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Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Aug 1992
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Reference:
Composition 0
Objective of study:
absorption
Principles of method if other than guideline:
Percutaneous absorption of the 14C-labelled test substance calculated from the amount of 14C eliminated already from the body (72 h after administration) plus the amount of 14C still being present in the carcass.
GLP compliance:
yes
Test material information:
Composition 1
Radiolabelling:
yes
Remarks:
14C-labelling
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Forschungsinstitut für Versuchstierzucht, A-2325 Himberg, Austria
- Age at study initiation: males ca. 6 - 7 weeks, females 9 - 10 weeks
- Weight at study initiation: approx. 200 g
- Fasting period before study:
- Housing: single caging. Metabolism cages (UNO B.V., Zevenaar,Holland)
- Individual metabolism cages: yes
- Diet (e.g. ad libitum): Altromin 1321ff, diet for rats, ad libitum
- Water (e.g. ad libitum): tap water in Makrolon bottles with stainless steel canules, ad libitum
- Acclimation period: 1 week


ENVIRONMENTAL CONDITIONS
- Temperature (°C): average of 23
- Humidity (%): average of 75
- Air changes (per hr): 12
- Photoperiod (hrs dark / hrs light): 12/12
Route of administration:
dermal
Vehicle:
other: A solution of 14C-thioglycolic acid was gradually neutralized with a 25 % solution of ammonia resulting in three final solutions of 11 % ammonium 14C-thioglycolate with pH 6, pH 7 and pH 8, respectively (concentration calculated as thioglycolic acid).
Details on exposure:
TEST SITE
- Area of exposure: 3x3 cm on the dorsal, median thoracic to lumbar area
- % coverage: 2.65% of body surface
- Type of wrap if used: After rinsing and neutralisation, the skin was covered with 4 layers of gauze fixed by adhesive tape. Additional covering by fixation of an air permeable, plastic, truncated cone to prevent licking of the treated area.
- Time intervals for shavings or clipplings: one day before application of the test substance


REMOVAL OF TEST SUBSTANCE
- Washing (if done): The solution was rinsed off with water of about 37 °C. Then the skin was dabbed dry with absorbent cellulose tissue.
- Time after start of exposure: 30 min


TEST MATERIAL
- Amount(s) applied (volume or weight with unit):
Mean values
Study A: 0.295 g of the solution applied, corresponding to 32.5 mg of the test substance
Study B: 0.300 g of the solution applied, corresponding to 33.0 mg of the test substance
Study C: 0.304 g of the solution applied, corresponding to 33.4 mg of the test substance.
- concentration (if solution): 11% (w/w)
Duration and frequency of treatment / exposure:
30 min, one application
Remarks:
Doses / Concentrations:
Mean values
Study A: 158 mg/kg bw
Study B: 164 mg/kg bw
Study C: 166 mg/kg bw
No. of animals per sex per dose:
5
Control animals:
no
Details on study design:
- Dose selection rationale: In humans a maximum of 75 ml of the 11 % test substance solution is applied to the hair. The scalp which has an estimated average surface of 500 cm2 is only reached by a small part of the solution estimated to be at most 1/10, corresponding to 0.015 ml per cm2.
In order to have reproducible conditions the fur of the rats was clipped, the test substance was therefore applied mainly on the skin. 0.3 ml were used on an area of 9 cm2, larger amounts of test substance solution would flow off during exposure time. The applied volume was with 0.033 ml per cm2 two times higher then in hunans which is a "worst case".
Details on dosing and sampling:
PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled (delete / add / specify): urine, faeces, carcass, cage washes
- Time and frequency of sampling: daily
Statistics:
t-test was used for analysis of differences between the sexes and the studies. P = 0.05.
Details on absorption:
Study A: 0.27% of the applied dose
Study B: 0.24% of the applied dose
Study C: 0.26% of the applied dose
Details on excretion:
Urine: 76.5 - 80.3% of the eliminated 14C
Faeces: 19.7 - 23.5% of the eliminated 14C
Metabolites identified:
not measured

