Sodium O-isobutyl dithiocarbonate

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 day study
July 08, 2021 -December 29, 2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Deviations:

yes

Remarks:

Principles of OECD Guideline 23 on testing of unstable substances

Principles of method if other than guideline:

Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (Guideline 23) was followed.
The method allows for mixing hydrolytically unstable substances in water to mimic the release to the environment via waste-water systems.
Analysis for xanthates was not possible and instead dissolved organic carbon analysis was performed to give a quantitative assessment of test material added.

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Sodium isobuthyl xanthate (Sodium O-isobuthyl dithiocarbonate);
batch no.: MK/01/04/2021;
the content of
active substance: 94.0 ±1% (analytical w/w);

Analytical monitoring:

yes

Details on sampling:

The samples of the test item concentrations and the control water solutions were analysed after 0, 3, 7, 10, 14, 19, 21 days of exposure.

Vehicle:

no

Remarks:

Mixed in water

Test organisms (species):

Daphnia magna

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Test temperature:

19.3 – 20.9ºC,

pH:

7.70 – 8.52

Dissolved oxygen:

8.3–9.1 mg/L

Nominal and measured concentrations:

5.0, 2.5, 1.25, 0.63, 0.31 mg/L plus control.

Reference substance (positive control):

no

Key result

Duration:

21 d

Dose descriptor:

EC10

Effect conc.:

ca. 1.25 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

immobilisation

Remarks:

Parental effects.

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

> 5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality: Number of living offspring produced per surviving parental animal {for Daphnia magna, TG 211}

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

>= 5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

morphology

Remarks:

Mean body length of parent

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

2.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth

Remarks:

Mean intrinsic rate of population growth

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

5 mg/L

Nominal / measured:

nominal

Basis for effect:

other: Mean intrinsic rate of population growth

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

ca. 0.31 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

immobilisation

Remarks:

of parent

Duration:

21 d

Dose descriptor:

EC50

Effect conc.:

2.5 mg/L

Nominal / measured:

nominal

Basis for effect:

immobilisation

Remarks:

of parent

Details on results:

The choice of final test concentrations in the main study was based on levels of immobilisation of adults in the preliminary acute study and preliminary reproductive toxicity study. However, it is noted that the toxic effects seen in the main study were lower than expected from these preliminary tests, meaning that reproductive the EC50 value could not be accurately determined. This is not considered to impact on the validity of the results which demonstrate that the test concentration leading to chronic effects is close to the concentrations resulting in acute toxicity and does not impact on final GHS classification.
The results of the different examinations on survival of adults, numbers of young and vigour of young make the use of statistical analysis in appropriate. Therefore, the data has been assessed to give approximate results for use in deriving the PNEC and for Classification.

Validity criteria fulfilled:

yes

Conclusions:

The results of the different examinations on survival of adults, numbers of young and vigour of young make the use of statistical analysis in appropriate. Therefore, the data has been assessed to give approximate results for use in deriving the PNEC and for Classification.

Survival of adults NOEC ca 1.25 mg/l, EC10 ca 2.5 mg/l and EC50 ca 5 mg/l
Growth of surviving adults, NOEC > 5 mg/l
Reproduction indices based on surviving adults, NOEC > 2.5 mg/l < 5 mg/l. Estimated EC10 ca 5 mg/l

The fact that statics could not be used to generate more precise figures for EC10 or EC50 does not impact on the classification of the substance (effects in range 1 – 10 mg/l) and it is assumed that the concentration of 1.25 mg/l can be used to generate a PNEC.

Executive summary:

In a semi-static reproduction test, young Daphnia magna (< 24 h old) were exposed for 21 days to the test item Sodium isobuthyl xanthate (Sodium O-isobuthyl dithiocarbonate), in the following test item concentrations: 0.31, 0.63, 1.25, 2.5, 5.0 mg/L plus the control.

Ten replicates were used for each treatment and the control.

In a preliminary study, the immobilisation Daphnia magna was: 10, 30, 10, 40 and 60% in the test item concentrations of 0.31, 0.63, 1.25, 2.50, 5.0 mg/L 

The mean body length of parent Daphnia magna was 101.4, 103.8, 102.2, 109.1 and 106.2% in the respective test item concentrations 0.31, 0.63, 1.25, 2.5, 5.0 mg/L in comparison with the control.

No changes of parent Daphnia magna appearance (e.g. discoloration, deformation, trapping on the surface) in comparison with the control were observed.

In all test item concentrations and the control no aborted broods, dead offspring or ephippia were observed.

The intrinsic rate of population growth for the test item concentrations and control demonstrate that Daphnia magna populations were growing. The intrinsic rate of population growth was 99.1, 101.4, 104.0, 89.1 and 74.8% in the respective test item concentrations of 0.31, 0.63, 1.25, 2.5, 5.0 mg/L in comparison with the control.

The concentrations of Sodium isobuthyl xanthate (Sodium O-isobuthyl dithiocarbonate) were not chemically analysed do to the known hydrolytic instability. Instead of chemical determination of the test item concentrations the characterization the exposure levels of the test item over time using a validated Total Organic Carbon (TOC) method was performed.
The samples of the test item concentrations and the control water solutions were analysed after 0, 3, 7, 10, 14, 19, 21 days of exposure. In fresh samples at exposure initiation, day 7, day 14, and day 19, the determinations of
the TOC was in the range 0.990 – 3.416 mgC/L. In spent samples at day 3, day 10, day 17, and at exposure termination thedeterminations of the TOC was in the range 1.159 – 4.834 mgC/L. There results were
corrected by the value measured for the control sample in series.

The choice of final test concentrations in the main study was based on levels of immobilisation of adults in the preliminary acute study and preliminary reproductive toxicity study. However, it is noted that the toxic effects seen in the main study were lower than expected from these preliminary tests, meaning that reproductive the EC50
value could not be accurately determined. This is not considered to impact on the validity of the results which demonstrate that the test concentration leading to chronic effects is close to the concentrations resulting in acute toxicity and does not impact on final GHS classification.
The endpoint values were determined based on the nominal test item concentrations.

Description of key information

The results of the different examinations on survival of adults, numbers of young and vigour of young make the use of statistical analysis in appropriate. Therefore, the data has been assessed to give approximate results for use in deriving the PNEC and for Classification.

 

Survival of adults NOEC ca 1.25 mg/l, EC10 ca 2.5 mg/l and EC50 ca 5 mg/l

Growth of surviving adults, NOEC > 5 mg/l

Reproduction indices based on surviving adults, NOEC > 2.5 mg/l < 5 mg/l.  Estimated EC10 ca 5 mg/l

 

The fact that statics could not be used to generate more precise figures for EC10 or EC50 does not impact on the classification of the substance (effects in range 1 – 10 mg/l) and it is assumed that the concentration of 1.25 mg/l can be used to generate a PNEC.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

EC10

Remarks:

Parental

Effect concentration:

ca. 1.25 mg/L