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Long-term toxicity to fish

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Endpoint:
fish early-life stage toxicity
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: OECD 210 Guideline test, conducted under GLP
Justification for type of information:
see attachment “Read-across concept – Human Health/Environment - Category approach for Inorganic sulfites/thiosulfates/dithionite" in section 13.
Qualifier:
according to guideline
Guideline:
OECD Guideline 210 (Fish, Early-Life Stage Toxicity Test)
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Details on test solutions:
The stock solution was prepared once per week by dissolving 10.428 g of the test item (nominal; actually weighed amounts: 10.4284 to 10.432 g) in 3 L of dilution water (reconstituted water) using a 3 L graduated flask. This stock solution (S1, 3476 mg/L) was stirred for 1 min. Immediately thereafter, the stock solution was used to prepare the test solutions.
The test solutions were delivered directly from the tanks to the designated test vessels using teflon tubing and a multi-channel peristaltic pump set to deliver the desired volume per day. During dosing into the flow-through system (between renewals), the test solutions were stored at room temperature in the dark. During storage, the tanks were closed with a lid to reduce air-exchange and evaporation.
Test organisms (species):
Danio rerio (previous name: Brachydanio rerio)
Details on test organisms:
Danio rerio Hamilton-Buchanan 1822 (Zebrafish). Fertilised eggs were collected from adult zebrafish from in-house cultures, which have been maintained and bred at ECT since May 2004.
In the culture tanks, the fish were kept in reconstituted water (OECD guideline 203, 1992) supplemented with 1% of artificial seawater (Tropic Marin, Dr. Biener GmbH Aquarientechnik, Wartenberg, Germany; salinity 28 ‰ ± 2 ‰). Fish were held in glass aquaria with internal ceramic filters at 26°C ± 2°C with a 12 h/12 h photoperiod. They were fed a combined diet of newly hatched nauplii of Artemia sp. (Sanders Brine Shrimp Co., Morgan, UT 84050, U.S.A.) and TetraMin (Tetra Werke, Melle, Germany).

On the evening before test start, glass bowls covered with stainless steel mesh were introduced in the holding tanks of the adult zebra fish. Water plants (Microsorum pteropus) were placed on the mesh, allowing the fish to spawn. The spawning bowls were removed from the holding tanks on the day of test start shortly after onset of illumination, which triggers fertilization. The content of the bowls was poured over a sieve (mesh size 0.5 mm), rinsed with reconstituted water and collected in a glass vessel filled with reconstituted water. Immediately afterwards groups of 10 - 20 eggs were transferred to glass dishes containing test solution of each designated exposure vessel (acclimated at test temperature), until all dishes contained approximately 130 eggs. The dishes were placed into an incubator set to 25°C for two hours. Unfertilized and damaged eggs were removed and the number of eggs per dish was reduced to 30. Subsequently the eggs were transferred to the exposure vessels.
Test type:
flow-through
Water media type:
freshwater
Limit test:
no
Total exposure duration:
34 d
Hardness:
min: 164 mg/L as CaCO3
max: 193 mg/L as CaCO3
Test temperature:
23.8 - 25.6 degrees Celcius
pH:
min: 7.0
max: 7.5
Dissolved oxygen:
min: 5.2 mg/L (=64% of air saturation value)
max: 9.0 mg/L (108% of air saturation value)
Nominal and measured concentrations:
Nominal test concentrations: 316, 100, 31.6, 10, and 3.2 mg test item/L plus a control
Details on test conditions:
Reconstituted water according to OECD guideline No. 203 was used to dilute the test item and to keep the fish before and during the period of the test. Local tapwater was treated by reverse osmosis and ion-exchanger to prepare deionised water. Therefore a contamination with heavy metals, pesticides and TOC is excluded.

