Opperhuizen, A.; Serne, P.; Van der Steen, J. M. D. Environ. Sci. Technol. 1988, 22, 286. Method 608-Organochlorine Pesticides and PCBs; 49 FR 43321-43336; US.Environmental Protection Agency, U.S. Government Printing Office: Washington, DC, 1984. Methods for Chemical Analysis of Water and Wastes; EPA-600/4-79-020; U.S.Environmental Protection Agency, U.S. Government Printing Office: Washington, DC, 1979. SAS Institute Inc. S A S I S T A T User's Guide, Release 6.03; SAS Institute Inc.: Cary, NC, 1988. Sodergren, A. Ecotoxicol. Environ. S a f . 1990, 19, 143. Gobas, F. A. P. C.; Lahittete, J. M.; Garofalo, G.; Shiu, W. Y.J. Pharm. Sci. 1988, 77, 265. Lyman, W. J.; Reehl, W. F.; Rosenblatt, D. H. Handbook
of Chemical Property Estimation Methods: Environmental Behavior of Organic Compounds; McGraw-Hill: New York, 1982. (27) Risk Reduction Engineering Laboratory Treatability Database. U.S. Environmental Protection Agency, Cincinnati, OH. Received for review January 18,1991. Revised manuscript received J u n e 11, 1991. Accepted J u n e 15, 1991. Views and opinions in this paper are solely those of the author and do not reflect policy of the Pennsylvania Department of Environmental Resources. Nor does the mention of any products or trade names constitute endorsement.
2,5-Dichloro-3,6-dihydroxybenzo-1,4-quinone: Identification of a New Organochlorine Compound in Kraft Mill Bleachery Effluents Mlkael Remberger, Per-Ake Hynnlng, and Alasdair H. Nellson"
Swedish Environmental Research Institute, Box 21060, S-1 00 31 Stockholm, Sweden
2,5-Dichloro-3,6-dihydroxybenzo-1,4-quinone (chloranilic acid) and the corresponding hydroquinone have been identified in C/D-stage and E-stage bleachery effluents from kraft pulp production using both softwoods and hardwoods. The concentrations of the quinone in these effluents were comparable to those of established individual major chlorophenolic components such as chloroguaiacols and chlorocatechols. Whereas the chlorinated quinone has been identified in samples of biologically treated effluent, only the corresponding hydroquinone was found in a sediment sample collected in the neighborhood of the discharge of kraft pulp mill effluents. The quinone was chemically stable in aqueous solutions a t high pH, under anaerobic conditions in the presence of sulfide, and in organic solvents in the light. Current data including its water solubility and low toxicity suggest, however, that it is unlikely to pose a major environmental hazard. Introduction Substantial quantities of structurally diverse chlorinated organic compounds are formed during production of bleached pulp ( I ) and are subsequently discharged into the aquatic environment, generally after treatment. Considerable effort has therefore been directed to assessing the environmental impact of these compounds, in particular the chlorophenolic components (2). Since chlorinated guaiacols and catechols are partitioned into the sediment phase (3)from which they may be recovered in substantial quantities ( 4 ) ,increasing effort has been directed to their persistence in the sediment phase and the significance and extent of dechlorination by anaerobic bacteria ( 5 ) . Concentrations of total organic chlorine in cyclohexane extracts of both sediment and biota have been used for assessing distribution of organochlorine compounds emanating from bleachery effluents (6), although only a small fraction of these components has hitherto been identified. In a comprehensive study of cyclohexane extracts from contaminated sediments (7), chlorinated benzo-1,2quinones were considered, since these had been tentatively identified in bleachery effluents (8) even though the analytical method used was not unequivocal. No evidence for the presence of these compounds was found, and subsequent investigations revealed that their half-lives in aqueous media at pH 7 were less than 0.5 h. (9). It was shown that, in aqueous media, the principal transformation 0013-936X/91/0925-1903$02.50/0