No pH dependence of the results was detectable.
The majority of the applied 14C was removed from the skin by rinsing after the actual exposure and after the neutralization 

step (means of  96.1 to 96.8 % of the applied dose).
The mean 14C-content of the skin at the site of application was 0.82 %,  0.57 % and 0.60 % (study A, B and C, respectively) of the administered 14C-amount.
Means of 0.139 %, 0.119 % and 0.137 % of the applied 14C were recovered  in urine and faeces within 72 hours. 14C was 

excreted to a larger extent via urine (means 79 %, 76 % and 80 % of the eliminated amounts). The mean excretion was fast:

92 %, 83 % and 93 % of the totally eliminated amounts were excreted in the first 24 hours after application.
The remaining mean amounts of 14C in the carcass 3 days after the  application were 0.126 %, 0.116 % and 0.121 % of the 

administered  14C-amount. This corresponds to 46.7 %, 48.3 % and 46.5 % of the absorbed 14C-amount.
The red foci that appeared in the application site of several animals of all pH groups did not have a distinct influence on the 

absorption.
In the three studies the cutaneous absorption as well as the 14C-concentration found in urine, faeces and carcass were 

higher in males than in females without gaining statistical significance.
Means of 97 % to 97.9 % of the applied 14C-doses were recovered in the various types of samples in the three studies.
From these results the mean absorption was calculated to be 0.27 %, 0.24  % and 0.26 % of the applied dose.

Endpoint:
dermal absorption in vivo
Type of information:
experimental study
Adequacy of study:
key 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
Reference:
Composition 0
Qualifier:
no guideline followed
Principles of method if other than guideline:
The aim of the study was to investigate the influence of the pH (pH 6, 7, 8) on the percutaneous absorption of thioglycolic acid
GLP compliance:
yes
Test material information:
Composition 1
Radiolabelling:
yes
Remarks:
14C-labelled thioglycolic acid
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
ANIMALS:
Supplier: Forschnugsinstitut für Versuchstierzucht, A-2325 Himberg, Austria.
Weight: approx. 200 g
Age: male ca. 6-7weeks, females ca. 9-10 weeks
Housing: Single caging in metabolism cages (UNO B.V., Zevenaar, Holland)
Diet: ad libitum Altromin 1321ff
Water: ad libitum tap water
Acclimatization: 1 week

CONDITIONS:
Temperature: average 23°C
Relative humidity: average 75%
Air changes: 12/hour
Light-Dark cycle: 12/12
Type of coverage:
open
Vehicle:
water
Duration of exposure:
30 min
Doses:
165 mg/kg bw
No. of animals per group:
5
Control animals:
no
Details on study design:
Groups of 5 male and 5 female Sprague-Dawley rats were used to investigate the dermal bioavailability and excretion of ammonium thioglycolate.

Approx. 300 mg of the solutions (equivalent to 165 mg/kg bw) were applied to the clipped dorsal skin of the rats for 30 min and then washed off. The treatment was followed by a neutralization step where 0.3 ml of a "Natural styling solution" containing 2.1 % hydrogen peroxide was applied for 10 min and then washed off. The treated area was then covered with 4 layers of gauze fixed by adhesive tape and the animals were subsequently placed into metabolism cages for 72 hours.

The concentration of the test material (11 %), the time of exposure (30 min), the area of exposure (ratio application site to body surface: 0.026) and the neutralization step were chosen to mimic human exposure during the application of hair waiving products.
Solutions from the two rinsings were united. Urine and faeces were collected daily.
The animals were killed after 72 hours.
The application area plus some surrounding skin was excised and dissolved in Soluene-350 for analysis of radioactivity.
The radioactivity of the carcass was determined after removal of the remaining skin to avoid false 14C concentrations in the carcass due to skin, possibly contaminated e.g. by urine.
Signs and symptoms of toxicity:
not specified
Dermal irritation:
yes
Remarks:
small focal redness appeared on the treated skin during application and remained at least until the area was covered
Absorption in different matrices:
Most of the 14C was removed from the rat skin during washing of the test material and neutralization solution (mean 96.1 - 96.8%). The mean 14C recovered in urine and faeces in the pH 6, pH 7, and pH 8 exposure groups was 0.139%, 0.119%, and 0.137%, respectively. The mean 14C-content of the skin at the application site for the pH 6, pH 7, and pH 8 exposure groups was 0.82%, 0.57%, and 0.60%, respectively. The mean cutaneous absorption for 11% Ammonium 14C-thioglycolate at pH 6, pH 7, and pH 8 was 1.09%, 0.81%, and 0.86%, respectively. Cutaneous absorption and 14C concentrations in urine, feces, and carcasses were higher in males than females, but it was determined that this was not statistically significant
Total recovery:
Total mean (sd) recovery was 97.9% (1.1), 97.5% (2.1) and 97.0% (1.5) at pH 6, 7 and 8, respectively.
Key result
Time point:
30 min
Dose:
165 mg/kg bw
Parameter:
percentage
Absorption:
ca. 1 %
Remarks on result:
other: rinsing after 30 min

