Environ. Sci. Technol. 1993, 27, 1610-1620
Chlorinated Structural Elements in High Molecular Weight Organic Matter from Unpolluted Waters and Bleached-Kraft Mill Effluents Olof Dahlman,t Roland Morck,? Pierre L/ungquist,t Anders Relmann,t Carina Johansson,* Hans Bor6n,* and Anders Grlmvall'~* Swedish Pulp and Paper Research Institute, P.O. Box 5604, S-114 86 Stockholm, Sweden, and Department of Water and Envlronmental Studies, Llnkoping University, S-58 1 83 Linkoping, Sweden
An oxidative degradation method was used to study the occurrence of aromatically bound halogens in high molecular weight organic matter isolated from natural waters and bleached-kraft mill effluents. Gas chromatographic analysis of the degradation products revealed that monoand dichlorinated compounds were present in all analyzed samples. Furthermore, degradation of organicmatter from natural and industrial waters resulted in the same chlorinated degradation products, although the relative distribution of these compounds variedstrongly with the type of sample. The identification of aromatically bound chlorine in fulvic acids from natural waters represents the first successful determination of structural elements that can explain the widespread occurrence of adsorbable organic halogens (AOX) in unpolluted environments. Introduction Measurements of the amount of adsorbable organic halogens (AOX) in soil and water have shown that halogenated compounds are more widespread than previously assumed and that there is a substantial natural production of organohalogens in terrestrial environments (1). Furthermore, there are strong indications that humic substances play a key role in the turnover of organohalogens in the environment: the occurrence of AOX in unpolluted waters is correlated to the color of the water, humic substances isolated from soil and water contain measurable amounts of AOX, and a chloroperoxidaselike catalyst capable of chlorinating humic matter occurs in soil (1-4). So far, only a few attempts have been made to identify the structural elements responsible for the halogen content of naturally occurring humic substances. Knuutinen and Mannila (5)used high-performance liquid chromatography (HPLC) to analyze aromatic aldehydes formed during oxidation of humic substances by copper oxide, but this analytical procedure was not sufficientlysensitive to enable detection of chlorinated compounds. By combining pyrolysis of peaty soils with GC-MS analysis, de Lijser and co-workers (6) were able to obtain some evidence of chlorinated structures. However, low molecular weight organohalogenswere detected in amounts too low to permit any conclusions to be drawn about the major chlorinated structures in the analyzed soil samples. Studies of the binding of halogens to organic macromolecules in industrial bleaching processes have been considerably more successful. For example, it has been shown that a number of chlorinated aromatic structures are formed during chlorine bleaching of pulp (7-11).The role of humic substances in the formation of chloroorganics + Swedish Pulp and Paper Research Institute.
Linkdping University. 1616 Envlron. Sci.
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during drinking water chlorination has also been extensively investigated. In particular, the role of humic substances as precursors of low molecular weight chlorination products has been studied in detail (12,13). The aim of the present study was to investigate whether chlorinated, aromatic structural elements known from the characterization of bleached-kraft mill effluents (BKME) also occur in humic substances from unpolluted environments. A weak ion-exchange resin was used to isolate fulvic acids from surface and groundwater and fulvic acidlike substances from BKME. The samples obtained were then subjected to oxidative degradation, and the monomers formed were derivatized and analyzed by gas chromatography. To minimize the risk of analytical artifacts, three different detection methods were used in the gas chromatographic analyses. Furthermore, it was investigated whether the isotope distribution of the chlorinated monomers was changed when the degradation was carried out in the presence of sodium chloride enriched with 36Clto almost 100% . Experimental Section Sampling and Isolation of Fulvic Acids. Surface water and groundwater were sampled at sites not affected by industrial discharges to water. More precisely, surface water was sampled in a humus-rich oligotrophic lake (Hageltorpsgolen) in the County of Jonkoping in southern Sweden, and groundwater was taken from an aquifer at Skagen on the Jutland Peninsula in Denmark. Bleachplant effluents were obtained from two bleached-kraft mills respectively producing bleached softwood and hardwood pulps. The bleaching processes were in both cases based on a combination of oxygen delignification and modern bleaching technology that included 100% chlorine dioxide in the first bleaching stage and reinforcement of the first alkaline extraction stage with oxygen andlor peroxide. The organohalogen content, measured in an AOX analyzer, and other characteristics of the samples are given in Table I. Fulvic acids (FAs) or fulvic acid-like organic macromolecules were isolated from nonpretreated water samples by adsorption on a weak anion-exchange resin, diethylaminoethyl (DEAE)-cellulose (14). After desorption with sodium hydroxide and acidification with concentrated HC1 to pH 1,humic acids were removed from the soluble FA fraction by centrifugation. An XAD-8 column was used to desalt the FA, which was then desorbed with sodium hydroxide, passed through a strong cation-exchange resin, and finally freeze-dried. Oxidative Degradation.Aliquots of 10-50 mg of FA dissolved in 10 mL of a mixture of 1,2-dimethoxyethane, ethanol, and water (35:35:30) were treated according to a degradation procedure originally developed to study lignin structures (15-18). Free phenolic groups were protected 0013-936X/93/0927-1616$04.00/0
