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Ecotoxicological information

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Description of key information

Studies on the aquatic toxicity of dipotassium disulfite are only available for fish (acute toxicity). Thus, read-across to sulfite/disulfite and thiosulfate substances is applied.Upon contact with water, salts of sulfur oxyacids including dipotassium disulfite dissociate into sulfur oxyacid anions and the respective counterions. Only the properties of the sulfite anion are considered a relevant determinant of environmental toxicity since potassium cations are essential element and have a very low potential for toxicity to freshwater and saltwater organisms. Please refer to the respective endpoint summary for potassium (K) for further details.

Acute toxicity studies with sulfite/disulfite and thiosulfate substances are available for three trophic levels. In studies in with controlled oxygen concentrations and pH, acute toxicity for all three trophic levels (freshwater fish and algae and freshwater and marine invertebrates) is only observed at concentrations above the respective OECD test limit of 100 mg/L.

Chronic toxicity studies with sulfite/disulfite and thiosulfate substances are available for three trophic levels. In studies in with controlled oxygen concentrations and pH, effect values are unbounded (D. rerio, D. magna, P. subcapitata) or above the chronic OECD test limit of 10 mg/L (D. subspicatus, C. vulgaris, C. reinhardtii).

Effects of sulfite and thiosulfate substances on the respiration of activated sludge were not observed at the OECD test limit of 1000 mg/L, respectively.

It is thus concluded that sulfite/disulfite and thiosulfate substances, including dipotassium disulfite, are not toxic to freshwater fish, invertebrates, algae and microorganisms.

Additional information

Sulfite/disulfite and thiosulfate substances -Summary of acute toxicity data

Reliable acute toxicity data are available for several aquatic freshwater species covering three trophic levels (primary producers, primary and secondary consumers) and one saltwater species (invertebrates). The Table below provides an overview of the effect values for the acute toxicity of sulfite/disulfite and thiosulfate substances applied in a weight of evidence approach.

 

Table: Overview of reliable acute toxicity data for sulfite/disulfite and thiosulfate substances

Species

Parameter

Endpoint

EC [mg SO32-/L]

Observed interference

Test substance

Reference

Oncorhynchus mykiss

mortality

96 h LC50

149.6

pH decrease*

disodium disulfite

BASF, 1981

Leuciscus idus

mortality

96 h LC50

200.5

oxygen depletion**

sodium sulfite

BASF, 1989

Leuciscus idus

mortality

96 h LC50

159.7

oxygen depletion**

potassium sulfite

BASF, 1989

Danio rerio

mortality

96 h LC50

490

oxygen depletion**

dipotassium disulfite

BASF, 1995

Lepomis macrochirus

mortality

96 h LC50

275.5

oxygen depletion**

ammonium thiosulfate

Springborn Binomics Inc, 1986

Oncorhynchus mykiss

mortality

96 h LC50

416

oxygen depletion**

ammonium thiosulfate

Springborn Binomics Inc, 1986

Daphnia magna

mobility

48 h EC50

74.9

oxygen depletion**

disodium disulfite

BASF, 1990

Daphnia magna

mobility

48 h EC50

124.2

none

ammonium thiosulfate

Springborn Binomics Inc, 1986

Mysidopsis bahia

mortality

96 h LC50

41.6

oxygen depletion**

ammonium thiosulfate

Springborn Binomics Inc, 1994

Desmodesmus subspicatus

growth rate

72 h EC50

36.8

pH decrease*

disodium disulfite

BASF, 1989

Pseudokirchneriella subcapitata

growth rate

72 h EC50

>54

none

ammonium thiosulfate

ECT, 2010

*pH decrease: solution pH at “toxic” test concentrations is outside OECD test criteria

**oxygen depletion: oxygen concentration of medium at “toxic” test concentrations is outside OECD test criteria

 

Acute effect concentrations (EC/LC50s) are i) unbounded, ii) above the test limit of 100 mg/L as defined in the respective OECD guideline (OECD 201, 202, 203), and/or iii) presumably caused by to oxygen depletion and/or a pH decrease and do not represent the intrinsic toxicity of sulfite/disulfite and thiosulfate substances.

