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Mutagenic properties of spent bleaching liquors from sulphite pulps and a comparison with kraft pulp bleaching liquors
Mutation Research, 172 (1986) 89-96 Elsevier
89
MTR 01104
Mutagenic properties of spent bleaching liquors from sulphite pulps and a comparison with kraft pulp bleaching liquors M. M~ller
1, G.E.
Carlberg 1 and N. Soteland 2
I Center for Industrial Research, P.O. Box 350 Blindern, 0314 Oslo 3, and 2 The Norwegian Pulp and Paper Research Institute, P.O. Box 250 Vindern, 0319 Oslo 3 (Norway)
(Received 7 June 1985) (Revision received 27 May 1986) (Accepted 30 May 1986)
Summary Parameters influencing the mutagenic properties of spent bleaching liquors from sulphite pulps have been studied. In addition a comparison has been made between the properties of spent liquors from sulphite and kraft pulp bleaching. In the sulphite process the cooking base had no influence on the mutagenicity of the chlorination stage. In contrast, removing the extractives before chlorination especially for dissolving pulp resulted in an increase in mutagenic activity. The mutagenicity decreased significantly after substituting 40% of the chlorine with chlorine dioxide. Sequential addition of chlorine and chlorine dioxide resulted in higher activity than simultaneous or premixed chlorination as observed for liquors from kraft pulp. Increasing the pH of the extracts or addition of sulphur dioxide decreased the mutagenicity. Expressed as 10 7 revertants per kappa number and ton pulp the mutagenicity varied between 10 and 40 for sulphite pulp while the corresponding figures for kraft pulp were 100-225.
The discharge of spent bleaching liquors is currently considered to be one of the most important environmental aspects within the pulp and paper industry. The chlorination stage effluent has been found to exhibit considerable mutagenic activity in the Ames Salmonella mutagenicity test (Ander et al., 1977; Eriksson et al., 1979; Bjorseth et al., 1979; Douglas et al., 1980; Nazar and Rapson, 1980; Donnini, 1981; Lee et al., 1981; Carlberg et al., 1982a). There are several reported ways to reduce the mutagenicity of chlorination effluent: biological treatment (Eriksson et al., 1979; Lee et al., 1981; Walden and Howard, 1977; Dence et al., 1980), raising the pH into the alkaline region (Eriksson et al., 1979; Sameshima et al., 1979; Betts and Wilson, 1967; Rapson et al., 1980; Carlberg et al., 1980), high chlorine dioxide substitu-
tion for chlorine during bleaching (Nazar and Rapson, 1980; Dence et al., 1980; Wong et al., 1978; Rapson et al., 1977; Carlberg et al., 1982a) and effluent treatment with sulphur dioxide (Donnini, 1981; Betts and Wilson, 1967; Eriksson et al., 1982; Donnini and Jankey, 1983). These studies have mainly been performed on softwood kraft pulps, and Kringstad and LindstriSm (1984) have recently given an excellent review on the properties of spent liquors from this process. Few data seem to be available on the mutagenicity of spent bleach liquors from sulphite pulps. In this paper we report the results from studies on parameters influencing the mutagenicity in spent bleach liquors from sulphite pulps. Finally a comparison has been made between the mutagenicity found in the chlorination effluent from spruce kraft pulp and the correspond-
0165-1218/86/$03.50 © 1986 Elsevier Science Publishers B.V. (Biomedical Division)
90 ing activity from spruce sulphite pulp of the same lignin content.
Experimental
Wood raw material and cooking Fresh chips of spruce were air-dried and screened. Both magnesium and sodium bisulphite cooking liquors were used. In both cases the pH was kept at 4 and the cooking acid contained 4% total SO 2 and 2% combined SO 2. To reach a kappa number around 30 the temperature was kept at 155°C for 5 h. Kappa is the industrial term for residual lignin, kappa number 10 corresponds to 1.5% lignin. To prepare sulphite pulps with kappa numbers 20 and 8, the acid magnesium sulphite process was used. The cooking acid contained 6.5% total SO 2 and 0.9% combined SO 2. The maximum temperature was 142°C. Resin-free sulphite pulps were prepared by acetone extraction of wet pulp in Soxhlet apparatus for 6 h, after which the pulp was thoroughly washed before chlorination. The acetone-extractable substances amounted to 2.1% for the kappa number 20 pulp, and 2.0% for the kappa number 8 pulp. The kraft cooking liquor had a sulphidity of 24.5% and 17.5% active alkali calculated as % N a O H on chips. The maximum temperature was 175°C. After cooking the pulp was disintegrated and screened. Bleaching Sulphite pulps were bleached with a C E H D sequence, using conventional conditions ( C = chlorination, E = alkaline extraction, H = hypochlorite, D = chlorodioxide). Chlorine dioxide addition in the C stage was carried out with 40% substitution and both simultaneous and sequential (1 and 5 rain) addition was used. The amount of chlorine used in the C stage in bleaching of both sulphite and kraft pulps is on average 0.2 x kappa number. However, in mill practice great variations can occur, and overchlorination is probably more common than underchlorination. For studying the effect of chlorine charge versus mutagenic activity, the chlorination
factor has been varied from 0.14 to 0.26 x kappa number under otherwise unchanged conditions. The consumption of active chlorine was at least 95% in all chlorination runs. When comparing C-stage effluent from kraft and sulphite pulps (kappa number 30) the same chlorine charge and chlorination conditions were used for both pulps. The kraft pulps were bleached with a CED sequence using conventional conditions.
Chemical treatment of spent bleach liquors (1) Treatment with NaOH. Experiment A: Equal volumes from the C and E stage were mixed together and resulted in a pH of 2.3. The pH was then adjusted to 1.3, 6.3, 8 and 10 with 0.2 M NaOH. Experiment B: Equal volumes from all bleaching stage effluents were mixed (pH = 2.7) and adjusted to the desired pH by the addition of 0.1 M NaOH. (2) Treatment with S02. SO2-water was added to the combined bleaching state effluent at pH 2.4, 4.0 and 6.5. The amount of SO/ added varied from 0.5 to 1.5 g/100 g pulp. The treated effluent was tested after 0.5 h or 1 week of storage. Mutagenicity testing The mutagenicity of the single and combined effluents were determined in the Salmonella microsome assay, as described by Ames et al. (1975) after concentration (200 x ) by diethylether extraction (Carlberg et al., 1982a). The Salmonella strain TA100 was kindly supplied by Prof. B.N. Ames. The testing was made with duplicate plates and the extracts were tested in 3-6 doses and repeated at least once. The mutagenic response was calculated from the linear part of the dose-response curve. All assays included tests with the positive control compounds benzo[a]pyrene (BaP) and 1-nitropyrene (1NP). In the presence of $9, 5/~g BaP gave 1200 net revertants/plate. In the absence of $9, 1/~g 1NP resulted in 500 net revertants/plate. Results and discussion
Influence of cooking base on the mutagenicity of effluents The influence of the base used in the cooking
91 process on the C-stage mutagenicity was tested by using both magnesium and sodium base (kappa 30). No difference was observed in the mutagenicity (results not shown) which is in accordance with previous investigations of the same bases at kappa 8 (Carlberg et al., 1982b). This indicates that the base has very little influence on the mutagenicity of the bleaching effluent.