- Test medium: Reconstituted water (OECD guideline No. 203) mixed with deionised water (1:1; v/v), supplemented with 1% artificial seawater
- Biological material: Newly fertilised eggs were exposed to the test item dissolved in water in a flow-through system for 30 days post-hatch. The method of administration is in accordance with the requirements of the test guideline
- Loading: did not exceed a loading of 5 g fish/L of solution, or a loading rate of 0.5 g fish/L per 24 hours at any time of the test.
- Endpoints: ECx, NOEC, LOEC
- Biological parameters: –Hatching success: for eggs and embryos (particularly in the early stages) mortality was related to a marked loss of translucency and change in colouration, caused by coagulation and/or precipitation of protein, leading to a white opaque appearance
– Mortality (post-hatch success): immobility and/or absence of respiratory movement and/or absence of heart-beat and/or white opaque colouration of central nervous system and/or lack of reaction to mechanical stimulus.
– Body abnormalities
– Behavioural abnormalities
– Length of the surviving fish
– Dry weight of the surviving fish
- Test duration: 34 days
- Temperature: Max.: 25.5°C, Min.: 24.8°C (online measurement)
- Photoperiod: 12/12 hours light/dark cycle
- Light intensity: 281 to 600 lx
- Test units: Glass vessels, 0.5 L volume
- Dimensions of test vessels: Diameter: 14 cm, Height: 6 cm; vessels were fitted with a meshed overflow: center of outflow: 3.5 cm, diameter of outflow: 1 cm. The vessels were covered with a transparent lid to reduce air-exchange and evaporation.
- Volume of test solution per test vessel: 0.3 L (nominal).
- No. of replicates per treatment: 2
- Renewal of test solution during exposure: Permanent (flow-through)
- Flow-through test equipment (hardware): Peristaltic pump: Type Ismatec IPC 24, tubing type: TYGON ST, Ismatec, Wertheim Mohnfeld; Teflon tubing
- Flow rates: measured volumetrically at least 3 times per week. The volume measured per per time unit (2 minutes per measurement), multiplied by the number of minutes per day, results in the daily volume. Dividing the daily volume by the nominal vessel volume (0.3 L) results in the daily vessel-volume exchange rate (+/- five velles volumes per vessel and day).
- Aeration: test vessels were aerated
- Feeding: On the day after the first larva per test vessel was recorded to swim up (day 3 of exposure), feeding was started by adding food to the vessels. The test organisms were fed dry food (NovoBaby 01 and 02, Tetra), live Artemia nauplius larvae and parametia (Paramecium caudatum) ad libitum; the daily ration was fed in 3 - 4 equal portions on workdays. On weekends the daily ration was fed in 2 - 3 portions. Uneaten food was removed at least once daily. The food ration was adjusted to the number of living fish per test vessel. Food was withheld from the fish for 24 hours prior to test end.
- Dead eggs, embryos or fish were removed from the test vessels daily upon observation throughout the test.

The actual measured flow rates per treatment were within ± 20% of the mean flow rates as described above. This is higher than recommended in the test guideline, but since in this study the test solutions were not prepared by use of the flow-through system (e.g. by automatically dosing stock solution into dilution water) but by direct delivery of test solution into the test vessels, this slightly higher variation of the flow rate has no influence on the actual test concentration
Reference substance (positive control):
no
Duration:
34 d
Dose descriptor:
NOEC
Effect conc.:
>= 316 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: hatching success, mortality (post-hatch success), numbers of healthy fish, length of surviving fish, dry weight of the surviving fish
Details on results:
Validity criteria:
- 97% post-hatch success in the controls (required: 70% post-hatch success)
- Dissolved oxygen level during routine water quality analyses was 64% (or higher) of air saturation (required minimum: 60%)
- Water temperature differed ≤ 0.5 degrees Celcius) between test vessels on the same day or ≤ 1.4 °C per vessel between successive measuring days (allowed: maximum difference of 1.5 degrees Celcius between test vessels or between successive days)
- The water temperature should be within a range of 2 degrees Celcius of the desired test temperature: maximum was 26.0 degrees Celcius, minimum was 24.0 degrees Celcius (online measurement) (difference of 2 degrees Celcius); For manual measurement, the maximum was 25.6° degrees Celcius and the minimum was 23.8 degrees Celcius (difference of 2 degrees Celcius)

