+
Hiroyasu Ito for the measurement of fatty acids by GCI MS.
corresponding (M K)+ ions of poly(oxyethy1ene) octylphenyl ethers may overlap with isotope ions of quasi-molecules (M Na) of poly(oxyethy1ene) nonylphenyl ethers a t mlz 509,553,597,641,685,729,773,817,861,and 905. The relative intensities of these poly(oxyethy1ene) alkylphenyl ethers are considered to reflect their distributions in the extract fairly exactly, assuming that each poly(oxyethy1ene) alkylphenyl ether could have the same ionization efficiency in the FD-MS. These results of identification agree with an interpretation of the NMR spectrum which shows the presence of a -CHZO-group at -3.7 ppm. These poly(oxyethy1ene) alkylphenyl ethers including polyethylene glycols may probably come from detergents used for tanning leather. The same compounds were determined from the water sampled on March 31, 1979, a t the same station. I t is interesting that the NMR signal arising from the oxyethylene unit (3.7 ppm) is remarkably small when compared to that of fatty acids, while poly(oxyethy1ene)alkylphenyl ethers gave predominant ion peaks in the FD-MS. This may be due to large differences in the ionization efficiency between the poly(oxyethy1ene) alkylphenyl ethers and the fatty acids. However, no attempt was made to quantify these poly(oxyethy1ene) alkylphenyl ethers by FD-MS at the present time, but studies are now in progress. Some compounds identified in this study are very soluble in water and pose difficulties for direct extraction by organic solvents. The successful determination of both volatile and nonvolatile compounds in this study is due mainly to the use of vacuum distillation under a frozen state and the appropriate combination of GC/MS and FD-MS.
+
Literature Cited (1) McAuliffe, C. CHEMTECH. 1971,1,46. (2) Rook, J. J. Water Treat. Exam. 1972,21, 259. (3) Mieure, J. P.; Dietrich, M. W. J . Chromatogr. Sci. 1973, 11, 559. (4) Zlatkis, A.; Lichtenstein, H. A.; Tishbee, A. Chromatographia 1973,6, 67. (5) Grob, K. J. Chromatogr. 1973,84,255. (6) Zlatkis, A.; Lichtenstein, H. A,; Tishbee, A.; Bertsch, W.; Shunbo, F.; Liebich, H. M. J. Chromatogr. Sci. 1973,11, 299. (7) Bellar, T. A,; Lichtenberg, J. J. J. Am. Water Works Assoc. 1974, 66,739. ( 8 ) Dowty, B.; Carlisle, D.; Laseter, J. Science 1975,187, 75. (9) Dowty, B.; Carlisle, D.; Laseter, J. Enuiron. Sci. Technol. 1975, 9, 762. (10) Burnham, A. K.; Calder, G. V.; Fritz, J. S.; Junk, G. A.; Svec, H. J.; Willis, R. Anal. Chem. 1972,44, 139. (11) Junk, G. A.; Richard, J. J.; Grieser, M. D.; Witiak, D.; Witiak, J. L.; Arguello, M. D.; Vick, R.; Svec, H. J.; Fritz, J. S.; Calder, G. V. J. Chromatogr. 1974,99,745. (12) Coleman, W. E.; Melton, R. G.; Kopfler, F. C.; Barone, K. A.; Aurand, T. A.; Jellison, M. G. Enuiron. Sci. Technol. 1980, 14, 576. (13) Nickerson, G. B.; Likens, S. T. J. Chromatogr. 1966,21,1. (14) Shiraishi, H.; Otsuki, A.; Fuwa, K. Bull. Chem. SOC. Jpn. 1979, 52,2903. (15) Maine, J. W.; Soltmann, B.; Holland, J. F.; Toung, N. D.; Gerber, J. N.; Sweeley, C. C. Anal. Chem. 1976,48,427. (16) Schulten, H.-R.; Beckey, H. D. Org. Mass Spectrom. 1972,6,
885. (17) Beckey, H. D.; Heindrichs, A.; Winkler, H. U. Int. J . Mass Spectrom. Ion Phys. 1970,3,11. (18) Yasuhara, A.; Fuwa, K. Chemosphere 1977,6,179. (19) Okuno, T.; Tsuji, M.; Yamazaki, T. “Report on Odor Pollution in Hyogo Prefecture”; The Environmental Science Institute of Hyogo Prefecture: Kobe, Japan, 1977; pp 22-33. (20) Otsuki, A.; Shiraishi, H. Anal. Chem. 1979,51,2329.