0 1993 American Chemical Society
Table I. Samples Subjected to Oxidative Degradation and Gas Chromotographic Analysis of Formed Monomers. organohalogen content remarks sampling site type of sample (wg of Cl/g of FA) Hageltorpsgdlen, Sweden
FA from surface water
2000
Skagen, Denmark
FA from groundwater
700
Bleached-kraft mill, Sweden
FA-like substances from hardwood effluent FA-like substances from softwood effluent
Bleached-kraft mill, Sweden a
11200 16300
water from a lake surrounded by bogs and coniferous forests water from an old marine sediment; sampling depth 15 m bleaching sequence, OD (EP) DED; K no. after oxygen delignification: 12 bleaching sequence, OD (EOP)DED; K no. after oxygen delignification: 17
Abbreviations: FA = fulvic acid; 0 = oxygen; D = chlorine dioxide; E = alkaline extraction; P = hydrogen peroxide. Table 11. Characteristic Mass Numbers Used in GC-HR-MS-SIM Analysis of Methyl Esters of Mono- and Dichlorinated Aromatic Structures OMe
Q0;;I
OH
bEt
I
OEt
bEt
Figure 1. Reaction sequence for protection of free phenolic groups, oxidative degradation of organic macromolecules, and derivatiration of formed carboxylic groups.
as ethyl ethers by the addition of diethyl sulfate (2 mL), and aromatic monomers were then produced by oxidation of the ethylated samples (Figure 1). The oxidation step was comprised of treatment with potassium permanganate at 80-100 "C for 10-24 h and then hydrogen peroxide at 50 "C for 10 min. After acidification with sulfuric acid to pH 2, the degraded FA was extracted with a mixture of acetone and diethyl ether, evaporated to dryness, and redissolved in a mixture of methanol and diethyl ether (1:3). To make the reaction products amenable to gas chromatographic (GC) analysis, the carboxyl groups formed during the degradation were derivatized with diazomethane. The obtained extract was redissolved in diethyl ether. One part of the diethyl ether extract was then analyzed with respect to AOX. The remaining part was again evaporated to dryness and redissolved in dichloromethane prior to GC analysis. All samples of FA were divided into two portions which were respectively subjected to oxidative degradation at Linkoping University (LiU) and the Swedish Pulp and Paper Research Institute (STFI). In the experiments carried out at STFI, potassium periodate was used to control the permanganate concentration during the degradation, whereas at LiU, small amounts of potassium permanganate were continuously added to the reaction mixture. The former method may allow better control of the permanganate concentration, but the presence of periodate makes evaluation by AOX analyses impractical. In one degradation experiment a t LiU, 830 pg of 55C1in the form of sodium chloride was added to the FA solution prior to the degradation. The total amount of chlorine (organic plus inorganic) in the FA sample to be degraded was approximately 165 pg. Analytical Procedures. The chemical characterization of degradation products focused on gas chromatographic analysis of methyl esters of lignin-derived phenolic structures. Nonchlorinated structures were analyzed by gas chromatography-mass spectrometry in the full-scan mode (GC-MS-TIC). The most abundant chlorinated structures were analyzed by full-scan GC-MS as well as by gas chromatography with microwave-induced plasma atomic emission detection (GC-AED). Chlorinated structures present in very low concentrations were analyzed by gas chromatography-mass spectrometry in the selected ion-
aromatic structure 4-ethoxybenzoic acid 4-ethoxy-3-methoxybenzoic acid 3,4-diethoxybenzoicacid 3,5-dimethoxy-4-ethoxybenzoic acid
mass numbers of monochlorinated species
mass numbers of dichlorinated species
214.0396,216.0367 248.0006,249.9977 244.0502,246.0472 278.0112,280.0083 258.0658, 260.0629 292.0269,294.0239 276,0578,278.0608 308.0218,310.0188
monitoring mode (GC-MS-SIM and GC-HR-MS-SIM). The mass numbers used in the GC-HR-MS-SIM analyses are summarized in Table 11. I n s t r u m e n t s a n d GC Parameters at Linkiiping University. AOX in fulvic acid (FA)was determined using a Euroglas AOX analyzer Model 84/85. The same instrument was also used to determine the organohalogen content of the ether extracts of degraded FA. GC-MS analyses were performed using a Shimadzu QP2000 mass spectrometer equipped with a fused silica column (J&W DB-1, 60 m X 0.32 mm, 0.25 pm phase thickness). Temperature program: 40 "C for 5 min, then raised 5 "C/min to 250 "C, finally kept at 250 "C for 20 min. Split injection: 1.6 pL, 1:40. Carrier gas: He, 29 cm/ 8.