products from tetrachlorobenzo-1,2-quinonewere tetrachlorocatechol, formed by reduction of the quinone with water, and 2,5-dichloro-3,6-dihydroxybenzo-1,4-quinone, formed by nucleophilic displacement of chloride. The question then arose whether or not 2,5-dichloro-3,6-dihydroxybenzo-1,Cquinone was itself a normal component of bleachery effluents. More extensive studies have now revealed that this compound-and the corresponding hydroquinone-are indeed significant chlorophenolic components of both bleachery effluents and biologically treated total mill effluents, and that the hydroquinone can be recovered from a sample of contaminated sediment. Experimental Methods Chemicals. 2,5-Dichloro-3,6-dihydroxybenzo-1,4quinone (chloranilic acid, CA) was purchased from BDH (Poole, England). The acetate of the corresponding hydroquinone (CAHJ, 1,2,4,5-tetraacetoxy-3,6-dichlorobenzene was prepared by reductive acetylation with zinc, sodium acetate, and acetic anhydride and recrystallized from acetic acid. The reference chlorinated guaiacols and catechols were synthesized in this laboratory (IO). Solvents were purchased from Burdick and Jackson Labs (Muskegon, MI). Effluents. Samples of C/D- and E-stage bleachery effluents (C means chlorine, D chlorine dioxide, and E extraction with NaOH), and total mill effluents after aerobic biological treatment were obtained from four kraft pulp mills during production from pine (Pinus syluestris) or birch (Betula sp.). A sediment sample contaminated with chlorophenoliccompounds putatively originating from the production of bleached pulp, and an essentially uncontaminated sample, were recovered from the Gulf of Bothnia by using an Ekman dredge. Concentrations of adsorbable organic halogen (AOX) in effluent samples were determined with a combined pyrolysis-microcoulometer instrument (Euroglas, Delft, Holland) following a standardized procedure (11). Total organic matter in sediment samples was estimated from the loss during combustion of acidified and dried samples at 550 "C for 5 h. Identification of CA. This was carried out by conversion of the quinone into the 0-methyl ether, which was significantly more stable than the corresponding 0-acetate. Effluent samples (20 mL) were acidified (0.1 mL, 18 M H,SO,), saturated with solid NaC1, and extracted with tert-butyl methyl ether (2 X 3 mL). The extracts were
0 1991 American Chemical Society
Environ. Sci. Technol., Vol. 25, No. 11, 1991 1903
dried (Na,SO,) and concentrated to a volume of ca. 0.5 mL under a stream of N2. It is essential that the product is dissolved in tert-butyl methyl ether before methylation with diazomethane in diethyl ether for ca. 1 min. The samples were then evaporated under a stream of Nz, dissolved in hexane, and chromatographed on silica gel (350 mg; Merck 60, mesh 70-230) in a Pasteur pipet. Elution was carried out successively with hexane (3-4 mL) and with benzene (1.5 mL); the following 0.8 mL, which contained the product, was collected. Authentic samples of the di-0-methyl ether of the quinone and of the tetramethyl ether of the hydroquinone (prepared by reduction of the quinone with a solution of sodium dithionite (300 pL, 0.1 g/mL) by gentle mixing for 1 min) were prepared similarly. These solutions were used for GC and GC-MS analysis (EI) under conditions already described (12). Quantification of CA, CAH,, and Chlorophenolic Compounds in Effluent Samples. Analysis of phenolic compounds-including CAHz-was carried out by acetylation, and the concentration of the quinone was deduced from the additional concentration of 1,2,4,5-tetraacetoxy3,6-dichlorobenzene produced when reduction with dithionite was carried out before acetylation. (a) Analysis of Chlorophenolic Compounds Including CAH, Produced from CA. Effluent samples (2-5 mL) were reduced with a solution of sodium dithionite (300 pL, 0.1 g/mL) by gentle mixing for 1 min. Samples were then acidified with two drops of 18 M H2S04,a solution of 4,5-dibromocatechol(20 pL, 20 pg/mL) was added as a surrogate standard, and the solution was saturated with solid NaCl and extracted with tert-butyl methyl ether (3 X 1.5 mL). Hexane (1mL) was added and the solution dried (NaZSO4).The volume was reduced to ca. 2 mL by evaporation under a stream of N,, and the phenolic components were acetylated with acetic anhydride (125 pL) and pyridine (50 pL) by heating at 75 "C for 30 min. Excess pyridine was removed by shaking with HCl(4 mL, 0.5 M) for 2 min and excess acetic anhydride by shaking with water (4 mL) for 15 min. Pentachlorobenzene (150 ng) was added as internal standard and the organic phase analyzed by GC (ECD) using a standard program (12). (b) Analysis of Chlorophenolic Compounds Excluding CAH2Produced from CA. This was carried out as described above with omission of the sodium dithionite reduction step. Analysis of CA and CAHzin Sediment Samples. A sediment sample from an area of the Gulf of Bothnia that was known to be contaminated with compounds originating from bleachery effluents (5 g, wet weight) was acidified (2-3 drops of 18 M H,SO,) and