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Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

o-cresol reveals no gene mutation activity and the clastogenic activity in vitro was not confirmed by respective in vivo studies.

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vitro gene mutation study in bacteria
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: guideline test but no data on GLP
Qualifier:
according to guideline
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
GLP compliance:
not specified
Type of assay:
bacterial reverse mutation assay
Species / strain / cell type:
other: Salmonella typhimurium TA98, TA100, TA1535, TA1537, TA1538
Additional strain / cell type characteristics:
other: Salmonella typhimurium TA98, TA100, TA1535, TA1537, TA1538
Metabolic activation:
with and without
Metabolic activation system:
A 9000 x g supernatant from Sprague-Dawley rat liver pretreated with Aroclor 1254.
Test concentrations with justification for top dose:
0, 5, 50, 500, 5000 µg/plate dissolved in DMSO
Vehicle / solvent:
DMSO
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
not specified
Positive controls:
yes
Positive control substance:
other: Sodium azide, 2-nitrofluorene, 9-Aminoacridine, 2-Aminoanthracene
Details on test system and experimental conditions:
Ames test: plate incorporation methodology
Evaluation criteria:
A dose-related significantly increased number of revertants was evaluated as a positive result.
Statistics:
Joncheere test
Species / strain:
other: Salmonella typhimurium TA98, TA100, TA1535, TA1537, TA1538
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
other: 5000 µg/plate
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
Positive controls were functional.

o-cresol yielded a negative result in the Ames test performed according to OECD TG 471 in the presence and in the absence of an additional metabolic activation system (Pool 1982).

Executive summary:

o-cresol yielded a negative result in the Ames test performed according to OEDCD TG 471 in the presence and in the absence of an additional metabolic activation system.

Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)
GLP compliance:
yes
Type of assay:
in vitro mammalian chromosome aberration test
Target gene:
no data
Species / strain / cell type:
other: Chinese Hamster Ovary (CHO) cells
Details on mammalian cell type (if applicable):
- Type and identity of media: McCoy`s 5a culture medium
- Properly maintained: yes
- Periodically checked for Mycoplasma contamination: yes
- Periodically checked for karyotype stability: yes
Additional strain / cell type characteristics:
not specified
Metabolic activation:
with and without
Metabolic activation system:
A 9000 x g supernatant prepared from adult male rat liver induced by Aroclor 1254.
Test concentrations with justification for top dose:
without: 150, 200, 250, 300 µg/ml
with: 250, 375, 500, 750, 1000 µg/ml
Vehicle / solvent:
DMSO
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
not specified
Positive controls:
yes
Positive control substance:
other: Mitomycin C , Cyclophosphamide
Details on test system and experimental conditions:
According to OECD guideline 473.
Evaluation criteria:
Concentration related increase.
Statistics:
Fisher's exact test with an adjustment for multiple comparisons.
Species / strain:
Chinese hamster Ovary (CHO)
Metabolic activation:
with and without
Genotoxicity:
positive
Cytotoxicity / choice of top concentrations:
other: determined in the range-finding study:| with metabolic activation: >= 1000 µg/ml; without metabolic activation: >= 300 µg/ml
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid

o-cresol showed clastogenic activity when tested for chromosome aberrations in Chinese Hamster Ovary (CHO) cells in vitro according to OECD TG 473 in the presence and in the absense of a metabolic activation system.

Executive summary:

o-cresol showed clastogenic activity when tested for chromosome aberrations in Chinese Hamster Ovary (CHO) cells in vitro according to OECD TG 473 in the presence and in the absense of a metabolic activation system.