- In controls the hatching success was 100%. In all treatments up to the highest concentration the hatching success was above 90%.
- At test end, out of 60 introduced eggs, the final number of healthy fish in controls was 58. In the treatments the number of living, healthy fish ranged from 45 at 10 mg/L to 54 at 316 mg/L, respectively.
- All surviving fish appeared healthy at the end of exposure, i.e. behavioural or morphological abnormalities were not observed. Therefore, a separate statistical evaluation was not performed on the number of healthy fish.
- Statistically significant differences of weight were not observed between treated and control groups at p ≤ 0.05. No correlation was observed between the concentration of the test item and the dry weight of fish.
- Statistically significant differences of length were not observed between treated and control groups at p ≤ 0.05. No correlation was observed between the concentration of the test item and the length of fish.
Results with reference substance (positive control):
The following biological parameters were recorded during and/or at the end of the test:
- cumulative mortality
- numbers of healthy fish
- time to start of hatching and end of hatching
- number of larvae hatching each day
- number of deformed larvae
- number of organisms exhibiting abnormal behaviour
- length and weight of surviving fish

The following biological parameters were evaluated from a biological point of view:
- time to start of hatching and end of hatching
- number of larvae hatching each day
- macroscopic morphological abnormalities
- behavioural abnormalities
Reported statistics and error estimates:
The following biological parameters were evaluated statistically in comparison to the control fish where the data allowed such comparisons:
- hatching success, mortality (post-hatch success), numbers of healthy fish : Fisher's Exact Binomial Test with Bonferroni Correction
- dry weight of the surviving fish, per treatment means: Williams' test
- length of the surviving fish, per treatment means: Williams' test

Due to a lacking concentration-response relationship LCx or ECx values were not calculated. Variance homogeneity was checked with Levene´s Test. The statistical software package ToxRat 2.10 Professional (ToxRat Solutions GmbH, Naheweg 15, D-52477 Alsdorf, Germany) was used for these calculations.
Conclusions:
An OECD No.210 test was conducted, using sodium sulfite as test substance. Newly fertilised eggs of zebrafish were exposed to a series of 7 test concentrations plus a control without test item under flow-through conditions. The test was continued until 30 days after 50% of of the control fish had hatched. Lethal and sub-lethal effects on eggs, larvae and juvenile fish were assessed in comparison with control values to determine the ECx (concentration that is expected to cause an effect in x% of the animals), the lowest observed effect concentration (LOEC) and the no observed effect concentration (NOEC). No significant effects were found for any of the tested concentrations. Based on this study, an unbounded NOEC of >= 316 mg test item/L is put forward. These data can be used for the effects assessment of sodium sulfite and other (bi-)sulfite compounds (read-across principle).
Endpoint:
fish early-life stage toxicity
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Experimental phase completed. The evaluation of the chemical analyses and the preparation of the study report are currently ongoing and awaiting finalization. The study record will be updated upon receipt of the final study report.
Qualifier:
according to guideline
Guideline:
OECD Guideline 210 (Fish, Early-Life Stage Toxicity Test)
Principles of method if other than guideline:
Early-life stages of zebrafish (Danio rerio) were exposed to five concentrations of sodium dithionite and a control for 35 days under semi-static conditions, according to Annex 2 of OECD TG 210.

In order to minimize the background sulfur concentration of the test medium, the ISO medium was modified. The composition of ISO Medium is described in OECD TG 203. For conducting the FELS test, the component MgSO4 was replaced by MgCl2. A pre-test (non-GLP) was conducted to confirm that the biological performance of fish was in accordance with guideline requirements regarding hatch and post hatch survival. In this pre-test, 20 eggs each were placed in four test beakers containing the modified ISO medium. Hatch was complete in all beakers, and the mean post hatch survival was calculated to be 78.8%. Thus, both quality criterions were fulfilled.

