Registration Dossier

Administrative data

Key value for chemical safety assessment

Genetic toxicity in vivo

Description of key information
The weight of evidence suggests that NaTG is not genotoxic.
Link to relevant study records
Reference
Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study
Qualifier:
according to
Guideline:
OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)
GLP compliance:
yes
Type of assay:
other: Micronucleus assay on mouse bone marrow
Species:
mouse
Strain:
NMRI
Sex:
male/female
Details on test animals and environmental conditions:
- Animals . 
. Source: Harlan Winkelmann GmbH D-33178 Borchen
. Number of Animals: 72 (36 males/36 females), 6 males and 6 females per  group
. Initial Age at Start of Acclimatisation: 8-10 weeks
. Acclimatisation: minimum 5 days
. Initial Body Weight at Start of Treatment: males mean value 37.1 g (SD  ± 2.9 g) females mean value 31.5 g (SD ± 1.9 g)

- Environmental conditions
. Housing: single Cage Type: Makrolon Type I, with wire mesh top (EHRET  GmbH, D-79302 Emmendingen)
. Bedding: granulated soft wood bedding (Harlan Winkelmann GmbH, D-33178  Borchen)
. Temperature 22 ± 3 °C
. Relative humidity 30 - 70 %
. Artificial light 6.00 a.m. - 6.00 p.m.

- Food and water
. Feed: pelleted standard diet, ad libitum (Harlan Winkelmann GmbH,  D-33178 Borchen)
. Water: tap water, ad libitum, (Gemeindewerke, D-64380 Roßdorf)
Route of administration:
oral: gavage
Vehicle:
Name: deionised water         
Route and Frequency of Administration: orally, once         
Volume Administered: 10 mL/kg b.w.
Duration of treatment / exposure:
single administration
Frequency of treatment:
single
Post exposure period:
24 and 48 hours
Remarks:
Doses / Concentrations:
0, 62.5, 125 and 250 mg/kg bw
Basis:
actual ingested
No. of animals per sex per dose:
5
Control animals:
yes, concurrent vehicle
Positive control(s):
Name: CPA; Cyclophosphamide         
Dissolved in: deionised water         
Dosing: 40 mg/kg b.w.         
Route and frequency of administration: orally, once         
Volume administered: 10 mL/kg b.w.
Tissues and cell types examined:
Bonne marrow
Details of tissue and slide preparation:
- Preparation of the bone marrow smears
Ten animals (5 males, 5 females) per test group (all groups after 24  hours and only the high dose group after 48 hours) were killed by CO2  inhalation, following by bleeding. The femurs of the animals were removed  and the bone marrow was flushed out using foetal calf serum. After  centrifugation, the supernatant was removed and the cells in the sediment  were resuspended by shaking. A drop of this cell suspension was placed  and spread on a slide. The slides were air dried and stained with  May-Grünwald. The slides were coded so that the scorer is unaware of the  treatment group of the slide under evaluation ("blind" scoring).

- Microscopic examination of the slides
For each animal, the number of the micronucleated polychromatic  erythrocytes (MPE) was counted in 2000 polychromatic erythrocytes; the  polychromatic (PE) and normochromatic (NE) erythrocyte ratio was  established by scoring a total of 1000 erythrocytes (PE + NE). 
Evaluation criteria:
The study was considered valid as the following criteria are met:
- the negative controls are in the range of our historical control data.
- the positive controls are in the range of our historical control data.
- at least 4 animals per group and sex can be evaluated
- PCE to erythrocyte ratio should not be less than 20 % of the negative  control.

A test item is classified as mutagenic if it induces either a  dose-related increase or a clear increase in the number of micronucleated  polychromatic erythrocytes in a single dose group. 
Statistics:
Statistical methods (nonparametric Mann-Whitney test (8)) will be used  as an aid in evaluating the results. However, the primary point of  consideration is the biological relevance of the results. A test item that fails to produce a biological relevant increase in the  number of micronucleated polychromatic erythrocytes is considered  non-mutagenic in this system.
Sex:
male/female
Genotoxicity:
negative
Toxicity:
yes
Remarks:
clinical signs
Vehicle controls validity:
valid
Negative controls validity:
not examined
Positive controls validity:
valid
Additional information on results:
As estimated by a pre-experiment 250 mg Sodium Thioglycolate 98%, Pure  per kg b.w. was suitable.
The mean number of polychromatic erythrocytes was not decreased after  treatment with the test item as compared to the mean value of PCEs of the  vehicle control indicating that Sodium Thioglycolate 98%, Pure had no  cytotoxic properties in the bone marrow. In comparison to the corresponding vehicle controls there was no  statistically significant or biologically relevant enhancement in the  frequency of the detected micronuclei at any preparation interval and  dose level after administration of the test item. 
The mean values of micronuclei observed after treatment with Sodium Thioglycolate 98%,  Pure were below or near to the value of the vehicle control group.
40 mg/kg b.w. cyclophosphamide administered orally was used as positive  control which showed a statistically significant increase of induced  micronucleus frequency.

Summary of Micronucleus Test Results

test group

dose (mg/kg b.w)

sampling time (h)

PCEs with micronuclei (%)

range

PCE per 2000 erythocytes

vehicle

0

24

0.050

0 - 2

1098

test item

62.5

24

0.060

0 - 2

1124

test item

125

24

0.025

0 - 1

1123

test item

250

24

0.055

0 - 3

1100

Positive control

40

24

1.500

10 -43

1099

test item

250

48

0.095

0 - 6

1123

Historical Controls (1999 – 2004)

Vehicle Controls

Positive Controls (CPA)

Males

Females

Total

Males

Females

Total

Mean*±SD

0.078±0.04

0.058±0.033

0.069±0.028

1.867±0.57

1.368±0.497

1.632±0.468

Range**

0.01 - 0.23

0.0 - 0.19

0.01 - 0.15

0.70 -3.46

0.49 -3.55

0.77 - 3.48

No. of Experiments

229

217

230

228

217

229

*: mean value (percent micronucleated cells)

**: range of the mean group values (percent micronucleated cells)

Conclusions:
Interpretation of results (migrated information): negative
Sodium Thioglycolate 98%, Pure is considered to be non-mutagenic in this micronucleus assay.
Executive summary:

The clastogenic potential of sodium thioglycolate was evaluated in a micronucleus assay on mouse bone marrow performed according to the OECD guideline # 474.Sodium thioglycolate was administered by single gavage to three groups of five male and five female NMRI mice at dose-levels of 0, 62.5, 125 and 250 mg/kg bw. The positive control was the cyclophosphamide administered orally. The polychromatic erythrocytes/normochromatic erythrocytesratios (PE/NE) in the treated groups were equivalent to those of the control groups. However, systemic exposure was confirmed by the clinical signs observed in males and females receiving 250 mg/kg bw of sodium thioglycolate. No increase of the frequency of the micronucleated polychromatic erythrocytes was observed in the bone marrow harvested 24 or 48 hours after the treatment. Positive and vehicle controls gave the expected results.

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

Additional information

Additional information from genetic toxicity in vivo:

Several in vitro and in vivo genotoxicity studies were performed with thioglycolic acid and its salts. The conducted genotoxicity studies on thioglycolic acid or its salts described in this chapter can be bridged to each other, because in aquous solutions only the organic thioglycolate anion may have the potential to cause genotoxic effects in vitro or in vivo. All genotoxicity studies conducted to date have either negative results or are of douptful significance. Therefore, the weight of evidence suggests that thioglycolic acid and its salts are non-genotoxic.

Justification for classification or non-classification

Conclusive, but not sufficient for classification.