Potassium thiosulphate

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

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: Guideline study with acceptable restrictions, no analytical dose verification

Justification for type of information:

see attachment “Read-across concept – Human Health/Environment - Category approach for Inorganic sulfites/thiosulfates/dithionite" in section 13.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Version / remarks:

Cited as EEC Guideline XI/681/86, Draft 4

Principles of method if other than guideline:

The chronic toxicity to the water flea Daphnia magna STRAUS was investigated in a 21 day semistatic test according to EEC Guideline XI/681/86, Draft 4, "Prolonged toxicity study with Daphnia magna: effects on reproduction".

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

- At the beginning of the test and before changing the test solutions a stock solution of the test substance was freshly prepared. A defined amount of the substance was weighed out and suspended directly in the test medium by stirring.
- The nominal concentration of the stock solutions was 100 mg/L.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Source: The clone of Daphnia magna STRAUS used was supplied by Institut National de Recherche Chimique Appliquée, France, in 1978. The daphnids are cultured under standard conditions in the laboratory of ecotoxicology, BASF AG, "Ludwigshafen".
- Age of parental stock: 2-4 weeks
- Age of the animals at the start of the test: 2 -24 h
- Culture conditions: The daphnid tests are performed under the same environmental conditions as the culture itself.
- Feeding during test: During the test daphnids were fed live green algae (Scenedesmus subspicatus, cultured in a synthetic medium) daily. The algae were separated from culture medium by centrifugation, resuspended in daphnid's medium (M4) and daphnids were fed this- concentrate. The algae were stored in a refrigerator (dark, about 4°C) for 8 days (in general, maximum storage for up to 14 days). Through feeding the concentrate (maximum: 0.3 mL/50 mL test solution/day) the test solution was diluted in the worst case (Friday-Monday, 3 feedings) by 0.9 mL (= 1.8%).

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Hardness:

2.2-3.2 mmol/L

Test temperature:

20±2°C

pH:

7.5-8.0

Dissolved oxygen:

> 7 mg/l

Nominal and measured concentrations:

0, 1, 5, 10 mg/l (nominal)

Details on test conditions:

TEST SYSTEM
- Test vessel: Numbered glass beakers, nominal volume 100 mL, covered with numbered glass caps
- Fill volume: 50 mL
- Renewal of test solution: three times per week
- No. of organisms per vessel: 1 parent animal
- No. of vessels per concentration (replicates): 10
- No. of vessels per control (replicates): 10

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: synthetic medium M4
- This synthetic medium has the following properties:
Total hardness 2.20 - 3.20 mmol/L
Alkalinity up to pH 4.3: 0.80 - 100 mmol/L
Molar ratio Ca/Mg: about 4:1
pH value: 7.5-8.5
Conductivity : 550 - 650 µS/cm

OTHER TEST CONDITIONS
- Photoperiod: Artificial Iight, day/night-rhythm = 16 / 8 hours
- Light intensity: About 5 - 6 µE/(m2xS) in the range of 400 - 700 nm

EFFECT PARAMETERS MEASURED
- Reproduction and mortality, daily observation intervals

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

> 10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: reproduction rate and mortality

Duration:

21 d

Dose descriptor:

other: LC0

Effect conc.:

> 10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Conc. (mg/L)	Survival parent animals (%)	Live young / live parent animal (%)
0	100	108.3
1	100	105.0
5	100	119.2
10	90	107.7

Validity criteria fulfilled:

yes

Remarks:

In the control : - mortality of parent animals up to the end of the test was < 10%. - the mean number of live young per parent animal, which survived the test, was > 60. - the coefficient of variation of the mean number of live young per parent animal, wh

Conclusions:

A chronic invertebrate toxicity test was conducted with the cladoceran D.magna, using sodium disulfite as test compound. A NOEC of >10 mg test item/L was derived and this data point can be used for hazard/effects asessment purposes for sodium disulfite and other sulfite compounds (read-across principles)

Description of key information

An effect of disodium disulfite on the reproduction and mortality ofDaphnia magnawas not observed in a 21-d chronic reproduction test (21 d NOEC ≥ 8.41 mg SO32-/L), indicating that sulfite/disulfite substances are not chronically toxic to freshwater invertebrates. Furthermore, potassium as essential element has a very low potential for toxicity to aquatic invertebrates. Based on read-across to thiosulfate/sulfite/disulfite substances and soluble potassium substances and taking into account ubiquitousness and essentiality of potassium and sulfur, the potential of potassium thiosulfate for chronic toxicity to aquatic invertebrates is expected to be low.

Additional information

Studies on the long-term toxicity of potassium thiosulfate to aquatic invertebrates are not available, and thus, read-across to thiosulfate and sulfite/disulfite substances is applied. Upon contact with water, salts of sulfur oxyacids including potassium thiosulfate dissociate into sulfur oxyacid anions and the respective counterions. Only the properties of the thiosulfate anion are considered a relevant determinant of environmental toxicity since potassium cations are essential and have a very low potential for chronic toxicity to freshwater and marine invertebrates. Please refer to the respective endpoint summary for potassium (K) for further details.Thiosulfate anions are unstable under environmentally relevant conditions, will disproportionate to sulfite and will further be oxidized to sulfate or reduced to sulfide.

 

Thiosulfate and sulfite/disulfite substances –Long-term toxicity to aquatic invertebrates

In a reliable key study (BASF, 1990) on the chronic toxicity of disodium disulfite (Na2S2O5) to the cladoceran Daphnia magna, an unbounded 21 d-NOEC ≥ 10 mg/L was derived for reproduction and mortality, corresponding to ≥ 8.41 mg SO32-/L. Physico-chemical properties of the test media were monitored during the test, and pH (7.5-8.0) and oxygen content (>7 mg/L) met respective validity criteria.