- Parameters analysed/observed: Hatching success, post-hatch survival, wet- and dry weight, body length.
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 0 (control), 0.1, 0.32, 1.0, 3.2, 10 mg sodium dithionite/L
- Sampling method: Samples were filtered to remove any particulate matter and immediately stabilized with formaldehyde.
- Sample storage conditions before analysis: Samples were measured immediately within 24 h after sampling or were stored at -18 °C until analysis.
- Sampling regime, see any other information.
Vehicle:
no
Details on test solutions:
During a pre-test (non-GLP), a decomposition of the test item in the aqueous medium was observed.Sodium dithionitet dissociates into dithionite anions and sodium cations in solution. Dithionite anions are unstable and rapidly disproportionate to (bi-)sulfites (HSO3- / SO3-), thiosulfates (S2O32-) and sulfates. Under aerobic conditions, oxiddised decomposition products are sulfate and sulfite. To prevent the conversion to sulfate and sulfite in the stock solution, it was prepared under an argon atmosphere. Subsequently, the application solutions of appropriate concentrations were prepared by dilution of the stock solution. One application solution was prepared for each test beaker. The respective stock and application solutions containing the test item were prepared freshly on the application day under an argon atmosphere. The test medium, i.e. the modified ISO medium, was equilibrated before by heating to the target water temperature and gentle aeration.
Test organisms (species):
Danio rerio (previous name: Brachydanio rerio)
Details on test organisms:
TEST ORGANISM
- Common name: Zebrafish
- Source: Test facility bred, originally obtained from West Aquarium GmbH, 37431 Bad Lauterberg, Germany
- Age at study initiation: eggs, early blastula stage (four cell stage)

METHOD FOR PREPARATION AND COLLECTION OF FERTILIZED EGGS
- Method of collection of fertilised eggs: Eggs will be collected in a glass spawning-tray, which will be placed at the bottom of the holding vessels. The tray will be covered with a stainless steel lattice to prevent adult fish from predating the eggs. An artificial substrate will be attached to the lattice to stimulate spawning into the tray.
- Subsequent handling of eggs: The collected eggs will be transferred from the spawning-tray into a sieve, rinsed with clean water in order to remove any debris and then put into glass dishes. Fertilized eggs will then be transferred by means of a widened and de-burred pipette tip into the test chambers. Time from spawning until transferring into the test solutions will be kept as short as possible.

POST-HATCH FEEDING
- When hatch is finished, e.g. from day 5 dpf on (dpf = days post fertilization), larvae will be fed at least twice daily with ground breeding food (TetraMin Baby, Tetra Werke, Melle, Germany). Drops of liquid rearing feed will be added thrice a day. From approximately day 14 (dpf) on, brine shrimp nauplii (Artemia salina) will be added to the daily feed, instead of the liquid feed. Ground breeding food will be added twice a day.
Test type:
semi-static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
35 d
Test temperature:
25.7 - 26.7 °C (Min-Max)
pH:
7.75 - 7.86 in fresh test media; 7.72 - 7.80 in aged test media
Dissolved oxygen:
94% - 95% average O2 saturation in fresh application solution; 88% - 89% average O2 saturation in aged application solution
Salinity:
-
Nominal and measured concentrations:
Nominal: 0 (control), 0.1, 0.32, 1.0, 3.2, 10 mg sodium dithionite/L
Assessment of analytical data ongoing
Details on test conditions:
TEST SYSTEM
- Emybro cups: fry chamber
- Test vessel: Glass aquaria with a total volume of 3 L
- Fill volume: 2 L
- Renewal rate of test solution (frequency/flow rate): 3 times per week
- No. of fertilized eggs/embryos per vessel: 20
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4
- Biomass loading rate: < 5 g/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Modified ISO medium (MgSO4 is substituted by MgCl)

OTHER TEST CONDITIONS
- Photoperiod: 12:12 h light:dark
- Light intensity: 1000 lux
- The water temperature was measured each working day in all test vessels and in the control. Additionally, the water temperature was measured continuously in at least two control vessels.
Reference substance (positive control):
no
Key result
Duration:
35 d
Dose descriptor:
NOEC
Effect conc.:
>= 10 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: hatching success, post-hatch survival
Details on results:
- No effect on hatching success observed: Control (100%), 0.1 mg/L (100%), 0.32 mg/L (100%), 1 mg/L (98.8%), 3.2 mg/L (100%), 10 mg/L (100%)
- No significant effects on post-hatch survival compared to control, after 35 days: Control (86.3%), 0.1 mg/L (82.5%), 0.32 mg/L (83.8%), 1 mg/L (84.7%), 3.2 mg/L (83.8%), 10 mg/L (76.3%)
- No significant difference in fish dry weight over all concentrations, after 35 days (mean dry weight): Control (5.4 mg), 0.1 mg/L (5.0 mg), 0.32 mg/L (5.1 mg), 1 mg/L (5.0 mg), 3.2 mg/L (5.4 mg), 10 mg/L (5.7 mg)
- No significant difference in fish lenght over all concentrations, after 35 days (mean lenght): Control (14 mm), 0.1 mg/L (13 mm), 0.32 mg/L (13 mm), 1 mg/L (14 mm), 3.2 mg/L (14 mm), 10 mg/L (14 mm)