Influence of extractives and overchlorination on the mutagenicity of effluents It is known that extractable substances, especially resin adds, in sulphite pulps contribute considerably to the acute toxicity of chlorination effluent (Donnini and Jankey, 1983), but the effect of extractives on the mutagenicity during chlorination is less studied. Two pulp samples (kappa 20 and kappa 8) were extracted with acetone to remove extractives before chlorination. The results are presented in Fig. 1. After removal of the extractives, the mutagenicity of the kappa 20 effluent increased 25% and that of the kappa 8 effluent increased 3-fold compared to the controls. This observation demonstrates that the extractives are not responsible for the mutagenicity of the effluent. Furthermore, the data indicate that by removal of the extractives the lignin is either more easily chlorinated, thereby creating more mutagens, that toxic components which will inhibit the mutagens are removed, or that matter consuming chlorine has been removed,
thereby causing an overchlorination of the lignin compared to the reference pulp. Possibly, a combination of the 3 effects is taking place. For kraft pulp effluents it has previously been demonstrated that the extractives are not responsible for the mutagenic activity of these liquors (Stockman et al., 1980; Rapson et al., 1980). Furthermore, it has been shown that certain treatments of extracts from kraft pulp bleach liquors will remove toxic compounds and thereby increase the mutagenicity (Rapson et al., 1980; Rannug et al., 1981). Chlorination of sulphite pulp normally requires a chlorine charge of 0.2 times the kappa number. In mill practice, however, it is difficult to keep a certain ratio between chlorine charge and kappa number, and a slight overchlorination is normally common. The effect of chlorine charge on the amount of mutagenicity has been studied and the results are given in Fig. 2. As can be seen from the figure a slight overchlorination increases the mutagenicity considerably for both kraft and sulphite pulp effluents.
Molecular weight fractionation Work on liquors from kraft pulp bleaching has shown that the compounds responsible for the Kraft
kappa 30
~0 35
C-stage effluents Acetone extrocted prior to the C-stage
= 25
Reference 20 x
o.
g
E
15
n,
10
kap
36
5
"C
,
nr"
'I 20
20
8
8
kappa number
Fig. 1. The influence of extractives on the mutagenicity of C stage effluents from sulphite pulp with kappa numbers 20 and 8.
0.1/,
° 0.18
I' 0.22
;'. ehtorine on pulp
18.,o.oo,,oo 0.26
factor
Fig. 2. Influence of chlorine charge on the mutagenicity of
extracts from the C stage effluentsof kraft pulp, kappa 30, and sulphite pulp, kappa 36.
92 mutagenic activity are found in the molecular weight fractions MW < 500 (Stockman et al., 1980). In order to relate mutagenic activity to specific molecular weight fractions in sulphite pulp, the effluent from the chlorination stage was separated into 3 fractions with MW > 10000, 500 < MW < 10 000 and M W < 500. The results re-
C 10 No sulphite pulp, koppo 30 o~ O x
C,,E 1:1
Gt. C o
C:
C* E,,H*D
I:1:1:1
> rY
E
H
I1"111 H
D I~l
2.0 11.6 11.2 2.5
2.3
2.7
pH
10
No sulphite pulp, koppo 30 =c2 7.5 x
C÷E 16hrs storoge
a. C
o
5
C
~, 2.5
tY
11
C*E+H÷D no storage
27 6.0 80 l0 pH 2.0 2.3 13 6.3 Fig. 3. (a) Mutagenic activity of extracts from the single bleaching stages C, E, H and D and combined stages (C + E) and (C + E + H + D) from sodium sulphite pulp, kappa 30. (b) Mutagenic activity of extracts from combined bleaching stages (C + E), 16 h storage and (C + E + H + D), no storage, at different pH. The first column of the combined stages (C+E), pH 2.3, represents no storage.
vealed that more than 90% of the activity was found in the fraction MW < 500 (data not shown).
Mutagenicity of single stage and combined effluents The mutagenic activity of the spent bleach liquors from each bleaching stage is shown in Fig. 3a. The results are given relative to the activity of the C stage effluent. The p H of the effluents is also indicated. As can be seen from the figure the alkaline extraction, hypochlorite, and chlorine dioxide stages contained very little or no mutagenic activity relative to the chlorination stage effluent. In a pulp and paper plant the effluents from the different bleaching stages will usually be combined before discharging into the environment. To study the mutagenic activity of a combination of spent bleach liquors, two mixtures were made. The first one consisted of a 1 : 1 mixture of the C and E stage effluents and the second was a mixture of all the effluents. The p H s of the two mixtures were 2.3 and 2.7, respectively, and this was only slightly higher than the p H of the chlorination stage effluent (2.0). The mutagenic activity of the two mixtures was found to be about 50% and 25% of the activity of the C stage effluent, respectively (Fig. 3a). A dilution effect was therefore the only observable effect on the mutagenic activity after mixing the different bleach stage effluents. These results are in accordance with those observed for mutagenic activity from single and combined bleaching stage effluents from kraft pulps (Ander et al., 1977).
Reduction of rnutagenic actioity in spent bleach liquors p H adjustment. The effect of p H adjustment on the mutagenic activity of the combined bleachery effluent is shown in Fig. 3b. In order to eliminate the mutagenic activity it was necessary to adjust the p H above 7. Similar effects have been observed with spent bleach liquors from kraft pulp (Stockman et al., 1980; Rapson et al., 1980; Eriksson et al., 1979). SO 2 addition. The results of sulphur dioxide addition are given in Fig. 4. At p H 2.4 sulphur dioxide was added in 3 different concentrations. A reduction in mutagenic activity was observed for all concentrations. The highest SO 2 concentration
93
[] 1/2 h storage [] lweek storage
"10
~20 O o rD
E
10
i i
i~
:::i
ii
::i:
~j
i?iii
: :
Ref. Ref.