Acknowledgment
We thank Mr. Tomio Yamazaki and Mr. Hideo Yasuhara for the sampling of the Hayashida River water, Mr. Masayuki Kunugi for the measurement of the NMR spectrum, and Mr.
Received for review July 31,1980. Accepted January 5,1981
Effects of Dechlorination on Early Life Stages of Striped Bass (Morone saxatilis) Lenwood W. Hall, Jr.,*t Dennis T. Burton,? William C. Graves,t and Stuart L. Margreyt Academy of Natural Sciences of Philadelphia, Benedict Estuarine Research Laboratory, Benedict, Maryland 20612
Effects of sulfur dioxide (S02) dechlorination on estuarine striped bass (Morone sazatilis) eggs and larvae were evaluated by exposing the organisms to the following conditions: total residual chlorine (TRC); S02; TRC-SO2 dechlorination, and control. Continuous exposure to TRC concentrations ranging from 0.06 to 2.0 mg/L were lethal to both life stages over a 96-h exposure period. The same range of SO2 (sulfite) concentrations caused an effect on the eggs after 36 h; however, percent mortality did not increase with concentration of S02. Few mortalities occurred a t exposures less than 36 h. Mortality of larvae was higher than the the controls at all SO2 conditions after 96 h although the mean mortality a t all concentrations was only 20% greater than the controls. Minimal mortality occurred at shorter exposure intervals. Mean mortality of test organisms exposed to TRC-SO2 dechlorination conditions was only 11%higher for eggs (36 h) and 22% higher for larvae (96 h) than controls. Dechlorination caused significant reductions in TRC toxicity a t all exposure periods less than 36 and 96 h for eggs and larvae, respectively.
+ Present address: The Johns Hopkins University, Applied Physics Laboratory, Aquatic Ecology Section, Shady Side, MD 20867. 0013-936X/81/0915-0573$01.25/0
Introduction
Dechlorination has been used as a means to reduce the residual toxicity of chlorinated industrial effluent to aquatic life. In recent years, the following methods of chemical dechlorination have been used: (1)sodium bisulfite ( 1 , 2 ) ; (2) sulfur dioxide (3-6); (3) sodium sulfite (7,8); and (4) sodium thiosulfate (9-12). Although all of the preceding chemical agents have been used to dechlorinate water used in industrial operations, sulfur dioxide (SO2) is considered one of the most feasible methods to use for large volumes of water ( 1 3 , 1 4 ) . This chemical agent provides an excellent means of dechlorination because its handling and metering are similar to those of chlorine. Various investigators (3-6) have evaluated the response of aquatic biota exposed to SO2 dechlorination in freshwater systems; however, the use and the possible ecological effect of this chemical in estuarine waters are limited. This study was designed to evaluate the effects of SO2 dechlorination on striped bass (Morone saratilis) eggs and larvae in estuarine water. These developmental stages of striped bass were selected for this investigation because of their occurrence in estuaries where chlorinated industrial effluent is discharged.
