Phenol, 2,4-bis[(dodecylthio)methyl]-6-methyl-

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

1998-05-04 to 1998-05-15

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP-guideline study. According to ECHA guidance, a study with a read-across substance can have no reliability of higher than 2. The study itself is valid without restriction.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1998

Report date:

1998

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

GLP compliance:

yes (incl. QA statement)

Test material

Test material information

Constituent 1

Reference substance name:

4,6-bis(octylthiomethyl)-o-cresol

EC Number:

402-860-6

EC Name:

4,6-bis(octylthiomethyl)-o-cresol

IUPAC Name:

402-860-6

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

For analysis of the actual test article concentrations, duplicate samples from the freshly prepared test medium (the undiluted filtrate of the supersaturated stock emulsion) and the control without algae were taken just before the start of the test (hour 0).

For determination of the stability of the test article under the test conditions or the maintenance of the test article concentrations during the test period, sufficient volumes of the freshly prepared test media of the undiluted filtrate were incubated under the same conditions as in the actual test (but without algae), and were sampled in duplicate after the 72-hour test period.

The concentration of the test article was analyzed in all test samples from both sampling times (0 and 72 hours). From the control only one of the duplicate samples was analyzed per sampling time. All samples are kept stored at about -20 °C to enable additional analyses.

Test solutions

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
Due to the low water solubility of the test article the following dosage of the test article was chosen:

A supersaturated stock emulsion of the test article with a nominal concentration of 100 mg/l was prepared by dispersing 200 mg of the test article by means of ultrasonic treatment for fifteen minutes in two litres test water. No auxiliary solvent or emulsifier was used. This supersaturated stock emulsion was stirred by a magnetic stirrer at room temperature in the dark for 96 hours to dissolve and/or disperse a maximum concentration of the test article in the stock emulsion. After stirring, the stock emulsion was allowed to stand at room temperature in the dark for one hour. Undissolved or unemulsified oily drops of the test article were removed from the surface of the supersaturated stock emulsion by means of a pasteur pipette.

The remaining test medium of the stock emulsion was filtered through a membrane filter (pore size 0.45 µm) just before test start. The first 100 ml of the filtrate was discarded to avoid a potential loss of test article due to adsorption on the filter.

Test organisms

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Details on test organisms:

TEST ORGANISM
- Common name: Green alga
- Strain: SAG 86.81
- Source (laboratory, culture collection): SAG
- Age of inoculum (at test initiation): 72h
- Method of cultivation: standardized conditions, Medium according to OECD 201

Study design

Test type:

static

Water media type:

freshwater

Total exposure duration:

72 h

Test conditions

Test temperature:

24°C

pH:

control: 8.0-9.1
100 mg/L: 8.0-9.2

Nominal and measured concentrations:

100 mg/l loading rate, nominal; (0.013 mg/L measured at test start)

Details on test conditions:

TEST SYSTEM
- Type (delete if not applicable): closed
- Material, size, headspace, fill volume: 50 ml glass flasks 15 ml test volume

- Initial cells density: 10000 cells/ml
- Control end cells density: yes
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 3
- No. of vessels per vehicle control (replicates): 3

GROWTH MEDIUM
- Standard medium used: yes


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: according to OECD 201

OTHER TEST CONDITIONS
- Adjustment of pH: not during test
- Photoperiod: continous, 7060 to 8370 lux

EFFECT PARAMETERS MEASURED
- Determination of cell concentrations: cell counts after 0, 24, 48, 72 hours
- pH values: after 0 and 72 hours

Reference substance (positive control):

not specified

Results and discussion

Effect concentrations

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 100 mg/l loading rate

Any other information on results incl. tables

The mean analytically determined test article concentration in the samples from the freshly prepared test medium of the main test (stock emulsion filtrate with a nominal concentration of 100 mg/l) amounted to 0.013 mg/l at the start of the test. In this test medium which was incubated under the test conditions during the test period without algae, the mean concentration decreased to a value below the limit of detection (LOD) of 0.005 mg/l after 72 hours of exposure. In this way a total mean measured test article concentration of 0.008 mg/l was calculated. The loss could possibly be caused by degradation of the test article due to the intense irradiation during incubation, or due to oxidation of the test article.

 

Biological results are however reported on the basis of a loading rate of 100 mg test article/I rather than on the basis of measured concentrations in the test medium. The mean algal cell densities in the test medium of the stock emulsion filtrate were higher than in the parallel control culture after 24, 48 and 72 hours of exposure. Thus, the test article clearly had no inhibitory effect on the growth (biomass and growth rate) of Scenedesmus subspicatus during the exposure period of 72 hours at a loading rate of 100 mg/l. This loading was therefore determined to be the 72-hour NOEL (highest test article loading without toxic effects after a test period of 72 hours). The 72-hour LOEL (lowest test article loading with toxic effects), and the 72-hour EL50 for the algal biomass b and the growth rate p were determined to be at a loading rate >100 mg/l. Loading rates in excess of 100 mg/l were not tested (based on the test guidelines).

 

Prior to filtration of the supersaturated stock emulsion oily drops of the test article were floating on the surface which were removed by means of a pasteur pipette. After filtration through a 0.45 µm membrane filter the test medium was homogeneous and clear, and remained homogeneous and clear throughout the 72-hour testing period. No abnormal observation was made concerning the shape of the algal cells in the undiluted filtrate compared to the algal cells in the control after 72 hours of exposure.

 

Applicant's summary and conclusion

Validity criteria fulfilled:

yes