Endpoint:
in vitro gene mutation study in mammalian cells
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: no information on colonie size and no information of purity of TS
Qualifier:
according to guideline
Guideline:
OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)
GLP compliance:
yes
Type of assay:
mammalian cell gene mutation assay
Target gene:
no data
Species / strain / cell type:
other: mouse lymphoma cells L5178Y TK+/-
Details on mammalian cell type (if applicable):
no further data
Metabolic activation:
with and without
Metabolic activation system:
A 9000 x g supernatant prepared from Fisher 344 adult male rat liver induced by Aroclor 1254.
Test concentrations with justification for top dose:
without: 15.6, 31.3, 62.5, 125.0, 250.0 µg/ml
with: 3.91, 7.816, 15.600, 31.300, 62.5 nl/ml
Vehicle / solvent:
DMSO
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
not specified
Positive controls:
yes
Positive control substance:
other: Dimethylnitrosamine, Ethylmethane sulfonate
Details on test system and experimental conditions:
Mouse lymphoma assay
Evaluation criteria:
The minimum criterium for a positive response in this assay was a mutant frequency exceeding 30.6 x 10 [exp-6].
Statistics:
no data
Species / strain:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
other: without: at and above 500 µg/ml; with: at and above 15.6 nl/ml
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid

No information on colony size. The positive controls were functional.

Executive summary:

o-cresol yielded a negative result when tested with the Mouse Lymphoma assay in-vitro according to OECD TG 476 in the presence and in the absence of a metabolic activation system. The positive controls were functional.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed (positive)

Genetic toxicity in vivo

Description of key information

o-cresol reveals no gene mutation activity and the clastogenic activity in vitro was not confirmed by respective in vivo studies.

Endpoint Conclusion:No adverse effect observed (negative).

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vivo mammalian germ cell study: cytogenicity / chromosome aberration
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 478 (Genetic Toxicology: Rodent Dominant Lethal Test)
GLP compliance:
yes
Type of assay:
rodent dominant lethal assay
Species:
mouse
Strain:
ICR
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMAL
- Age at study initiation: 8 weeks
- Assigned to test groups randomly: yes
- Housing: males : individually females: in groups
- Diet : ad libitum
- Water : ad libitum
- Acclimation period: 4 days
-body weights at initialtion and at termination of the assay

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 25
- Humidity (%): 50
- Photoperiod (hrs dark / hrs light): 12/12
Route of administration:
oral: gavage
Vehicle:
corn oil
Details on exposure:
no further data
Duration of treatment / exposure:
once
Frequency of treatment:
once
Post exposure period:
6 weeks
Remarks:
Doses / Concentrations:
0, 75, 250, 750 mg/kg bw in corn oil
Basis:
actual ingested
No. of animals per sex per dose:
25 males per dose.
Control animals:
yes, concurrent vehicle
Positive control(s):
Triethylenemelamine
- Justification for choice of positive control(s):
- Route of administration: single i.p. injection
- Doses / concentrations: 0.3 mg/kg as a volume of 10 ml/kg,
Tissues and cell types examined:
All females were examined for the number of live and dead implants within the uterine horn and whether the dead implants had occurred early or late in gestation. Live fetuses were identified as those which appeared to have a functional circulatory capacity.
Details of tissue and slide preparation:
no data
Evaluation criteria:
Statistically significant dose-related increase in the number of dominant leathals is considered as mutagenic in this system.
Statistics:
Chi-square test, ANOVA, Dunnett's one-tailed t test.
Sex:
male
Genotoxicity:
negative
Toxicity:
not specified
Remarks:
concentrations were chosen based on dose-range toxicity study
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
see section : "Remarks on results"

--high dose males:
Mortality: 8/25 within 6 days post dosing.
Signs of intoxication: lethary, rough haircoat, languid, tremor, distended abdomen, squinted eyes; all surviving males recovered from these effects within 6 days after dosing.
No effects were observed on fertility index, total implants, mean implants per pregnant female, total live implants, total dead implants, and body weight gain of males.
The test article was considered negative for inducing dominant lethal mutations in germ cells of male mice under conditions of this assay.

Conclusions:
The test article was considered negative for inducing dominant lethal mutations in germ cells of male mice under conditions of this assay.
Executive summary:

The test article was considered negative for inducing dominant lethal mutations in germ cells of male mice under conditions of this assay.

Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: no data on the ratio of normochromatic to polychromatic erythrocytes, no positive control
Reason / purpose for cross-reference:
reference to same study
Principles of method if other than guideline:
Method: Smears were prepared from peripheral blood samples obtained by cardiac punction of dosed and control animals at the termination of the 13 week study. Polychromatic and normochromatic erythrocytes from each animal were scored for micronuclei.
GLP compliance:
yes
Type of assay:
micronucleus assay
Species:
mouse
Strain:
B6C3F1
Sex:
male/female
Details on test animals or test system and environmental conditions:
see the respective record in the chapter 7.5.1
Route of administration:
oral: feed
Vehicle:
see the respective record in the chapter 7.5.1
Details on exposure:
see the respective record in the chapter 7.5.1
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
daily
Post exposure period:
no
Remarks:
Doses / Concentrations:
0, 5000, 10000, 20000 ppm
Basis:
nominal in diet
No. of animals per sex per dose:
10
Control animals:
yes, concurrent no treatment
Positive control(s):
no data
Tissues and cell types examined:
Erythrocytes from peripheral blood samples.
Details of tissue and slide preparation:
Slides were stained with Hoechst 33258/pyrcein Y according to MacGregor et al (1983, no further data).
Evaluation criteria:
Positive if a significant elevation in the frequenciy of micronucleated erythrocytes was observed either in males or in females.
Statistics:
Yes, but method not mentioned
Sex:
male/female
Genotoxicity:
negative
Toxicity:
not specified
Vehicle controls validity:
valid
Negative controls validity:
valid
Positive controls validity:
not examined

Compound consumption:
dose---------male------female
[ppm]---------[mg/kg bw/d]
-----------------------------
5000 ---------794 -------935
10000--------2723------1663
20000--------2723------3205

No significant elevation in the frequency of micronucleated erythrocytes was observed in either male or female mice. NOAEL for systemic toxicity is 1250 ppm (199 and 237 mg/kg bw/d, respectively) based on increased relative and absolute liver and kidney weights without histopathological correlate from 2500 ppm onwards.

Executive summary:

Following repeated oral dosing of mice over a period of 13 weeks with o-cresol, the MNT with peripheral erythrocytes yielded a negative result.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

In several Ames tests according to the respective guideline, in the absence and in the presence of a metabolic activation system, tested up to the cytotoxicity o-cresol revealed no genotoxic activity (Pool 1992, Pepper, Hamilton & Scheetz 1981, Haworth 1993). E.Coli or S.typhimurium TA 102 were not included in the tests, but this is not necessary as o-cresol has no oxidising or cross-linking properties nor is it a hydrazine derivative (OECD TG 471). A negative result in the mouse lymphoma assay performed according to the respective guideline with and without a metabolic activation system was found (Pepper, Hamilton& Scheetz 1981).

However, positive results were reported in assays for chromosomal aberrations for o-cresol in Chinese hamster cells (CMA 1988). The available respective in vivo studies do not confirm this result The Dominant Lethal Assay (DLA) in the mouse was negative (CMA 1989). Following repeated dosing of mice with 0, and 1250-20000 ppm for 13 weeks a MNT with peripheral erythrocytes in mice that were dosed with 0, 5000, 10000 and 20000 ppm was carried out. The NOAEL for general toxicity is 1250 ppm based on increased relative kidney and liver weights at higher doses. In the erythrocytes of the chosen mice o-cresol did not induce a significant elevation in the frequency of micronucleated erythrocytes. (US Department of Health and Human Services 1991).

Thus, o-cresol reveals no gene mutation activity and the clastogenic activity in vitro was not confirmed by respective in vivo studies.

In summary, these data indicate that o-cresol can induce chromosomal aberrations and increase SCEs in vitro but does not do so in vivo (OECD SIDS o-Cresol, CAS N°: 95-48-7, UNEP publication).

Overall, cresols do not seem to pose a genotoxic threat to humans under normal environmental exposure conditions (U.S. DEPART- MENT OF HEALTH AND HUMAN SERVICES, Public Health Service, Agency for Toxic Substances and Disease Registry September 2008).


Justification for selection of genetic toxicity endpoint
In vitro assays (Ames tests, SCE assays, CA tests, UDS tests, and a comet assay) and in-vivo assays (MN tests, dominant lethal tests and a SCE test) are available.

Justification for classification or non-classification

According to CLP classification criteria (Regulation (EC) No 1272/2008) a classification is not justified.