Methanethiol

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:

from 06/11/03 to 15/03/04

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: 2b: study with acceptable restrictions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2004

Report date:

2004

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

yes

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

Test guideline 3

Qualifier:

according to guideline

Guideline:

other: Water Quality- guidance for algal growth inhibition tests with poorly soluble organic and inorganic solids, volatile compounds, heavy metals and waste water (1999)

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Sodium methanethiolate

EC Number:

225-969-9

EC Name:

Sodium methanethiolate

Cas Number:

5188-07-8

IUPAC Name:

sodium methanethiolate

Details on test material:

- Name of test material: sodium methyl mercaptide at 32.9 % in water
- Lot/batch No.: SMM33 0050-7
- Physical state: clear liquid at 40 °C, waxy solid at 20 °C
- Solubility: completely soluble at 20 °C

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
not relevant

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

Treatment of the sample: dilution in the ISO C3 medium after obtaining a basic-pH sample with sodium hydroxide

Test solutions

Vehicle:

yes

Details on test solutions:

Preparation:
A stock solution of the test item diluted in water was prepared just a few minutes before the beginning of the test by mixing 119 mg (100 µL) of sodium methyl mercaptide in 119 mL of dilution water, with minimum headspace.

Test organisms

Test organisms (species):

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

Details on test organisms:

TEST ORGANISM
- Common name: Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum)
- Freshwater green algae

ACCLIMATION
- Culturing media and conditions:
- 2 flasks containing 100 mL of axenic stock culture of algae incubated at 23 °C (+ or - 1 °C)
- Aeration: continuous (air filtered at 0.22 µm)
- Lighting: photoperiod: 16 hours of illumination, 8 hours of darkness
- 3 to 5 days bofore the beginning of the study, 2 pre-cultures were prepared by inoculating each stock suspension of algae (5 mL) into sterile dilution water (500 mL). The pre-cultures were incubated under the same conditions as those used for the stock cultures.

Study design

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test conditions

Hardness:

no data

Test temperature:

23 ± 1°C

pH:

from 7.56 to 8.03

Dissolved oxygen:

from 8.4 to 16.2 mg/L

Salinity:

no data

Nominal and measured concentrations:

Nominal concentrations: 0 - 0.5 - 1 - 5 - 10 - 50 and 100 mg active ingredient (a.i.)/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 120 ml glass bottles stoppered with PTFE bungs and sealed with aluminium caps
- Approximately 10,000 algae cells/ml were added to each inoculated control or test flask
- Inoculated control flasks (algae control), non-inoculated blanks (dilution water), non-inoculated flasks with sodium methanethiolate and inoculated flasks with sodium methanethiolate were prepared in triplicate.

OTHER TEST CONDITIONS
- Continuously shaken with a rotation of 20 rpm
- Constantly illuminated by 8 fluorescent tubes.

EFFECT PARAMETERS MEASURED
- Algae concentrations determined by cytofluorimetry

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

6.3 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

biomass

Remarks on result:

other: 95% CL: 4.1 - 9.3 mg/L

Effect concentrations 2

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

15 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% CL: 10 - 23 mg/L

Effect concentrations 3

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.81 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

biomass

Effect concentrations 4

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

4.1 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Effect concentrations 5

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

2.1 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

biomass

Effect concentrations 6

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

6 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

- The test solutions were clear and colorless at test initiation and termination.  No precipitate was observed.
- All algae examined microscopically at test termination appeared normal.
- Since the final test substance concentrations measured in non-inoculated flasks at 72 hours decreased (>80%) in respect to the initial test substance concentrations, geometric averages of the initial and final measured test substance concentrations were used to calculate the EC and NOEC values.

Applicant's summary and conclusion

Validity criteria fulfilled:

no

Remarks:

See conclusion

Conclusions:

The validity criteria of the study were not all respected:
- The increase in cell density, measured in the control solution between the end and the beginning of the test, was greater than a factor of 16.
- The final concentrations of sodium methyl mercaptide were not maintained within the designated limit of 80 % of the initial concentrations in non-inoculated flasks.

Executive summary:

Acute toxicity to Pseudokirchnerella subcapitata has been investigated according to OECD Guideline 201 and EU Method C.3.

Pseudokirchnerella subcapitata were exposed for 72 hours to an aqueous solution of sodium methyl mercaptide at different nominal concentrations of 0.5 - 1 - 5 - 10 - 50 and 100 mg active ingredient (a.i.)/L.

The EC50 - 72h values for cell growth and growth rate were 6.3 and 15 mg a.i./L, respectively. The NOEC values for cell growth and growth rate were 0.81 and 4.11 mg a.i./L, respectively.