Environ. Sci. Technol. 1986, 20,260-267
Individual measurements of adsorption coefficient by either method varied by approximately 30% across a 0.64-ha field. Furthermore, indexes that should represent equivalent measures of adsorption under conditions where equilibrium is reached yielded estimates with little or no correlation to each other on samples that were spaced as near as possible to each other across the field. This lack of correlation should be taken as a warning that transport under natural conditions may be too complex to permit a simple index such as a distribution coefficient to be used for describing the adsorption process. However, a 30% coefficient of variation across a 0.64-ha field does not represent an insurmountable level of variability. Use of an average value based on a limited number of replicates may actually characterize behavior adequately for use in model characterization of a new candidate chemical, consistent with the goals discussed at the beginning of this paper. However, it remains to be shown whether these indexes actually describe important characteristics of pesticide transport under natural conditions. Registry No. Napropamide, 15299-99-7. L i t e r a t u r e Cited (1) Hornsby, A. G.; Davidson, J. M. Soil Sci. SOC.Amer. Proc. 1973,37,823-828. (2) Van Genuchten, M. Th.; Davidson, J. M.; Wierenga, P. J. Soil Sci. SOC.Am. Proc. 1974,38,29-34. (3) Van Genuchten, M. Th.; Wierenga, P. J.; O’Connor, G. A. Soil Sci. SOC.Am. J. 1977,41,278-285. (4) Davidson, J. M.; Chang, R. K. Soil Sci. SOC.Amer. Proc. 1972,36,251-261. (5) King, P. H.; McCarty, P. L. Soil Sci. 1968,105,248-255. (6) Huggenberger, F.; Letey, J.; Farmer, W. J. Soil Sci. SOC. Amer. Proc. 1972,36,544-548. (7) Huggenberger, F.; Letey, J.; Farmer, W. J. Calif.Agric. 1973,
27(2),8-10. ( 8 ) Swartzenbach, R. P.; Westall, J. Enuiron. Sci. Technol. 1981,11, 1360-1367. (9) Travis, C. C.; Etnier, E. L. J. Environ. Qual. 1981,10,8-17. (10) Hamaker, J. W.; Thompson, J. M. In “Organic Chemicals in the Soil Environment”; Hamaker, J. W., Goring, C. A.
I., Eds.; Marcel Dekker: New York, 1972; Vol. I, Chapter 2. (11) Kenaga, E. E. Ecotoxicol. Enuiron. Saf. 1980,4, 26-38. (12) Kenaga, E. E.; Goring, C. A. I. In “Aquatic Toxicology ASTM Special Technical Paper 707”; Eaton, J. C., Ed.; American Society for Testing and Materials: Philadelphia, 1980. (13) Briggs, G. G. Aust. J. Soil Res. 1981,19,61-68. (14) Briggs, G. G. J. Agric. Food Chem. 1981,29,1050-1059. (15) Rao, P. S. C.; Davidson, J. M. In “Environmental Impact of Nonpoint Source Pollution”; Overcash, M. R., Davidson, J. M., Eds.; Ann Arbor Science: Ann Arbor, 1980; pp 23-67. (16) Green, R. E.; Corey, J. C. Soil Sci. SOC.Am. Proc. 1971,35, 561-565. (17) Jackson, D. R.; Garrett, B. C.; Bishop, T. A. Enuiron. Sci. Technol. 1984,18,668-673. (18) Rao, P. S. C.; Green, R. E.; Balasubramanian, V.; Kanehiro, Y. J. Enuiron. Qual. 1974,3, 197-202. (19) Elabd, H. Ph.D. Dissertation, University of California, Riverside, CA, 1984. (20) Biggar, J. W.; Nielsen, D. R. Water Resour. Res. 1976,12, 78-84. (21) Wild, A.; Babiker, I. A. J. Soil Sci. 1976,27, 460-466. (22) Van der Pol, R. M.; Wierenga, P. J.; Nielson, D. R. Soil Sci. SOC.Am. J. 1977 41,10-13. (23) Jury, W. A.; Stolzy, L. H.; Shouse, P. Water Resour. Res. 1982,18,369-375. (24) Jury, W. A.; Spencer, W. F.; Farmer, W. J. J. Environ. Qual. 1983,12,558-563. (25) Ehlers, W. E.; Letey, J.; Spencer, W. F.; Spencer, W. J. Soil Sci. SOC.Am. Proc. 1969,33,501-504. (26) Allison, L. E. In “Methods of Soil Analysis”; Black, C. A., Argon.: Madison, WI, 1965; Vol. 2, Chapter Eds.; h e r . SOC. 90. (27) Himmelblau, D. “Process Analysis by Statistical Methods”; Sterling Swift: Manchaca, TX, 1970; pp 51-52. (28) Nielsen, D. R.; Tillotson, P. M.; Vieira, S.R. Agric. Water Manage. 1983,6,93-109.
Received for review April 19,1985.Revised manuscript received September 12, 1985. Accepted November 4, 1985. Southern California Edison Co. is acknowledged for financial assistance on this project.
Photooxidation of 2,4-Dinitrotoluene in Aqueous Solution in the Presence of Hydrogen Peroxide Patience C. Ho Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
The synergistic effect of hydrogen peroxide and UV radiation from a medium-pressure mercury vapor lamp on the decomposition of 2,4-dinitrotoluene (DNT) in water was studied. The results suggest that the degradation pathways of DNT in aqueous solution in the presence of hydrogen peroxide and UV light are (1) side-chain oxidation, which converts DNT to 1,3-dinitrobenzene, (2) hydroxylation of the benzene ring, which converts 1,3-dinitrobenzene to hydroxynitrobenzene derivatives, (3) benzene ring cleavage of these hydroxynitrobenzenes, which produces lower molecular weight carboxylic acids and aldehydes, and (4) further photooxidation, which eventually converts the lower molecular weight acids and aldehydes to C 0 2 , H20, and HN03. H
Introduction
Manufacturing and handling operations in military munitions facilities generate significant volumes of aqueous 260
Environ. Sci. Technol., Vol. 20, No. 3, 1986
effluents contaminated with nitrated organics, particularly 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitrohexahydro1,3,5-triazine(RDX), and smaller amounts of others, such as 2,4-dinitrotoluene (DNT), which is particularly hazardous to biota. Release of these compounds into the surrounding environment constitutes an environmental hazard. Among many methods of degradation of explosive nitrobodies, a promising approach is the synergistic combination of ultraviolet (UV) irradiation and an oxidizing agent, generally hydrogen peroxide (1-3) or ozone (4-6). Although these methods were clearly demonstrated t o degrade TNT and related materials completely to carbon dioxide, water, and nitric acid, the underlying photochemical and chemical pathways are not understood. The objective of this study was to find out the reaction pathway of the degradation reaction of dinitrotoluene in aqueous solutions by means of UV irradiation with the presence of an oxidizing agent. This paper presents the results of
0013-936X/86/0920-0260$01.50/0
0 1986 American Chemical Society
photooxidation of 2,4-dinitrotoluene and some of the reaction intermediates produced during the photooxidation of DNT, which is exposed in aqueous solution to hydrogen peroxide and radiation from a medium-pressure mercury vapor lamp. Reaction pathways and mechanisms of photooxidation of aqueous DNT solutions are suggested.