:i:X
0.Sg O5g PH2.4
Ig
Ig
15g tSg
Ref. J
0.5g 0.Sg
~
PHI,
Ig
Ig
Ref. ~
~
0.Sg 0.5g PH6.5
Fig. 4. The influence of SO 2 on the mutagenicity of combined effluents (C, E, H, D) from sulphite pulp during storage at different pH. SO 2 was added in the concentrations 0.5, 1.0, and 1.5 g / 1 0 0 g pulp and the effluents were stored for 0.5 h and for 1 week at pH 2.4, 4.0 and 6.5 before testing.
resulted in the largest reduction. On average the reduction in mutagenic activity after 0.5-h storage was 15% per 0.5 g sulphur dioxide added. At pH 4.0 two sulphur dioxide concentrations were used (0.5 and 1.0 g). The relative reduction in mutagenic activity was larger at pH 4.0 than at pH 2.4. After 1 week of storage the mutagenic activity of the 0.5 g SO 2 extract was reduced by another 50% while the activity of the 1-g sample was increased by about 30%. At pH 6.5 0.5 g sulphur dioxide was added, and after 1 week, only about 15% of the original mutagenic activity could be recovered. Similar results have been reported by Donnini and Jankey (1983). Previous studies on the effects of sulphur dioxide and pH on the mutagenicity of chlorination effluents from kraft pulp showed that by a similar combination of SO 2 addition and elevation of the pH the mutagenicity of these liquors could also be markedly reduced (Donnini, 1981; Eriksson et al., 1982).
shown in Fig. 5. In this case, the chlorine and chlorine dioxide were added simultaneously. In separate experiments the chlorine dioxide was added 1 or 5 min before the chlorine. The reduction in mutagenic activity was lower when the chlorine dioxide was added before the chlorine than when J
10
Mg sutphitepulp,kappa 30 40160 D/C 5 rain.
x
40160 D/C 1 rnin
~-
C÷D 5
Chlorine dioxide substitution in the chlorination stage
Substituting 40% of the chlorine in the chlorination stage by chlorine dioxide reduced the mutagenic activity in the effluent by about 45%, as
Fig. 5. Mutagenic activity of bleaching extracts from magnesium sulphite pulp, kappa 30, adding chlorine dioxide 5 min or 1 min before chlorine or together with chlorine.
94
the two were added simultaneously. The longer the reaction time of the chlorine dioxide before chlorination, the smaller was the reduction in mutagenic activity. It has been reported in the literature that high chlorine dioxide substitution reduces the mutagenicity of chlorination effluents from kraft pulps (Eriksson et al., 1979; Nazar and Rapson, 1980). Sequential chlorination was shown to give higher activity than simultaneous or premixed addition (Carlberg et al., 1982a).
Mutagenic activity in effluents from bleacheries after different bleaching sequences comparison between kraft and sulphite pulps -
-
In order to compare the influence of the pulping process on the subsequent bleaching effluent, sulphite and kraft pulps were taken down to the same lignin content (kappa = 30) before bleaching. In an industrial process, however, the lignin content of the sulphite pulp would have been further reduced.
A summary of the data expressed as revertants per ton pulp and kappa number is given in Fig. 6. The results from previous studies on oxygen and ozone delignification pretreatment are also included in the figure (Carlberg et al., 1981, 1982a, b; Lor~s and Soteland, 1982). As demonstrated in the figure the mutagenicity of the spent bleach liquor from the kraft pulp is nearly one order of magnitude higher than from sulphite pulp. Furthermore, the mutagenicity of the effluents from conventional bleaching is increasing with increasing lignin content in a nonlinear fashion for both kraft and sulphite pulps. For both pulp types overchlorination gives an increase in mutagenicity and substitution of chlorine by chlorine dioxide reduces the mutagenicity. Oxygen or ozone delignification of sulphite pulp resulted in a large increase in the mutagenicity of the subsequent chlorination stage effluent, probably due to a modification of the lignin by oxygen or ozone. Oxygen or ozone delignification of the kraft
SULPHITE
KRAFT R=r e f e r e n c e O=oxygen Z = ozone
o (32.3) X
e.-
= 0
200 (28.7)
¢J v
v... :~ZI:z ~.Z.[ v.. ;.X .X.
"¢o 0
D
(17.8)
8 100
,.... .... -.v :-X X.Z.X.:
IB.4)
4-P
tO
iiiiii
:+I (15.8)
:i:i:i
::1
,v.
:!8 X.Z ~:zZ:
:" ::.H :Z:Zz]... v.'.
i:i:i: x.:. • -. zZz:::
25 R
R
:z~zZ:
.X':
Z.X'
::::::
'XI
O
O
(301
:':+
120) 1101
Z
R
R
R
O
Z
Z
Fig. 6. Influence of kappa number and delignification processes on the mutagenicity of extracts from the C stage of kraft and sulphite pulps. The results are expressed as revertants per ton pulp and kappa unit. The number above each column represents the kappa number.
95 TABLE 1 COMPARISON BETWEEN MUTAGENIC PROPERTIES OF SULPHITE AND KRAFT PULP BLEACHERY EFFLUENTS Properties
Kraft
Sulphite
Bleaching stage showing mutagenicity Revertants/kappa number and ton, chlorination stage x 1 0 7 Size fractionation MW of mutagens Mutagenicity at alkaline pH Effect of increasing pH on mutagenicity Influence of SO2 on mutagenicity Influence of prebleaching with 02 Influence of prebleaching with ozone Effects of: Extractives Overchlorination Effect of substituting CIO2 for C12 in the chlorination stage
C
C
100-225 MW < 500 very low decrease decrease no effect no effect
10-40 MW < 500 very low decrease decrease increase increase
not mutagenic increase decrease largest decrease when C and D are added simultaneously
not mutagenic increase decrease largest decrease when C and D are added simultaneously
p u l p d i d n o t result in a n y significant change in m u t a g e n i c i t y c o m p a r e d to a c o n v e n t i o n a l bleaching at the same k a p p a n u m b e r . However, starting at a certain k a p p a n u m b e r , oxygen t r e a t m e n t to r e d u c e the lignin c o n t e n t followed b y c h l o r i n a t i o n w o u l d of course result in lower total m u t a g e n i c activity c o m p a r e d to the reference using only chlorine treatment. I n a recent investigation C a r l b e r g et al. (1986) i d e n t i f i e d a n u m b e r of m u t a g e n i c c o m p o u n d s such as c h l o r i n a t e d aldehydes, ketones a n d h y d r o c a r b o n s in spent b l e a c h liquors from sulphite pulps. These c o m p o u n d s have previously been f o u n d in b l e a c h e r y effluents from kraft p u l p s ( K r i n g s t a d et al., 1981; K r i n g s t a d a n d L i n d s t r S m , 1984). These results indicate that the same comp o u n d s are r e s p o n s i b l e for the m u t a g e n i c activity in spent bleach liquors o f b o t h p u l p types.
