2-ethyl-2-[(3-mercapto-1-oxopropoxy)methyl]propane-1,3-diyl bis[3-mercaptopropionate]

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Justification for type of information:

This selected scenario covers the category approach for which the read-across hypothesis is based on structural similarity. For the REACH information requirement under consideration, the property investigated in studies conducted with different source substances is used to predict the property that would be observed in a study with the target substance if it were to be conducted. Similar properties are observed for the different source substances; this may include absence of effects for every member of the category.
There are expected to be differences in strength of the effects forming a regular pattern. The prediction will be based on a worst-case approach or trend analysis as appropriate for the respective endpoint. The read-across is a category approach based on the hypothesis that the substances in this category share structural similarities with common functional groups. This approach serves to use existing data on aquatic toxicity for substances in this category.
The hypothesis corresponds to Scenario 4 of the RAAF. The substances MMP, BuMP, EHMP, iOMP, iC13MP, ODMP, GDMP, TMPMP, PETMP, and Di-PETMP are esters of a common acid, 3-mercaptopropionic acid (3-MPA). The key functionality and main driver for ecotoxicity of the substances within this category is the presence of free SH-groups. It can be predicted with high confidence that the substances within this category will lead to the same type of effects.
For details, please refer to the category document attached to Iuclid section 13.

Reason / purpose for cross-reference:

read-across: supporting information

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

> 0.55 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 0.55 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Conclusions:

The estimated 72-h ErC50 and 72-h ErC50 of TMPMP to algae are >0.55 mg/L

Description of key information

The estimated 72-h EC50 of TMPMP to algae is >0.55 mg/L; 72 h NOEC=0.55 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:

0.55 mg/L

EC10 or NOEC for freshwater algae:

0.55 mg/L

Additional information

No experimental data are available for the target substance TMPMP. An algal toxicity study was conducted with the source substance PETMP. A justification for read-across is attached to Iuclid section 13.

A study according to OECD TG 201 was performed to assess the effect of the test material on the growth of the green alga Desmodesmus subspicatus.

Pre-study solubility work conducted indicated that the test material was insoluble in water using traditional methods of preparation e.g. ultrasonication and high shear mixing. The highest dissolved test material that could be obtained (by visual inspection) was 1.0 mg/l using a preliminary solution in tetrahydrofuran. Based on this information the test material fell into the category of a ‘difficult substance’ as defined by the OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (OECD 23, 2000).
A pre-study media preparation trial indicated that the use of a solvent spike method of preparation followed by centrifugation to remove the undissolved test material was the most appropriate method of preparation for the test material giving a dissolved test material concentration of approximately 0.85 mg/l.
Following a preliminary range-finding test, Desmodesmus subspicatus was exposed to an aqueous solution of the test material at a 0-Hour measured test concentration of
0.65 mg/l (six replicate flasks) for 72 hours, under constant illumination and shaking at a temperature of 24 + 1°C.
Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter® Multisizer Particle Counter.

The test material was known to be unstable. Based on this and at the request of the Sponsor chemical analysis of the test preparations was conducted at 0, 24 and 72 hours.

Analysis of the test preparations at 0 hours showed measured test material concentrations to range from 0.57 to 0.73 mg/l.
Exposure of Desmodesmus subspicatus to the test material gave ECs» values based on the 0-Hour measured test concentrations of greater than 0.65 mg/l and correspondingly the No Observed Effect Concentration was 0.65 mg/I.
Analysis of the test preparations at 24 hours showed a decline in measured test material concentrations to 0.11 mg/l.
Exposure of Desmodesmus subspicatus to the test material gave ECs values based on the 0 — 24 Hour geometric mean measured test material concentrations of greater than 0.27 mg/l and correspondingly the No Observed Effect Concentration was 0.27 mg/l. At 72 hours measured concentrations of less than the LOQ were obtained. The decline in measured concenirations observed over the test period was inline with.the preliminary stability analyses conducted.

These values don't represent the real environmental conditions because the test substance is rapidly oxidized by the oxygen content in the aqueous phase. Therefore, nominal values will be used for hazard assessment.

After correction for molecular weight differences, the 72 h ErC50 and NOEC for TMPMP are >0.55 mg/L