extracted, first with a mixture of acetonitrile (0.5 mL) and tert-butyl methyl ether (1.5 mL), and then with tert-butyl methyl ether (2 x 1.5 mL). The organic extracts were combined, acetonitrile was removed by shaking with acidified water (5 mL, 0.1 M HCl), the extracts were dried (NaZSO4),and the quinone-if present-was converted into the hydroquinone tetraacetate as described above. The solution was chromatographed on a column of silica gel (350 mg; Merck 60, mesh 70-230) in a Pasteur pipet; the column was washed with hexane (4 mL) and tert-butyl methyl etherhexane (3 mL, 1:3), and CA and trichlorotrihydroxybenzene acetates were eluted with tert-butyl methyl ether-hexane (5 mL, 1:l). Partition of CA and CAH, between the Water and Sediment Phases. A sediment sample putatively free from contamination with organochlorine compound from bleachery effluents (2.5 g, wet weight) was mixed with deaerated water (10 mL, pH 7) in a screw-cap tube and 1904
Envlron. Sci. Technol., Vol. 25, No. 11, 1991
spiked with acetone solutions of CA or CAHz (20 pL, 32 pg/mL). The tubes were equilibrated with shaking at 22 "C for 8 h, the phases separated by centrifugation, and analyses for CA and CAH2 carried out as described above for quantification in effluents. Chemical Stability of CA. Photochemical stability in the light was examined by dissolving CA in 5 mL of acetonitrile, acetone, tetrahydrofuran, or propan-2-01 at a concentration of 1 mg/L and incubating the tubes a t 22 "C in the light as described previously (9). Samples were periodically removed during 20 h and portions analyzed for CA and CAH, as described above. Stability at high pH was evaluated by adding an acetone solution of CA (20 pL, 32 pg/mL) to phosphate buffer (10 mL, 0.02 M, pH 10). At intervals up to 20 h, samples were removed and the pHs lowered to ca. pH 7 by addition of phosphate buffer (0.25 mL, 1 M, pH 6.2); the resultant mixtures were analyzed as described above. Stability in sulfide solutions under anaerobic conditions was carried out by introducing an acetone solution of CA (50 pL, 6 pg/mL) into 5-mL glass ampules. The solvent was removed in the transport box of an anaerobic chamber (Anaerobe Systems, San Jose, CA) and anaerobic basal medium containing 3.5 g/L Na2S.9H20 (3 mL, pH 9) added in the chamber; the medium lacked vitamins and trace elements (13) but contained resazurin as redox indicator. After the ampules were closed in the chamber, they were removed and sealed by melting (13). One ampule was sacrificed daily over 5 days and analyzed as described above. Toxicity Tests. Details on the Brachydanio rerio (zebra fish) embryo/larvae test and of the Microtox assay carried out in MOPS-buffered medium have been described (14). Results and Discussion 2,5-Dichloro-3,6-dihydroxybenzo-1,4-quinone was identified by comparing the mass spectrum of the methylated sample extract,ed from an effluent sample with that of 2,5-dichloro-3,6-dimethoxybenzo-1,4-quinone prepared by methylation of an authentic sample of the quinone. Although the mass spectra (Figure l) corresponded to that of the hydroquinone (1,4-dihydroxy-2,5-dichloro-3,6-dimethoxybenzene) [C8H804C1,,mass spectrum m/z M+ 238, 240 (3:2)], several observations showed that it was the quinone that was present in the original effluent sample: (i) The hydroquinone was not an artifact produced by reduction of the quinone during methylation, since acetylation of the product after methylation did not produce the hydroquinone dimethyl ether di-0-acetate [C12Hl,0,C1,, mass spectrum m/z M+ 322,324 (3:2)],which was obtained only after incorporation of a reductive step. (ii) In the effluent sample, both the dimethyl ether of the quinone and the tetramethyl ether of the hydroquinone were clearly identified by GC and GC-MS and corresponded to the relative concentrations of the quinone and the hydroquinone analyzed as the hydroquinone tetraacetate with and without dithionite reduction. (iii) Direct-probe MS analysis of the quinone di-0heptafluorobutyrate revealed only the hydroquinone diO-heptafluorobutyrak [C14H206C12F14, mass spectrum m/z M+ 602,604 (3:2)], even though no hydrogen atoms were present in the original molecule. It was therefore presumed that reduction had occurred during mass spectrometric examination, and it was concluded that the quinone was present in the original samples. For routine analysis, use of the hydroquinone tetraacetate [Cl4Hl2O8Cl2,mass spectrum m/z M+ 378, 380 (3:2)] whose mass spectrum is shown in Figure 2 was,
188-
":
A
88
78.