@ 1981 American Chemical Society
Volume 15, Number 5, May 1981 573
Materials and Methods
General. Fertilized striped bass eggs (water-hardened) were obtained from Brookneal Hatchery in Brookneal, VA, and reared in standard hatchery jars a t -18 "C. Larvae were reared under continuous-flow conditions in standard hatchery trays from egg stock at 18-20 "C. Larvae were fed natural plankton introduced via the seawater system and supplemented with high densities of brine shrimp. The ambient water quality range during the egg study was as follows: temperature = 18.0-19.5 "C; dissolved oxygen = 4.6-5.6 mg/L; salinity = 2.0-3.0 ppt (15);pH 7.2-7.9; and ammonia nitrogen = 0.10-0.15 mg/L. Ranges of water quality during the larvae studies were as follows: temperature = 20.0-20.5 "C; dissolved oxygen = 4.7-5.8 mg/L; salinity = 7.5-8.0 ppt; pH 7.0-7.4; and ammonia nitrogen = 0.10-0.15 mg/L. Photoperiods were set to simulate natural light-dark conditions. Previous investigators (6) have shown that sulfite can influence dissolved-oxygen concentrations in freshwater; however, we did not observe a significant difference in dissolved oxygen a t the various SO2 concentrations. Apparatus Description and Experimental Procedures. Estuarine water for all tests was pumped from the Patuxent River, Maryland. Total residual chlorine (TRC) and SO2 (measured as sulfite) concentrations were established in stock tanks. Water leaving each respective stock tank flowed through Tygon tubing and entered a series of 7.6-L test aquaria. Pipet tips located on the end of the tubing and hose clamps controlled water flow and subsequent concentrations through the system. Both life stages were tested in cylindrical plastic testing chambers (volume 11250 mL) covered with 350-nm nylon mesh on all sides and suspended in appropriate 7.6-L test aquaria. The following four types of experiments were conducted with each life stage of striped bass: (1)total residual chlorine exposures; (2) sulfur dioxide exposures; (3) TRC-SO2 dechlorination exposures; and (4) control exposures. A geometric series of TRC concentrations (0.06,0.13,0.25,0.50,1.00,and 2.00 mg/L) was used in this study in order to simulate a range of concentrations present in both sewage and power plant effluents in estuarine water (16,17).Concentrations of SO2 used in this study were the same as those for TRC because a ratio of 1:l (0.90/1.0 = actual ratio) is needed for dechlorination (18).The TRC-SO2 dechlorination exposures were conducted by using the series of TRC concentrations mentioned above along with subsequent SO2 concentrations necessary for complete dechlorination (0.00 mg/L TRC). A series of controls was conducted on all life stages in order to determine natural mortality. All concentrations and controls used in the above tests were run in triplicate by using a sample size of 50 organisms. All tests were conducted by using continuous exposure conditions. The effects of condenser entrainment (Le., power plants) and subsequent mechanical damage and rapid AT stress from plant entrainment were additional variables beyond the scope of this study. Tests with fertilized eggs -12 h old were conducted a t -18 "C for 36 h or until hatching occurred (19).Larvae 10-12 days old were tested for 96 h a t -20
Statistical Analysis. An arcsine-square root transformation of percent mortality was used in all analyses to stabilize variances among treatments (21).All striped bass egg and larvae data were analyzed a t 36 and 96 h, respectively. Each experimental group (TRC, SOz, and TRC-SO2) was analyzed for both life stages by a one-way analysis of variance (ANOVA) ( a = 0.01) to determine whether significant mortality occurred. Duncan's multiple range test ( a = 0.01) was used to determine whether significant differences occurred (22). A two-way ANOVA ( a = 0.01) was used to compare the differences between SO2 and TRC-SO2 (dechlorination) for each life stage.
