and PCDFs with time. They confirmed that the concentration of PCDDs and PCDFs increased by a factor of 10 and 15, respectively, at 300 "C and decreased to an amount below the detection *Present address; Institute of Environmental Science and Technology, Yokohama National University, 240 Yokohama, Japan. 0013-936X/92/0926-0797$03.00/0
limit at 600 "C. Hagenmaier et al. heated the same samples under oxygen-deficientconditions and observed that about 99% of the PCDD and PCDF were dechlorinated at 300 "C in 2 h. They stated that the fly ash [and also copper (5)] showed evidence of catalytic activity in the reaction. Hanai et al. (6) also heated the municipal incinerator fly ash at 300 "C in a closed container containing air. They found no increase of the concentration of PCDD and PCDF below 300 "C and found that dechlorination began at 300 "C. Their results would agree with those of Hagenmaier et al. if we were to think that the dechlorination had occurred because the volume of the container of the fly ash used by Hanai et al. was relatively small compared with the amount of the fly ash samples and that the amount of oxygen was limited. Hagenmaier et al. reported that the dechlorination of PCDD and PCDF was inhibited under the condition of surplus oxygen and especially in the presence of HC1 or Clz. The above experiments showed that the dechlorination reactions of PCDD and PCDF proceeded under oxygen-deficient conditions. However, it is not yet well understood how PCDD and PCDF were dechlorinated. Any discussion of the processes in incinerators is hampered by the lack of thermodynamic data of the involved chemical species. Such data, especially for the chlorinating-dechlorinating reactions at temperatures prevalent between the burner and the separators or chimneys, should be useful in any attempt to construct incinerators with lowor zero-level PCDD and PCDF production. In this paper, a number of equilibria between exhaust gases and inorganic substances, abundant in fly ashes, are calculated. Equilibrium data are useful even if equilibrium is not obtained in a real incinerator since all reactions will proceed at least in the direction toward equilibrium. Method of Calculation Thermodynamic data for the involved organic substances were calculated by statistical thermodynamics, Translational degrees of freedom by molecular masses, rotational degrees of freedom by structural models, are derived from the group coordinates of all the chemical groups from which the molecules can be composed. The vibrational data are calculated using a special set of characteristic group frequencies that take into account the neighboring effects from different substitutions (7) (cf. Appendix). The accuracy of the calculated thermodynamic functions was tested against the literature values of 21 organic compounds (7-1 1). The highest observed differ-
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