Isooctyl 3-mercaptopropionate

Short-term toxicity to aquatic invertebrates

Administrative data

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-09-08 to 2009-03-20

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2009

Report date:

2009

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Deviations:

no

Remarks:

; modification for poorly soluble substances according to OECD 23 (saturated solution method)

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method C.2 (Acute Toxicity for Daphnia)

Deviations:

no

Remarks:

; modification for poorly soluble substances according to OECD 23 (saturated solution method)

GLP compliance:

yes (incl. QA statement)

Remarks:

The Department of Health of the Government of the United Kingdom

Test material

Test material information

Constituent 1

Reference substance name:

Isooctyl 3-mercaptopropionate

EC Number:

250-157-6

EC Name:

Isooctyl 3-mercaptopropionate

Cas Number:

30374-01-7

Molecular formula:

C11H22O2S

IUPAC Name:

2-methylheptyl 3-sulfanylpropanoate

Details on test material:

- Name of test material (as cited in study report): Isooctyl 3-mercaptopropionate (IOMP)
- Physical state: liquid
- Analytical purity: 99.8%
- Lot/batch No.: 0000023757
- Expiration date of the lot/batch: 1.07.2009
- Storage condition of test material: room temp. in the dark under nitrogen
- Other:
appearance: clear colourless
a certificate of analysis is given in the report

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

sampling periods: fresh media: 0 and 24 h; old media: 24 and 48 h;
the samples of each 2 replicates were pooled;
no storage of test samples: the analyses were performed immediately after sampling due to the instability of the test item in test medium (duplicate samples were taken and stored at approx. -20°C for further analysis if necessary)

Test solutions

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method, preparation of test item (stock) solution: 550 mg of test material stirred for 24 h in 11 L of reconstituted water (propeller stirrer, 1500 rpm, ca. 21°C); filtration through 0.2 µm filter (first approx. 1 L was discarded in order to re-condition the filter); resulting saturated solution approx. 6.8 mg test item/L
- Method, application of test item/preparation of test solutions: Aliquots of the test item stock solution (2.0, 3.5, 6.5, 11.2, 20, 35, 65, 112, 200 mL) were each separately dispersed in a final volume of 2.0 L of reconstituted water to prepare the test solutions in the nominal test item concentrations.
- Control: reconstituted water without test item (positive control tested in a separate study; see below)
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): no vehicle used
- Evidence of undissolved material (e.g. precipitate, surface film, etc): undissolved test item removed by filtration after 24 h stirring period; no undissolved material during incubation period

Test organisms

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: daphnid (Daphnia magna)
- Source: in-house labortory culture
- Age at study initiation: less than 24 h
- Feeding during test: no


ACCLIMATION
- Acclimation period: no (media and further conditions same in breeding and study)
- Acclimation conditions (same as test or not): same as test


BREEDING
- Type and amount of food: green algae Chlorella sp.
- Feeding frequency: daily
- Temperature: 20°C
- Light/dark cycle: 16 h : 8 h (with 20 min dawn and dusk transition period)

Study design

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Test conditions

Test temperature:

20-21°C (fresh media at 0 and 24 h);
21°C (old media at 24 and 48 h)

pH:

7.8-8.1 (fresh media at 0 and 24 h);
7.8-8.0 (old media at 24 and 48 h)

Dissolved oxygen:

always at least 8.2 mg/L throughout the study (i.e. 92% of air saturation value)

Nominal and measured concentrations:

0.0068, 0.012, 0.022, 0.038, 0.068, 0.12, 0.22, 0.38, 0.68 mg/L (nominal);
0.0068, 0.0032, 0.011, 0.017, 0.038, 0.076, 0.14, 0.26, 0.49 mg/L (time-weighted mean measured)

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): glass jars, open but covered (to reduce evaporation)
- Material, size, headspace, fill volume: glass, 250 mL
- Aeration: no active aeration
- Renewal rate of test solution (frequency): 24 h (semi-static)
- No. of organisms per vessel: 10
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 2
- No. of vessels per vehicle control (replicates): no vehicle used


OTHER TEST CONDITIONS
- Photoperiod: Light/dark cycle: 16 h : 8 h (with 20 min dawn and dusk transition period)


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : mobility, determined 24 and 48 h after test initiation

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Results and discussion

Effect concentrations

Effect concentrations 1

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

0.44 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Effect concentrations 2

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

0.31 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 95% CL: 0.13-13 mg/L

Details on results:

- Behavioural abnormalities: no (immobility was the only reported effect)
- Mortality of control: no
- Other adverse effects control: no (e.g. immobility)
- Abnormal responses: no
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: no; clear colourless test solutions throughout the test
- Effect concentrations exceeding solubility of substance in test medium: no

Results with reference substance (positive control):

nominal reference substance concentrations: 0.32, 0.56, 1.0, 1.8, 3.2 mg/L (performed in 2008-12);
EC50 (48 h) = 0.78 mg/L

Reported statistics and error estimates:

The EC50 values and associated confidence limits 24 and 48 h and the slope of the response curve and its standard error were calculated by the maximum-likelyhood probit method (Finney 1971) using the ToxCalc computer software package (ToxCalc 1999).

Any other information on results incl. tables

respective biological results based on nominal test item concentrations:

EC50 (24 h) = 0.82 mg/L; 95% CL: 0.71-0.94 mg/L; NOEC (24 h) = 0.32 mg/L

EC50 (48 h) = 0.71 mg/L; 95% CL: 0.62-0.81 mg/L; NOEC (48 h) = 0.32 mg/L

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

The 48 hEC50 was determined to be 0.44 mg/L based on nominal concentrations.

Executive summary:

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.
A pre-study media preparation trial indicated that a dissolved test material concentration of approximately 6.8 mg/l was obtained from a saturated solution method of preparation indicating this to be the limit of water solubility of this material under test conditions.
Following preliminary range-finding tests, twenty daphnids (2 replicates of 10 animals) were exposed to an aqueous solution of the test material at concentrations of 0.0068, 0.012, 0.022, 0.038, 0.068, 0.12, 0.22, 0.38 and 0.68 mg/l for 48 hours at a temperature of approximately 20°C under semi-static test conditions. The number of immobilised Daphnia 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. Immobilisation and any adverse reactions to exposure were recorded after 3, 24 and 48 hours.

Analysis of the saturated solution at 0 and 24 hours showed measured concentrations of 5.83 and 8.24 mg/l respectively.
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.