Results The cumulative mean percent mortality of striped bass eggs exposed to TRC, SO*, and TRC-SO2 conditions is summarized in Table I. Statistical analysis of the striped bass egg data after 36 h of exposure to TRC, S02, and TRC-SO2 conditions is shown in Table 11. All concentrations of TRC caused 100% mortality to the eggs after 36 h of continuous exposure; less mortality occurred at the shorter time intervals (see Table I). Sulfur dioxide concentrations caused an effect on the eggs after 36 h, as shown by the one-way ANOVA in Table 11; however, the mortality did not increase with concentrations of SOP. Results from the dechlorination tests with the eggs indicate that an effect was present after 36 h although the mean mortality for all test concentrations was only 11% greater than the controls. Minimal mortality (51%) occurred after 4 h of exposure a t any concentration (Table I). No difference was found between the dechlorination (TRC-S02) and
Table 1. Cumulative Mean Percent Mortality of Striped Bass Eggs Exposed to Triplicate Control, TRC, SO2, and TRC-SO2 Dechlorination Conditions a mortality observation periods, h
concn, 0
1
2
0.00
0
0.06 0.25 0.50
0 0 0 0
0 0 0 0 0
1.00 2.00
0 0
0 0
0 0 0 1 1 3
SO2 0.00
0
0
0
1
0
0
0
0
1.00
0 0 0 0
0 1 1 0
0 1 1 0
0 1 1 0
1 0 0 1 1 0
2.00
0
0
0
0
0
mg/L
4
8
12
16
20
0.13
0.06 0.13 0.25 0.50
4
1
1
1
1
3
3
6
0
1
4
4
15
58
100
0 3 3
0 3 4 57 59
5
37
17
31
69 60
100 100
100 100
5
9
16
61
100
100
100
100
100
100
100
100
100
100
100
100
100
1 0 0 1 1 1 0
1 0 0 1 1 1 0
3
3
6
4
8 1 1
4
7 1 1
5 7
6
4
13
21
3
6
4
8
8 1 3 7 8
TRC-SO2
0.00
0
0
0
1
1
1
1
3
Mortality observations of eggs in all studies were recorded a t 0, 1,2,4,8,12,16,20,24,and 36 h. Mortality of larvae was assessed a t the same time intervals only extended through a 96-h period to include 48,60,72,84,and 96 h. Total residual chlorine concentrations (20) and sulfite concentrations ( 4 ) were measured amperometrically by using a Princeton Applied Research polarographic analyzer (Model 174A) every 4 h during the study. The other water-quality parameters mentioned in this section were recorded a t each mortality observation period.
0.06 0.13 0.25 0.50 1.00 2.00
0 1 0 0 0 0
0 1 0 0 0 0
0 1 0 0 0 0
0
0 1
0 1 0 3 1 3
0 1 0 3 1 3
4
Environmental Science & Technology
36
TRC
"C.
574
24
1 0 0 0 0
0
0 0 0
Fifty eggs were used in each of the triplicate tests. TRC were dechlorinated with SOPto 0.00 mg/L TRC. a
6 5 7 7 9
6 1 1 8 1 2 1 1 1 8 13 19 9 1 7 13 22
All concentrations of
SO2 conditions for this developmental stage (Table 111).The concentration of both of these treatments did not cause significantly different mortality to the test organisms. The cumulative mean percent mortality of striped bass larvae exposed to TRC, S02, and TRC-SO2 conditions is summarized in Table IV. The analysis of the larvae data after exposure to all test conditions is shown in Table V. Total residual chlorine concentrations of 0.06 mg/L caused 75% mortality after 96 h; 100% mortality occurred at all of the higher concentrations. Examination of data in Table IV shows that 100%mortality occurred a t TRC concentrations greater than or equal to 0.25 mg/L TRC after 4 h of exposure. Striped bass larvae were affected by SO2 conditions after 96 h of continuous exposure (Table V); however, mean mortality at all test concentrations was only 20% higher than the controls. No mortality occurred to larvae exposed to SO2 for 4 h or less (Table IV). Dechlorination tests with the larvae indicated an
effect after 96 h of exposure; however, the mean mortality a t all concentrations was only 22% higher than the controls. Examination of these data at various exposure periods shows less than 8%mortality after 20 h and 0% mortality after 4 h or less. There was no significant difference between SO2 and TRC-SO2 for striped bass larvae (Table 111); no significant difference was found for concentration at each treatment.