Experimental Section Materials. 2,4-Dinitrotoluene (Aldrich, 97%), 1,3-dinitrobenzene (Fluka, puriss >99%), and 2,4-dinitrobenzaldehyde (Aldrich, 97%) were purified by liquid chromatography (with a Brinkmann MN-Kieselgel60 column) to a purity greater than 99.5% (as measured by thin-layer chromatography) before using. 2,4-Dinitrobenzoic acid (Fluka, purum >98% (T))was recrystallized twice from water. 2,4-Dinitrophenol (Fluka, puriss >99%) moistened with 20% water, glyoxal (Fluka, practical -30% in water), and glyoxylic acid (Fluka, 50% in water) were extracted with benzene and dried under Nz to remove water. 3Nitrophenol (Aldrich,99%), 4-nitrocatechol (Fluka, >98% (T)), maleic acid (Fluka, >99% (T)),hydrogen peroxide (Mallinckrodt, 30%), and formic acid (puriss >98%, Fluka) were used as received without further purification. Water was deionized and double distilled in glass. Photolysis Procedures. Mixtures of the organic and hydrogen peroxide in aqueous solution were irradiated mostly with a 450-W (sometimes with a 200-W) Hanovia medium-pressure mercury vapor lamp with or without filters. Such a medium-pressure mercury vapor lamp produces a broad spectrum from the far-UV to the infrared region. A low-pressure mercury lamp (GE, G15T8), which is rich in a 253.7-nm line, was also used for comparison. The fiiters were Pyrex (to remove light < 280 nm) or Vycor (to remove light < 220 nm) sleeves and a liquid filter of aqueous C0S04 solution (to isolate the 253.7-nm region from the medium-pressuremercury arc spectrum (7)). The temperatures of the reaction mixtures in the borosilicate glass reactor (ACE Glass) were maintained at 27-35 "C with circulating cooling water in the quartz cooling chamber (ACE Glass). The residence time of the solution in the reactor was monitored by a timer. The aqueous organic solutions were prepared with double distilled deionized water and stirred at room temperature and up to 40 OC for several days, depending on the solubility of the organics. Hydrogen peroxide was added to the aqueous organic solution just before it was transferred into the reactor. Samples were collected after the desired time of irradiation. The aqueous reaction mixtures, which were to be analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) analyses, were extracted twice with ethyl ether before and after the aqueous phase was acidified with concentrated HC1 to about pH 1. The ether solutions were dried over Na2S04before ether was removed. Confirmation of the structure of intermediates whenever possible was done by comparison of the spectra with authentic compounds. Suitable authentic compounds (phenols and acids) and the reaction mixtures were silylated with MSTFA (N-methyl-N-(trimethylsily1)trifluoroacetamide; Pierce) before GC and GC/MS analyses unless noted otherwise. Analytical Methods. The rates of disappearance of a given organic compound, such as DNT, 2,4-dinitrobenzaldehyde, or 173-dinitrobenzene,in reaction mixtures were monitored by a high-performance liquid chromatograph (HPLC) equipped with a Varian Vari-Chrom UV-vis detector. Reverse-phase columns, 25 cm long, 10 mm i.d. and 25 cm long, 4.6 mm i.d., packed with Alltech C18, 10 pm, were used for separation and analyses, respectively.
Mixtures of glass distilled methanol (Boldman Chemicals) and deionized double distilled water were used as the mobile phase. The instrument was calibrated with aqueous standard compound solutions. Besides HPLC, reaction intermediates were also characterized (after silylation) by a Hewlett-Packard 5880 gas chromatograph and a Hewlett-Packard H P 5995A gas chromatograph/mass spectrometer system, both fitted with a 30-m Durabond I narrow-bond fused silica column (J. W. Scientific). The column temperature was programmed from 50 OC (60 OC for GC) (3-min hold) to 325 "C (275 OC for GC) with an increase of 10 "C/min. Quantitative analyses were done by use of GC and HPLC. The HPLC measurements were conducted by monitoring the absorption at 254 nm (with reverse-phase C18 column and eluting with methanol/water (3:2) mixtures) for aromatic compounds. Oxalic acid was measured by monitoring the absorption at 200 nm with an ion-exchange RSiL CAT column (Alltech), eluting with an aqueous solution of phosphoric acid (buffered with KHzPO4 to pH 2.9)(8). Owing to the overlap of the HPLC peaks of formic acid with hydrogen peroxide by this method, the amount of the former could not be given quantitatively. The total amount of aldehydes, which included glyoxal and glyoxylic acid, in the reaction mixture was determined by HPLC with the reverse-phase C18 column and by a Perkin Elmer 559 UV-vis spectrophotometer after the aldehydes were converted to 2,4-dinitrophenylhydrazones (9,10).