68. 58.
69
238
48 36.
IEE
183 87
195
288
/,II.
I.
_1,11
'": B Be 78. 68. 50. 48. 38.
238
IBR
69
28.
!,
1J.. . . I , ~ I
,218.
,
,
258 ,
Flgure 1. Comparison of the mass spectrum of the methylated product isolated from a bleachery effluent (A) with that of authentic 2,5dichloro-3,6dlmethoxybenzo-l ,Cquinone (a).
$","I
A
88. 78. 68. 58. 48. 38. 28.
252 294 ;I96
18 8
m,, 123
,,, 235
,
,I/
292
'XI'S
I,).
XI
336 314
I
I,.
'X3'0
378 I
,
,
+XIO'O
B 88. 78. 68. 58.
252
49.
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le. 8 5 ! . 69 1681 87
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Ill
le9
147 I57 165 17$1!!
192
, 1 ~. . , .
336 378
235
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276
I,I.
I I,.
I,
,
,
Figure 2. Comparison of the mass spectrum of the product isolated from a bleachery effluent after reduction and acetylation (A) with that of authentic 1,2,4,5-tetraacetoxy-3,6dichlorobenzene (B).
however, more convenient. The relative GC retention times of the relevant compounds are given in Table I. The data in Tables I1 and I11 give concentrations in effluents from a single mill, but are representative of those found in effluents from the other mills examined. Although 2,5-dichloro-3,6-dihydroxybenzo1,4-quinone represented a class of compound not hitherto identified in bleachery effluents, the data in Table 11 clearly showed that the quinone was one of the major chlorophenolic compounds in a number of bleachery effluents. It was present at concentrations comparable to those of individual chloroguaiacols and chlorocatechols, which have traditionally been considered the dominant chlorophenolic
Table I. GC Retention Times of Derivatives of Chloranilic Acid and Related Compounds Relative to That of Tetrachloroguaiacol-0-acetate 2,5-dichloro-3,6-dimethoxybenzo-1,4-quinone 1,2,4,5-tetraacetoxy-3,6-dichlorobenzene 1,4-diacetoxy-2,5-dichloro-3,6-dirnethoxybenzene tetrachloroguaiacolacetate
0.65 1.66 1.17 1 .oo
components of bleachery effluents (I): the concentration of the quinone in single-stream effluents was generally similar to that of 4,5-dichloroguaiacol and 3,4-dichlorocatechol, whose concentrations in these effluents equaled, or exceeded those of the tri- and tetrachlorinated anaEnviron. Sci. Technol., Vol. 25, No. l l , 1991
1905
Table 11. Concentrations (rg/L) of Selected Chlorophenolic Compounds, Chloranilic Acid (CA), and the Corresponding Hydroquinone (CAH,) in Effluent Samples from a Single Mill
chloroauaiacol effluent E stage (pine) C/D stage (pine) E stage (birch) C/D stage (birch) total effluent (pine) total effluent (birch)
CA 700
30 6 60
1 0.2
CAHp 30 40 3 3 2 0.5
chlorocatechol
4,5-
3,4,5-
tetra-
3,4-
3,4,5-
tetra-
770 20 80 25
250 6 10 1
30 3 2 1
20 100 5 60
50 30 10 3
15 130 6 4
8 2
19 2
1 1
19 2
3 0.2
5 0.4
using chemical methods directed to identification and quantification of novel and specific functional groups such as quinones, rather than exclusive reliance on derivatization procedures for alcohols, phenols, and carboxylic acids, which are traditionally applied to the analysis of many total complex industrial effluents. (ii) The limitation imposed chlorototal by use of ascorbic acid, which is the traditional reductant effluent phenolics (CA + CAH2) AOX used for chlorinated benzo-1,2-quinones. Reduction with E stage (pine) 4100 730 120 000 ascorbic acid would have failed to reveal the presence of C/D stage (pine) 570 70 43 000 2,5-dichloro-3,6-dihydroxybenzo-1,4-quinone, whose redox E stage (birch) 145 9 32 000 potential (Eo, 25 "C) of 0.422 is significantly lower than 165 60 38 000 C/D stage (birch) that of either tetrachlorobenzo-1,2-quinone(0.873) or total effluent (pine) 195 3 24 000 tetrachlorobenzo-1,4-quinone(0.703)(15). 