Discussion Total Residual Chlorine Toxicity. Middaugh et al. (23) reported 0, 3.5, and 23% hatch for striped bass eggs continuously exposed for -40 h to 0.21,0.07, and 0.01 mg/L TRC, respectively. We found 0%hatch (100%mortality) for striped bass eggs exposed to TRC concentrations ranging from 0.06 to 2.00 mg/L after 36 h of continuous exposure. Results from the Middaugh et al. (23) study and our investigation are
Table II. One-way ANOVA and Duncan’s Multiple Range Test for Percent Mortality of Striped Bass Eggs Exposed to TRC, SO2, and TRC-SO2 Conditions
6 14 20
concn error cor
One-way ANOVA-TRC sum of squares mean square
DF
source
total
4.5185 0.0036 4.5220
F value
0.7530 0.0002
2885.25
PR
>F
0.0001
Duncan’s Multiple Range Tests-TRC
-
0.13
0.00 6.0%
concn mean a
~00.0%
6 14 20
concn error cor total
0.25 100.0%
0.50 100.0%
One-way ANOVA-SO2 sum of squares mean square
DF
source
0.06 100.0%
0.1126 0.0676 0.1 a03
0.0187 0.0048
2.00 100.0%
1 .oo 100.0%
>F
F value
PR
3.89
0.01
Duncan’s Multlple Range Test-SO2
0.00 6.0 %
concn mean a source
0.25
1 .oo
8.0%
8.0%
concn
0.50 12.7%
One-Wav ANOVA-TRC-SOg sum of squares mean square
DF
6 14 20
error cor total
0.13 10.7%
0.1283 0.0569 0.1853
0.06 14.7% F value
5.26
0.0213 0.0040
2.00 21.3% PR
>F
0.0050
Duncan’s Multlple Range Test-TRC-SO2
concn
0.00
mean a
6.0%
a
0.06 10.7% . .
1.oo
0.13 12,0%,
0.25 18.0%
17.3%
0.50 19.3%
2.00 22.0%
These values represent the mean % mortality at each concentration after 36 h; transformed values were used in the analysis.
Table 111. Two-way ANOVA Comparing SO2 and TRC-SO2 Conditions with Eggs and Larvae source
DF
sum of squares
mean square
F value
PR
>F
Eggs concn chem concn X chem error cor total
5 1 5 24 35
0.0839 0.0328 0.0542 0.1173 0.2883
5 1 5 24 35
0.0341 0.0048 0.1344 0.1393 0.3127
0.0167 0.032 0.0108 0.0048
3.44 6.73 2.22
0.0175 0.0159 0.0855
0.0068 0.0048 0.2689 0.0058
1.18 0.83 4.63
0.3501 0.3721 0.0042
Larvae concn chem concn X chem error cor total
Volume 15,Number 5,May 1981
575
Table IV. Cumulative Mean Percent Mortality of Striped Bass Larvae Exposed to Triplicate Control, TRC, SO2, and TRC-SO2 Dechlorination Conditions a concn, mg/L
0
1
2
0.00 0.06 0.13
0 0 0
0
0 0
0.25 0.50
0
0
0
1.oo
0
2.00
0
0 0
mortallty observation perlods, h 16 20 24
4
0
12
0
0
0
0 0 79
0
15
0 95
0 0 100
100
100
100
100
100
100
100
100
3
73
100
100
100
100 100
100 100
100
100
100 100
100 100
100
100
100
100
100
100
100
100
100
0 0
0
0
0
0
0 1
0 3 5 1
0 5
0 2 0
0 2
1
0
48
36
60
72
04
96
5
5
16
23 100
5 33
6 47
6 75
100
100
100
100
100
100
100 100 100 100 100
TRC 0
0
1
1
2
5
2 9 100 100
100 100
100
100
100
100
100 100
000
100 100
100
100
100
100
100
100
1 9 6
2
5
6
6
18
5 20
5
10
25
28
29
7
14
14
23
33
34
3
5 8
5
16
21
23
10
15
16
17
13 11
21
23
25
21
23
25
5
5
10
13 8
5 19 18
6 21
6 21
18
19
23
26
27 31
so2 0.00 0.06 0.13
0
0
0
0
0.25
0 0
0
0
0
0
0
0
0 0
0
0
0
0
0 0 5 1 0 2 0
0 0
0 0
0 0
0 0
0 0
0.50 1.oo 2.00
0 0
5 1
6 2
3 1
4
3 1
4 1
5 1
0 1 1
0 1
1 1
2 3
3
7
3 7
5 4
5
3 7
14
7
5 9
14
15 15
25
29
0 2
4
4
4
11
13
21
26
29
3
5
7
12
14
27
32
39
0
13 9
TRC-SO2 0.00 0.06
0
0.13
0 0
0
0
0
0.25
0
0
0
0
0.50 1.oo
0
0
0
0
0
0 0
6
0
2.00
0
0
0
0
0
1 1 3 7 0 1
0
Fifty eggs were used in each of the triplicate tests.