GC-AED analyses were performed using an HP 5890 gas chromatograph equipped with an H P 5921A microwave-inducedplasma atomic emissiondetector and a fused silica column (HP Ultra-l,50 m X 0.32 mm, phase thickness 0.17 pm). The carrier gas velocity was 39 cm/s. All other GC parameters were the same as in the GC-MS analyses. The responses to hydrogen, carbon, chlorine, and bromine in the AED system were measured at 486,496,479, and 478 nm, respectively. Instruments and GC Parameters at the Swedish P u l p a n d P a p e r Research Institute. GC-HR-MS-SIM analyses were performed using a VG-250 SE mass spectrometer connected to an H P 5890 gas chromatograph equipped with a fused silica column (Supelco PTE-5,60 m X 0.32 mm, phase thickness 0.25 pm). Temperature program: 50 "C for 1min, then raised 30 "C/min to 100 "Cy4 "C/min to 230 "Cyand finally 20 "C/min to 310 OC. Splitless injection: 2 pL. Carrier gas: He. Mass spectrometric conditions: electron energy 28 eV, resolution 5000. Chemicals. The fibrous anion-exchanger diethylaminoethyl (DEAE)-cellulose was of type Whatman DE23. Amberlite XAD-8 (20-50 mesh) was obtained from Fluka, and the acidic cation exchanger was of type Dowex 50WX8 Envlron. Scl. Technol., Vol. 27, No. 8, WQ3 1617
@
@OMe
MeO@OMe
@OEt
I OEt
bEt
&Et
OEt
A
B
C
D
IS
I
k
Figure 2. Aromatic compounds identified in samples of degraded fulvic acid from natural waters and bleached-kraft mill effluents: the methyl esters of 4-ethoxybenzolc acld (A), 4-ethoxy-3-methoxybenzoic acid (B), 3,4dlethoxybenzolc acid (C), and 3,5dlmethoxy-4-ethoxybenzoic acld (D). FOZMe
@Cl
F02Me
Cl@Cl
F02Me
FOzMe
“@OMe
@ zOM ’ce I
I
bEt
OEt
OEt
bEt
A1
A2
E1
82
CI OEt I
OEt
OMe Me0
Me0
OMe
OEt
bEt
OEt
bEt
c1
c2
D1
D2
Figure 3. Chlorinated aromatic compounds identified In samples of degraded fulvic acid from both natural waters and bleached-kraft mill effluents.
