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Long-term toxicity to aquatic invertebrates

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Description of key information

The 21-d NOEC is 0.08 mg/L in aquatic invertebrates (D. magna).

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.

The chronic toxicity to aquatic invertebrates was examined in a study in accordance with OECD 211 and in compliance with GLP criteria (BASF, 2014). In this study 10 replicates of 1 daphnid were exposed to nominal test substance concentrations up to 0.16 mg/L, a blank control and a buffer control. As all test concentrations were below the LoQ of the analytical method, concentration control analyses could not be conducted on the test solutions directly and instead the stock solution (10 mg/L) and the controls were analyzed as a surrogate analysis for stability. Based on a 78% time-weighted mean recovery of test substance in the stock solution, 'corrected' nominal concentrations were determined at 0.0078, 0.0156, 0.0312, 0.0624 and 0.1248 mg/L. The M4 test medium used in this study was modified to enhance the stability of the test substance by adding 750 mg/L MOPS buffer at pH 7. Mortality, reproduction and sublethal effects were observed daily. At the highest corrected nominal test concentration of 0.1248 mg/L all parent animals were dead by day 6. In all other test groups no parental deaths or significant effects on reproduction, other sub-lethal effects or behavior were observed. Based on these findings, the 21-d LOEC is determined at 0.1248 mg/L based on parental mortality. The 21-d NOEC is determined at 0.0624 mg/L. After correction for molecular weight difference (for read-across) the 21-d NOEC is 0.08 mg/L