- As total sulfur concentrations of application solutions ranged within ± 20% of the nominal concentrations, the NOEC is based on nominal concentrations.

Table 1: Mean water temperatures [°C] with min and max values in each replicate throughout the test.

.

control

0.10 mg/L

0.32 mg/L

1.00 mg/L

3.20 mg/L

10.00 mg/L

replicate

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

Mean

26.5

26.4

26.4

26.4

26.4

26.4

26.4

26.4

26.4

26.4

26.3

26.3

26.5

26.4

26.4

26.4

26.4

26.3

26.4

26.4

26.4

26.4

26.4

26.3

Min

26.0

25.8

25.9

26.0

25.7

25.8

25.7

26.0

25.8

25.8

25.7

26.0

25.9

25.9

26.0

25.9

25.8

26.0

26.0

25.9

26.0

26.0

26.0

26.1

Max

26.7

26.7

26.6

26.6

26.7

26.6

26.6

26.6

26.6

26.6

26.6

26.5

26.6

26.6

26.6

26.6

26.7

26.5

26.6

26.6

26.6

26.6

26.5

26.5

 

Table 2: Mean O2-saturation [%] with min and max values in each replicate in fresh and aged test media.

.

control

0.10 mg/L

0.32 mg/L

1.00 mg/L

3.20 mg/L

10.00 mg/L

replicate

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

fresh test media

Mean

95

95

95

95

94

94

95

94

94

94

94

94

94

94

94

94

95

94

94

94

94

94

94

94

Min

92

91

92

92

92

91

93

90

92

91

90

92

92

92

92

92

92

92

93

91

91

91

91

91

Max

98

98

98

98

96

96

96

96

96

97

97

97

96

97

97

97

97

96

97

97

97

97

96

96

aged test media

Mean

89

89

89

88

89

89

89

89

89

89

89

89

89

88

88

89

89

88

88

88

88

88

88

88

Min

85

86

86

83

86

86

85

85

85

85

83

85

85

82

84

84

85

85

83

81

84

84

83

84

Max

93

93

92

92

92

92

91

93

93

92

92

92

94

93

93

93

93

92

93

92

91

92

92

91

 

Table 3: Mean pH values with min and max values in each replicate in fresh and aged test media throughout the test.

.

control

0.10 mg/L

0.32 mg/L

1.00 mg/L

3.20 mg/L

10.00 mg/L

replicate

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

A

B

C

D

fresh test media

Mean

7.86

7.86

7.86

7.86

7.85

7.85

7.86

7.85

7.84

7.84

7.84

7.85

7.85

7.83

7.83

7.83

7.82

7.82

7.81

7.81

7.77

7.75

7.75

7.75

Min

7.8

7.8

7.8

7.8

7.8

7.8

7.8

7.8

7.8

7.8

7.8

7.8

7.7

7.8

7.7

7.7

7.7

7.7

7.7

7.7

7.7

7.6

7.6

7.6

Max

8.0

8.0

8.0

8.0

8.0

8.0

8.0

8.0

8.0

8.0

8.0

8.0

8.0

8.0

7.9

8.0

7.9

7.9

7.9

7.9

7.9

7.8

7.9

7.9

aged test media

Mean

7.79

7.80

7.80

7.77

7.80

7.80

7.80

7.80

7.78

7.79

7.78

7.79

7.80

7.76

7.77

7.78

7.78

7.77

7.76

7.76

7.74

7.72

7.72

7.72

Min

7.6

7.7

7.7

7.7

7.7

7.7

7.6

7.6

7.6

7.6

7.6

7.6

7.7

7.5

7.6

7.7

7.7

7.7

7.6

7.6

7.5

7.6

7.5

7.6

Max

7.9

7.9

7.9

7.9

7.9

7.9

7.9

7.9

7.9

7.9

7.9

7.9

7.9

7.8

7.9

7.9

7.9

7.9

7.8

7.9

7.9

7.8

7.8

7.8

 

