LBX98

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Remarks:

Type of genotoxicity: gene mutation

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

weight of evidence

Justification for type of information:

No data are available for the target substance. Studies of genotoxicity in vitro with the individual (o-, m- and p-) cresol isomers report negative results in Ames tests and mammalian cell mutation assays and positive results in studies of chromosomal aberration in vitro. Studies of genotoxicity in vivo report negative results. Studies of genotoxicity in vitro with xylenol (mixed isomers) report negative results in Ames tests and mammalian cell mutation assays and positive results in studies of chromosomal aberration in vitro. Studies of genotoxicity in vivo report negative results for 3,5-, 2,4- and 2,6-xylenol. Based on the consistent response seen for the source substances, it can be concluded that the target substance is also not genotoxic.

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

no

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

Reaction mass of 2,4-xylenol and 2,5-xylenol

EC Number:

905-287-4

Cas Number:

1638758-52-7

Molecular formula:

(CH3)2C6H3OH

IUPAC Name:

Reaction mass of 2,4-xylenol and 2,5-xylenol

Test material form:

solid: bulk

Method

Species / strain

Species / strain 1

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100

Additional strain / cell type characteristics:

not specified

Species / strain 2

Species / strain / cell type:

E. coli WP2 uvr A

Additional strain / cell type characteristics:

not specified

Metabolic activation:

with and without

Metabolic activation system:

S9 derived from Aroclor 1254 induced male Sprague-Dawley rats

Test concentrations with justification for top dose:

6.7, 10, 33, 67, 100, 333, 667, 1000, 3333 and 5000 µg/plate for strains TA98, TA100, TA1535, TA1537 and WP2 uvrA for the preliminary toxicity study (with and without metabolic activation).75, 200, 600, 1800 and 5000 µg/plate for TA98, TA100, TA1535, TA1537 and WP2 uvrA for the bacterial mutation assay (with and without metabolic activation).

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: dimethyl sulfoxide (DMSO) (and water for sodium azide dilution in the positive control)- Justification for choice of solvent/vehicle: Not stated, commonly used solvent

Controls

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

other:

Remarks:

2-aminoanthracene for WP2 uvrA in the presence of metabolic activation. 2-nitroluorene for TA98; sodium azide for TA100 and TA1535; 9-aminoacridine for TA1537; methyl methanesulfonate for WP2 uvrA in the absence of metabolic activation.

Details on test system and experimental conditions:

METHOD OF APPLICATION: in agar (plate incorporation)DURATION- Preincubation period: 12 hours- Exposure duration: 48 - 72 hours- Expression time (cells in growth medium): not stated- Fixation time (start of exposure up to fixation or harvest of cells): not stated

Evaluation criteria:

All cultures must demonstrate the characteristic mean number of spontaneous revertants in the vehicle controls.The mean of each positive control must exhibit at least a 3.0 fold increase in the number of revertants over the mean value of the respective control. A minimum of three non toxic dose levels is required for evaluation. A dose level is considered to be toxic if there is a >50% reduction in the mean number of revertants per plate compared to the mean vehicle control value and at least a moderate reduction in the background lawn.

Results and discussion

Test results

Test results 1

Species / strain:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

not specified

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Test results 2

Species / strain:

E. coli WP2 uvr A

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

not specified

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

COMPARISON WITH HISTORICAL CONTROL DATA: Historical control data were found to support the study outcome.

Remarks on result:

other: all strains/cell types tested

Remarks:

Migrated from field 'Test system'.

Any other information on results incl. tables

The results of the genotoxicity study found that mixed xylenols were not genotoxic at any dose level tested. A summary of the results is presented below.

Table 1: Summary of results of the mutagenicity assay

Dose (µg/plate)	Average revertants per plate ± standard deviation
	TA98	TA100	TA1535	TA1537	WP2 uvrA
In the absence of metabolic activation
Vehicle control	17 ± 2	153 ± 13	16 ± 2	7 ± 2	24 ± 3
75	14 ± 5	126 ± 3	23 ± 5	7 ± 1	24 ± 2
200	17 ± 2	126 ± 31	19 ± 4	6 ± 2	20 ± 5
600	14 ± 5	133 ± 26	19 ± 2	6 ± 1	15 ± 3
1800	16 ± 3	125 ± 11	21 ± 7	4 ± 1	13 ± 3
5000	3 ± 1	0 ± 0	3 ± 1	0 ± 0	1 ± 2
Positive control	115 ± 12	551 ± 8	272 ± 6	644 ± 121	117 ± 7
In the presence of metabolic activation
Vehicle control	20 ± 2	151 ± 15	17 ± 5	6 ± 2	20 ± 6
75	22 ± 5	163 ± 20	17 ± 2	5 ± 1	19 ± 6
200	18 ± 5	168 ± 6	19 ± 2	6 ± 2	16 ± 2
600	22 ± 3	154 ± 6	21 ± 4	6 ± 3	16 ± 3
1800	22 ± 2	144 ± 11	23 ± 2	6 ± 2	9 ± 3
5000	4 ± 2	0 ± 0	6 ± 2	0 ± 0	0 ± 0
Positive control	1000 ± 147	74 ± 74	108 ± 9	128 ± 17	794 ± 95

 

Applicant's summary and conclusion

Conclusions:

Mixed xylenols were found to be negative for genotoxicity.

Executive summary:

All criteria for a valid study were met. The results indicate that mixed xylenols did not cause a positive response either in the presence or absence of metabolic activation by Aroclor-induced rat liver S9. Mixed xylenols were therefore concluded to be negative for genotoxicity.

The above results are suitable to be used for read across for Reaction mass of 2,4-xylenol and 2,5-xylenol, due to the category being based on structural similarity and comparable physicochemical properties, leading to similar (eco)toxicological properties.