(2-hydroxyethyl)ammonium mercaptoacetate

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

Justification for type of information:

REPORTING FORMAT FOR THE CATEGORY APPROACH

1. HYPOTHESIS FOR THE CATEGORY APPROACH
This scenario covers the category approach for which the hypothesis is based on transformation to a common compound. For the REACH information requirement under consideration, the effects obtained in studies conducted with different source substances are used to predict the effects that would be observed in a study with the target substance if it were to be conducted. The same type of effect is observed for the different source substances; this may include absence of effects for every member of the category. No relevant differences in strengths of effect are observed for several source substances.
There are no relevant variations in properties among source substances and the same potency is predicted for all target substances. This corresponds to Scenario 5 of the RAAF (ECHA, 2017). The substances ATG, MEATG, KTG, CaTG, and NaTG are different inorganic salts of a common acid, thioglycolic acid (TGA; synonym: 2-mercaptoacetic acid). They dissociate rapidly in aqueous media to the common thioglycolate anion and to their different counter ions. The water solubility of all category members is high.
This approach serves to use existing data on aquatic toxicity endpoints for substances in this category.
It can be predicted with high confidence that the target substances will display the same mode of action and lead to the same type and strength of effects as observed with the source substances.


2. CATEGORY APPROACH JUSTIFICATION
For details, refer to Justification for read-across attached to Iuclid section 13

Reason / purpose for cross-reference:

read-across: supporting information

Key result

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

5.3 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

other: read-across, molecular weigth correction

Basis for effect:

reproduction

Conclusions:

After molecular weight correction, the 21 d NOEC for MeaTG is 5.3 mg/L, and the LOEC is 12.7 mg/L.

Description of key information

21-Day NOEC = 5.3 mg/L (OECD TG 211, Daphnia magna, RL2, GLP; read-across from TGA, molecular weight correction)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

NOEC

Effect concentration:

5.3 mg/L

Additional information

No experimental data on long-term toxicity to aquatic invertebrates is available for the target substance MeaTG. However, a study was conducted with teh source substance TGA. A category justification is attached to Iuclid section 13.

A Daphnia magna reproduction test was conducted according to OECD Guideline 211 (Draft, April 1997). Daphnids, aged less 24 hours at the start of the test, were exposed to thioglycolic acid at nominal concentrations of 0.0 (control), 5.4, 8.6, 13.7, 21.9, and 35.0 mg/L; corresponding to measured concentrations of 0.0, 1.2, 1.7, 2.7, 6.5, and 24.2 mg/L) for 21 days under semi-static conditions (daily renewal). At the end of the test, the total number of living offspring produced was assessed. Because the measured concentrations were outside of ± 20% of the nominal concentrations, the time-weighted average of the measured concentration was used to calculate the test results.

The mortality rate of the parent Daphnia magna in the control was 10% at the end of exposure, meeting the test acceptance criteria of 20% or less.

In the concentrations, as the test substance concentration increased, the number of deaths and mortality rate of parent Daphnia magna increased at the end of exposure, and in the concentration of 1.7 mg/L, the mortality rate of parent Daphnia magna was 30%, and it was 100% in the maximum concentration (24.2 mg/L)

The first hatching date for the parent Daphnia magna in the control was 10 to 11 days after the start of exposure. In the concentration of 1.7 mg/L, the first hatching date for the parent Daphnia magna was 10 to 14 days after the start of exposure, and in the highest concentration (24.2 mg/L), no offspring of the parent Daphnia magna was found.

The mean cumulative number of litter per parent Daphnia magna during the 21-day control zone was 67.8, meeting the test acceptance criteria of 60 or more.

The mean cumulative number of offspring per parent Daphnia magna during the 21-day concentrations was 74.4 animals in the lowest concentration (1.7 mg/L), and all of the parent Daphnia magna died in the highest concentration (24.2 mg/L) at 21 days of exposure.

No dormant eggs, etc. occurred in the control or any of the concentration.

Results:

21-Day No Observed Effect Concentration (NOECr) = 2.7 mg/L

21-Day Lowest Observed Effect Concentration (LOECr) = 6.5 mg/L

21-Day 50% Lethal Concentration of Parent Daphnia magna (LC50) = 5.7 mg/L (95% confidence interval: 3.4 mg/L - 11.2 mg/L)

21-Day 50% Reproductive Inhibition Concentration (ErC50) = 4.1 mg/L (95% confidence interval: 3.6 mg/L - 4.8 mg/L)

 

Conclusion

After molecular weight correction, the 21 d NOEC for MeaTG is 5.3 mg/L, and the LOEC is 12.7 mg/L.