Table 4: Hatching success at 5 dpf [%] with mean values and standard deviation (SD) in each replicate.

.

replicate

Control

0.10 mg/L

0.32 mg/L

1.00 mg/L

3.20 mg/L

10.00 mg/L

Hatched larvae 5 dpf [%]

A

100

100

100

100

100

100

B

100

100

100

100

100

100

C

100

100

100

95.0

100

100

D

100

100

100

100

100

100

Mean

100

100

100

98.8

100

100

SD

0.0

0.0

0.0

2.5

0.0

0.0

 

Table 5: Post-hatch survival at 35 dpf [%] with mean values and standard deviation (SD) in each replicate.

.

replicate

Control

0.10 mg/L

0.32 mg/L

1.00 mg/L

3.20 mg/L

10.00 mg/L

Survived, 35 dpf [%]

A

85.0

75.0

90.0

95.0

90.0

80.0

B

90.0

90.0

90.0

85.0

95.0

80.0

C

85.0

75.0

80.0

78.9

75.0

80.0

D

85.0

90.0

75.0

80.0

75.0

65.0

Mean

86.3

82.5

83.8

84.7

83.8

76.3

SD

2.5

8.7

7.5

7.3

10.3

7.5

 

 

Table 6: Group dry weight [mg] at test end (35 dpf) with mean values and standard deviation (SD) in each replicate.

.

replicate

control

0.10 mg/L

0.32 mg/L

1.00 mg/L

3.20 mg/L

10.00 mg/L

Dry weight, 35 dpf [mg]

A

5.4

5.1

4.1

4.7

4.3

5.6

B

5.7

4.7

5.0

4.9

4.8

5.0

C

5.2

5.3

5.7

5.5

6.7

6.4

D

5.4

4.8

5.6

5.0

6.0

5.9

Mean

5.4

5.0

5.1

5.0

5.4

5.7

SD

0.2

0.3

0.7

0.3

1.1

0.6

 

 

Table 7: Individual total length [mm] of fish at test end (35 dpf) with mean values and standard deviation (SD) in each replicate.

.

replicate

control

0.10 mg/L

0.32 mg/L

1.00 mg/L

3.20 mg/L

10.00 mg/L

Total length, 35 dpf [mm]

A

14

13

13

14

13

14

B

14

13

13

13

13

13

C

14

14

14

14

15

14

D

13

13

14

13

14

13

Mean

14

13

13

14

14

14

SD

0.4

0.4

0.5

0.5

0.9

0.4

Table 8: Total sulfur concentrations [mg/L] in freshly prepared application solutions at day 0 and day 33.

Nominal concentration [mg/L]

date

Total sulfur

Total sulfur (background corrected)

[mg/L

[% of nominal]

[mg/L]

[% of nominal]

control

d0, fresh

1.60

-

-

-

d33, fresh

0.070

-

-

-

20

d0, fresh

8.13

110

6.53

89

d33, fresh

7.26

99

7.19

98

64

d0, fresh

23.8

101

22.2

94

d33, fresh

22.8

97

22.8

97

200

d0, fresh

74.8

102

73.2

99

d33, fresh

69.7

95

69.6

94

640

d0, fresh

244

103

242

103

d33, fresh

235

100

235

99

2000

d0, fresh

835

113

834

113

d33, fresh

773

105

773

105

LOD, total sulfur: 0.003 mg/L; LOQ, total sulfur: 0.008 mg/L.

 

Table 9: Background corrected total sulfur concentrations [mg/L] in fresh and aged test media.

