Dipotassium disulphate

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

No data were found for the test substance. The read-across chemicals Na2SO4 and H2SO4 were negative in a bacterial reverse mutation assay, and Na2SO4 was negative in an in vitro chromosome aberration assay and mouse lymphoma assay.

Link to relevant study records

Reference

Endpoint:

in vitro gene mutation study in bacteria

Remarks:

Type of genotoxicity: gene mutation

Type of information:

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

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study was selected as the key study because the information provided for the hazard endpoint is sufficient for the purpose of classification and labelling and/or risk assessment.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

no

Remarks:

Conducted according to guideline dated 1997

GLP compliance:

not specified

Type of assay:

bacterial reverse mutation assay

Target gene:

histidine

Species / strain / cell type:

other: Salmonella typhimunum: TA100, TA97, TA102, TA98, and TA1535

Metabolic activation:

with and without

Metabolic activation system:

liver homogenates of Sprague-Dawley rats induced with Aroclor 1254

Test concentrations with justification for top dose:

pH: 4.0, 5.0, 5.5, 6.0, 6.3, 6.8, 7.0, 7.4, 7.8, 8.0 and 9.0

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

sodium azide

methylmethanesulfonate

other: daunomycin

Details on test system and experimental conditions:

The effect of pH changes on bacterial reversion rate was evaluated by adopting tow modifications of the standard plate incorporation assay. First, a preincubation of bacteria with buffer solutions at pH’s ranging from 4 to 9 were made using H3PO4, H2SO4, and their sodium salts. Cultures of the tester strains (0.1 mL) were mixed with 0.5 mL of the buffer solutions, incubated at 37°C for 1 hour, and then added to the top agar, plated on Vogel-Bonner medium plates. These were then incubated at 37°C for 60 hours. The numbers of revertants per plate were eventually counted. For agar plate incorporation, a modified Vogel-Bonner medium was prepared. A 50x salt solution (10 g MgSO4•7H2O, 100 g citric acid•H2O, 500 g K2HPO4 and 175 g NaNH4HPO4•4H2O in 670 mL distilled water) was prepared and 10 mL was added to 220 mL of distilled water. The diluted solution was then adjusted to the final pH’s with 10 N NaOH. After sterilization, 220 mL agar solution (45 g agar per 1320 mL water) and 50 mL of 5% dextrose were added to the 230 mL of pH-adjusted salt solution. Plates were then poured with 25 mL of the above media in each. The pH was confirmed for each plate type by using a surface pH electrode. The pH of the total plate assay system was assumed to be the same as that of the initial base agar. All the plates were prepared with enough NaCl added to the medium to result in ionic strength identical to that of the pH 7.0 controls. The addition of S9 fraction was scheduled for some experiments in order to complete the bioassay protocol, as well as to check a previously reported detoxifying action of S9 for some inorganic. S9 microsomal fraction was prepared from liver homogenates of Sprague-Dawley rats induced with Aroclor 1254.

Evaluation criteria:

not reported

Statistics:

not reported

Species / strain:

other: Salmonella typhimunum: TA100, TA97, TA102, TA98, and TA1535

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

The incubation of S. typhimurium tester strains with different buffer solutions at pH ranging from 5.5 to 9 had no effect on the bacterial reversion rates. The acidification of incubation mixture to pH 5.0 produced toxic effects on bacteria as the appearance of survivors suggested; at lower pH values, complete bacterial death was observed. The same lack of effects was obtained by using the base agar plates at different pH values. As expected, the ineffectiveness of pH decrease was invariably unchanged by the addition of S9 fraction.

Remarks on result:

other: all strains/cell types tested

Remarks:

Migrated from field 'Test system'.

Conclusions:

Interpretation of results (migrated information):
negative

No effects were detectable in S. typhimurium tester strains following sublethal pH decrease.
This study and the conclusions which are drawn from it fulfil the quality criteria (validity, reliability, repeatability).

Executive summary:

Salmonella typhimurium (strains TA97, TA98, TA100, TA102, TA1535) were exposed to different pH levels of the test substance ranging from 4 to 9, by both liquid incubation and agar plate incorporation.

The incubation of S. typhimurium tester strains with different test substance buffer solutions at pH ranging from 5.5 to 9 had no effect on the bacterial reversion rates. The acidification of incubation mixture to pH 5.0 produced toxic effects on bacteria as the appearance of survivors suggested; at lower pH values, complete bacterial death was observed. The same lack of effects was obtained by using the base agar plates at different pH values. As expected, the ineffectiveness of pH decrease was invariably unchanged by the addition of S9 fraction. No genotoxic effects were detectable in S. typhimurium tester strains following sublethal pH decrease.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

Additional information from genetic toxicity in vitro:

No data were available for genetic toxicity with the test substance.  Bacterial reverse mutation assays with Na₂SO₄ and H₂SO₄, and in vitro chromosome aberration assay and mouse lymphoma assay with Na₂SO₄ were used as a read-across to fulfill the data gap for the test substance. The underlying hypothesis for the read-across between the test substance and the read across substances, Na₂SO₄ and H₂SO₄, is the likelihood of common precursors and/or breakdown products, via physical or biological processes, which result in structurally similar chemicals (e.g. the metabolic pathway approach of examining related chemicals such as acid/ester/salt). Additional documentation, provided within the IUCLID Assessment Reports section, supports the read-across approach.

 

Negative results were observed in an in vitro study in bacterial cells (Salmonella typhimurium), an in vitro study in mammalian cells (Chinese hamster V79), and a mouse lymphoma assay with the read-across substance (Na₂SO₄). H₂SO₄ has been shown to be negative in bacterial cells. H₂SO₄ did cause chromosomal aberrations in CHO cells (pH 3.5-7.4 both with and without S9). The chromosomal effects are known to be a consequence of reduced pH. Similar findings have been observed with other inorganic acids and have been ascribed to nongenotoxic effects mediated by marked reductions in media. Hence the effects reported here with H2SO4, in contrast to results with other sulphates, are considered to be artefactual in nature. Therefore, based on the data from the read-across substances, the test substance is not expected to be genetically active.

Justification for selection of genetic toxicity endpoint
In addition to the bacterial reverse mutation assay with H2SO4, multiple scientifically valid studies with the read-across chemicals, Na2SO4 and H2SO4, have been identified as pertinent to the hazard conclusion for this endpoint.

Justification for classification or non-classification

Based on negative results in genetic toxicity tests with the read-across chemicals, Na₂SO₄ and H₂SO₄, the test substance does not need to be classified for genetic toxicity according the EU Directive 67/548/EEC and EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.