Isooctyl 3-mercaptopropionate

Short-term toxicity to fish

Administrative data

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-09-14 to 2009-03-06

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 203 (Fish, Acute Toxicity 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.1 (Acute Toxicity for Fish)

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:

all fresh (at 0, 24, 48, 72 h) and old (at 24, 48, 72, 96 h) test media were sampled for chemical analysis;
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 dechlorinated tap water (propeller stirrer, 1500 rpm, ca. 14°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 (200, 353, 647, 1120, 2000 mL) were each separately dispersed in a final volume of 20 L of dechlorinated tap water to prepare the test solutions in the nominal test item concentrations.
- Control: dechlorinated tap water without test item
- 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):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM
- Common name: rainbow trout (juvenile)
- Source: Brow Well Fisheries Ltd., Hebden, near Skipton, Yorkshire, UK (maintained in-house the test facility since 09.02.2009 in a glass-fibre tank with a "single pass" water renewal system)
- Length at test end (mean, SD): 4.8 cm (SD = 0.2)
- Weight at test end (mean, SD): 1.36 (SD = 0.19)
- Feeding during test: no


ACCLIMATION
- Acclimation period: 18.02.2009 to 01.03.2009
- Acclimation conditions (same as test or not): same as test
- Type and amount of food: commercial trout pellets (up to 24 h prior to test start)
- Health during acclimation (any mortality observed): no mortality in the last 7 days prior to test start

Study design

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Test conditions

Test temperature:

14°C in the fresh test media;
14-15°C in the old test media

pH:

7.5-7.7 in the fresh test media;
7.8-7.9 in the old test media

Dissolved oxygen:

>8.9 mg/L throughout the test (equal to 88% of the air saturation value)

Nominal and measured concentrations:

0.068, 0.12, 0.22, 0.38, 0.68 mg/L (nominal);
0.012, 0.024, 0.077, 0.17, 0.38 mg/L (time-weighted mean measured)

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type: open but covered to reduce evaporation
- Material, size, headspace, fill volume: glass, 20 L
- Aeration: yes, via a narrow bore glass tube
- Renewal rate of test solution (frequency): daily (semi-static)
- No. of organisms per vessel: 7
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1
- No. of vessels per vehicle control (replicates): no vehicle used
- Biomass loading rate: 0.48 g bodyweight/L (static volume)


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


OTHER TEST CONDITIONS
- Temperature: 14°C
- Photoperiod: 16 h light : 8 h dark, with a 20 min dusk / dawn period


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : mortality and sub-lethal effects (at 6, 24, 48, 72, 96 h)

Reference substance (positive control):

no

Results and discussion

Effect concentrations

Effect concentrations 1

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

0.16 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Effect concentrations 2

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

0.043 mg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Remarks on result:

other: 95% CL: 0.024-0.077 mg/L

Details on results:

further results based on meas. (TWA):
LC50 (24 h), LC50 (48 h), LC50 (72 h) and LC50 (96 h) are all equal to 0.043 mg/L (95% CL: see Table above)
LC50 (3 h) = 0.11 mg/L (95% CL: 0.077-0.17 mg/L)
LC50 (6 h) = 0.087 mg/L (95% CL: 0.062-0.12 mg/L)

based on nominal concentrations: LC50 (96 h) = 0.16 mg/L (95% CL: 0.12-0.22 mg/L); NOEC (96 h) = 0.12 mg/L

Sublethal effects of exposure were observed at test concentrations of 0.077 mg/L and above. These responses were swimming at the bottom of the tank and moribund with swollen abdomens.

Reported statistics and error estimates:

analysis of the mortality data:
geometric mean method: 3, 24, 48, 72, 96 h values;
trimmed Spearman-Karber method (Hamilton et al 1977): 6 h values

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

The 96 h LC50 based on nominal concentration was determined to be 0.16 mg/L.

Executive summary:

A study was performed to assess the acute toxicity of the test material to rainbow trout (Oncorhynchus mykiss) in accordance with OECD TG 203.

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. 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, fish were exposed, in groups of seven, to an aqueous solution of the test material over a range of nominal test concentrations of 0.068, 0.12, 0.22, 0.38 and 0.68 mg/l for a period of 96 hours at a temperature of approximately 14°C under semi-static test conditions. The test material solutions were prepared by stirring an excess (50 mg/l) of test material in dechlorinated tap water using a propeller stirrer at approximately 1500 rpm at a temperature of approximately 14°C for 24 hours. After the stirring period any undissolved test material was removed by filtration (0.2 um Sartorius Sartopore filter, first approximate 1 litre 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.

The number of mortalities and any sub-lethal effects of exposure in each test and control vessel were determined 3 and 6 hours after the start of exposure and then daily throughout the test until termination after 96 hours.

Analysis of the saturated solution at 0, 24, 47 and 72 hours showed measured concentrations of 6.74 to 9.59 mg/l giving a mean measured concentration of 7.7 mg/l. Analysis of the fresh media at 0, 24, 47 and 72 hours showed the measured concentrations to range from less than the limit of quantitation to 0.610 mg/l. Analysis of the old media samples at 24, 47, 72 and 96 hours showed measured concentrations of
less than the limit of quantitation to 0.210 mg/l.
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.

The 96-Hour LCs based on the time-weighted mean measured test concentrations was 0.043 mg/l with 95% confidence limits of 0.024 — 0.077 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 96 h LC50 based on nominal concentration was determined to be 0.16 mg/L.