Results and Discussion Aromatic nitro compounds absorb intensely in the UV region (11-13). Specifically, dinitrotoluene in aqueous = 252 nm ( E = -15000; r r* solution (11) has A,, transition) with a tail extending to -350 nm (n r* transition). Detailed study of the quantum yields from photolysis of polynitro aromatics in dilute aqueous solution has been limited mostly to TNT (2,4,6-trinitrotoluene; in (14,15). However, low quantum yield the range of ( has been observed for DNT in hydrocarbon solvents (12). Thus photolysis by itself is inherently inefficient in destroying polynitro compounds in aqueous solution; rather, in some cases, more complex mixtures of stable photo products would be produced (16-18). Hydrogen peroxide is known to be photosensitive (19), and this property has often been used to induce oxidation of compounds that are not attacked by hydrogen peroxide in the dark. In this study a saturated aqueous solution of DNT was first exposed to the 450-W medium-pressure mercury lamp without the presence of an oxidizing agent. The disappearance of DNT vs. time is given in Table I. The results show that at the end of a 17-h reaction, solids and a minimum of at least eight products besides DNT in the liquid phase (solids were removed by filtration with a Rainin Millipore filter) had been formed (20). Table I also gives corresponding data on the disappearance of DNT vs. time in aqueous solution at various concentrations of hydrogen peroxide. Two sets of experiments with different initial DNT concentrations were conducted. The molar ratios of H202/DNTvaried from 13 to 104. These aqueous mixtures were exposed to the 450-W Hg lamp without a filter. Depending on the concentration of H202,the colorless initial mixtures turned yellow to deep orange to brown in 2-10 min, then faded gradually as exposure was continued, and finally became colorless. The pH values of the reaction mixtures changed
--
N
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261
Table I. Effect of Hydrogen Peroxide Concentration and Time of Exposure on the Extent of Photooxidative Degradation of DNT"
time of exposure, min 0
original concn of DNT in HzO, ppm
% DNT elimination a t various H2OZ/DNTmolar ratios
0
10
52
104
-b
67.7 86.8 99.3 99.7
72.2 93.7 99.7 -100 100
-
76.5 83.9 98.2
20 30 45 60
100 -
204.9
20 30 60 90 120 180 240 300 360
-
55.0 85.0
29.9 37.9 54.6 62.3 89.0
-
98.8
rr '
-
100 100 -
97.2
-
100 -
69.7 94.8 97.7 99.5 100 100
100
-
-
76.5c 91.0 97.8 94.4 100 -
-
--
89.2 96.8 97.1 100 100 47.2 50.3 50.3 54.4 -
66.9 73.8 82.7 88.1 95.9
420
99.0
-
-
450 480
-
600
99.7 >99.7
- 99.9
1015
"Incident light: 450-W medium-pressure vapor lamp with no filter. vvm.
with the changing of color. The pH of these initial aqueous mixtures, which ranged from 6.0 to 6.8 depending on the concentrations of H202,decreased to 2.8 when the orange color appeared and then to 2.4 at the dark orange to brown stage before starting to increase as the color gradually faded away. The pH of the colorless reaction mixture (at this stage, there was no DNT left in the solution) was about 3.6. It can be seen from Table I that at the lower initial concentration of DNT in solution, the effect of the concentration of H202on the degradation rate of DNT was not as obvious as at the higher concentration of DNT. Nevertheless, the most effective concentrations of H202 were those with the molar ratio of H202/DNTbetween 26 and 52. At these molar ratios, the disappearance rate of DNT was very fast. Therefore, it is clear that there is an optimum concentration range of H202 Excess H202in the solution actually retards the DNT degradation. This finding is in agreement with the conclusion in ref 1-3 for
TNT. The degradation rate of DNT in aqueous solution is also affected by the energy of the incident light. Aqueous mixtures of DNT and H202(molar ratio of H202/DNT= 26) were exposed to the 450-W Hg lamp equipped with either a Pyrex or a Vycor filter in order to block out or partially block out light in the far-UV region, in other words to reduce the energy of the incident light. The results show that the time for destruction of 70% of the original DNT is ca. 10 min with no filter, ca. 20 rnin with a Vycor filter, ca. 400 min with a Pyrex filter, and 950 rnin with a Pyrex filter and no H202added (20). Thus it appears that the presence of light in the far-UV region, as well as an excess of Hz02,is also a very important factor of the degradation of DNT in aqueous solution. In addition to the above experiments, an effort was also made to study the oxidation of DNT in aqueous solution with hydrogen peroxide without UV irradiation. Aqueous mixtures of DNT and H2O2at molar ratios of H202/DNT = 13-104 and 26-889 (20)were stirred at room temperature in the dark and under conventional indoor light, re262
26
75.8
5
0 10
13
Environ. Scl. Technol., Vol. 20, No. 3, 1986
100 -
b-,
Not determined. cOriginalconcentration of DNT in HzO was 210
spectively, for 7 days. The results show that oxidation of aqueous DNT solution with HzOzalone was very slow and elimination of DNT was probably never complete. However, the HPLC spectra of these reaction mixtures were very similar to those in similar systems that were exposed to UV light for short times (2-10 min). Although the amounts of intermediates found were fairly small, three of them that could be seen on the spectra were the same as in UV/Hz02 systems. These intermediates will be discussed later. As mentioned before, when DNT/H202was exposed to the Hg lamp without a filter, there was a stage at which the color of the UV-irradiated reaction mixtures would turn dark orange before the color began to fade away. HPLC spectra measured at the early stages had also revealed that several intermediates had been formed and disappeared during these periods. This is probably the optimum experimental region to search for reaction intermediates. To this end, four ptirtially photooxidized reaction mixtures were studied. Three were with a mixture of H202/DNT= 26 (molar ratio) and exposed to the 