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Short-term toxicity to aquatic invertebrates

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short-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:
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
48 h
Dose descriptor:
Effect conc.:
> 1.36 mg/L
Nominal / measured:
Conc. based on:
act. ingr.
Basis for effect:
The estimated 48 h EC50 for Di-PETMP in D.magna is >1.36 mg/L

Description of key information

Based on read across from PETMP, the estimated EC50 for DiPETMP against D.magna is >1.36 mg/L

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Dose descriptor:
Effect concentration:
> 1.36 mg/L

Additional information

No experimental data are available for the target substance Di-PETMP. A short-term toxicity study in Daphnia magna was conducted with the source substance PETMP. A justification for read-across is attached to Iuclid section 13.


A study according to OECD TG 202 was performed to assess the acute toxicity of PETMP to Daphnia magna.

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).

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, twenty daphnids (4 replicates of 5 animals) were exposed to an aqueous solution of the test material at a time-weighted mean
measured test concentration of 0.35 mg/I for 48 hours at a temperature of approximately 20°C under semi static test conditions. Immobilisation and any adverse reactions to exposure were recorded after 24 and 48 hours.

A positive control conducted approximately every six months used potassium dichromate as the reference material. Daphnia magna was exposed to an aqueous solution of the reference material at concentrations of 0.32, 0.56, 1.0, 1.8 and 3.2 mg/l for 48 hours at a temperature of approximately 20°C under static test conditions. [mmobilisation and any adverse reactions to exposure were recorded after 3, 24 and 48 hours.

The test material was known to be unstable. Based on this the test was conducted using a semi static regime with chemical analysis of the test preparations
being conducted at 0, 24 and 48 hours.
Analysis of the freshly prepared test media at 0 and 24 hours showed measured test concentrations to range from 0.42 mg/l at 0 hours to 0.49 - 0.67 mg/i at 24 hours. A decline in measured concentration was observed in the old media at 24 and 48 hours with measured concentrations in the range of 0.23 to 0.25 mg/l at 24 hours and 0.22 - 0.24 mg/l at 48 hours.
The decline in measured concentrations observed over the test period was in line with the preliminary stability analyses conducted.
The 48-Hour EC50 based on the time weighted mean measured test concentrations was greater than 0.35 mg/l.
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: the nominal EC50 was >0.85 mg/L. Correction for differences in molecular weight results in a 48 h EC50 of >1.36 mg/L for Di-PETMP.

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