All concentrations of TRC were dechlorinated with Sop to 0.00 mg/L TRC
Table V. One-way ANOVA and Duncan’s Multiple Range Test for Striped Bass Larvae Exposed to TRC, SO?, and TRC-S02 Conditions source
One-way ANOVA-TRC sum of squares mean square
DF
4.5963
0.7660 0.0028
concn
6
error
14
0.0402
cor total
20
4.6366
F value
PR
266.47
>F
0.0001
Duncan’s Multiple Range Test-TRC
concn mean a
- 0.00
0.06
0.13
0.25
6.0%
75.3%
100.0%
100.0%
source
0.50 100.0%
One-way ANOVA-SO2 sum of squares mean square
DF
concn
6
0.2657
error
14
0.0685
cor total
20
0.3342
0.0442 0.0048
1.oo
2.00
100.0%
100.0%
F value
9.04
PR
>F
0.0004
Duncan’s Multlple Range Test-SO2
concn mean a
-
0.50 17.3%
0.00
6.0%
source
concn
1.oo 25.3%
2.00 25.3%
One-way ANOVA-TRC-SO2 sum 01 squares mean square
DF
6 14 20
error cor total
0.25 22.7%
0.3403
0.5672
0.0707
0.0050
0.06 29.3% F value
11.22
0.13 34.0% PR
>F
0.001
0.41 11 Duncan’s Multiple Range Test-TRC-SO2
concn mean a
0.00
0.13
0.06
0.25
1.oo
6.0%
18.7%
21.3%
.
29.3 %
26.7%
These values represent the mean % mortality at each concentration after 96 h; transformed values were used in the analysis
576
EnvironmentalScience & Technology
0.50 3 1.3 yo,
2.00 39.3 %
similar, thus suggesting that continuous exposure to TRC concentrations greater than 0.06 mg/L caused excessive mortality during embryo development. Morgan and Prince ( 2 4 ) have reported 24- and 48-h LC50 values of 0.36 and 0.20-0.22 mg/L TRC, respectively, for striped bass eggs. These investigators ( 2 5 ) have also shown that TRC concentrations of 0.05 mg/L had no significant effect on the percent hatch for this species. In our investigation we found this developmental stage to be more sensitive to continuous TRC exposure. The difference in sensitivity for striped bass eggs reported by Morgan and Prince ( 2 4 , 2 5 )and the results in our study may be related to the water-quality conditions present during each respective investigation since basic water-quality conditions can ultimately affect chlorine toxicity (26). Burton et al. ( 2 7 , 2 8 ) conducted chlorine (0.00, 0.15, and 0.30 mg/L TRC), AT (2,6, and 10 "C), and exposure duration (0.08, 2 , and 4 h) interaction studies with striped bass eggs. These investigators reported that TRC and exposure duration were the predominant factors that caused mortality to striped bass eggs. Although the study designs by Burton et al. (27,28) were different from those of the present study, isolated exposures of 0.30 mg/L TRC caused -84% mortality after 4 h of continuous exposure in the Burton et al. studies ( 2 7 , 2 8 ) while 100%mortality occurred a t 36 h in the present investigation. Previous investigators have reported a 48-h LC50 of 0.07 mg/L TRC for 12-day old striped bass larvae continuously exposed to TRC ( 2 3 ) . Although we did not calculate LC50 values in our investigation, it appears that similar mortality exists at approximately the same concentration. Morgan and Prince ( 2 4 )reported a 24-h LC50 value of 0.19 mg/L TRC for 70-h old striped bass prolarvae after continuous chlorine exposure. Larvae tested in our study were found to be more sensitive. This difference in sensitivity may be related to the water-quality conditions present during each respective investigation or the age of the test organisms. We have shown in this study that both striped bass eggs and larvae continuously exposed to TRC concentrations above 0.06 