(50-100mesh). Sodium chloride with 99.90% 35C1 and 0.10% 37Cl was purchased from Oak Ridge National Laboratory, Oak Ridge, TN. Mixtures of chlorinated analogues of compounds designated A, B, and D in Figure 2 were synthesized at Linkoping University. All chemicals used were of analytical grade. The diethyl ether used for extraction was distilled prior to use. Results Nonchlorinated Aromatic Structures. By using fullscan GC-MS, several lignin-derived aromatic structures were identified in all dichloromethane extracts of degraded organic matter. The four compounds shown in Figure 2 were found in samples of both industrial and natural origin. However, the relative distribution of the studied structures varied significantly with the type of sample. The degradation products from the two samples of natural origin were dominated by 4-ethoxybenzoic acid methyl ester (compound A), whereas 4-ethoxy-3-methoxybenzoic acid methyl ester (compound B) was the main degradation product in the softwood effluent sample. The hardwood effluent sample contained considerable amounts of both compound B and 3,5-dimethoxy-4-ethoxybenzoicacid methyl ester (compound D). Further information about nonchlorinated aromatic structures in the analyzed samples has recently been presented elsewhere (19). Chlorinated Aromatic Structures: Qualitative Aspects. GC-MS analyses of chlorinated compounds in the extracts of degraded FA demonstrated that such compounds were present in all analyzed samples. By using GC-MS in the full-scan mode, the methyl esters of one monochlorinated and one dichlorinated 4-ethoxybenzoic acid (compounds A1 and A2 in Figure 3) were identified in both the surface water and groundwater samples. In addition, chlorinated analogues of compounds B-D in Figure 2 were identified in at least one of the BKME samples. When using GC-HR-MS-SIM, a larger number 1818 Envlron. Scl. Technol., Vol. 27, No. 8, 1993
20
30
Time
40
50
( m i n . )
Figure 4. GC-AED chromatograms of degraded fulvic acld isolated from an unpolluted surface water. The chromatograms show the response in the carbon (496-nm) and chiorlne (479-nm) channels of the AED system. Compounds A and B denote the methyl esters of 3-chioro-4-ethoxybenzoic acldand 3,5dichloro-4-ethoxybenzolcacld, respectively: 1-chiorotetradecane (100 ng/pL) was used as Internal standard, IS.
of chlorinated compounds were detected in all samples; these compounds are shown in Figure 3. The results of the GC-AED analyses confirmed the presence of chlorinated aromatic structures in FA from unpolluted natural waters. In addition, the chromatograms of the C1 channel of the AED system showed that the compounds identified by full-scan GC-MS were the main chlorinated compounds in the analyzed samples; this is illustrated for the surface water sample in Figure 4. There were no indications of organically bound bromine in any of the analyzed samples. To confirm the structure of the mono- and dichlorinated degradation products found in the analyzed samples, model compounds were synthesized and analyzed by GC-MS and GC-AED. Comparison of retention times gave further evidence that the detected degradation products were correctly identified. In addition, the two chlorinated methyl esters of 4-ethoxybenzoic acid were identified as 3-chloro-4-ethoxybenzoicacid methyl ester and 3,5dichloro-4-ethoxybenzoic acid methyl ester. The mass spectra of 3-chloro-4-ethoxybenzoicacid methyl ester in Figure 5 show that addition of 36Clto the reaction mixture had no significant impact on the isotope distribution. This implies that the detected chlorinated structural elements were not experimental artifacts produced during the oxidative degradation. Chlorinated Aromatic Structures: Quantitative Aspects. The amounts of specific chlorinated aromatic structures in different types of samples followed approximately the same pattern as the corresponding nonchlorinated structures. The results in Figure 6 show that the chlorinated degradation products from the softwood BKME sample were strongly dominated by monochlori-
155
100 T
50
%
lwOl
I
lA
9,2
21
81-a
81-b
0
II
186 214
100
150
81-c
SURFACE WATER
lo1
0
50
SOFTWOOD EFFLUENT
I
%9 5001
I
0
1
HARDWOOD EFFLUENT
81-a
I
lo1
81-b
B1 c
GROUNDWATER
I
200
155
I
B
loo]
0
50
81-a
150
100
200
MMsspecaaofl h e m W e s t e r o f 3 & k m 4 @ h o ~ & addoMeineduponQGMSanaiysbofsuiacewaterfuMcaclddegaded without aMMn of sodlum dlloMe (A) and wlth addnbn of sodlum chloride containhg 99.9% %I and 0.1 % s'Ci (B). -5.
HARDWOOD EFFLUENT
100
Bl~c
81-a
81-b
81-c
2
1000
. m m I
100
10
SOFTUWD EFFLUENT
1
Hardwood Softwood Surface Groundeffluent effluent water water FIgun 8. Total concentralbn of chlorinated aromatic cornpourida A1 A2 81 E2 C1 C2 D1 02
SURFACE WATER
100, %501,
0
81-b
Concentrations of me three monochlorinated I ~ o m ( y sof 4-elhoxy&nethoxybenrdcacid methylesters in sampb of degraded fuivic aclds and BKME material of dlnerenl orlgln. The ikomers are given in order of Increasing retention Ume In lhe gas chromalographk anatpis W r e 7.