Conclusion A s u m m a r y of the p r o p e r t i e s of kraft a n d sulphite b l e a c h e r y effluents is given in T a b l e 1. C h l o r i n e t r e a t m e n t of p u l p s at similar k a p p a n u m b e r clearly resulted in a m u c h higher m u t a g e n i c activity in the kraft p u l p effluents than in the c o r r e s p o n d i n g sulphite samples. In b o t h processes the m u t a g e n s were small ( M W < 500) a n d were alkaline labile. T r e a t m e n t with SO 2 resulted in a
decrease in activity for b o t h types of effluents. However, p r e b l e a c h i n g with oxygen or ozone resuited in an increase in activity for chlorine effluents from sulphite pulp, while no such effect was o b s e r v e d for the c o r r e s p o n d i n g kraft effluents. S u b s t i t u t i n g chlorine with chlorine d i o x i d e r e d u c e d the m u t a g e n i c activity for b o t h p u l p types.
Acknowledgement This w o r k was financially s u p p o r t e d b y the R o y a l N o r w e g i a n C o u n c i l for Scientific a n d Industrial Research.
References Ames, B.N., J. McCann and E. Yamasaki (1975) Methods for detecting carcinogens and mutagens with the Salmonella/ mammalian-microsome mutagerficity test, Mutation Res., 31, 347-364. Ander, P., K.-E. Eriksson, M.-C. Kolfir, K. Kringstad, U. Rannug and C. Ramel (1977) Studies on the mutagenic properties of bleaching effluents, Svensk Papperstidn., 80, 454-459. Betts, J.L., and G.G. Wilson (1967) New methods for reducing the toxicity of kraft mill bleachery wastes to young salmon, Pulp Paper Can., 68(2), T53-T56, T58. Bjorseth, A., G.E. Carlberg and M. Moiler (1979) Determination of halogenated organic compounds and mutagenicity testing of spent bleach liquors, Sci. Total Environ., 11, 197-211.
96 Carlberg, G.E., N. Gjos, M. Moiler, K.O. Gustavsen, G. Tveten and L. Renberg (1980) Chemical characterization and mutagenicity testing of chlorinated trihydroxybenzenes identified in spent bleach liquors from a sulphite plant, Sci. Total Environ., 15, 3-15. Carlberg, G.E., V. Lor~, M. Moller, N. Soteland and G. Tveten (1981) Die Bleiche von Chemiesulfitzellstoffen, Papier, 35(7), 257-264. Carlberg, G.E., M. Moiler, G. Tveten, V. Lorfis and N. Soreland (1982a) Bleaching of sulphite and sulphate pulps using conventional and unconventional sequences, In: Proceedings of Tappi Annual Meeting 1982, Tappi Press, pp. 381-390. Carlberg, G.E., S. Johansen, V. Lor~ts, M. Moller, N. Soteland and G. Tveten (1982b) Die Bleiche yon Sulfitzellstoffen unter Anwendung konventioneller und unkonventioneller Sequenzen, Papier, 36(6), 270-278. Carlberg, G.E., H. Drangsholt, and N. Gjos (1986) Identification of chlorinated compounds in the spent bleach liquor from differently treated sulphite pulps with special emphasis on mutagehic compounds, Sci. Total Environ., 48, 157-167. Dence, C.W., C.-J. Wang and P. Durkin (1980) Toxicity reduction through chemical and biological modification of spent pulp bleaching liquors, U.S. EPA Environ. Prot. Technol. Rep. EPA-600/2-80-039. Donnini, G.P. (1981) Reduction of toxicity and mutagenicity of chlorination effluents with sulphur dioxide, Pulp Paper Can., 82(11), 106-111. Donnini, G.P., and S.G. Jankey (1983) Reduction of the environmental impact of pulp bleaching effluents, Svensk Papperstidn., 86(12), Rl15-R119. Douglas, G.R., E.R. Nestmann, J.L. Betts, J.C. Mueller, E.G.-H. Lee, H.F. Stich, R.H.C. San, R.P. Brouzes, A.L. Chmelanskas, H.D. Paavilla and C.C. Walden (1980) Mutagenic activity in pulp mill effluents, in: R.L. Jolley, W.A. Brungs and R.B. Cumming (Eds.), Water Chlorination: Environmental Impact and Health Effects, Vol. 3, Ann Arbor Sci., pp. 865-880. Eriksson, K.-E., M.-C. Kolar and K. Kringstad (1979) Studies on the mutagenic properties of bleaching effluents, Part 2, Svensk Papperstidn., 82(4), 95-104. Eriksson, K.-E., K. Kringstad, F. de Sousa and L. StriSmberg (1982) Studies on the mutagenic properties of spent bleach-
ing liquors, Elimination of mutagenicity by treatment with alkali or sodium bisulfite, Svensk Papperstidn., 85(9), R73-R76. Kringstad, K.P., and K. Lindstr~m (1984) Spent liquors from pulp bleaching, Environ. Sci. Technol., 18(8), 562-566. Kringstad, K.P., P.O. Ljungquist, F. de Sousa and L.M. Str~Smberg (1981) Identification and mutagenic properties of some chlorinated aliphatic compounds in the spent liquor from kraft pulp chlorination, Environ. Sci. Technol., 15(5), 236-248. Lee, E.G.-H., J.C. Milller, C.C. Walden and H. Stich (1981) Mutagenic properties of pulp mill effluents, Pulp Paper Can., 82(5), T149-T154. Lor&s, V., and N. Soteland (1982) Paper presented at the 1982 International Pulp Bleaching Conference, Portland, OR, May 24-27. Nazar, M.A., and W.H. Rapson (1980) Elimination of the mutagenicity of bleach plant effluents, Pulp Paper Can., 82(5), T191-T196. Rannug, U., D. Jenssen, C. Ramel, K.-E. Eriksson and K. Kringstad (1981) Mutagenic effects of effluents from chlorine bleaching of pulp, J. Toxicol. Environ. Health, 7, 33-47. Rapson, H., C.B. Anderson and D. Reeve (1977) The effluentfree bleached kraft pulp mill, VI. Substantial substitution of chlorine dioxide for chlorine in the first stage of bleaching, Pulp Paper Can., 78(6), T137-T148. Rapson, H., M.A. Nazar and V.V. Bulsky (1980) Mutagenicity produced by aqueous chlorination of organic compounds, Bull. Environ. Contam. Toxicol., 24, 590-597. Sameshima, K., B. Simson and C.W. Dence (1979) The fractionation and characterization of toxic materials in kraft spent bleaching liquors, Svensk Papperstidn., 82(6), 162-170. Stockman, L., L. Str~Smberg and F. de Sousa (1980) Mutagenic properties of bleach plant effluents: Present state of knowledge, Cellulose Chem. Technol., 14, 517-526. Walden, C.C., and T.E. Howard (1977) Toxicity of pulp and paper mill effluents, A review of regulations and research, Tappi, 60(1), 122-125. Wong, A., M. Lebourhis, R. Wostradowski and S. Prahacs (1978) Toxicity, BOD and color of effluents from novel bleaching processes, Pulp Paper Can., 79(7), T235-T241.