mg/L for 36 and 96 h, respectively, exhibited high mortality. Striped bass larvae had 100%mortality after a 4-h exposure to TRC concentrations greater than or equal to 0.25 mg/L (Table IV). If one assumes that larvae may be exposed to chlorinated effluent for a period of 4 h or less, TRC concentrations should be reduced below 0.25 mg/L in order to reduce effects on the larval stage of this recreationally and commercially important fish. Sulfur Dioxide Toxicity. In previous freshwater studies, Arthur et al. ( 4 ) reported 7-day LC50 values of 67.0 and 10.0 mg/L residual sulfite for fathead minnows (Pirnephales promelas) and amphipods (Gammarus pseudolimnaeus) respectively. These investigators reported that residual sulfite concentrations used to neutralize secondary domestic sewage effluent dissipated readily and had no measurable effect on the test species. Sulfur dioxide concentrations used in our study did have an effect on striped bass eggs after 36 h (Table IV); however, the mortality did not increase with concentration of SO2 and the average mean mortality at all concentrations was only 7% higher than the controls. Larvae subjected to SO2 had higher mortality than the controls at 96 h even though the average mortality for all test concentrations was less than 26%. Although different types of water were used in our study (estuarine) and the Arthur et al. study ( 4 ) (freshwater), it appears in both cases that the concentrations of SO2 used for dechlorination would have minimal effect on the test organisms. Ward and DeGraeve ( 6 )reported that 14 species of freshwater fish exhibited little mortality after 96 h of continuous exposure with sulfite residuals ranging from 0.00 to 1.94 mg/L.
The few mortalities that did occur in these tests were partially attributed to depressed oxygen concentrations. The minimal mortalities that we found for striped bass eggs and larvae are similar to the results of Ward and DeGraeve (6);however, low dissolved-oxygen concentrations were not a factor. It appears from these studies that the tolerance of the test organisms is adequate to prevent death from concentrations of residual sulfite which might be expected in waters receiving dechlorinated discharges. Beeton et al. (8) reported that the dechlorinating agent sodium sulfite was not toxic to the freshwater invertebrates Cyclops bicuspidatus thornasi or Keratella cochlearis when continuously exposed for 96 h at 0.637 mg/L and 4 h at 0.821 mg/L. These authors concluded that sodium sulfite was not toxic a t concentrations sufficient to reduce chlorine residual observed in chlorinated sewage in the Lake Michigan study area. The present study indicates that sulfur dioxide is similar in an estuarine system. Our results and those of other investigators suggest that SO2 concentrations associated with most utility dechlorination operations are relatively nontoxic to several aquatic organisms in both estuarine and freshwater systems. We found no significant differences in toxicity between concentrations of SO2 ranging from 0.06 to 2.0 mg/L sulfite; therefore, facilities that may use excessive amounts of SO2 for dechlorination purposes would probably cause minimal effects to striped bass eggs and larvae in the discharge if sulfite residuals were below 2.0 mg/L. Striped bass ichthyoplankton exposed to SO2 conditions up to 2.0 mg/L would experience minimal mortality (
