Proxan-sodium

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 1.06.2021 to 14.09.2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Guideline study
A weak positive (equivocal) result was obtained even after repeating the assay
This result is similar to that seen for the main metabolite carbon disulphide

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

read-across: supporting information

Cross-reference 2

Reason / purpose for cross-reference:

read-across: supporting information

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Justification for type of information:

Special study performed to confirm rapid hydrolysis of potassium and sodium xanthates in simulated gastric fluid with identification of key metabolites.
This study is used to justify the use of surrogate data in animal testing on the basis that if ingested, the substance will rapidly degrade.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Study of the decomposition of eight samples of xanthates in simulated gastric fluid; sodium isoamyl xanthate, sodium isobutyl xanthate, sodium ethyl xanthateр potassium isoamyl xanthate, potassium ethyl xanthate (PEX). sodium isopropyl xanthate (SIPX), Potassium amyl xanthate and potassium isobutyl xanthate
The chemical reaction for this decomposition is:

Xanthate Salt + Hydrochloric acid Alcohol + Sodium Chloride + Carbon Disulphide

The reaction between simulated gastric fluid and the xanthate salts was carried out at 0oC for reasons of safety, as the reaction was expected to occur very quickly. The reaction mixture was then allowed to warm to room temperature over 1 hour, the final temperature being 25oC. A high degree of degradation at this temperature would lead to the inference that degradation would be at least as complete, if not more so, in actual gastric conditions.
Following the reaction solvent was added to produce a biphasic mixture, and the resulting organic
phases were analysed by GC-MS to confirm the presence of the corresponding alcohols. These
alcohols were quantified by comparison to known standards in order to confirm the completeness of the reaction, and to show that these salts behave in the same way under these reaction conditions.

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

Performed at pH 1.5 in synthetic gastric fluid

Details on test conditions:

Performed at 5 g/l to simulate possible concentration following ingestion
Performed at low temperatures for safety reasons due to exothermic nature of reaction

Duration:

1 h

pH:

1.5

Temp.:

0 °C

Initial conc. measured:

ca. 5 000 mg/L

Remarks:

Performed at initial temperature of 0 C, but in view of exothermic reaction, temperature will have risen by the end of the reaction.

Number of replicates:

One replicate per substance
A number of xanthates were evaluated as part of this study; all showed the same outcome

Positive controls:

no

Negative controls:

no

Statistical methods:

Not required

Preliminary study:

No

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

Details on hydrolysis and appearance of transformation product(s):

Exothermic reaction. No direct measurement of carbon disulphide possible, but elemental sulphur noted (estimated to be as dissolved sulphur dioxide or sulphates

% Recovery:

0

pH:

1.5

Temp.:

0 °C

Duration:

1 h

Remarks on result:

other: No parent material detected

Remarks on result:

not determinable because of methodological limitations

Remarks:

Too rapid to determine a rate constant

Details on results:

Rapid exothermic reaction in simulated gastric fluid at a loading of 5g/l

Sodium isoamyl xanthate, sodium isobutyl xanthate, sodium ethyl xanthateр  potassium isoamyl xanthate, potassium ethyl xanthate (PEX), sodium isopropyl xanthate (SIPX), Potassium amyl xanthate and potassium isobutyl xanthate were added to separate solutions of simulated gastric fluid at 0 C over 1 hour. The low starting temperature was to prevent reaction occurring too quickly, for reasons of safety.

Following the reaction, a liquid-liquid extraction was performed with ethyl acetate and the organic solvent analysed using GCMS. The extracts were compared to a standard curve of ethanol, isoamyl alcohol and isobutyl alcohol were quantified.

Based on analysis of the alcohols. degradation of sodium isopropyl xanthate (SIPX), was found to be  100% under the experimental conditions and degradation of potassium amyl xanthate was found to give 93% under the experimental conditions , potassium isobutyl xanthate was found to give 94%, sodium isobutyl xanthate was found to give 96% under the experimental conditions .  However, no xanthates could be found at the end of the exposure period.

To confirm that potassium salts will behave in a similar manner, potassium xanthates was added to simulated gastric fluid under the same conditions as the sodium salts above. A liquid-liquid extraction was performed with ethyl acetate and the organic solvent analysed using GCMS. Isoamyl alcohol was observed in the resulting gas chromatogram, as expected.

NMR spectroscopy did not provide any further evidence of the presence of xanthate post addition to gastric fluid. 

To confirm that the sodium or potassium remains in solution as the chloride salt, ICP-OES analysis was carried out on the aqueous phase of the reaction mixture, as well as on the simulated gastric fluid with the difference between the two measurements being an indication of how much sodium or potassium has been added as a result of the xanthate degradation. The analysis showed increased levels of potassium and sodium in the gastric fluid phase upon addition of potassium and sodium xanthates respectively. This provides further evidence that the potassium salts behave in a similar manner to the sodium salts under the experimental conditions.

The increase in sodium could not be quantified owing to the high levels of Na observed, and the addition of Na from processing.

For Potassium Xanthates, a significant increase in potassium was observed and the potassium and sodium salts can be considered as behaving in identical manner.

Carbon disulphide was not detected and due to limitations of the methods detection of carbon dioxide or sulphur dioxide was not possible.  There was no reported odour of carbon dislulphide.