450-W Hg lamp for 2, 5, and 10 min. For comparison, one run was with a mixture of H202/DNT= 13 and exposed to a 200-W Hg lamp for 14 min. According to HPLC and GC/MS spectra, the intermediates produced from the above four reactions were very similar. A major intermediate, which amounted to about 90% of the total detected (excluding unreacted DNT), and many minor intermediates were found. The major intermediate (which was separated from others by preparative HPLC) and minor intermediates were characterized by HPLC, GC, and GC/MS studies. From comparison with authentic compounds, the major intermediate was confirmed as 2,4-dinitrobenzoic acid, and other confirmed intermediates were 2,4-dinitrobenzyl alcohol (the MSTFA silylated compound has a base ion peak at m l e 239 and a fragment ion peak at m / e 255, which matched the mass spectrum of silylated 3,4-dinitrobenzyl alcohol (commercially available) except with different GC retention time, as usually happens with isomers); 2,4-dinitrobenzaldehyde;lJ-dinitrobenzene;
Table 11. Concentration of DNT and Other Intermediates at Various Reaction Times of Photooxidation of DNT/H202 Mixturesa H&z/DNT, molar ratio 13
time of exposure, min 0 10
20 30 45 60 90 26
0
5 10
20 30 45 52
0
6 10
20 33 45 104
0
10 20 30 45 60 44
0
5 11.7 20 30 45 60 92f 123 146 180
DNT 75.8 17.8 12.2 1.4 0 0 0
75.8 24.5 10.0 0.5 0.2 0
75.8 21.1 4.8 0.22 0 0
75.8 8.2 2.4 2.2
0
81.7 66.3 43.3 9.1 1.1
0.8 0.4 0 0 0 0
concn of DNT and other intermediates in reaction mixtures, ppm 2,l-dinitro2,4-dinitrootherb benzyl alcohol benzaldehyde aldehydes DNBAc DNBd trace trace 0
0.85 0.15 0.15
15.4 14.5 5.9
0.15 0.35 0.70
0 0
0 0 0
1.2
0.9 0.3
-0 0 0
0
trace trace
10.8 10.8
1.1
0.6 trace 0 0
1.3 0.15 trace
14.6 5.5 1.4
0.07 0.15 trace
1.2
0
0 0
0.2
0 0
trace trace -0
0.6 trace trace
10.2 3.9 0.3
trace -0 0 0
0
-
0.105 0.04 0.03 trace
1.5
0.8 0.4 trace
10.5 14.6 9.9 4.8
0.15 0.30 0.25 0.15
2.2
-0 0 0 0 0 0
0 0 0
-
-
-0 0
0
0 0 0
-
trace 0.2 trace
1.6 1.6 0.45
-0 0 0
oxalic acid
-
-
-
0.2
-0 0 0 0 0 0
1.4 0.4 trace trace 0
-
-
-
128 135 134 134 0
aIncident light: 450-W medium-pressure mercury vapor lamp with no filters. *Other aldehydes = total amount of aldehydes - 2,4-dinitrobenzaldehdye. DNBA, 2,4-dinitrobenzoic acid. dDNB, 1,3-dinitrobenzene. e -, Not determined. f From here on neither formic acid nor hydrogen peroxide could be detected.
2,4-dinitrophenol; 3-nitrophenol; 2-hydroxy-maleic acid (2-hydroxy-2-butenedioicacid) (mass spectrum: base ion peak at m / e 147, a typical fragment ion, (CH,),-Si-OSi+-(CH3)2,of silylated dicarboxylic acids, hydroxy acids, and terminal diols (21,ZZ); and M - 15 (Mminus methyl group) ion peak at m / e 333); and maleic acid, oxalic acid, glyoxylic acid and glyoxal. Some of these intermediates are probably responsible for the color changes during the early stage of the reaction. Compounds such as 2,4-dinitrobenzoic acid and 2,4-dinitrophenol give an intense yellow aqueous solution even at a very low concentration. The acids (aromatic and aliphatic) produced during reactions probably account for the resulting pH drops. Aqueous DNT and HzOzmixtures with molar ratios of HZO2/DNT = 26 and 13 were also exposed to largely monochromatic light at 253.7 nm, which was produced either from the 450-W medium-pressure Hg lamp with an aqueous CoS04 filter solution or from a low-pressure Hg lamp (a germicidal lamp from General Electric). After 10-20 min of exposure, 2,4-dinitrobenzoic acid was again found as the major intermediate in both cases, and the number of other intermediates was markedly reduced and only a small amount of maleic and oxalic acids was observed.
The large amount of 2,4-dinitrobenzoic acid produced at short times probably indicates that a major part of the degradation in the beginning is side-chain oxidation, that is FHO
I
NOn
NO2
The relatively small amount of dinitrobenzyl alcohol and dinitrobenzaldehyde revealed that the rate of oxidation of the alcohol and aldehyde derivatives is faster than the rate of decomposition of the dinitrobenzoic acid. Table I1 gives the formation and decomposition rates of these intermediates. It can be seen in Table I1 that at every ratio of H2OZ/DNTdinitrobenzyl alcohol, which formed probEnvlron. Sci. Technol., Vol. 20, No. 3, 1986
263
ably starting from the beginning of the reaction, would disappear in less than 20 min, and dinitrobenzaldehyde disappeared in about 30 min. Dinitrobenzoic acid, which also started to form at the beginning of the reaction in relatively higher amounts, increased with increasing time of exposure, reached a maximum, then decreased very slowly. 2,4-Dinitrobenzoic acid is found in the reaction mixture even after all DNT has long been eliminated. After DNT, dinitrobenzoic acid, and others had been eliminated, the only organic compound left in the solution was oxalic acid. Further light exposure would eventually convert oxalic acid to C02. HPLC and GC/MS spectra of the 3-h-exposed reaction mixture of the above system revealed that no organic compound was present. It is reasonable to suggest that the attack on the methyl group, which induced the side-chain oxidation, is initiated by hydroxyl radicals (1-3,23-25), as it is well-known that hydroxyl radicals are the main oxidant formed by photolytic cleavage of Hz02in water (19,26-30). Although the mechanism of the reaction of DNT with Hz02without UV irradiation was not yet determined, the similarity of intermediates that were produced during the oxidation of DNT in aqueous solution either by UV/H20z in short times (2-10 min) or by Hz02alone for 7 days (intermediates in these cases were identified as small amounts of 2,4-dinitrobenzoic acid, 2,4-dinitrobenzaldehyde,and 1,3dinitrobenzene) could convince one that the predominant oxidizing species in the latter case probably was also hydroxyl radicals. Nevertheless, the DNT degradation rate in the UV/H2OZsystems was greatly enhanced by the presence of the UV light. The existence of 3-nitrophenol and 2,4-dinitrophenol in the reaction mixtures will be