Recovery of the radioactivity after dermal administration of ammonium14C-thioglycolate to rats

Analysed sample

14C-activity in % of applied dose,
mean (SD)

pH 6

pH 7

pH 8

Rinsings

96.8 (1.2)

96.7 (2.1)

96.1 (1.4)

Adsorption
(application site)

0.82 (0.43)

0.57 (0.24)

0.60 (0.34)

Urine (0-72 h)

0.11 (0.12)

0.091 (0.073)

0.11 (0.11)

Faeces (0-72 h)

0.029 (0.032)

0.028 (0.025)

0.027 (0.025)

Carcass

0.126 (0.087)

0.116 (0.076)

0.121 (0.089)

Total recovery*

97.9 (1.1)

97.5 (2.1)

97.0 (1.5)

Cutaneous absorption

1.09

0.81

0.86

*Total of urine, faeces, adsorption at the application site and carcass14C recovery.

Conclusions:
The mean cutaneous absorption20for 11% Ammonium14C-thioglycolate at pH 6, pH 7, and pH 8 was 1.09%, 0.81%, and 0.86%, respectively.
Executive summary:

Three groups of rats (5/sex; ~200 g) received on the clipped dorsal skin approximately 300 mg of ammonium14C-thioglycolate (radiochemical purity 97.6%) as an 11% solution (equivalent to 165 mg a.i./kg bw or 133 mg/kg bw as thioglycolic acid) at pH 6, pH 7, and pH 8 for 30 minutes followed by a washing of the site. The test site was then neutralized with 0.3 ml of a “natural styling solution” containing 2.1% hydrogen peroxide for 10 minutes followed by a washing of the site. These applications were to mimic human exposure to hair waving products. After the second wash, the test sites were covered with four layers of gauze and the rats were placed into metabolism cages for 72 hours. Following the observation period, the animals were sacrificed. The test sites and surrounding skin were excised and dissolved in Soluene-350 for radioactivity analysis. The radioactivity of the waste wash water, urine, and feces as well as the carcasses was also measured.

Most of the14C was removed from the rat skin during washing of the test material and neutralization solution (mean 96.1 - 96.8%). The mean14C recovered in urine and faeces in the pH 6, pH 7, and pH 8 exposure groups was 0.139%, 0.119%, and 0.137%, respectively. The mean14C-content of the skin at the application site for the pH 6, pH 7, and pH 8 exposure groups was 0.82%, 0.57%, and 0.60%, respectively. The mean cutaneous absorption20for 11% Ammonium14C-thioglycolate at pH 6, pH 7, and pH 8 was 1.09%, 0.81%, and 0.86%, respectively. Cutaneous absorption and14C concentrations in urine, feces, and carcasses were higher in males than females, but it was determined that this was not statistically significant.

