Sodium 3,5,5-trimethylhexanoate

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Name: Potassium 3,5,5-trimethylhexanoate
CAS No.: 93918-10-6
Batch No.: PURS151015
Purity: 99.4%
Physical State: solid
Colour: white
Molecular Weight: 196.33 g/mol
Storage Conditions: room temperature
Re-certification Date: 14 October 2016

Analytical monitoring:

yes

Details on sampling:

TOC analysis
Samples of 5 mL were taken from each additional vessel for TOC-analysis (without test organisms in order to not disturb the TOC-analysis) of treatment A, C, E and NC at 0 h, 24 h, 48 h and 72 h. Of these 4 samples per treatment and time, 2 were measured directly after sampling using a TOC-analyser and 2 samples were stored as retain samples in the freezer at ≤ -18 °C until finalization of the study.

Vehicle:

no

Details on test solutions:

The test was performed with OECD TG 201 medium according to OECD 201 (2006).

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

The test organism Raphidocelis subcapitata (Strain No. 61.81 SAG) originates from the Culture Collection of Algae at the University of Goettingen and was cultivated in suspension culture. The strain used for this study has been cultured at Hydrotox GmbH since October 2015. Twice a week, the stock suspension is inoculated into fresh Holm-Hansen medium under axenic conditions to keep it in exponential growth.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

The test was performed with OECD TG 201 medium according to OECD 201 (2006).

Test temperature:

The temperature during the exposure was 23.3 - 23.5 °C.

pH:

The pH was 7.6 - 7.7 in the control and 7.7 - 7.9 in the test item concentrations.

Salinity:

The test was performed with OECD TG 201 medium according to OECD 201 (2006).

Conductivity:

The test was performed with OECD TG 201 medium according to OECD 201 (2006).

Nominal and measured concentrations:

The measured TOC-concentrations in the test item treatment were 79.5 – 89.2 % of the nominal concentrations and stable during the exposure period. The TOC-concentrations in the control were below the limit of quantification.

Reference substance (positive control):

yes

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Basis for effect:

biomass

Key result

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

> 200 g/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

> 200 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Basis for effect:

biomass

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

189.87 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat. (total fraction)

Basis for effect:

biomass

Results with reference substance (positive control):

Quality assurance takes place at regular intervals by testing the sensitivity of the test organisms to the reference item potassium dichromate. The recent quality testing was performed in November 2015 which resulted in an ErC50 of 0,831 mg/L.

Reported statistics and error estimates:

ECX and NOEC/LOEC values were determined with the statistical software ToxRat 3.2.1 (ToxRat Solutions GmbH, Alsdorf) as far as mathematically possible.

The test and control vessels were sealed with cellulose stoppers and kept in the light incubator with continuous lighting. The test vessels were clipped to rotary discs, which provided space for 21 vessels on each level. The rotation of about 2 rpm ensures that each test vessel is exposed to identical light conditions. Each rotation included 5 sudden stops by which the test suspensions were shaken. The flasks were illuminated continuously by eight lateral fluorescent tubes (58 W each), which were separated from the incubation chamber by heat absorbing glass. Mean light intensity was 74.7 µE m-² s-1 ± 4.8 %. The pH was measured at the start (0 h) and at the end of the test (72 h).

The increase of algal biomass was monitored by measuring the chlorophyll fluorescence in each test vessel after 0 h, 24 h, 48 h and 72 h. From each test vessel, 200 µL test solution was transferred into a 96-well microplate and the fluorescence measured with the fluorescence microplate reader at an excitation wavelength of 465 nm and an emission wavelength of 670 nm. Each measurement was conducted in duplicate. If the variation coefficient was > 10 %, the measurement was repeated. OECD TG 201 medium was measured as blank value and subtracted from the fluorescence values in the test vessels.

Validity criteria fulfilled:

yes

Conclusions:

A static algal growth inhibition test with Raphidocelis subcapitata was performed using nominal concentrations of 12.5 - 200 mg/L test item. All results are given in relation to nominal test item concentrations with NOEC >= 100 mg/l (yield and growth rate) and LOEC >= 200 mg/l (yield and growth rate).

Executive summary:

A static algal growth inhibition test with Raphidocelis subcapitata was performed using nominal concentrations of 12.5 - 200 mg/L test item. All results are given in relation to nominal test item concentrations with NOEC >= 100 mg/l (yield and growth rate) and LOEC >= 200 mg/l (yield and growth rate).

Description of key information

A static algal growth inhibition test with Raphidocelis subcapitata was performed using nominal concentrations of 12.5 - 200 mg/L test item. All results are given in relation to nominal test item concentrations with NOEC >= 100 mg/l (yield and growth rate) and LOEC >= 200 mg/l (yield and growth rate).

In this test, the substance was the K salt

Key value for chemical safety assessment

EC50 for freshwater algae:

190 mg/L

EC10 or NOEC for freshwater algae:

100 mg/L

Additional information

Clearly, sodium and potassium 3,5,5-trimethylhexanoateare closely related, being the respective acid and salts. The only difference between the two substances is the alkali metal cation, which generally exhibit similar properties as a salt once associated with an acid, in this case3,5,5-trimethylhexanoic acid.They can therefore be considered together in terms of safety assessment and the K salt has been assessed as being a good read-across substance for the Na salt.