discussed below. In order to investigate the reaction pathway subsequent to the formation of 2,4-dinitrobenzoic acid and 1,3-dinitrobenzene, photooxidations of several of the identified intermediates were studied. Aqueous 2,4-dinitrobenzoic acid (DNBA) (545 ppm) was mixed with hydrogen peroxide at a molar ratio of H202/ DNBA = 26 and esposed to the 450-W Hg lamp without a filter. As mentioned before, the degradation rate of DNBA in aqueous solution is very slow, and the high concentration of DNBA in the reaction solution would contribute another 'factor to affect the rate. According to the HPLC spectrq, l,3-dinitrobenzene (DNB) was the first major intermediate obtained after 10 min and 3-nitrophenol was the second major intermediate after 30 min. It was later confirmed by GC/MS spectra that DNB and 3-nitrophenol were the two major intermediates. The quantities of these intermediates increased with time of exposure, reached a maximum, and then started to decline. Besides these two, other intermediates appeared to be present as well. However, awing to the overlap of the large amount of unreacted DNBA with other polar intermediates, identification of the others by both HPLC and GCGC/MS became difficult. The residues of the reaction mixture, after exposure to the. 450-W Hg lamp for 1h, were separated by preparative HPLC in order to remove a large portion of the unreacted DNBA. Two more intermediates were discovered in this way. They were 2,4-dinitrophenol and oxalic acid. The presence of 1,3-dinitrobenzene, 3nitrophenol, and 2,4-dinityophenol not only confirmed reaction 1, but suggested reactions 2 and 3 as well (illustrated for ortho-para attack). Such reactions of hydroxyl radicals have been previously suggested (16, 23, 31-34). In reaction 2, addition to an unsubstituted position of the benzene ring gives a hydroxycyclohexadienyl radical (32,33,35-38),which is ox264
Environ. Sci. Technol., Vol. 20, No. 3, 1986
OH
NO2
I
I
NO2
NOn
OH
I
NO2
NOn
I
NO2
idized further to the phenol derivatives. Similar reactions were observed during UV ozonation of nitrobenzene in aqueous solution, which gave mixtures of nitrophenols (16). In reaction 3, addition to an ipso position again achieves ring hydroxylation but now with loss of the nitro substituent. To test this suggestion further, aqueous 1,3-dinitrobenzene (DNB) was photooxidized. An aqueous solution of 1,3-dinitrobenzene (328 ppm) was mixed with H202at a molar ratio of HZO2/DNB= 26 and expased to the 450-W Hg lamp. The colorless aqueous mixture turned yellow after 10 min and became colorless again after about 2 h, while the pH of the mixture dropped from an initial value of 5.7 to 2.5. A t the end of the 2-h exposure 99% of the original DNB was eliminated. Samples of the 20min- and 1.8-h-exposed reaction mixtures were analyzed (silylated with MSTFA for GC and GC/MS). Major intermediates found in the 20-min-exposed sample were 3-nitrophenol and three isomers of dinitrophenols, the predominant one of which proved to be 2,4-dinitrophenol. The ratio of the total amount of the three dinitrophenols to 3-nitrophenol was about 161(quantified by GC). Other intermediates found in this sample were maleic acid and oxalic acid. The 1.8-h-exposedreaction mixture contained no aromatic compounds. Instead, oxalic acid, mesoxalic acid semialdehyde ((HO),C(COOH)(CHO);mass spectrum: base ion peak at m / e 73, a typical trimethylsilyl ion from silylated carboxylic acid or alcohols (21,22),and a fragment ion of m / e 321, which corresponds to the M - 15 ion peak), and hydroxymaleic acid semialdehyde (2(or 3)-hydroxy4-oxo-2-butenoic acid; mass spectrum: base ion peak at m / e 73, M - 15 ion peak at m / e 245; the pattern is similar to the spectrum of silylated maleic acid except for having a longer retention time) were observed. Glyoxal and glyoxylic acid were also found in this 1.8-h-exposedsample. The presence of both 3-nitrophenol and isomers of dinitrophenols in the short-time exposed reaction mixture once again demonstrated the occurrence of reactions 2 and 3. Photooxidation of aqueous 3-nitrophenol/HzOz and 2,4-dinitrophenol/HZO2mixtures was carried out under the same conditions. An aqueous 3-nitrophenol/H202mixture (497 ppm, HzOz/3-nitrophenol= 26) was exposed to the 450-W Hg lamp for a total of 5.5 b. At the end of the run, 3-nitrophenolcgm?d not be detected by HPLC and GC/MS spectra. Oxalic acid was the only detectable intermediate left in the reaction mixture. Qualitative analysis of the 15-min-exposed reaction mixture by HPLC and GC/MS revealed that very large amounts of dihydroxynitrobenzenes (three isomers) and moderate amounts of trihydroxynitrobenzenes (three isomers) were present. Quantitative analysis (with GC) showed that at this stage the unreacted 3-nitrophenol accounted for 65% of the trimethylsilylated residue of the reaction mixture, while the total amount of dihydroxynitrobenzene isomers accounted for 29.9 % and trihydroxynitrobenzeneisomers for
0.56%. The ratios of the three dihydroxynitrobenkenes were 1.3 (isomer 1,named by increase of retention time) to 1.0 (isomer 2) to 1.0 (isomer 3). Isomer 3 was proven to be 4-nitrocatechol by comparison with the authentic compound. The ratios of the three trihpdroxynitrobenzenes were 4.7 (isomer 1)to 13 (isomer 2) to 1 (isomer 3). The GC/MS spectrum of the commercially available 1,3,5-trihydroxy-2-nitrobenzene (Pfaltz and Bauer) (base ion peak at m / e 73, M - 15 ion peak at m / e 372, and molecular ion peak at m / e 387) was used as a guide to identify the three isomers. In addition to the polyhydroxynitrobenzenes, other intermediates present were maleic acid and oxalic acid, both in trace quantities. The presence of large amounts of dihydroxynitrobenzenes and moderate amounts of trihydroxynitrobenzenes in the reaction mixture presumably implies that photooxidation of aqueous 3-nitrophenol in the presence of HzOzproceeds as shown in eq 4. OH I
trihydroxynitrobenzene
cleavage of
--
OH
-benzene - - - ring - -OH
I
kO,
N0,
OH
6H
.1 0 2 N W C O O H HO&CHO A02
t
t etc.
