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Short-term toxicity to aquatic invertebrates

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Description of key information

The 48-h EC50 value is 0.15 mg/L for aquatic invertebrates.   

Key value for chemical safety assessment

Additional information

No data on aquatic toxicity is available for sodium 2 -mercaptoethanolate (target chemical). Read across can however be made to 2- mecaptoethanol (CAS 60 -24 -2). The (sodium) 2-mercapthoethanolate ion is a conjugated base, the read across substance 2-mercaptoethanol its undissociated acid. With a pKa value of ca. 9.5 for both substances, in an aqueous environment with pH 7, they will be present almost exclusively as 2-mercaptoethanol. Further, no effects on aqueous toxicity from the sodium cation is to be expected

Reliable data on the toxicity of 2 -mercaptoethanol to aquatic invertebrates is available from two different sources.

The first one is a report of the Japanese authorities (National Institute of Technology and Evaluation (NITE; former MITI)) of 2010. In this OECD 202 study the toxicity of 2- mercaptoethanol to aquatic invertebrates is examined in a 48 -h static test. Although the used test organisms is not specified, normally in invertebrate toxicity studies performed by the Japanese Authorities Daphnids (D. magna) are used. The 48-h EC50 is reported to be 0.12 mg/L. After correction for molecular weight difference (for read-across) the 48 -h EC50 is 0.15 mg/L.

In the second study, the acute toxicity of Mollescal SF to aquatic invertebrates was determined in a study according to OECD guideline No 202 and in compliance with GLP criteria (BASF, 2008). In this study daphnids (D. magna, 20 per concentration) were exposed to nominal test substance concentrations of 0 (control), 0.22, 0.5, 1.0, 2.2, 5, 10, 22, 50 and 100 mg/L for 48 hours under static conditions. Analytical confirmation of nominal test concentrations showed that all test concentrations remained well within ±20% of nominal concentrations throughout the test. Therefore, effect concentrations are expressed as nominal. Immobilization was recorded after 24 and 48 hours exposure. No immobilization was observed up to the 0.5 mg/L test groups. At test concentrations of 1 to 5 mg/L a steep increase to 90% immobility was seen which remained relatively stable at higher test concentrations. At 100 mg/L immobility was 100%. Based on these findings the 48-h EC50 value was determined at 2.72 mg/L. After correction for molecular weight difference (for read-across) and purity (49.9%) the 48-h EC50 is 1.74 mg/L.

The NITE study (2010) is considered as key study as it provides the lowest effect concentration for aquatic invertebrates.