Description of key information

No kinetic data are available on the absorption of thioglycolic acid and its salts by inhalation or oral exposure. However, the physico-chemical properties of thioglycolates, small ionisable water-soluble molecules with a very low log Kow, as well as, the acute oral and inhalation toxicity data suggest that thioglycolic acid and its salts are significantly absorbed by the inhalation and oral routes. The available information are provided from former studies performed by parenteral administration.
Short description of key information on absorption rate:
Under testing conditions that take into account realistic use conditions for cosmetic formulations (30-min exposure and rinsing), the dermal absorption of ammonium thioglycolate (pH between 6 and 9) seems very limited, about 1% of a dose of 133 mg/kg bw (as thioglycolic acid) was absorbed within 72h in rats and 0.77% of a dose of 2.1 mg thioglycolic acid/cm² was systemically available in an in vitro dermal absorption/penetration assay with excised skin of pigs.
Overall, for the purpose of risk assessment, a dermal absorption rat of 1% is assumed for MeaTG.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
100
Absorption rate - dermal (%):
1
Absorption rate - inhalation (%):
100

Additional information

No data are available on the absorption of thioglycolic acid and its salts by inhalation or oral exposure. However, the physico-chemical properties of the thioglycolates, small ionisable water-soluble molecules with a very low log Kow as well as the acute oral and inhalation toxicity data suggest that thioglycolic acid and/or its salts are significantly absorbed by the inhalative and oral routes.

Regarding dermal absorption, it seems that the dermal penetration of thioglycolate is pH-dependent, the more acidic the pH, the fewer molecules are ionized and the more it is absorbed. A former study, performed under exaggerated exposure conditions (no rinsing) and at an unknown pH, suggests an extensive dermal absorption of the sodium salt in the rabbits, with at least 30-40% of the dose (up to 660 mg/kg bw as thioglycolic acid) excreted in the urine within 5 hours in the form of neutral sulphate (Freeman, 1956). However, under testing conditions that take into account realistic use conditions for cosmetic formulations (30-min exposure and rinsing), the dermal absorption of ammonium thioglycolate (pH between 6 and 9) seems very limited, about 1% of a dose of 133 mg/kg bw (as thioglycolic acid) was absorbed within 72h in rats (Reindl, 1993). In an in vitro dermal absorption/penetration assay with excised skin of pigs performed according to OECD Guideline 428, the amount of ammonium thioglycolate systemically available (epidermis/dermis plus receptor fluid) was found to be 19.83 µg/cm², corresponding to 0.77% of a dose of 2.63 mg ammonium thioglycolate/cm² (Toner, 2007).

After i. v. injection,35S-thioglycolate is mainly distributed in the kidneys, lungs, and spleen of a female monkey (Freeman 1956), in the small intestine and kidneys of a rat (Bakshy and Gershbein, 1972). Residual 35S blood concentrations at 0.5 to 7 h post-injection did not exceed 5.3% in rats (Bakshy and Gershbein, 1972). Significant concentrations of dithiodiglycolate were detected in the urine of rabbits 24 h after thioglycolic acid was injected i. p. negligible concentrations of thioglycolic acid were detected (Bakshy and Gershbein, 1972).

 

Absorption and excretion

The pulmonary excretion of sodium thioglycolate as hydrogen sulphide was investigated in the rat (weight and strain not stated). The animal was injected i. p. with 150 mg/kg of sodium thioglycolate. Expired air from the animal was analyzed for hydrogen sulphide over a period of 10 h. Hydrogen sulphide was not detected in expired air at any time during the study (Freeman et al. 1956a; reliability 2).

The urinary excretion of sodium thioglycolate was evaluated using rabbits (weights and strain not stated). Four animals were injected i. v. with a 5% solution of sodium35S-thioglycolate (doses of 70, 80, 80, and 123 mg/kg, respectively). Two animals served as controls. Urine was then collected over a period of 24 h. A few drops of liquid petrolatum were placed in each container to prevent air oxidation of possible sulfhydryl compounds. Quantities of organic sulphate, inorganic sulphate, and neutral sulphur in each urine sample were expressed as the percentage of administered radioactivity. Sodium thioglycolatecaused a considerable increase in excretion of iodine reducing material; more than enough to account for the compound administered indicating the breakdown of body constituent and was excreted mostly as inorganic sulphate and neutral sulphur.The radioactivity in the urineindicatedthat 63-83% of the compound was excreted in the first 24 hours after its administration(Freeman et al. 1956a; reliability 2).