etc
phenol/HZOzsystem, hydroxylation proceeds faster than ring cleavage. Since 4-nitrocatechol was one of the intermediates produced during photooxidation of both the 3-nitrophenol Similar studies on ozonation and UV ozonation of niand 2,4-dinitropheriol systems, this compound was further trobenzene in water have demonstrated ring hydroxylation photooxidized in the presence of H202. Several experito give di- and trihydroxynitrobenzenes (16). ments have been carried out with various molar ratios of Since dinitrophenols were also major intermediates in H202/4-nitrocatecholand different incident light sources the photooxidized aqueous 1,3-dinifrobehzeny reaction in order to understand the reaction mechiinism better. mixture, an Bqueous mixture of 500 ppm 2,4-dihitrophenol The results are given in Table 111. It can be seen that the and H202(H202/dinitrophenol= 26) was exposed to the major intermediate(s) produced were isomers (three) of 450-W k g lamp for a total of 3.4 h. Samples exposed for trihydroxynitrobenzenes (the same isomers have been seen 20,52, tind 204 (3.4 h) minutes were collected for analyses. in the photooxidized 3-nitrophenol/H20zmixtures) or The major intermediate found in the 20- and 52-min-exoxalic acid; the ratio of these compounds was highly deposed samples was a compound, to our surprise, with the pendent on the concentration of H202,on the intensity of following mass spectrum data: base ion peak at m / e 73 incident light, and on the length of exposure. For example, and molecular ion peak (?) at m / e 331, which could corafter 1.4 h of exposure, at H20z/4-nitrocatechol= 26, the respond to either trimethylsilylated hydroxynitromuconic acid semialdehyde (cis,cis-3-nitro-4-hydroxy-6-oxo-2,4- remaining 4-nitrocatechol amounted to 61% of the residue of the reaction mixture, while the trihydroxynitrobenzene hexadienoic acid) or nitromuconic acid (cis,cis-3-nitroisomers produced amounted to 34.6% (possibly some ni2,4-hexadienedioic acid). The second major intermediate tromuconic acid derivatives were also included, however, was 4-nitrocatechol along with trace amounts of a triowing to the overlap of the GC peaks of nitromuconic acid hydroxynitrobenzene isomer (corresponding to isomer 2 derivatives with one of the trihydroxynitrobenzene (isomer in the photooxidized 3-nitrophenol reaction mixture), maleic acid, and oxalic acid. The 3.4-h-exposed reaction 3) peaks, the former compound could not be clearly mixture contained mainly oxalic acid and a trace amount identified) along with 0.5% oxalic acid and 0.3% maleic of nitromaleic acid semialdehyde (cis-2 (or 3)-nitro-4acid. The ratios of the three isomers were 4.2 (isomer 1) oxo-2-butenoic acid; mass spectrum: b&e ion peak at m / e to 1.0 (isomer 2) to 3.2 (isomer 3). 73, M - 15 ion peak at m / e 202, and molecular ion peak It appears that photooxidation of aqueous dihydroxyat m / e 217) and mesoxalic acid semialdehyde. nitrobenzene/Hz02mixtures produces trihydroxynitroIt seems that during photooxidation of aqueous 2,4-dibenzenes, and continuing photooxidation of the trinitrophenol/H202mixtures with the medium-pressure Hg hydroxynitrobenzene eventually leads to benzene ring lamp, several competing reactions occurred (see eq 5). cleavage. This has also been demonstrated in UV ozonaSince dinitromuconic acid derivatives were not found tion of aqueous 4-nitrocatechol solution (16). in any of the reaction mixtures, the first step of the reIn order to further support the above reaction pathways, action followed route I, that is, a nitro group was removed a mixture of trihydroxynitrobenzene isomers was isolated from the benzehe ring and replaced with a hydroxyl group. from the photooxidized 4-nitrocatechol reaction mixture Routes 11-IV were the attack of hydroxyl radicals on the by preparative HPLC. The aqueous trihydroxynitrobenzene ring to bring about the cleavage of the ring, or benzenes (40 ppm) solution was mixed with HzOZ(molar addition to the benzene ring similar to the ozonation of ratio of Hz02/trihydroxynitrobenzene= 19.5) and exposed phenol or catechol or hydroquinone in water (9). The to the 450-W Hg lamp for 20 min. The GC/MS spectrum presence of larger amounts of nitromuconic acid derivatives of the reaction mixture revealed that mesoxalic acid semthan di- and trihydroxynitrobenzenes in these reaction ialdehyde and oxalic acid were the two major intermedimixtures presumably implies either that hydroxylation and ates. Fairly small amounts of hydroxymaleic acid, hybenzene ring cleavage both occurred very rapidly or that droxymaleic acid semialdehyde, mesoxalic acid, glyoxal, benzene ring cleavage occurred prior to hydroxylation. and glyoxylic acid were also found in this reaction mixture. Note that we suggested above that, for the 3-nitroBecause of the relatively low concentration of the starting @TOH
No2
NO,
Environ. Sci. Technol., Vol. 20, NO. 3, 1986 265
Table 111. Photooxidation Products of 4-Nitrocatechol in Aqueous Solution
uv
Hz02/4-NC? molar ratio
source, W
time of exposure, min
26 26 26 26 26 6.7 2.0
450 450 450 450 200 200 200 (Vycor)
35 84 (1.4 h) 246 (4.1 h) 134 (2.24 h) 132 (2.2 h) 63 (1.05 h)
10
major intermediates b b b e e e b
other identifiable intermediates (small to trace amt) c , d, e
e, f , e e
d , g, h e, d , g
c, d c, d
4-Nitrocatechol. *Isomers of trihydroxynitrobenzenes. Maleic acid. Hydroxymaleic acid semialdehyde (2(or 3)-hydroxy-4-oxo-3(or 2)-butenoic acid). e Oxalic acid. f Hydroxymaleic acid. BNitromaleic acid semialdehyde (2(or 3)-nitro-4-oxo-3(or 2)-butenoic acid). Nitromaleic acid.