0.7N.O.1.9 0.1 0.3 0.2 A, A2 01 02 C1 C2 01 02
AI
A2 B i E2 C1 C2 01 02
(A1.A2.B1.82,C1.C2,D1,andD2InFigure3)Inexbactaofdegraded fuMc aclds and BKME malertsl of differentsin. Ouantnlcation by GCMCMS-SIM at STFI and by OCMS-TIC and OCAED at Link6ping
1 %.:I; 1 100,
GROUNDWATER
0.5 0.1 3.9 0.1 0.6 0.7
A1 ii2 01 02 C1 C2 01 02
Fbur 8. Relatlve dMbuUon of CMOrlnated ammatk comwMd8 in exiracta 01 dlfferamtypes of Mvlc acids and BKME material subJected to oxkhtlve degadatlon. Compound designation is the same as in Figure 3. Resented data are mean values of results from Unk6ping University and STFI.
nated guaiacyl structures (Bl), whereas the degraded hardwood BKME sample contained a large amount of monochlorinated 3,5-dimethoxy-4-ethoxybenzoicacid methyl ester (DI).In both of the two aquatic FA samples mono- and dichlorinatedkethoxybenzoic acid methylester (A1 and A2) were the major, chlorinated degradation produets. By comparing the amounts of chlorinated and nonchlorinated 4-ethoxybenzoic acid methyl ester, it was estimated that up to 10% of the analyzed aromatic structures were chlorinated. A special study of the three isomers of monochlorinated kethoxy-3-methoxybenzoicacid (B1) indicated that samples of natural and industrial origin were characterizedby different isomer distributions. As shown in Figure 7, the isomer with the longest retention time dominated in the BKME samples, whereas the isomers with the shortest andlongest retention times were present in approximately the same amounts in the surface water and groundwater samples. Comparison of the results from Linkcping University with those from STFI showed that the two laboratories obtained almost the same relative distribution of the most
Univershy.
abundant chlorinated compounds. In addition, there was good agreement between the GC-AED and GC-MS-TIC quantifications a t LinkBping University,whereas the GCHR-MS-SIM quantifications a t STFI resulted in somewhat higher yields of chlorinated compounds (Figure 8). Exchange of samples between the two laboratories indicated that the observed differenceswere primarily due to the slightly different degradation techniques. By using the AOX analyzer, the total amount of organohalogens in the ether extra& was estimated to be 400 rg/g of starting material in the softwood BKME sample, 430 wg/g in the hardwood BKME sample, and 180 pg/g in the sample prepared from surface water FA; these amountscorrespondedt2.4-9 % ofthetotal AOXcontent of the untreated FA samples. The chlorinated derivatives that were analyzed by gas chromatography accounted for 9 1 9 % of the residual organohalogen content after oxidative degradation.
Discussion The results of the present study represent the first successfulidentificationof chlorinated structural elements in naturally occurring humic substances. The discussion ofthis findingwill f o e o n threeaspects (i) thepossibility of analytical artifads, (ii) the presence of considerable amounts of adsorbable organic halogens (AOX) in unpolluted environments;and (iii)similaritiesand differences between high molecular weight organohalogensin blenchedkraft mill effluents and natural waters. The use of several different, very selective detection methods clearly showed that chlorinated aromatic strucEnvtOn. Scl. T&nlOl., Vol. 27. No. 8. 100.9
?El#
tures were present in all analyzed samples. Furthermore, the experiment involving 36Clshowed that the identified chloroorganic compounds were not formed during the oxidative degradation, and there was no evidence of blank problems caused by contaminants in the chemicals or equipment used. Together these findings prove that the detected cbhrinsted structures were actually present in the original water and effluent samples studied. Several surveys of the group parameter adsorbable organic halogens (AOX) in unpolluted waters and soils have shown that the observed concentrations are much too high to be explained by known industrial sources of organohalogens (1-3?20-22). Although the structures idmtified in the present study cannot alone be responsible for the observed AOX concentrations, they do rule out the possibility that the widespread occurrence of AOX in unpolluted environments is merely an analytical artifact. In