30 0.7 7 000 total effluent (birch) 2,5-Dichloro-3,6-dihydroxybenzo-l,4-quinone was stable for at least 20 h in (a) solutions of organic solvents in the logues. In kraft mill softwood effluents, concentrations light without evidence for dehydrogenation of the solvent of the quinone were generally greater in E-stage than in and formation of the hydroquinone, (b) aqueous solutions C/D-stage effluents. This is also the case for chlorinated at pH 10, and (c) 15 mM sulfide solution under anaerobic guaiacols but not for chlorinated catechols ( I ) . The corresponding hydroquinone (analyzed as 1,2,4,5-tetraacetconditions. The stability at high pH is consistent with its presence in E-stage effluents, and it could be recoveredoxy-3,6-dichlorobenzene)was found in these effluent albeit in rather low concentrations-from effluent samples satnples-though not necessarily in all effluent samples-in that had been subjected to biological treatment (Table 11). considerably lower concentrations: this was not an artifact The stability of 2,5-dichloro-3,6-dihydroxybenzo-1,4of the analytical procedure since the quinone was stable quinone was therefore in marked contrast to the extreme under the conditions used for extraction and analysis. Although 2,5-dichloro-3,6-dihydroxybenzo-1,4-quinone instability of chlorinated benzo-1,2-quinones under comparable conditions (9); this is consistent with the redox has not been identified in other kinds of industrial efpotentials of these quinones (15). Nonetheless, on the basis fluents, its recovery from environmental samples would of currently available data, this quinone does not appear not necessarily indicate a source of bleachery effluents likely to present a major environmental hazard for several unless use of tetrachlorobenzo-1,2-quinonefor chemical reasons. manufacture could be excluded, since 2,5-dichloro-3,6(i) It is freely soluble in water, and the partition coefdihydroxybenzo-1,4-quinoneis one of the major stable ficient between a sediment sample and the aqueous phase transformation products (9). was 36 L/kg organic matter compared with a value of 1150 The sum of the concentrations of the oxidized and reL/kg organic matter for the hydroquinone: the quinone duced forms of the quinone (CA CAH,), the total conwould therefore be expected neither to partition into the centration of chlorophenolic compounds, and the concensediment phase nor to exhibit a significant propensity for tration of adsorbable organic halogen (AOX) are given in concentration in biota. Table 111. Although both the quinone and the hydro(ii) It had a low acute toxicity in the Microtox test quinone were found in effluents from production using system [E& (15 min) > 50 mg/L], and a low threshold either softwoods or hardwoods as raw materials, the total toxicity to Brachydanio rerio (zebra fish), which has been concentration of chlorophenolic compounds-including extensively employed in Sweden for assessing toxicity of those of the quinone and the hydroquinone-was signifipulp mill effluents. Values of the lowest observable effect cantly lower in effluents during production from birch. concentration (LOEC) were 1.4 mg/L with a no observable Detailed quantitative comparison should not, however, be effect concentration (NOEC) of 1.0 mg/Lsomewhat less made due to different water consumption in the production that that of 4,5-dichlorocatechol (9). schedules. Nonetheless, for single-stream effluents, CA It proved impossible to carry out standard toxicity tests together with CAHz alone contributed between 6% and using the crustaceans Ceriodaphnia dubia or Nitocra 37% to the total concentrations of all the chlorophenolic spinipes (14) since insoluble precipitates were formed with compounds. It is also obvious, however, that the total calcium and magnesium ions (16),which are necessarily concentrations of