Nominal concentration [mg/L]

replicate

day 0, fresh

day 2, aged

day 21, fresh

day 23, aged

day 33, fresh

day 35, aged

[mg/L]

[%]

[mg/L]

[%]

[mg/L]

[%]

[mg/L]

[%]

[mg/L]

[%]

[mg/L]

[%]

control

A

-

-

-

-

-

-

-

-

-

-

-

-

B

-

-

-

-

-

-

-

-

-

-

-

-

C

-

-

-

-

-

-

-

-

-

-

-

-

D

-

-

-

-

-

-

-

-

-

-

-

-

0.10

A

0.048

129.5

0.026

70.2

-

-

-

-

0.068

185.6

0.040

108.0

B

-

-

-

-

0.041

111.6

0.079

213.2

-

-

-

-

C

0.054

146.4

0.026

71.5

-

-

-

-

-

-

-

-

D

-

-

-

-

0.054

147.0

0.106

288.9

-

-

-

-

0.32

A

0.191

162.2

0.095

80.8

-

-

-

-

0.140

119.0

0.101

85.3

B

-

-

-

-

0.127

107.3

0.031

26.4

-

-

-

-

C

0.162

137.5

0.086

73.4

-

-

-

-

-

-

-

-

D

-

-

-

-

0.123

104.7

0.136

115.1

-

-

-

-

1.0

A

0.287

78.0

0.337

91.6

0.385

104.5

0.283

76.9

B

-

-

-

-

0.340

92.3

0.551

149.4

-

-

-

-

C

0.392

106.5

0.362

98.2

-

-

-

-

-

-

-

-

D

-

-

-

-

0.381

103.4

0.337

91.4

-

-

-

-

3.2

A

1.231

104.4

1.037

87.9

-

-

-

-

1.156

98.0

0.999

84.7

B

-

-

-

-

1.071

90.8

1.263

107.1

-

-

-

-

C

1.462

124.0

1.076

91.3

-

-

-

-

-

-

-

-

D

-

-

-

-

1.028

87.2

1.243

105.4

-

-

-

-

10

A

7.024

190.7

3.499

95.0

-

-

-

-

3.381

91.8

3.461

94.0

B

-

-

-

-

3.417

92.8

3.490

94.7

-

-

-

-

C

3.514

95.4

3.553

96.4

-

-

-

-

-

-

-

-

D

-

-

-

-

3.666

99.5

3.911

106.2

-

-

-

-


 

 

Table 10: Summary of total sulfur concentration [mg/L] in test media presented in Table 9. The geometric mean was calculated from mean fresh and mean aged total sulfur concentrations. The percentage [%] of nominal concentrations are based on geometric mean values and a sulfur content of 37% of sodium dithionite.

Nominal concentration [mg/L]

Arithmetic mean, fresh[mg/L]

Arithmetic mean, aged[mg/L]

Geometric mean (fresh, aged)[mg/L]

% nominal concentration

0.10

0.053

0.055

0.054

147.2

0.32

0.149

0.090

0.116

98.0

1.0

0.357

0.374

0.365

99.2

3.2

1.190

1.123

1.156

98.1

10

4.200

3.583

3.879

105.3

 

Range finding test:

- In a non-GLP range finding test for the fish early-life stage toxicity test (OECD 210) with sodium dithionite, significant effects on hatching, post-hatch survival and fish length of Danio rerio were not observed up to the limit concentration of 10 mg/L after 21 days.

- Semi-static design (3 test media renewals per week), 20 eggs per vessel, 2 replicates each, 21 days exposure.

- Tested concentrations of sodium dithionite: 0 (control), 0.1, 1, 10 mg/L.

- Test temperature 25.3 - 26.7 °C, pH 7.9 - 8.3, dissolved oxygen O2 saturation >= 90 - 98 % (measured approx. two hours after substance application).

- No effect on Hatching Success (n = 20 in all treatments and control).

- Reduced Post-hatch survival, but not dose-respondent (control: 72.5%; 0.1 mg/L: 75%; 1 mg/L: 55%; 10 mg/L: 72.5%).

