Isooctyl 3-mercaptopropionate

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-09-11 to 2009-03-14

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 201 (Alga, Growth Inhibition 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.3 (Algal Inhibition test)

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:

Samples were taken from the control and each test group at 0, 24 and 72 hours for immediate quantitative analysis. Duplicate samples were taken at 0 hours and stored at approximately 20ºC for further analysis if necessary. Sample volumes required for chemical analysis precluded the storage of duplicate samples at 24 and 72 hours.

Test solutions

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test substance is poorly water soluble. A modification of the standard method for the preparation of aqueous media was performed. Based on the results of media preparation pre-studies, the test solution was prepared using a saturated solution method of preparation stirred for a period of 24 hours at approx. 1500 rpm prior to removal of any undissolved test material by filtration through a 0.2 μm Gelman Acrocap filter (first approximate 500 ml discarded) to give a nominal concentration of 6.8 mg/l.
- Eluate: A solvent Spike Preparation was done in a pre-test, but yielded lower test concentrations, thus test solutions were prepared as saturated solutions
- Control: same conditions, not exposed to test material

Test organisms

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Common name: green algae Desmodesmus subspicatus
- Strain: CCAP 276/20
- Source (laboratory, culture collection): Culture Collection of Algae and Protozoa (CCAP), Dunstaffnage Marine Laboratory, Oban, Argyll, Scotland.
- Method of cultivation: Master cultures were maintained in the laboratory by the periodic replenishment of culture medium. The master cultures were maintained in the laboratory under constant aeration and constant illumination at 24 ± 1°C until the algal cell density was approx. 10^4 - 10^5 cells / mL

Study design

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test conditions

Test temperature:

24 ± 1°C

pH:

7.3 - 7.7 (0 h)
7.5 - 7.8 (72 h)

Nominal and measured concentrations:

0.0068, 0.022, 0.068, 0.22 and 0.68 mg/l (nominal)
0.013, 0.043, 0.17, 0.39, and 1.5 mg/L (initial measured)

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): closed
- Material, size, headspace, fill volume: 250 mL glass conical flasks, containing 100 mL solution
- Initial cells density: 4.81 x 10^3 cells / mL
- Control end cells density: 2.37 x 10^5 cells /mL
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6


GROWTH MEDIUM
- Standard medium used: yes, AAP-medium (US-EPA)


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: reconstituted water
- Culture medium different from test medium: no


OTHER TEST CONDITIONS
- Sterile test conditions: no
- Adjustment of pH: yes
- Photoperiod: continuous
- Light intensity and quality: approx. 7000 lux, warm white lightning (380 - 730 nm)
- other: constantly shaken at approx. 150 rpm for 72 h


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: electronic particle counter: Coulter Multisizer Particle Counter; 0, 23, 48, 72 h
- Other: growth rate, yield, biomass


TEST CONCENTRATIONS
- Range finding study
- Test concentrations: 0.00068, 0.0068, 0.068, 0.68, and 6.8 mg/L (nominal)
- Results used to determine the conditions for the definitive study: Based on the results of the range finding study an initial test was conducted at nominal concentrations of 0.068, 0.22, 0.68, 2.2, and 6.8 mg/L. Significant inhibition was observed to occur at all test concentrations. Therefore for the definitive test nominal test concentrations of 0.0068, 0.022, 0.068, 0.22, and 0.68 mg/L were employed. Difference between the measured concentrations obtained from saturated solution preparation in the pre-study media preparation trial and the definitive test were considered to be due to the different media types used.

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Results and discussion

Effect concentrations

Effect concentrations 1

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

1.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Effect concentrations 2

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

5.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Effect concentrations 3

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

0.024 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Effect concentrations 4

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

0.046 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Effect concentrations 5

Duration:

24 h

Dose descriptor:

NOEC

Effect conc.:

0.12 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

other: same value for growth rate, yield and biomass

Details on results:

All test and control cultures were observed microscopically. No abnormalities were detected.

Results with reference substance (positive control):

- Results with reference substance valid? yes
- EC50: EC50 growth (0-72h): 0.52 mg/L, EC50 yield (0-72h): 0.29 mg/L, EC50 biomass (0-72h): 0.30 mg/L

Reported statistics and error estimates:

One way analysis of variance incorporating Bartlett's test for homogeneity of variance (Sokal and Rohlf 1981) and Dunnett 1955) was carried out on the growth rate, yield and biomass integral data after 24 and 72 hours for the control and all test concentrations to determine any statistically significant differences between the test and control groups. All statistical analysis were performed using the SAS computer software package (SAS 1999-2001)

Any other information on results incl. tables

Validation criteria:

Cell concentration of the control cultures increased by a factor of 49 after 72 hours (at least factor 16 required acc. to OECD guideline).

Mean coefficient of variation for section by section specific growth rate for the control cultures was 29% (not exceeding 35% acc. to OECD guideline).

Coefficient of variation for average specific growth rate for the control cultures over the test period (0 -72 h) was 4% (not exceeding 7% acc. to OECD guideline).

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

72 h EC50 = 5.8 mg/L, EC10=1.5 mg/L, nominal

Executive summary:

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.

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 ¢.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. 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 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 a preliminary range-finding test Desmodesmus subspicatus was exposed to solutions of the test material at O-Hour measured concentrations of 0.013, 0.043, 0.17, 0.39 and 1.5 mg/l (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 + 1°C. The test material solutions were prepared by stirring an excess (50 mg/l) of test material in culture medium using a propeller stirrer at approximately 1500 rpm at a temperature of approximately 21°C for 24 hours. After the stirring period any undissolved test material was removed by filtration (0.2 um Gelman Acrocap filter, first approximate 500 ml discarded in order to precondition the filter) to produce a saturated solution of the test material. This saturated solution was then further diluted as necessary, to provide the remaining test groups.

Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group.

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.