Executive summary:

Based on analysis of the alcohols. degradation of sodium isopropyl xanthate (SIPX), was found to be  100% under the experimental conditions and degradation of potassium amyl xanthate was found to give 93% under the experimental conditions , potassium isobutyl xanthate was found to give 94%, sodium isobutyl xanthate was found to give 96% under the experimental conditions .  However, no xanthates could be found at the end of the exposure period.

 

To confirm that potassium salts will behave in a similar manner, potassium xanthates was added to simulated gastric fluid under the same conditions as the sodium salts above. A liquid-liquid extraction was performed with ethyl acetate and the organic solvent analysed using GCMS. The corresponding alcohol was observed in the resulting gas chromatogram, as expected.

NMR spectroscopy did not provide any further evidence of the presence of xanthate post addition to gastric fluid. 

To confirm that the sodium or potassium remains in solution as the chloride salt, ICP-OES analysis was carried out on the aqueous phase of the reaction mixture, as well as on the simulated gastric fluid with the difference between the two measurements being an indication of how much sodium or potassium has been added as a result of the xanthate degradation. The analysis showed increased levels of potassium and sodium in the gastric fluid phase upon addition of potassium and sodium xanthates respectively. This provides further evidence that the potassium salts behave in a similar manner to the sodium salts under the experimental conditions.

The increase in sodium could not be quantified owing to the high levels of Na observed, and the addition of Na from processing.

For Potassium Xanthates, a significant increase in potassium was observed and the potassium and sodium salts can be considered as behaving in identical manner.

Carbon disulphide was not detected and due to limitations of the methods detection of carbon dioxide or sulphur dioxide was not possible.  There was no reported odour of carbon dislulphide.

 

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2021

Report date:

2021

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test using the Hprt and xprt genes)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

22/2020/DPL

Type of assay:

in vitro mammalian cell gene mutation test using the Hprt and xprt genes

Test material

Test material information

Constituent 1

Reference substance name:

Sodium O-isobutyl dithiocarbonate

EC Number:

246-805-2

EC Name:

Sodium O-isobutyl dithiocarbonate

Cas Number:

25306-75-6

Molecular formula:

C5H10OS2.Na

IUPAC Name:

sodium O-isobutyl dithiocarbonate

Constituent 2

Reference substance name:

Sodium isobutyl xanthate

IUPAC Name:

Sodium isobutyl xanthate

Test material form:

solid: particulate/powder

Method

Species / strain

Species / strain / cell type:

human lymphoblastoid cells (TK6)

Metabolic activation:

with and without

Test concentrations with justification for top dose:

In the main test, positive control (PC; 3-Methylcholanthrene at 100 μg/mL) and a negative control (NC; solvent) were used simultaneously
5 concentrations of the test item (360 μg/mL, 167 μg/mL, 78 μg/mL, 36 μg/mL, 17 μg/mL.
As the result for treatment without metabolic activation system (S9-) was equivocal and was repeated with the following concentrations: 360 μg/mL, 227 μg/mL, 143 μg/mL, 90 μg/mL, 57 μg/mL.

Controls

Untreated negative controls:

yes

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

3-methylcholanthrene

Results and discussion

Test results

Test results 1

Species / strain:

human lymphoblastoid cells (TK6)

Metabolic activation:

without

Genotoxicity:

ambiguous

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

True negative controls validity:

not applicable

Positive controls validity:

valid

Test results 2

Species / strain:

human lymphoblastoid cells (TK6)

Metabolic activation:

with

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

True negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

The results for treatment with presence of the metabolic activation system (S9+, run 2) were clearly negative. However, the results for the treatment in the absence of the metabolic activation system (S9-, run 1) were equivocal (neither clearly negative nor clearly positive). Therefore the experiment was repeated with modified conditions (S9-, run 3). In this repeated experiment the clearly positive result was only observed at the highest concentration, where the RS was below 10% (very high cytotoxicity). Therefore, this positive result should be taken with care.

Applicant's summary and conclusion

Conclusions:

A weak positive (equivocal) result was obtained without S-9 even after repeating the assay
Negative in the presence of S-9
This result is similar to that seen for the main metabolite carbon disulphide

Executive summary:

A preliminary test (solubility test and cytotoxicity test) was performed prior to the main test.
In the main test, positive control (PC; 3-Methylcholanthrene at 100 µg/mL) and a negative control
(NC; solvent) were used simultaneously with 5 concentrations of the test item (360 µg/mL, 167
µg/mL, 78 µg/mL, 36 µg/mL, 17 µg/mL. However, the result for treatment without metabolic
activation system (S9-) was equivocal and was repeated with the following concentrations: 360
µg/mL, 227 µg/mL, 143 µg/mL, 90 µg/mL, 57 µg/mL.

Results of the studies:
The results for treatment with presence of the metabolic activation system (S9+, run 2) were clearly
negative. However, the results for the treatment in the absence of the metabolic activation system
(S9-, run 1) were equivocal (neither clearly negative nor clearly positive). Therefore the experiment
was repeated with modified conditions (S9-, run 3). In this repeated experiment the clearly positive
result was only observed at the highest concentration, where the RS was below 10% (very high
cytotoxicity). Therefore, this positive result should be taken with care.

Interpretation of the study results:
All acceptance criteria were met but the results remained equivocal even after repeating the
experiment. Therefore, the test should be considered likely to be positive in this study and further
testing with another system is recommended to clarify the genotoxicity properties of the test item.

Note that this is consistent with the main metabolite, carbon disulphides and the result was not unexpected.