Butyl 3-mercaptopropionate

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

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

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

0.77 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Conclusions:

BAsed on read across from MMP, the 48 h EC50 for BuMP is estimated to be 0.77 mg/L, nominal

Description of key information

The toxicity of BuMP to Daphnia magna was estimated by read-across from MMP and iOMP. The estimated EC50 is 0.53 mg/L.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

EC50

Effect concentration:

0.53 mg/L

Additional information

No experimental data is available for BuMP. However, short-term toxicity studies to Daphnia were conducted with MPA, MMP, iOMP, ODMP and PETMP. However, as for ODMP and PETMP no effects were observed at the highest concentrations, these values cannot be used for trend analysis. Since this leaves only 3 data points, a read-across applying a worst-case approach from the closest analogue(s) seems more appropriate for data gap filling than a trend analysis. Corrections were made for molecular weight. The closest analogues of BuMP were MMP and iOMP. A justification for read-across is attached to Iuclid section 13.

 

MMP

A study was performed to assess the acute toxicity of the test material MMP to Daphnia magna in accordance with OECD TG 202. This study encompassed 6 treatment groups (control + 0.06, 0.13, 0.29, 0.64, 1.41, 3.10, 6.82, 15.00 mg/L) each containing 20 individuals. The mobility of the daphnids was determined in a static 48-hour test by visual observation after 24 and 48 hours.

The 48 h EC50 based on initial measured concentrations was 0.55 mg/L.

Measured values may represent the real environmental conditions because the test substance is rapidly oxidized by the oxygen content in the aqueous phase.

As the transformation products are less toxic than the parent substances (no free –SH groups) regulatory endpoints calculated on the basis of nominal concentrations represent a realistic worst case approach.  Moreover, for thiochemicals nominal concentrations represent the real environmental conditions, because the test substance is rapidly oxidized by the oxygen content in the aqueous phase.  The effect values therefore reflect the toxicity of the system – in the sense of the UVCB approach – rather than the toxicity of the original chemical substance. Under these conditions it is more meaningful to assess their toxicities on the basis of nominal concentrations instead of measured concentrations during exposure. This may better correspond to the situation under environmental conditions as recommended for multi-component-substances (OECD23).

The 48 h EC50 based on nominal concentrations was 0.57 mg/L.

 

iOMP

A study was performed to assess the acute toxicity of the test material  iOMP to Daphnia magna in accordance with OECD TG 202.

Pre-study solubility work conducted indicated that it was not possible to obtain a testable solution of the test material using traditional methods of preparation e.g. ultrasonication. The highest dissolved test material concentration that could be prepared (by visual examination) was 0.80 mg/l using a preliminary solution in tetrahydrofuran.
Analysis of the freshly prepared media at 0 and 24 hours showed measured concentrations to range from less than the limit of quantitation (LOQ) to 0.811 mg/l. Analysis of the old media at 24 and 48 hours showed measured test concentrations to range from less than the limit of quantitation (LOQ) to 0.437 mg/l. This decline in measured concentration was in-line with the stability analysis which showed the test material to be unstable in the test medium.

The time-weighted mean measured test concentrations were calculated to be: 0.0068, 0.0032, 0.011, 0.017, 0.038, 0.076, 0.14, 0.26 and 0.49 mg/i. The 48-Hour EC50 for the test material to Daphnia magna based on time-weighted mean measured test concentrations was 0.31 mg/l with 95% confidence limits of 0.13 - 13 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. As the transformation products are less toxic than the parent substances (no free –SH groups) regulatory endpoints calculated on the basis of nominal concentrations represent a realistic worst case approach. The 48 hEC50 was determined to be 0.44 mg/L based on nominal concentrations.

 

Based on the interpolation from MMP and iOMP the 48 h EC50 for BuMP was estimated to be 0.53 mg/L, nominal.