- Slight increase in Fish Length over concentration (control: 0.66 cm; 0.1 mg/L: 0.71 cm; 1 mg/L: 0.72 cm; 10 mg/L: 0.9 cm)

- Detection method: HPLC-ICP-MS; sulfite, sulphate, thiosulphate and total sulfur were determined.

- Detection limits (LOD, LOQ): sulfite: LOD= 0.092 (d0), 0.197 (d2), LOQ= 0.342 (d0), 0.726 (d2); sulphate: LOD= 0.122 (d0), 0.169 (d2), LOQ= 0.452 (d0), 0.623 (d2); thiosulphate: LOD= 0.136 (d0), 0.070 (d2), LOQ= 0.509 (d0), 0.265 (d2).

Validity criteria fulfilled:
yes
Remarks:
Dissolved oxygen concentration >60% & water temperature did not differ by more than ± 1.5 °C in all test chambers throughout the test; hatching success >70%, post-hatch survival in controls >75%.
Conclusions:
In a GLP fish early-life stage toxicity test (OECD TG 210) with sodium dithionite under semi-static conditions, significant effects on hatching success, post-hatch survival and fish length and weight of zebrafish (Danio rerio) were not observed up to the highest test concentration of 10 mg/L. Thus, a NOEC of ≥10 mg/L was derived for sodium dithionite. Since the evaluation of the chemical analyses and the preparation of the study report are currently ongoing, the study record will be updated upon receipt of the final study report.

Description of key information

In a GLP fish early-life stage toxicity test (OECD TG 210) with sodium dithionite under semi-static conditions, significant effects on hatching success, post-hatch survival and fish length and weight of zebrafish (Danio rerio) were not observed up to the highest test concentration of 10 mg/L. Thus, a NOEC of ≥10 mg/L was derived for sodium dithionite (Teigeler 2022).

Effects of sodium sulfite on the early life stages of zebrafish (Danio rerio) were also not observed in a GLP-OECD 210 early life stage toxicity test and a 34-d NOEC ≥ 316 mg test substance/L (i.e., ≥ 200.5 mg SO32 -/L) was derived. Furthermore, sodium as essential element has a very low potential for chronic toxicity to fish. Based on data available for sodium dithionite and read-across to thiosulfate/sulfite/disulfite substances and soluble sodium substances and taking into account ubiquitousness and essentiality of sodium and sulfur, the potential of sodium dithionite for chronic toxicity to fish is expected to be low.

Key value for chemical safety assessment

Additional information

A GLP fish early-life stage (FELS) toxicity test (OECD TG 210) with sodium dithionite documenting the lack of intrinsic toxicity is available. In addition, read-across to dithionite, thiosulfate and sulfite/disulfite and soluble sodium substances is applied. Upon contact with water, salts of sulfur oxyacids including sodium dithionite dissociate into sulfur oxyacid anions and the respective counterions. Only the properties of the dithionite anion are considered a relevant determinant of environmental toxicity since sodium cations are essential and have a very low potential for chronic toxicity to freshwater and marine fish. Please refer to the respective endpoint summary for sodium (Na) for further details. Dithionite anions are unstable under environmentally relevant conditions and will rapidly disproportionate to (bi-)sulfites and thiosulfates (S2O32-) in aqueous media.Sulfites and thiosulfates are unstable in the environment, subject to transformation processes including oxidation to sulfate or reduction to sulfide, and will ultimately become part of the natural sulfur cycle.

 

Dithionite, thiosulfate and sulfite/disulfite substances –Long-term toxicity to fish

In a 35-d fish, early-life stage toxicity test (OECD 210) with sodium dithionite, significant effects on hatching, post-hatch survival and fish length of Danio rerio were not observed up to the highest test concentration of 10 mg/L (Teigeler, 2022). In a reliable OECD TG 210 study on the effects of sodium sulfite (Na2SO3) to the early-life stages (ELS) of Danio rerio, adverse effects on number of healthy fish, hatching, post–hatch mortality, health, length and dry weight of surviving fish (Danio rerio) were also not observed. Consequently, a chronic 34-d NOEC of ≥ 316 mg Na2SO3/L, corresponding to ≥ 200.5 mg SO32-, was derived.