material (trihydroxynitrobenzenes)and the relatively long (20 min) light exposure, the anticipated intermediates, nitromuconic acid derivatives, produced after the benzene ring cleavage could not be detected. Rather, they must be rapidly degraded to lower molecular weight acids and aldehydes. Further photooxidation of the lower molecular weight carboxylic acids and aldehydes, such as maleic acid, oxalic acid, glyoxylic acid, and glyoxal was not performed in this study, but there is considerable information in the literature. From oxidation of maleic acid in water by ozone (8, 9,39)glyoxylic acid and formic acid have been obtained as the reaction products, and further oxidation converted these acids into oxalic acid and COz. in addition, from oxidation of oxalic acid and formic acid in water by ozone (9),C 0 2 was obtained as the end product. Similarly, from photooxidation of an aqueous maleic acid solution with UV/ozone (16), formic acid was found as the major intermediate, along with small amounts of glyoxylic acid and oxalic acid. UV ozonation of aqueous glyoxal produced oxalic acid and COz (16). The observation of maleic acid and its derivatives, oxalic acid, glyoxal, and glyoxylic acid, in the 2- to 14-min-e~posed-photooxidized aqueous DNT/HZO2solution and in the 10- to 20-min-photooxidized aqueous intermediates (DNT degradation products)/H2O2solutions, suggests that similar degradation sequences of the lower molecular weight carboxylic acids and aldehydes to COz would also occur when they were photooxidized with UV/H202. The data shown in Table I1 were further proof of this scheme in that after the disappearance of 2,4-dinitrobenzoic acid, the final product left in the solution was oxalic acid and the oxalic acid eventually would decompose to COz after prolonged light exposure. Indeed, in the GC/MS spectrum of the last reaction mixture in Table 11, after 3 h of exposure, no organic compound could be found. Based on ‘intermediates identified after each photooxidation of aqueous DNT solution and of its degradation intermediates in this study, we suggest the following reaction pathway for photooxidation of aqueous DNT solutions with UV/H2OZ:
-
H202
2,4-DNT 2,4-dinitrobenzyl alcohol -, 2,4-dinitrobenzaldehyde 2,4-dinitrobenzoic acid -, 1,Sdinitrobenzene 3-nitrophenol + dinitrophenols (+ NO3-) dihydroxynitrobenzenes trihydroxynitrobenzenes -,
-
-
nitromuconic acid derivatives (+ NO3-) -,maleic acid nitro- and hydroxymaleic acid derivatives + glyoxal + glyoxylic acid (+ NO3-) -, oxalic acid formic acid (+ NOB-) CO2 + HzO
+
+
266
-+
Environ. Sci. Technol., Vol. 20, No. 3, 1986
Acknowledgments
I express my thanks to M. L. Poutsma, Division Head, Oak Ridge National Laboratory Chemistry Division, for many helpful discussions. Registry No. DNT, 121-14-2;DNBA, 610-30-0; DNB, 99-65-0; 4-NC, 3316-09-4; HzOz, 7722-84-1; (HO)&(COOH)(CHO), 25666-25-5; 2,4-dinitrobenzyl alcohol, 4836-66-2; 2,4-dinitrobenzaldehyde, 528-75-6; oxalic acid, 144-62-7; 2,4-dinitrophenol, 51-28-5; 3-nitrophenol, 554-84-7; maleic acid, 110-16-7; hydroxymaleic acid semialdehyde, 99687-77-1; nitromaleic acid semialdehyde, 99687-78-2;hydroxymaleic acid, 1115-67-9;nitromaleic acid, 99687-79-3.
Literature Cited (1) Andrews, C. C.; Osmon, J. L. “The Effect of UV Light on
T N T and Other Explosives in Aqueous Solution”; Naval Weapons support Center, Crane, IN, 1977, WOEC/C 77-32, AD-A036132. (2) Andrews, C. C.; Klausmeier, R. E.; Osmon, J. L. US. Patent 4 038 116, 1977. (3) Andrews, C. C. “Photooxidative Treatment of T N T Contaminated Wastewaters”; Final Report, Naval Weapons Support Center, Crane, IN, 1980, WQEC/C 80-137, ADA084684. (4) Roth, M.; Murphy, J. M., Jr. “Ultraviolet-Ozone and U1traviolet-Oxidant Treatment of Pink Water”; U.S.Army Armament Research and Development Command, Large Caliber Weapon Systems Laboratory, Dover, NJ, 1978, Technical Report ARLCD-TR-78057, AD-E400263. (5) Roth, M.; Murphy, J. M., Jr. ”Evaluation of the Ultraviolet-Ozone and Ultraviolet-Oxidant Treatment of Pink Water”; P B 300763, EPA 600/2-79-129, 1979. (6) Layne, W. S.; Nickelson, R. A,; Wahl, R. M.; O’Brien, P. M. “Ultraviolet-Ozone Treatment of Pink Wastewater, A Pilot Scale Study”; Mason and Hanger-Silas Mason Co., Inc., Iowa Army Ammunition Plant, Middletown, IA, 1982, AD-BO68 215. (7) Calvert, J. C.; Pitts, J. N., Jr. “Photochemistry”; Wiley: New York, NY, 1966. (8) Yamamoto, Y.; Niki, E.; Kamiya, Y. J. Org. Chem. 1981, 46, 250-254. (9) Yamamoto, Y.; Nike, E.; Shiokawa, H.; Kamiya, Y. J . Org. Chem. 1979,44, 2137-2142. (10) Jupille, T. J. Chromatogr. Sci. 1979, 17, 160-167. (11) Sandus, 0.; Slagg, N. “Reactions of Aromatic Nitrocompounds, I. Photochemistry”; Feltman Research Laboratory, Picatinny Arsenal, Dover, NJ, 1972, AD-753923. (12) Bartolo, B. D.; Pacheco, D.; Schultz, M. J. “Spectroscopic Investigation of Energetic Materials and Associated Impurities”; Boston College: Boston, MA, 1979,AD-038157. (13) Wettermark, G.; Ricci, R. J. Chem. Phys. 1963, 39, 1218-1223. (14) Ronning, M. A.; Atkins, R. L.; Heller, C. A. J. Photochem. 1978, 9, 403-405. (15) Mabey, W. R.; Tse, D.; Baraze, A.; Mill, T. Chemosphere 1983,12,3-16.