chlorophenolic compounds, some of present in the standard dilution media. which are substantially toxic to fish (2), represented only There are a t least two issues that were not addressed a relatively small fraction of the concentration of AOX in this study. (expressed as originally bound chlorine). These results (i) The persistence of the quinone and its susceptibility unequivocally illustrate the caution that should be exerto microbial attack in the aquatic environment is unknown, cised in using sum parameters for evaluation of the enthough its recovery from biologically treated effluentsvironmental impact of industrial effluents (2). albeit in concentrations relatively low by comparison with Identification of the quinone emphasized the significance those of the total chlorophenolic compounds (Table 111)of the methodological procedures used: (i) The value of
Table 111. Concentrations (pg/L) of Chloranilic Acid Together with the Corresponding Hydroquinone (CA CAH2),Total Chlorophenolics, and AOX in Effluent Samples from a Single Mill
+
1906 Envlron. Scl. Technol., Vol. 25, No. 11, 1991
+
-would suggest that it was not readily degraded under such conditions. Whereas the quinone itself was not present in the sediment sample, the hydroquinone was recovered at a concentration of 0.9 mg/kg organic matter compared with a value of 207 mg/kg organic matter for the sum of all the chlorophenolic compounds extracted under identical conditions. The recovery of the hydroquinone is consistent with either (i) the observed watersediment partition or (ii) reduction of the quinone under the highly anaerobic conditions in the sediment. (ii) The pathway whereby the quinone is formed from aromatic precursors in lignin is unknown although 2,5dichloro-3,6-dihydroxybenzo-1,4-quinone might be formed by reactions with chlorine dioxide analogous to those which produce 2-chloro-5-methoxybenzo-1,4-quinone from vanillyl alcohol or 2-methoxybenzo-1,4-quinone from 1'methylvanillyl alcohol (17).
3978-67-4; 3,4,5-trichlorocatechol, 56961-20-7; tetrachlorocatechol, 1198-55-6; quinone, 106-51-4.
We thank Ake Lundberg for the AOX analyses and Ulrika Wallin for the Microtox value. Registry No. CAH2, 123-31-9;CA, 87-88-7; 2,5-dichloro-3,6-
L i t e r a t u r e Cited (1) Kringstad, K. P.; Lindstrom, K. Enuiron. Sci. Technol. 1984, 18, 236A. (2) Neilson, A. H.; Allard, A.-S.; Hynning, P.-A.;Remberger, M. Toxicol. Environ. Chem. 1991, 30, 3. (3) Remberger, M.; Allard, A.-S.; Neilson, A. H. Appl. Enuiron. Microbiol. 1986, 51, 552. (4) Remberger, M.; Hynning, P,-A.;Neilson, A. H. Enuiron. Toxicol. Chem. 1988, 7, 795. (5) Allard, A.-S.; Hynning, P.-A,; Remberger, M.; Neilson, A. H. Appl. Enuiron. Microbiol. 1991, 57, 77. (6) Martinsen, K.; Kringstad, A.; Carlberg, G. E. Water Sci. Technol. 1988, 20(2), 13. (7) Remberger, M.; Hynning, P.-A.; Neilson, A. H. J . Chromatogr. 1990, 508, 159. (8) Das, B. S.; Reid, S. G.; Betts, J. L.; Patrick, K. J. Fish. Res. Board Can. 1969,26, 3055. (9) Remberger, M.; Hynning, P.-A.; Neilson, A. H. Ecotoxicol. Environ. Saf., in press. (10) Neilson, A. H.; Allard, A d . ; Hynning, P.-A.; Remberger, M.; Landner, L. Appl. Enuiron. Microbiol. 1983,45, 774. (11) DIN 38409. Beuth-Verlag GmbH: Berlin, 1985; Teil 14. (12) Hynning, P.-A,; Remberger, M.; Neilson, A. H. J. Chromatogr. 1989, 467, 99. (13) Neilson, A. H.; Allard, A.-S.; Lindgren, C.; Remberger, M. Appl. Environ. Microbiol. 1987, 53, 2511. (14) Neilson, A. H.; Allard, A.-S.; Fischer, S.; Malmberg, M.; Viktor, T. Ecotoxicol. Enuiron. S a f . 1990, 20, 82. (15) Clark, W. M. Oxidation-reduction potentials of organic systems; The Williams and Wilkins Co.: Baltimore, MD, 1960. (16) Hart, W. G. Org. Chem. Bull. 1961, 33(3). (17) Dence, C. W.; Gupta, M. K.; Sarkanen, K. V. T a p p i 1962, 45, 29.
