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Toxicity to microorganisms

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Description of key information

The inhibition of the degradation activity of activated sludge is not anticipated when introduced in appropriate low concentrations.

Key value for chemical safety assessment

Additional information

Reaction mass of bis(2-hydroxyethanaminium) sulfite and 2-(methylamino)ethanol - oxosulfane oxide (1:1) is soluble in water and dissociates to 2 -(methylamino)ethanol, (2- hydroxyethyl)ammonium and sulphite ions.

Since no studies on the aquatic toxicity of the substance are available, study reports and published literature about the toxic effects of its dissociation products have been consulted alternatively.

In a short-term respiration test with 2-aminoethanol (CAS 141-43-5) an EC10 of > 1000 mg/L was determined [BASF AG, 1991]. Klecka et al. conducted an OECD guideline study and exposed domestic activated sludge to the test substance which resulted in an IC50 of > 1000 mg/L. In a P. putida growth inhibition test performed by Huels AG in 1996 an EC10 of 90 mg/L and an EC50 of 110 mg/L were determined.

As key study concerning acute toxicity of 2 -(methylammino)ethanol (CAS 109 -83 -1) to microorganisms a test performed by BASF (1993) according to OECD TG 209 was identified, using domestic activated sludge as inoculum. In the static test an EC20 >1000 mg/l after 30 minutes of exposure was calculated.

A respiration inhibition test was conducted with the read-across substance sodium sulfite Na2SO3 (CAS 7757-83-7) according to OECD guideline 209 [ECT 2010]. No respiratory effects were noticed at 1000 mg Na2SO3/L. Thus, the NOEC expressed as SO32- was equal to (or higher than) 634.4 mg/L.

Supporting growth inhibition tests with the bacteria Pseudomonas putida were conducted with three different sulphite compounds: potassium sulphite K2SO3(CAS 10117-38-1), disodium disulphite Na2S2O5(CAS 7681-57-4) and dipotassium disulphite K2S2O5(CAS 16731-55-8) [BASF AG, 1988]. At test termination after 17 hours, results show EC10 values ranging from 23.1 - 77.4 mg SO32-/L. As the respiration inhibition test with activated sludge is a more relevant test design for evaluating effects of a substance on microorganisms, and taking into account that the ECT-study was conducted as GLP-compliant OECD guideline study, these data (i.e. NOEC >= 634.4 mg/L) are put forward for the effects assessment of sulphite/disulphite compounds towards microorganisms.