2-Decyltetradecyl 3-[3-(2-decyltetradecoxy)-3-oxopropyl]sulfanylpropanoate

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

Study period:

March 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Thiobis Propanoic Acid Derivatives
The category covers thiiodipropionates that are symmetrically esterified by two linear aliphatic groups ranging in size from C10 to C24
The justification for the category is based on the expectation that the close structural similarity should result in properties that are either similar or follow a pattern that correlates with changes in the molecular weights of the compounds. The category members are high-molecular weight dithiopropionate esters that differ only in the chain length of the dialkyl ester functions and are expected to follow a regular pattern for all endpoints.
Based on the structures and molecularweights of the category members, as well as available data on category members, The predictive methods and extrapolation and interpolation of data within the category are acceptable. Data provided by other sources also demonstrate that these compounds generally have mammalian toxicities that are similar (e.g., acute oral LD 50, acute irritation thresholds, and genotoxicities) or follow a pattern that parallels changes in molecular weight (e.g., repeated-dose NOAEL).

The category is adequately supported based on chemical structure and available data.

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Guidance document on aquatic toxicity testing of difficult substances and mixtures, OECD series on testing and assessment number 23, December 14, 2000

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Samples for possible analysis were taken from all test concentrations and the control. In addition, samples were taken from the DCM stock solutions.

Frequency
Test solutions: at t=0 h, t=24 h and t=72 h
Stock solutions: on the day of spiking the test solutions, i.e. three days before the start of exposure

Volume: Test solutions: 4.0 mL, stock solutions: 1.0 mL

Storage: Samples were stored in a freezer (≤ -15°C) until analysis.

At the end of the exposure period, the replicates with algae were pooled at each concentration before sampling.

Compliance with the Quality criteria regarding maintenance of actual concentrations was checked by running a test vessel at an intermediate test concentration but without algae and samples for analysis were taken at the start, after 24 hours of exposure and at the end of the test period.

Vehicle:

yes

Remarks:

DCM to prepare a test material layer on the vessels, afterwards DCM was evaporated

Details on test solutions:

Saturated Solutions (SS) were prepared applying a solid-liquid separation system.

Vessel preparation and loading:
An exactly weighed amount of test item was mixed with Dichloromethane (DCM; 100.0%, VWR, France) to prepare a stock solution of 50 mg/mL. This stock was used to prepare 4 lower stocks of 0.5, 1.6, 5.0 and 16 mg/mL. A volume of 2 mL of the different stock solutions was then added using a pipette and spread over the bottom of 1L glass flasks. The organic solvent DCM was then evaporated overnight by aerating the flask leaving the test item as a film stuck to the flask bottom.

Preparation of test solutions:
The flasks were then carefully filled with test medium to make up loading rates of 1.0, 3.2, 10, 32 and 100 mg/L. Subsequently, the flasks were slowly shaken (~50 rpm) for 2 days to generate saturated solutions. The shaking was stopped and flasks were shortly left to settle before collection of the saturated solutions by means of siphoning the middle clear solutions. Note that the control received similar treatment (DCM only).

All test vessels were preincubated for at least one day with the respective SS before the start of exposure to minimize any adsorption of test item to glass surfaces. After preparation, volumes of 50 mL were added to each replicate of the respective test concentration. Subsequently, 1 mL of an algal suspension was added to each replicate providing a cell density of 104 cells/mL.

Observation:
The final test solutions were all clear and colourless except for the highest test concentration that contained a few particles floating through the solution.

Test medium: M2 according to OECD 201 using Milli-RO water
NH4Cl 15 mg/L
MgCl2.6H2O 12 mg/L
CaCl2.2H2O 18 mg/L
MgSO4.7H2O 15 mg/L
KH2PO4 1.6 mg/L
FeCl3.6H2O 64 μg/L
Na2EDTA.2H2O 100 μg/L
H3BO3 185 μg/L
MnCl2.4H2O 415 μg/L
ZnCl2 3 μg/L
CoCl2.6H2O 1.5 μg/L
CuCl2.2H2O 0.01 μg/L
Na2MoO4.2H2O 7 μg/L
NaHCO3 50 mg/L
Hardness (Ca+Mg) 0.24 mmol/L (24 mg CaCO3/L)
pH 8.1 ± 0.2

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Strain: Pseudokirchneriella subcapitata, strain: NIVA CHL 1
- Source (laboratory, culture collection): In-house laboratory culture
- Age of inoculum (at test initiation): 3 days before the start of the test, cells from the algal stock culture were inoculated in culture medium at a cell density of 1 x 104 cells/mL. The pre-culture was maintained under the same conditions as used in the test. The cell density was measured immediately before use.
- Method of cultivation: inoculating growth medium with algal cells from a pure culture on agar. continuous aeration and exposed to light in a climate room at a temperature of 21-24°C.
Light intensity 60 to 120 μE/m2/s when measured in the photosynthetically effective wavelength range of 400 to 700 nm.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test temperature:

22-23°C

pH:

7.8-8.0

Nominal and measured concentrations:

nominal (measured) after 0 - 3 days:
0 mg/L (The results of analysis of the samples taken from the test solutions showed that it was difficult, if not impossible, to accurately quantify the test concentrations. Measured concentrations in samples taken from the loading rates up to 32 mg/L were in general all below the limit of quantification (< 5 μg/L, lowest QC level). At the highest loading rate of 100 mg/L measured concentrations decreased from 196 μg/L at the start to 55 μg/L after 24 hours and to 29 μg/L after 72 hours. The TWA (Time Weighted Average) concentration was 61 μg/L. Hence, based on the water solubility limit (<4 μg/L) this remained clearly above that level. It was concluded that, based on the preparation method and the measured concentrations in the highest loading rate, the tested concentrations represented at least the maximum soluble
concentration in test medium.

Details on test conditions:

Stock solutions:
prepared individually at loading rates of 1.0, 3.2, 10, 3., 100mg/L
concentration control: (taken 3 days before the test): 95-109% of nominal

TEST SYSTEM
- Test vessel: 100mL, all glass, containig 50 mLof test solution, pre-incubated with stock solution before start exposure
- Initial cells density: 10000 cells /mL
- Final cell densities after 72h: 911000 (control), min 848000 (3.2 mg/L) - max 1127000 (100mg/L) for test concentrations
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6 (test medium without test item or other additives prepared in the same way as the stock solution


TEST MEDIUM / WATER PARAMETERS
M2

OTHER TEST CONDITIONS
Illumination: Continuously using TLD lamps with a light intensity of 90-91 microE.m-2.s-1

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: the test solution with the highest loading rate contained some flaoting material and particles in solution, therefore, algal density was determined with a microscope and a counting chamber (spectrophotometric measurements were not possible)

Incubation:
Capped vessels were distributed at random in the incubator and daily repositioned. During incubation the algal cells were kept in suspension by continuous shaking.

Reference substance (positive control):

yes

Remarks:

Potassium dichromate

Key result

Duration:

72 h

Dose descriptor:

EL50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

NOELR

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 61 µg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: above water solubility

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

>= 61 µg/L

Nominal / measured:

meas. (TWA)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: above water solubility

Details on results:

EL50 yield inhibition (72h-EYL50) > highest tested loading rate of 100 mg/L.
The EC50 yield inhibition (72h-EYC50) > TWA concentration of 61 μg/L, far above the water solubility (< 4 μg/L.)
The 72h-NOEL yield inhibition= highest tested loading rate of 100 mg/L.
The 72h-NOEC yield inhibition =TWA concentration of 61 μg/L.

Results with reference substance (positive control):

Feb 2017
ErC50 72h 1.2 mg/L (historical range 0.82-2.3 mg/L)
EyC50 72h 0.43mg/L (historical range 0.43-1.1 mg/L)

No significant differences were recorded between the values for growth rate or yield at any of the loading rates when compared to the control group.

Microscopic observations at the end of the test revealed a normal and healthy appearance of the algal cells exposed to the various test item loading rates when compared to the control.

Description of key information

No toxic effects occur at the range of solubility.

Key value for chemical safety assessment

EC50 for freshwater algae:

60 mg/L

Additional information

Two experimental studies are available.

In a new GLP guideline study according to OECD 201 (2017) with Pseudokirchneriella subcapitata saturated solutions with different loading rates were tested under consideration of OECD Guidance document on aquatic toxicity testing of difficult items and mixtures. Up to the highest test concentration no adverse effects on algae, growth and yield were observed. Concentration control analysis revealed that the highest test concentration were above the water solubility of < 4 μg/L.

In a supporting non-GLP guideline study using Scenedesmus subspicatus as test organism, an EC50 of 60 mg/L for biomass was determined. Lecithin was used as a solvent, however in a very high concentration 0.4 mg/L, which is above the vehicle limit of present guidelines. Almost 30 % of algae were inhibited in the solvent control (1992, Report 928155).

The data were re-evaluated to determine the effects on growth rate. In the test the ErC10 and ErC50 were above the water solubility. (ErC10(72h) = 73 mg/L. For further details on this re-evaluation see the corresponding attachment in the endpoint study record.

The effect concentrations are well above the solubility limit of the test substances (water solubility < 4 μg/L, see chapter 4.8 in IUCLID). In conclusion, the substance shows no effect to aquatic algae in the range of water solubility.