addition, the identified structures can explain why the compounds responsible for the AOX content in unpolluted waters seem to have approximately the same acid-base properties, polarity, and molecular weight distribution as humic substances (21-23). The chlorinated aromatic structures found in samples derived from natural waters and those found in samples from bleached-kraft mill effluents exhibited several striking similarities. This agrees well with the results of other studies of chlorination of lignins and humic substances. For example, it has been shown that both chlorine blwching of pulp and chlorine disinfection of humic drinking water results in low molecular weight organohalogens such as haloforms, chlorophenols, chloroacetic acids, and the strong mutagen MX [3-chloro-4-(dichloromethyl) -5-hydroxy-2(5H)-furanonel (24, 25). The present stiidy also confirmed that bleaching of pulp with chlorine dioxide can result in the formation of small amounts of the same chlorinated aromatic structures as bleaching withmolecular chlorine (8,10,26). This is most probahly due to the small amounts of reactive chlorine formed during chlorine dioxide bleaching (27). The distribution of nonchlorinated degradation products was approximately the same as in a study of deSousa and coworkers (28). Closer examination of the identified chlorinated struct u r d elements also revealed some noteworthy differences between the BKME samples and the two aquatic FA samples. First, the relative concentrations of the methyl esters of monochlorinated 4-ethoxybenzoicacid, 4-ethoxy3-methoxybenzoic acid, and 3,5-dimethoxy-4-ethoxybenzoic acid varied strongly with the type of sample. Secondly, samples of natural and industrial origin had different acid isomer distributions of 4-ethoxy-3-methoxybenzoic
1820 Envlron. Scl. Technol., Vol. 27, No. 8, 1993
methyl ester. Further studies are needed to identify the most reliable indicators of chloroorganics of different origin. Acknowledgment
The participation of H.B. was enabled by a grant from the European Community STEP Program (CT-900026). Literature Cited Asplund, G.; et al. Sci. Total Environ. 1989,81182, 239. Enell, M.; et al. In River Basin Management--V; Laikari, H., Ed.; Pergamon Press plc: Oxford, 1989; p 29. Asplund, G.; Grimvall, A. Environ. Sci. Technol. 1991,25, 1346. Asplund, G.; et al. Soil Biol. Biochem. 1993, 25, 41. Knuutinen, J.; Mannila, P. Water Sci. Technol. 1991,24, 437. de Lijser, H. J. P.;et al. In Humic substances in the aquatic and terrestrial environment; Allard, et al., Eds.; Springer Verlag: Berlin, 1991; p 485. van Buren, J. B.; Dence, C. W. Tappi 1970,53, 2246. Lindstrom, K.; Osterberg, F. Holzforschung 1984,38,201. herberg, F. Ph.D. Thesis, The Royal Institute of Technology, Stockholm, 1984. Osterberg, F.; Lindstrom, K. Holzforschung 1985,39,149. Morck, R.; et al. In Environmental fate and effects of bleached pulp mill effluents;Saergren, A., Ed.; Swedish Environmental Protection Agency: Solna, 1991; p 155. Kringstad, K. P.;Lindstrom, K. Environ. Sci. Technol. 1984, 18, 236A. Christman, R. F.; et al. Environ. Sci. Technol. 1983,17,625. Pettersson, C.; et al. Sci. Total Environ. 1989,81182, 287. Freudenberg, K.; et al. Chem. Ber. 1938, 71, 1810. Larsson, S.; Miksche, G. E. Acta Chem. Scand. 1967, 21, 1970. Erickson, M.; et al. Acta Chem. Scand. 1973, 27, 127. Gellerstedt, G.; Gustafsson, K. J. Wood. Chem. Technol. 1987, 7, 65. Johansson, C.; et al. Presented at the 6th International Meeting of International Humic Substances Society, Bari, Sep 20-25, 1992. Stevens, A. A.; et al. J.-Am. Water Works Assoc. 1985,77, 146. Wigilius, B.; et al. Chemosphere 1988,17, 1985. Gron, C. In Humicsubstances in the aquatic and terrestrial environment; Allard; et ai., Eds.; Springer Verlag: Berlin, 1991; p 495. Enell, M.;Wennberg, L. Water Sci. Technol. 1991,24,385. Kringstad, K. P.; et al. Environ. Sci. Technol. 1985,19,421. Hemming, J.; et al. Chemosphere 1986,15,549. Erickson, M.; Dence, C. W. Sven. Papperstidn. 1976, 79, 316. Kolar, J. J.; et al. Wood Sci. Technol. 1983, 117. de Sousa, F.; et al. Water Sci. Technol. 1988, 20, 153. Received for review December 18, 1992. Revised manuscript received April 13, 1993. Accepted April 14, 1993.