89
MTR 01104
Mutagenic properties of spent bleaching liquors from sulphite pulps and a comparison with kraft pulp bleaching liquors M. M~ller
1, G.E.
Carlberg 1 and N. Soteland 2
I Center for Industrial Research, P.O. Box 350 Blindern, 0314 Oslo 3, and 2 The Norwegian Pulp and Paper Research Institute, P.O. Box 250 Vindern, 0319 Oslo 3 (Norway)
(Received 7 June 1985) (Revision received 27 May 1986) (Accepted 30 May 1986)
Summary Parameters influencing the mutagenic properties of spent bleaching liquors from sulphite pulps have been studied. In addition a comparison has been made between the properties of spent liquors from sulphite and kraft pulp bleaching. In the sulphite process the cooking base had no influence on the mutagenicity of the chlorination stage. In contrast, removing the extractives before chlorination especially for dissolving pulp resulted in an increase in mutagenic activity. The mutagenicity decreased significantly after substituting 40% of the chlorine with chlorine dioxide. Sequential addition of chlorine and chlorine dioxide resulted in higher activity than simultaneous or premixed chlorination as observed for liquors from kraft pulp. Increasing the pH of the extracts or addition of sulphur dioxide decreased the mutagenicity. Expressed as 10 7 revertants per kappa number and ton pulp the mutagenicity varied between 10 and 40 for sulphite pulp while the corresponding figures for kraft pulp were 100-225.
The discharge of spent bleaching liquors is currently considered to be one of the most important environmental aspects within the pulp and paper industry. The chlorination stage effluent has been found to exhibit considerable mutagenic activity in the Ames Salmonella mutagenicity test (Ander et al., 1977; Eriksson et al., 1979; Bjorseth et al., 1979; Douglas et al., 1980; Nazar and Rapson, 1980; Donnini, 1981; Lee et al., 1981; Carlberg et al., 1982a). There are several reported ways to reduce the mutagenicity of chlorination effluent: biological treatment (Eriksson et al., 1979; Lee et al., 1981; Walden and Howard, 1977; Dence et al., 1980), raising the pH into the alkaline region (Eriksson et al., 1979; Sameshima et al., 1979; Betts and Wilson, 1967; Rapson et al., 1980; Carlberg et al., 1980), high chlorine dioxide substitu-
tion for chlorine during bleaching (Nazar and Rapson, 1980; Dence et al., 1980; Wong et al., 1978; Rapson et al., 1977; Carlberg et al., 1982a) and effluent treatment with sulphur dioxide (Donnini, 1981; Betts and Wilson, 1967; Eriksson et al., 1982; Donnini and Jankey, 1983). These studies have mainly been performed on softwood kraft pulps, and Kringstad and LindstriSm (1984) have recently given an excellent review on the properties of spent liquors from this process. Few data seem to be available on the mutagenicity of spent bleach liquors from sulphite pulps. In this paper we report the results from studies on parameters influencing the mutagenicity in spent bleach liquors from sulphite pulps. Finally a comparison has been made between the mutagenicity found in the chlorination effluent from spruce kraft pulp and the correspond-
0165-1218/86/$03.50 © 1986 Elsevier Science Publishers B.V. (Biomedical Division)
90 ing activity from spruce sulphite pulp of the same lignin content.
Experimental
Wood raw material and cooking Fresh chips of spruce were air-dried and screened. Both magnesium and sodium bisulphite cooking liquors were used. In both cases the pH was kept at 4 and the cooking acid contained 4% total SO 2 and 2% combined SO 2. To reach a kappa number around 30 the temperature was kept at 155°C for 5 h. Kappa is the industrial term for residual lignin, kappa number 10 corresponds to 1.5% lignin. To prepare sulphite pulps with kappa numbers 20 and 8, the acid magnesium sulphite process was used. The cooking acid contained 6.5% total SO 2 and 0.9% combined SO 2. The maximum temperature was 142°C. Resin-free sulphite pulps were prepared by acetone extraction of wet pulp in Soxhlet apparatus for 6 h, after which the pulp was thoroughly washed before chlorination. The acetone-extractable substances amounted to 2.1% for the kappa number 20 pulp, and 2.0% for the kappa number 8 pulp. The kraft cooking liquor had a sulphidity of 24.5% and 17.5% active alkali calculated as % N a O H on chips. The maximum temperature was 175°C. After cooking the pulp was disintegrated and screened. Bleaching Sulphite pulps were bleached with a C E H D sequence, using conventional conditions ( C = chlorination, E = alkaline extraction, H = hypochlorite, D = chlorodioxide). Chlorine dioxide addition in the C stage was carried out with 40% substitution and both simultaneous and sequential (1 and 5 rain) addition was used. The amount of chlorine used in the C stage in bleaching of both sulphite and kraft pulps is on average 0.2 x kappa number. However, in mill practice great variations can occur, and overchlorination is probably more common than underchlorination. For studying the effect of chlorine charge versus mutagenic activity, the chlorination
factor has been varied from 0.14 to 0.26 x kappa number under otherwise unchanged conditions. The consumption of active chlorine was at least 95% in all chlorination runs. When comparing C-stage effluent from kraft and sulphite pulps (kappa number 30) the same chlorine charge and chlorination conditions were used for both pulps. The kraft pulps were bleached with a CED sequence using conventional conditions.
