Butyl 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

Reason / purpose for cross-reference:

read-across source

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

3.37 mg/L

Nominal / measured:

nominal

Conc. based on:

act. ingr.

Basis for effect:

growth rate

Validity criteria fulfilled:

not applicable

Conclusions:

The predicted 72-h EC50 of BuMP to algae is 3.37 mg/L.

Description of key information

The predicted 72-h EC50 of BuMP to algae is 3.37 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:

3.37 mg/L

Additional information

No experimental data is available for BuMP. However, algal toxicity studies were conducted with MPA, MMP, EHMP, iOMP, ODMP and PETMP. However, as for EHMP, ODMP and PETMP no effects were observed at the highest tested 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

The influence of the test item 3-mercaptopropanoic acid methyl ester (MMP) on the growth of the green algal species Scenedesmus subspicatus CHODAT was investigated in a 72-hour static test according to OECD TG 201. Since the item is volatile, the test was performed in closed Erlenmeyer flasks. The nominal test concentrations were 0.10, 0.22, 0.46, 1.0, 2.2 and 4.6 mg/L in parallel with a control.
In the analyzed test media the measured test item concentrations at the start of the test ranged from 50 to 104% of the nominal values. During the test period of 72 hours a decrease of the test item concentrations in the test media was determined. At the end of the test period, the analyzed test item concentrations were in the range of < LOQ (limit of quantification: 0.023 mg/L) and 32% of nominal. The mean measured test concentrations (calculated as the geometric mean over all measurements per test concentration) varied in the range of 5.6 to 50% of the nominal values. The reported biological results are based on the mean measured test item concentrations.

The test item had a statistically significant inhibitory effect on the growth (biomass and growth rate) of Scenedesmus subspicatus after the exposure period of 72 hours at concentrations of 0.11 mg/L and above (results of Dunnett-tests). Thus, the test concentration of 0.11 mg/L was determined as the 72-hour LOEC (lowest concentration tested with toxic effects). The 72-hour NOEC (highest conceniration tested without toxic effects after a test period of 72 hours) was determined to be 0.025 mg/L, since at this test concentration both the mean biomass and the mean growth rate of the algae were not statistically significantly lower than in the conirol.

The EC values as well as the NOEC and LOEC were calculated for both parameters, the algal biomass (b) and the growth rate (r), after 72 hours test duration:

72 h ErC50: 0.65 mg/L, 72 h EbC50: 0.16 mg/L

72 h ErC10: 0.021 mg/L, 72 h EbC10: 0.008 mg/L

72 h NOEC: 0.025 mg/L

The nominal values are: 72 h ErC50 = 2.3 mg/L, 72 h ErC10=0.075 mg/L, 72 h NOEC = 0.1 mg/L

iOMP

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

The test material was known to be unstable in water. Given this, and at the request of the Sponsor chemical analysis of the test preparations was conducted for the parent test material at 0, 24 and 72 hours.
Analysis of the test preparations at 0 hours showed measured test material concentrations to range from 0.013 to 1.5 mg/l.

Analysis of the test preparations at 24 hours showed a decline in measured test material concentrations in the range of 0.0060 to 1.0 mg/l.

At 72 hours measured test material concentrations of less than the limit of quantitation (LOQ) were obtained for all test concentrations employed. The decline in measured test material concentrations was inline with the preliminary stability analyses conducted which indicated that the test material was unstable in water.

Exposure of Desmodesmus subspicatus to the test material gave the following results based on the 0 — 72 Hour geometric mean measured test concentrations:

ErC50 = 0.046 mg/L, NOErC = 0.017 mg/L

EyC50 = 0.027 mg/L, NOEyC = 0.17 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 nominal effect values were: 72 h EC50 = 5.8 mg/L, EC10=1.5 mg/L.

 

Based on the interpolation from MMP and iOMP, the 72 h ErC50 for BuMP was predicted to be = 3.37 mg/L.