Sodium O-isobutyl dithiocarbonate

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:

11.06.2021 - 28.09.2021
72 hours

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Guideline study
It is accepted that the parent substance will have hydrolysed in the course of the testing, but OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (Guideline 23) was followed.
The method allows for pre-mixing hydrolytically unstable substances in water to mimic the release to the environment via waste-water systems.
Analysis for parent material not possible.

Qualifier:

according 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:

Sodium isobutyl xanthate (Sodium O-isobutyl dithiocarbonate);
batch no.: MK/01/04/2021,
the content of sodium O-isobutyldithiocarbonate: 94.0 ±1%;
manufacturing date: April 15,2021, expiry date: April 15, 2022.

Analytical monitoring:

yes

Details on sampling:

At start and end of exposure period

Test organisms (species):

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

Details on test organisms:

The unicellular freshwater green algae, Raphidocelis
subcapitata (formerly Pseudokirchneriella subcapitata
(Korshikov) Hindák, Selenastrum capricornutum Prinz) SAG
61.81 cultivated at the Łukasiewicz Research Network –
Institute of Industrial Organic Chemistry Branch Pszczyna,
Ecotoxicology Research Group, Laboratory of Aquatic
Organisms Toxicology.
The algae were obtained from the Culture Collection of Algae at Göttingen University, Germany

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test temperature:

22.0 – 23.1°C

pH:

7.53 – 8.73

Nominal and measured concentrations:

10, 3.13, 0.98, 0.31, 0.095 mg/L plus the control.

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.31 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

yield

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

1.279 mg/L

95% CI:

> 0.798 - < 2.002

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

yield

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.31 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

2.1 mg/L

95% CI:

> 1.566 - < 2.971

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Validity criteria fulfilled:

yes

Executive summary:

The growth of the green algae Raphidocelis subcapitata SAG 61.81 (formerly Pseudokirchneriella subcapitata) exposed to the test item, Sodium isobutyl xanthate (Sodium O-isobutyl dithiocarbonate), was investigated during a 72-hour test.

The test was performed in glass flasks with a capacity of 250 mL containing 100 mL of either the test item concentration, or the control, per replicate. The initial density of the algae was 1 x 104 cells/mL.

The definitive test was performed with the following test item concentrations:
10, 3.13, 0.98, 0.31, 0.095 mg/L plus the control.
The number of algal cells was determined with an indirect method, which involves a spectrophotometric measurement of the absorbance of algal suspension at 670 nm and converting its value into the number of cells using a standard curve. The absorbance for each replicate of each test item concentration and the control were measured after 24, 48, and 72 h of exposure.
Calculated inhibition of growth rate for the test item concentrations ranging from 0.095 to 10 mg/L after 72 h of exposure was in the range of -0.5 – 86.1% when compared to the control. Inhibition of yield for the test item concentrations ranging from 0.095 to 10 mg/L after 72 h of exposure was in the range of -2.0 – 99.1% when compared to the control.
In all test item concentrations, no differences in shape, size and colour of algal cells were reported as compared to the algal cells in the control.
Morphology observations of the algae cells were performed at exposure termination. In the test item concentrations of 0.095, 0.031 and 0.98 mg/L, no differences in shape, size and colour of algal cells were reported as compared to the algae cells in the control. In the test item concentrations of 3.13 and 10 mg/L smaller algae cells were observed as compared to the algae cells in the control.
As hydrolysis would have occured and because a flow-through test is not possible to perform, it is accepted that the test material will quickly dissapear. Analysis by total organic carbon analyses was performed in fresh samples of all test item concentrations and the control at exposure initiation and in old samples of all test item concentrations and the control at exposure termination (72-h old). T

his analytical approach did not account for any degradation or metabolisation effects which may have occurred
during exposure. The results were corrected by the value determined for the control sample
in a series and presented as the concentrations of total organic carbon (TOC).
In samples collected at exposure initiation, the analysed total organic carbon concentrations were in the range of below the LoQ value (< 1.0 mg C/L) – 11.8 mg C/L.
In 48-h old samples collected at exposure termination, the analysed total organic carbon concentrations were in the range of below the LoQ value (< 1.0 mg C/L) – 11.8 mg C/L.

The endpoint values were determined based on the nominal test item concentrations.

The endpoint values based on nominal test item concentration is given below:
The ErC50/72 h value is 2.145 mg/L (95% confidence interval: 1.566 – 2.971).
The LOEC/72 h value for growth rate is 0.98 mg/L.
The NOEC/72 h value for growth rate is 0.31 mg/L.

The EyC50/72 h value is 1.279 mg/L (95% confidence interval: 0.798 – 2.002).
The LOEC/72 h value for yield is 0.98 mg/L.
The NOEC/72 h value for yield is 0.31 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:

2.1 mg/L