Chemical treatment of spent bleach liquors (1) Treatment with NaOH. Experiment A: Equal volumes from the C and E stage were mixed together and resulted in a pH of 2.3. The pH was then adjusted to 1.3, 6.3, 8 and 10 with 0.2 M NaOH. Experiment B: Equal volumes from all bleaching stage effluents were mixed (pH = 2.7) and adjusted to the desired pH by the addition of 0.1 M NaOH. (2) Treatment with S02. SO2-water was added to the combined bleaching state effluent at pH 2.4, 4.0 and 6.5. The amount of SO/ added varied from 0.5 to 1.5 g/100 g pulp. The treated effluent was tested after 0.5 h or 1 week of storage. Mutagenicity testing The mutagenicity of the single and combined effluents were determined in the Salmonella microsome assay, as described by Ames et al. (1975) after concentration (200 x ) by diethylether extraction (Carlberg et al., 1982a). The Salmonella strain TA100 was kindly supplied by Prof. B.N. Ames. The testing was made with duplicate plates and the extracts were tested in 3-6 doses and repeated at least once. The mutagenic response was calculated from the linear part of the dose-response curve. All assays included tests with the positive control compounds benzo[a]pyrene (BaP) and 1-nitropyrene (1NP). In the presence of $9, 5/~g BaP gave 1200 net revertants/plate. In the absence of $9, 1/~g 1NP resulted in 500 net revertants/plate. Results and discussion
Influence of cooking base on the mutagenicity of effluents The influence of the base used in the cooking
91 process on the C-stage mutagenicity was tested by using both magnesium and sodium base (kappa 30). No difference was observed in the mutagenicity (results not shown) which is in accordance with previous investigations of the same bases at kappa 8 (Carlberg et al., 1982b). This indicates that the base has very little influence on the mutagenicity of the bleaching effluent.
Influence of extractives and overchlorination on the mutagenicity of effluents It is known that extractable substances, especially resin adds, in sulphite pulps contribute considerably to the acute toxicity of chlorination effluent (Donnini and Jankey, 1983), but the effect of extractives on the mutagenicity during chlorination is less studied. Two pulp samples (kappa 20 and kappa 8) were extracted with acetone to remove extractives before chlorination. The results are presented in Fig. 1. After removal of the extractives, the mutagenicity of the kappa 20 effluent increased 25% and that of the kappa 8 effluent increased 3-fold compared to the controls. This observation demonstrates that the extractives are not responsible for the mutagenicity of the effluent. Furthermore, the data indicate that by removal of the extractives the lignin is either more easily chlorinated, thereby creating more mutagens, that toxic components which will inhibit the mutagens are removed, or that matter consuming chlorine has been removed,
thereby causing an overchlorination of the lignin compared to the reference pulp. Possibly, a combination of the 3 effects is taking place. For kraft pulp effluents it has previously been demonstrated that the extractives are not responsible for the mutagenic activity of these liquors (Stockman et al., 1980; Rapson et al., 1980). Furthermore, it has been shown that certain treatments of extracts from kraft pulp bleach liquors will remove toxic compounds and thereby increase the mutagenicity (Rapson et al., 1980; Rannug et al., 1981). Chlorination of sulphite pulp normally requires a chlorine charge of 0.2 times the kappa number. In mill practice, however, it is difficult to keep a certain ratio between chlorine charge and kappa number, and a slight overchlorination is normally common. The effect of chlorine charge on the amount of mutagenicity has been studied and the results are given in Fig. 2. As can be seen from the figure a slight overchlorination increases the mutagenicity considerably for both kraft and sulphite pulp effluents.
Molecular weight fractionation Work on liquors from kraft pulp bleaching has shown that the compounds responsible for the Kraft
kappa 30
~0 35
C-stage effluents Acetone extrocted prior to the C-stage
= 25
Reference 20 x
o.
g
E
15
n,
10
kap
36
5
"C
,
nr"
'I 20
20
8
8
kappa number
Fig. 1. The influence of extractives on the mutagenicity of C stage effluents from sulphite pulp with kappa numbers 20 and 8.
0.1/,
° 0.18
I' 0.22
;'. ehtorine on pulp
18.,o.oo,,oo 0.26
factor
Fig. 2. Influence of chlorine charge on the mutagenicity of
extracts from the C stage effluentsof kraft pulp, kappa 30, and sulphite pulp, kappa 36.
92 mutagenic activity are found in the molecular weight fractions MW < 500 (Stockman et al., 1980). In order to relate mutagenic activity to specific molecular weight fractions in sulphite pulp, the effluent from the chlorination stage was separated into 3 fractions with MW > 10000, 500 < MW < 10 000 and M W < 500. The results re-
C 10 No sulphite pulp, koppo 30 o~ O x
C,,E 1:1
Gt. C o
C:
C* E,,H*D
I:1:1:1
> rY
E
H
I1"111 H
D I~l
2.0 11.6 11.2 2.5
2.3
2.7
pH
10
No sulphite pulp, koppo 30 =c2 7.5 x
C÷E 16hrs storoge
a. C
o
5
C
~, 2.5
tY
11
C*E+H÷D no storage
27 6.0 80 l0 pH 2.0 2.3 13 6.3 Fig. 3. (a) Mutagenic activity of extracts from the single bleaching stages C, E, H and D and combined stages (C + E) and (C + E + H + D) from sodium sulphite pulp, kappa 30. (b) Mutagenic activity of extracts from combined bleaching stages (C + E), 16 h storage and (C + E + H + D), no storage, at different pH. The first column of the combined stages (C+E), pH 2.3, represents no storage.
vealed that more than 90% of the activity was found in the fraction MW < 500 (data not shown).
Mutagenicity of single stage and combined effluents The mutagenic activity of the spent bleach liquors from each bleaching stage is shown in Fig. 3a. The results are given relative to the activity of the C stage effluent. The p H of the effluents is also indicated. As can be seen from the figure the alkaline extraction, hypochlorite, and chlorine dioxide stages contained very little or no mutagenic activity relative to the chlorination stage effluent. In a pulp and paper plant the effluents from the different bleaching stages will usually be combined before discharging into the environment. To study the mutagenic activity of a combination of spent bleach liquors, two mixtures were made. The first one consisted of a 1 : 1 mixture of the C and E stage effluents and the second was a mixture of all the effluents. The p H s of the two mixtures were 2.3 and 2.7, respectively, and this was only slightly higher than the p H of the chlorination stage effluent (2.0). The mutagenic activity of the two mixtures was found to be about 50% and 25% of the activity of the C stage effluent, respectively (Fig. 3a). A dilution effect was therefore the only observable effect on the mutagenic activity after mixing the different bleach stage effluents. These results are in accordance with those observed for mutagenic activity from single and combined bleaching stage effluents from kraft pulps (Ander et al., 1977).
Reduction of rnutagenic actioity in spent bleach liquors p H adjustment. The effect of p H adjustment on the mutagenic activity of the combined bleachery effluent is shown in Fig. 3b. In order to eliminate the mutagenic activity it was necessary to adjust the p H above 7. Similar effects have been observed with spent bleach liquors from kraft pulp (Stockman et al., 1980; Rapson et al., 1980; Eriksson et al., 1979). SO 2 addition. The results of sulphur dioxide addition are given in Fig. 4. At p H 2.4 sulphur dioxide was added in 3 different concentrations. A reduction in mutagenic activity was observed for all concentrations. The highest SO 2 concentration
93
[] 1/2 h storage [] lweek storage
"10
~20 O o rD
E
10
i i
i~
:::i
ii
::i:
~j
i?iii
: :
Ref. Ref.