In studies in with controlled oxygen concentrations and pH, acute toxicity at all three trophic levels is only observed at concentrations above the respective OECD test limit of 100 mg/L. Thus, it may be assumed that the “substance-specific” EC/LC50 of sulfite substances for freshwater fish and algae and freshwater and marine invertebrates is higher than the EC50/LC50s derived in studies applying a test system with a limited buffering capacity for oxygen concentrations and pH.

It is thus concluded that sulfite/disulfite and thiosulfate substances, including dipotassium disulfite, are not acutely toxic to freshwater fish and algae and freshwater and marine invertebrates.Nevertheless, confirmatory studies on the acute effects of disodium disulfite to Daphnia magna and Raphidocelis subcapitata according to OECD 202 and OECD 201, respectively, with appropriate aeration and buffering of the test system are currently ongoing.

 

Sulfite/disulfite and thiosulfate substances -Summary of chronic toxicity data

 

Chronic toxicity data are available for several aquatic freshwater species covering three trophic levels (primary producers, primary and secondary consumers). The table below provides an overview of the effect values for chronic toxicity of sulfite/disulfite and thiosulfate substances.

 

Table: Overview of reliable chronic toxicity data for sulfite/disulfite and thiosulfate substances

Species

Parameter

Endpoint

EC [mg SO32-/L]

Observed interference

Test substance

Reference

Danio rerio

all (ELS)

34 d NOEC

≥ 200.5

none

sodium sulfite

ECT, 2010

Daphnia magna

reproduction, mortality

21 d NOEC

≥ 8.41

none

disodium disulfite

BASF, 1993

Desmodesmus subspicatus

growth rate

72 h EC10

28

pH decrease*

disodium disulfite

BASF, 1989

Pseudokirchneriella subcapitata

growth rate

72 h NOEC

≥ 54

none

ammonium thiosulfate

ECT, 2010

 *pH decrease: solution pH at “toxic” test concentrations is outside OECD test criteria

**oxygen depletion: oxygen concentration of medium at “toxic” test concentrations is outside OECD test criteria

 

Chronic effect values are i) unbounded, without effects at the highest test concentration (D. rerio, D. magna, P. subcapitata) or ii) above the chronic OECD test limit of 10 mg/L (D. subspicatus).

It is thus concluded that sulfite/disulfite and thiosulfate substances, including dipotassium disulfite, are not chronically toxic to freshwater fish, invertebrates and algae.

 

Toxicity to STP microorganisms

 

Regarding the toxicity to microorganisms, reliable studies of the respiration inhibition of activated sludge and supporting studies of the growth inhibition of Pseudomonas putida are available (see Table below).

 

Table: Overview of reliable toxicity data to microorganisms for sulfite/disulfite and thiosulfate substances

Species

Parameter

Endpoint

EC [mg SO32-/L]

Test substance

Reference

Activated sludge

respiration inhibition

3 h EC50

3 h NOEC

> 634.4

≥ 634.4

sodium sulfite

ECT, 2010

Activated sludge

respiration inhibition

3 h EC50

3 h NOEC

> 540.2

≥ 540.2

ammonium thiosulfate

ECT, 2010

Pseudomonas putida

growth inhibition

17 h EC50

17 h EC10

47.2

25.9

disodium disulfite

BASF, 1988a

Pseudomonas putida

growth inhibition

17 h EC50

17 h EC10

207.2

77.3

potassium sulfite

BASF, 1988b

Pseudomonas putida

growth inhibition

17 h EC50

17 h EC10

65.8

23

potassium disulfite

BASF, 1988c

 

The hazard assessment is based on effect concentrations for the respiration inhibition of activated sludge in accordance with ECHA guidance on IR & CSA, Chapter 7b (Version 4.0, 2017).

Effects on the respiration of activated sludge were not observed at the OECD test limit of 1000 mg/L in studies with sodium sulfite and ammonium thiosulfate, respectively.

It is thus concluded that sulfite/disulfite and thiosulfate substances, including dipotassium disulfite, are not toxic to aquatic microorganisms.