dimethoxybenzo-1,4-quinone,7210-71-1; 1,2,4,5-tetraacetoxy3,6-dichlorobenzene, 135646-90-1; 1,4-diacetoxy-2,5-dichloro3,6-dimethoxybenzene, 135646-91-2;tetrachloroquaiacol acetate, 85430-24-6; 4,5-dichloroquaiacol, 2460-49-3; 3,4,5-trichloroquaiacol, 57057-83-7; tetrachloroquaiacol, 2539-17-5; 3,4-dichlorocatechol,
Received for review April 8, 1991. Revised manuscript received June 24,1991. Accepted June 28,1991. Support from the K n u t and Alice Wallenberg Foundation for funding toward purchase of the mass spectrometer is gratefully acknowledged.
Conclusions
2,5-Dichloro-3,6-dihydroxybenzo-1,4-quinone has been identified in a number of different kinds of kraft mill bleachery effluents in concentrations comparable with those of currently dominant individual chloroguaiacols and chlorocatechols. Although its persistence in the environment has not been established, its low toxicity and its chemical properties do not suggest that on the basis of current evidence it would present a conspicuous environmental hazard. Acknowledgments
Photodissolution of Iron Oxides. 3. Interplay of Photochemical and Thermal Processes in Maghemite/Carboxylic Acid Systems Marta I . Lltter, Erwln C. Baumgartner, Gulllermo A. Urrutla, and Mlguel A. Blesa' Departamento Qdmica de Reactores, Comisidn Nacional de Enerda Atdmica, Avenida del Libertador 8250, 1429 Buenos Aires, Argentina
Irradiation of y-Fe203suspensions in the presence of oxalate and EDTA results in a complex interplay between photochemical and thermal electron-transfer reactions. In the thermal dissolution, surface >Fe"'-L complexes are slowly transferred by acid and reductive pathways until Fe'LL buildup in solution produces a strong acceleration. Irradiation accelerates the reaction by producing Fe2+, heterogeneously by photolysis of the oxide surface complexes, and by homogeneous photolysis of aqueous FemL. This latter process is responsible for the acceleration in photodissolution rates brought about by the addition of Fe3+8q:Experimental results are reasonably fitted by the analytical solution of the simplified set of kinetic equations.
in aquatic systems. These processes take place in the interface iron oxide/water, and it has been thoroughly documented (1)that dissolved ferrous ions greatly enhance the rates of incorporation of further iron [as iron(III)] to the aquatic medium; other reductants also dissolve iron oxides, this time as iron(II), in a process that is especially important in anoxic conditions (2-6) (eq 1; where > denotes the lattice surface of the oxide).
>Fe"-(L"-XH')
(1)
1
dissolution
(Fen-L)Zn,,
Introduction
The erosion of rocks and the dissolution of soils and sediments are sources for dissolved iron that is mobilized 0013-936X/91/0925-1907$02.50/0
+ (Fe"'-L)s",,
As in many other environmentally important reactions, light may greatly influence the above thermal processes.
0 1991 American Chemical Society
Environ. Sci. Technol., Vol. 25, No. 11, 1991 1007