:i:X
0.Sg O5g PH2.4
Ig
Ig
15g tSg
Ref. J
0.5g 0.Sg
~
PHI,
Ig
Ig
Ref. ~
~
0.Sg 0.5g PH6.5
Fig. 4. The influence of SO 2 on the mutagenicity of combined effluents (C, E, H, D) from sulphite pulp during storage at different pH. SO 2 was added in the concentrations 0.5, 1.0, and 1.5 g / 1 0 0 g pulp and the effluents were stored for 0.5 h and for 1 week at pH 2.4, 4.0 and 6.5 before testing.
resulted in the largest reduction. On average the reduction in mutagenic activity after 0.5-h storage was 15% per 0.5 g sulphur dioxide added. At pH 4.0 two sulphur dioxide concentrations were used (0.5 and 1.0 g). The relative reduction in mutagenic activity was larger at pH 4.0 than at pH 2.4. After 1 week of storage the mutagenic activity of the 0.5 g SO 2 extract was reduced by another 50% while the activity of the 1-g sample was increased by about 30%. At pH 6.5 0.5 g sulphur dioxide was added, and after 1 week, only about 15% of the original mutagenic activity could be recovered. Similar results have been reported by Donnini and Jankey (1983). Previous studies on the effects of sulphur dioxide and pH on the mutagenicity of chlorination effluents from kraft pulp showed that by a similar combination of SO 2 addition and elevation of the pH the mutagenicity of these liquors could also be markedly reduced (Donnini, 1981; Eriksson et al., 1982).
shown in Fig. 5. In this case, the chlorine and chlorine dioxide were added simultaneously. In separate experiments the chlorine dioxide was added 1 or 5 min before the chlorine. The reduction in mutagenic activity was lower when the chlorine dioxide was added before the chlorine than when J
10
Mg sutphitepulp,kappa 30 40160 D/C 5 rain.
x
40160 D/C 1 rnin
~-
C÷D 5
Chlorine dioxide substitution in the chlorination stage
Substituting 40% of the chlorine in the chlorination stage by chlorine dioxide reduced the mutagenic activity in the effluent by about 45%, as
Fig. 5. Mutagenic activity of bleaching extracts from magnesium sulphite pulp, kappa 30, adding chlorine dioxide 5 min or 1 min before chlorine or together with chlorine.
94
the two were added simultaneously. The longer the reaction time of the chlorine dioxide before chlorination, the smaller was the reduction in mutagenic activity. It has been reported in the literature that high chlorine dioxide substitution reduces the mutagenicity of chlorination effluents from kraft pulps (Eriksson et al., 1979; Nazar and Rapson, 1980). Sequential chlorination was shown to give higher activity than simultaneous or premixed addition (Carlberg et al., 1982a).
Mutagenic activity in effluents from bleacheries after different bleaching sequences comparison between kraft and sulphite pulps -
-
In order to compare the influence of the pulping process on the subsequent bleaching effluent, sulphite and kraft pulps were taken down to the same lignin content (kappa = 30) before bleaching. In an industrial process, however, the lignin content of the sulphite pulp would have been further reduced.
A summary of the data expressed as revertants per ton pulp and kappa number is given in Fig. 6. The results from previous studies on oxygen and ozone delignification pretreatment are also included in the figure (Carlberg et al., 1981, 1982a, b; Lor~s and Soteland, 1982). As demonstrated in the figure the mutagenicity of the spent bleach liquor from the kraft pulp is nearly one order of magnitude higher than from sulphite pulp. Furthermore, the mutagenicity of the effluents from conventional bleaching is increasing with increasing lignin content in a nonlinear fashion for both kraft and sulphite pulps. For both pulp types overchlorination gives an increase in mutagenicity and substitution of chlorine by chlorine dioxide reduces the mutagenicity. Oxygen or ozone delignification of sulphite pulp resulted in a large increase in the mutagenicity of the subsequent chlorination stage effluent, probably due to a modification of the lignin by oxygen or ozone. Oxygen or ozone delignification of the kraft
SULPHITE
KRAFT R=r e f e r e n c e O=oxygen Z = ozone
o (32.3) X
e.-
= 0
200 (28.7)
¢J v
v... :~ZI:z ~.Z.[ v.. ;.X .X.
"¢o 0
D
(17.8)
8 100
,.... .... -.v :-X X.Z.X.:
IB.4)
4-P
tO
iiiiii
:+I (15.8)
:i:i:i
::1
,v.
:!8 X.Z ~:zZ:
:" ::.H :Z:Zz]... v.'.
i:i:i: x.:. • -. zZz:::
25 R
R
:z~zZ:
.X':
Z.X'
::::::
'XI
O
O
(301
:':+
120) 1101
Z
R
R
R
O
Z
Z
Fig. 6. Influence of kappa number and delignification processes on the mutagenicity of extracts from the C stage of kraft and sulphite pulps. The results are expressed as revertants per ton pulp and kappa unit. The number above each column represents the kappa number.
95 TABLE 1 COMPARISON BETWEEN MUTAGENIC PROPERTIES OF SULPHITE AND KRAFT PULP BLEACHERY EFFLUENTS Properties
Kraft
Sulphite
Bleaching stage showing mutagenicity Revertants/kappa number and ton, chlorination stage x 1 0 7 Size fractionation MW of mutagens Mutagenicity at alkaline pH Effect of increasing pH on mutagenicity Influence of SO2 on mutagenicity Influence of prebleaching with 02 Influence of prebleaching with ozone Effects of: Extractives Overchlorination Effect of substituting CIO2 for C12 in the chlorination stage
C
C
100-225 MW < 500 very low decrease decrease no effect no effect
10-40 MW < 500 very low decrease decrease increase increase
not mutagenic increase decrease largest decrease when C and D are added simultaneously
not mutagenic increase decrease largest decrease when C and D are added simultaneously
p u l p d i d n o t result in a n y significant change in m u t a g e n i c i t y c o m p a r e d to a c o n v e n t i o n a l bleaching at the same k a p p a n u m b e r . However, starting at a certain k a p p a n u m b e r , oxygen t r e a t m e n t to r e d u c e the lignin c o n t e n t followed b y c h l o r i n a t i o n w o u l d of course result in lower total m u t a g e n i c activity c o m p a r e d to the reference using only chlorine treatment. I n a recent investigation C a r l b e r g et al. (1986) i d e n t i f i e d a n u m b e r of m u t a g e n i c c o m p o u n d s such as c h l o r i n a t e d aldehydes, ketones a n d h y d r o c a r b o n s in spent b l e a c h liquors from sulphite pulps. These c o m p o u n d s have previously been f o u n d in b l e a c h e r y effluents from kraft p u l p s ( K r i n g s t a d et al., 1981; K r i n g s t a d a n d L i n d s t r S m , 1984). These results indicate that the same comp o u n d s are r e s p o n s i b l e for the m u t a g e n i c activity in spent bleach liquors o f b o t h p u l p types.