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(29) Baxendale, J. H.; Wilson, J. A. Trans. Faraday SOC.1957, 53, 344-356. (30) Volman, D. H.; Chen, J. C. J. Am. Chem. SOC.1959,81, 4141-4144. (31) Loebl, H.; Stein, G.; Weiss, J. J. Chem. SOC.1949,2074-2076. (32) Walling, C.; Johnson, R. A. J. Am. Chem. SOC.1975, 97, 363-367. (33) Vysotskaya, N. A.; Shevchuk, L. G. Zh. Org. Khim. 1973, 9(10), 2080-2083. (34) Vysotskaya, N. A.; Shevchuk, L. G.: Pokrovskii, V. A. Zh. Org. Khim. 1977, 13(5), 1035-1038. (35) Eberhardt, M. K.; Martinez, G. A,; Rivera, J. I.; FuentesAponte, A. J. Am. Chem. SOC.1982,104, 7069-7073. (36) Fendler, J. H.; Gasowski, G. L. J . Org. Chem. 1968, 33, 1865-1868. (37) Jefcoate, C. R. E.; Lindsay Smith, J. R.; Norman, R. 0. J. Chem. SOC.1969, 1013-1018. (38) Gunter, K.; Filby, W. G.; Eiben, K. Tetrahedron Lett. 1971, 3, 251-254. (39) Gilbert, E. 2.Naturforsch.B Anorg. Chem. Org. 1977,32B, 1308-1313.
Leitis, E. “Investigationinto the Chemistry of the UV-Ozone Purifications Process”; Annual Report, Westgate Research Laboratory, Los Angeles, CA, 1979, U.S. Department of Commerce PB-296485. Burlinson, N. E.; Kaplan, L. A.; Adams, C. E. “Photochemistry of TNT”; Naval Ordinance Laboratory, White Oak, Silver Springs, MD, 1972, AD-767670. Kaplan, L. A.; Burlinson, N. E.; Sitzmann, M. E. “Photochemistry of T N T (Part 11)”; Naval Ordinance Laboratory, White Oak, Silver Springs, MD, 1975, ADA020072. Symons, M. C. R. In “Peroxide Reaction Mechanisms”; Edwards, J. O., Ed.; Interscience: New York-London, 1962. Ho, P. C. “Degradation Mechanism of 2,4-Dinitrotoluene in Aqueous Solution (Photooxidation Studies)”; Final Report, Oak Ridge National Laboratory, Oak Ridge, TN, 1984, AMXTH-TE-85001. Diekman, J.; Thomson, J. B.; Djerassi, C. J. Org. Chem. 1968,33, 2271-2284. Draffan, G. H.; Stillwell, R. N.; McCloskey, J. A. Org. Mass Spectrom. 1968, 1, 669-685. Merz, J. H.; Waters, W. A. J. Chem. SOC.1949,2427-2433. Hoigne, J.; Bader, H. Water Res. 1976, 10, 377-386. Hoigne, J.; Bader, H. Science 1975, 190, 782-784. Hunt, J. P.; Taube, H. J. Am. Chem. SOC.1952, 74, 5999-6002. Weeks, J. L.; Matheson, M. S. J. Am. Chem. SOC.1956, 78, 1273-1278. Dainton, F. S. J. Am. Chem. SOC.1956, 78, 1278-1279.
Received for review May 28,1985. Revised manuscript received August 29,1985. Accepted September 23,1985. This research was sponsored by the U.S. Army Toxic and Hazardous Materiak Agency under Interagency Agreement 40-1327-83, Army No. 0-3-78-15. ORNL is operated by Martin Marietta Energy System, Inc., for the US.Department of Energy under Contract DE-AC05-840R21400.
Fate of Hazardous Waste Derived Organic Compounds in Lake Ontario Rudolf Jaffe and Ronald A. Hltes”
School of Public and Environment Affalrs and Department of Chemistry, Indiana University, Bloomington, Indiana 47405
rn Dated sediment cores from Lake Ontario’s four sedimentation basins and sedentary fish from tributaries and embayments were analyzed by gas chromatographic, methane-enhanced, negative ion mass spectrometry for a group of fluorinated aromatic compounds. The historical record of these chemicals in Lake Ontario sediments agrees well with the use of the Hyde Park dump in the city of Niagara Falls, NY. These compounds first appeared in sediments in 1958 and rapidly increased until 1970. These dates coincide with the onset of dumping at Hyde Park and remedial action undertaken when this dump was closed, respectively. Chemicals introduced into Lake Ontario by the Niagara River distribute throughout the lake rapidly and uniformly and accumlate in sedentary fish taken from remote locations in the lake.
Introduction The one environmental problem that has most gripped the nation’s attention in the last few years is the disposal of hazardous wastes. The Love Canal area in western New York State is now famous as a chemical waste dump that went wrong. Almost every state has its equivalent; usually it is a chemical waste dump, and often it is regarded as a severe hazard to both people and the environment. The problem with these dumps is simple: they leak. Migration of chemicals from these dump sites pollutes the surrounding groundwater, surface water, and sometimes, people’s homes. We have previously studied the organic compounds migrating from dump sites in western New York (1,2),an area replete with potentially dangerous dumps. The State of New York has enumerated at least 150 dump sites in this area that are thought to contain hazardous wastes (3). 0013-936X/86/0920-0267$01.50/0
Having so many dumps in this location is particularly unfortunate given its proximity to the Niagara River and Lake Ontario. Our studies of Bloody Run Creek, Bergholtz Creek, and the 102nd Street Bay (see Figure 1)have shown that potentially toxic compounds are migrating out of these dump sites and into the Niagara River (1,2). Once in the river, these compounds are transported to Lake Ontario where they can undergo a variety of fates. For example, they may be accumulated in the sediment of the lake ( 4 , 5) and by the biota (5). Preventing hazardous wastes from entering Lake Ontario is important. Lake Ontario ranks about 10th in the world in size and volume and is a lake of great commercial and recreational importance. About 6.5 X lo6 people live on its shores and even more in its drainage basin; most of these people drink water taken from the lake. The lake’s area is about 19000 km2,and the lake itself occupies 32% of its drainage basin. Its average depth is 86 m, and the deepest spot is about 230 m (6). There are four major zones of sediment deposition, which have been named the Niagara, Mississauga, Rochester, and Kingston basins (7). These zones are outlined in Figure 2; the nearshore zone does not accumulate sediment. The Niagara River has a strong influence on Lake Ontario. The total flow into the lake from the Niagara averages 221 km3/year; this compares to a flow out of the lake (through the St. Lawrence River) of 265 km3/year. Thus, the Niagara River supplies 83% of the water to Lake Ontario (8). Because of the highly industrialized nature of the city of Niagara Falls and other areas along this river, “severe environmental stresses have been noted at the mouth of the Niagara” (6). These stresses include high pesticide concentrations and biological perturbations.
0 1986 American Chemical SockttY
Environ. Sci. Technol., Vol. 20, No. 3, 1986
267