Conclusion A s u m m a r y of the p r o p e r t i e s of kraft a n d sulphite b l e a c h e r y effluents is given in T a b l e 1. C h l o r i n e t r e a t m e n t of p u l p s at similar k a p p a n u m b e r clearly resulted in a m u c h higher m u t a g e n i c activity in the kraft p u l p effluents than in the c o r r e s p o n d i n g sulphite samples. In b o t h processes the m u t a g e n s were small ( M W < 500) a n d were alkaline labile. T r e a t m e n t with SO 2 resulted in a
decrease in activity for b o t h types of effluents. However, p r e b l e a c h i n g with oxygen or ozone resuited in an increase in activity for chlorine effluents from sulphite pulp, while no such effect was o b s e r v e d for the c o r r e s p o n d i n g kraft effluents. S u b s t i t u t i n g chlorine with chlorine d i o x i d e r e d u c e d the m u t a g e n i c activity for b o t h p u l p types.
Acknowledgement This w o r k was financially s u p p o r t e d b y the R o y a l N o r w e g i a n C o u n c i l for Scientific a n d Industrial Research.
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96 Carlberg, G.E., N. Gjos, M. Moiler, K.O. Gustavsen, G. Tveten and L. Renberg (1980) Chemical characterization and mutagenicity testing of chlorinated trihydroxybenzenes identified in spent bleach liquors from a sulphite plant, Sci. Total Environ., 15, 3-15. Carlberg, G.E., V. Lor~, M. Moller, N. Soteland and G. Tveten (1981) Die Bleiche von Chemiesulfitzellstoffen, Papier, 35(7), 257-264. Carlberg, G.E., M. Moiler, G. Tveten, V. Lorfis and N. Soreland (1982a) Bleaching of sulphite and sulphate pulps using conventional and unconventional sequences, In: Proceedings of Tappi Annual Meeting 1982, Tappi Press, pp. 381-390. Carlberg, G.E., S. Johansen, V. Lor~ts, M. Moller, N. Soteland and G. Tveten (1982b) Die Bleiche yon Sulfitzellstoffen unter Anwendung konventioneller und unkonventioneller Sequenzen, Papier, 36(6), 270-278. Carlberg, G.E., H. Drangsholt, and N. Gjos (1986) Identification of chlorinated compounds in the spent bleach liquor from differently treated sulphite pulps with special emphasis on mutagehic compounds, Sci. Total Environ., 48, 157-167. Dence, C.W., C.-J. Wang and P. Durkin (1980) Toxicity reduction through chemical and biological modification of spent pulp bleaching liquors, U.S. EPA Environ. Prot. Technol. Rep. EPA-600/2-80-039. Donnini, G.P. (1981) Reduction of toxicity and mutagenicity of chlorination effluents with sulphur dioxide, Pulp Paper Can., 82(11), 106-111. Donnini, G.P., and S.G. Jankey (1983) Reduction of the environmental impact of pulp bleaching effluents, Svensk Papperstidn., 86(12), Rl15-R119. Douglas, G.R., E.R. Nestmann, J.L. Betts, J.C. Mueller, E.G.-H. Lee, H.F. Stich, R.H.C. San, R.P. Brouzes, A.L. Chmelanskas, H.D. Paavilla and C.C. Walden (1980) Mutagenic activity in pulp mill effluents, in: R.L. Jolley, W.A. Brungs and R.B. Cumming (Eds.), Water Chlorination: Environmental Impact and Health Effects, Vol. 3, Ann Arbor Sci., pp. 865-880. Eriksson, K.-E., M.-C. Kolar and K. Kringstad (1979) Studies on the mutagenic properties of bleaching effluents, Part 2, Svensk Papperstidn., 82(4), 95-104. Eriksson, K.-E., K. Kringstad, F. de Sousa and L. StriSmberg (1982) Studies on the mutagenic properties of spent bleach-
ing liquors, Elimination of mutagenicity by treatment with alkali or sodium bisulfite, Svensk Papperstidn., 85(9), R73-R76. Kringstad, K.P., and K. Lindstr~m (1984) Spent liquors from pulp bleaching, Environ. Sci. Technol., 18(8), 562-566. Kringstad, K.P., P.O. Ljungquist, F. de Sousa and L.M. Str~Smberg (1981) Identification and mutagenic properties of some chlorinated aliphatic compounds in the spent liquor from kraft pulp chlorination, Environ. Sci. Technol., 15(5), 236-248. Lee, E.G.-H., J.C. Milller, C.C. Walden and H. Stich (1981) Mutagenic properties of pulp mill effluents, Pulp Paper Can., 82(5), T149-T154. Lor&s, V., and N. Soteland (1982) Paper presented at the 1982 International Pulp Bleaching Conference, Portland, OR, May 24-27. Nazar, M.A., and W.H. Rapson (1980) Elimination of the mutagenicity of bleach plant effluents, Pulp Paper Can., 82(5), T191-T196. Rannug, U., D. Jenssen, C. Ramel, K.-E. Eriksson and K. Kringstad (1981) Mutagenic effects of effluents from chlorine bleaching of pulp, J. Toxicol. Environ. Health, 7, 33-47. Rapson, H., C.B. Anderson and D. Reeve (1977) The effluentfree bleached kraft pulp mill, VI. Substantial substitution of chlorine dioxide for chlorine in the first stage of bleaching, Pulp Paper Can., 78(6), T137-T148. Rapson, H., M.A. Nazar and V.V. Bulsky (1980) Mutagenicity produced by aqueous chlorination of organic compounds, Bull. Environ. Contam. Toxicol., 24, 590-597. Sameshima, K., B. Simson and C.W. Dence (1979) The fractionation and characterization of toxic materials in kraft spent bleaching liquors, Svensk Papperstidn., 82(6), 162-170. Stockman, L., L. Str~Smberg and F. de Sousa (1980) Mutagenic properties of bleach plant effluents: Present state of knowledge, Cellulose Chem. Technol., 14, 517-526. Walden, C.C., and T.E. Howard (1977) Toxicity of pulp and paper mill effluents, A review of regulations and research, Tappi, 60(1), 122-125. Wong, A., M. Lebourhis, R. Wostradowski and S. Prahacs (1978) Toxicity, BOD and color of effluents from novel bleaching processes, Pulp Paper Can., 79(7), T235-T241.