The urinary excretion of sodium thioglycolate was also evaluated in rats (weight and strain not stated) injected i.p. with 12.5 to 75.0 mg/kg of a 2.5% solution of sodium35S-thioglycolate. Urine was collected over a period of 24 h. Quantities of inorganic sulphate excreted, expressed as % of administered radioactivity, ranged from 23 to 72%. The total labeled sulphur excreted during the first 24 hours was 59-96% of the dose. Two of the rats excreted 9% or 11% on the second day and 2% or 6% on the third day respectively (Freeman et al. 1956a; reliability 2).

35S-thioglycolic acid (100 mg/kg adjusted to pH 7.2-7.4 with NaOH) was administered to Holtzman rats (weight = 200-250 g), 12 rats were injected i. v. and to 10 i. p. Also, 2 rats were each given 75 mg/kg via i. p. injection. Animals injected i. v. (12 rats) comprised one group, and those injected intraperitoneally (12 rats) comprised the other. Urine samples were collected 24 h after injection, after which the administered35S was excreted, and excretion percentages were determined. The mean urine sulphate content for i. v. dosed rats was 82.3 ± 1.6% and for i. p. dosed rats was 90.6 ± 1.8%. Most of the radioactivity was excreted in the form of neutral sulphate (Bakshy and Gershbein, 1972; reliability 2).

Two male New Zealand rabbits (weights not stated) were injected i. p. with35S-thioglycolic acid (100 mg/kg adjusted to pH 7.2-7.4 with NaOH) and one rabbit was injected i. p. with 200 mg/kg. Urine samples were collected 24 h after injection. The mean urine sulphur content of the 3 rabbits was 88% of the administered dose. Most of the radioactivity was excreted in the form of neutral sulphate (Bakshy and Gershbein, 1972; reliability 2).

Distribution

The distribution of radioactivity was determined two hour after i. v. injection of 50 mg/kg35S-thioglycolic acid (adjusted to pH 7.2-7.4 with NaOH) to one Holtzman rat.The small intestine, kidney, liver and stomach exhibited the greatest activity, respectively 0.07, 0.03, 0.02 and 0.02 % of the dose. It is possibly consistent with the generally rapid elimination of thioglycolate in the urine and bile. The greatest content of35S, 0.66% of the total administered, was detected in the feces. This observation may have been due to contamination of the feces with urine missed during the rinsing of urine residue from the cage after collection (Bakshy and Gershbein, 1972; reliability 2).

The distribution of35S thioglycolic acid (adjusted to pH 7.2-7.4 with NaOH) in whole blood was evaluated in five Holtzman rats injected i. v. with 100 mg/kg of the test substance and bled during periods of up to 7 h. Four of the 5 had less than 3% residual activity at 1 hour, while one had 5.3% residual activity. At 4-7 hours after the injection, only 0.1% activity or less remained (Bakshy and Gershbein, 1972; reliability 2).

The distribution of35S-thioglycolic acid in the blood was further investigated in the New Zealand rabbit after i. v. injection of35S-thioglycolic acid (adjusted to pH 7.2-7.4 with NaOH), with emphasis on binding to the following serum protein fractions:α1,α2,β, andγ-globulins and albumin. The test substance (75 mg/kg) was injected i. v. Most of the radioactivity was bound to albumin. The extent of this uptake amounted to 0.14% at 20 min post-injection and had diminished to 0.016% at 3 h. The small amount of radioactivity detected in albumin might have been due to isotopic exchange (Bakshy and Gershbein, 1972; reliability 2).

A female monkey given 300 mg35S-labelled sodium thioglycolate/kg body weight by i. v. injection, excreted labeled sulphur in the urine (for up to 10 hours) entirely as neutral "sulphur". Tissue samples from 10 organs showed the largest amounts of label in the kidney, lungs and spleen (Freeman et al. 1956a; reliability 2).

Metabolism

Unlabeled thioglycolic acid (100 or150 mg/kg) was administered to a group of seven rats via i. p. injection. Significant concentrations of dithioglycolate (average concentration 28%) were detected in the urine at 24 h post-injection. Only negligible concentrations of thioglycolate were detected (Bakshy and Gershbein, 1972; reliability 2).

Discussion on absorption rate:

Studies performed with ammonium thioglycolate based cosmetic formulations are available

In vitro study

The dermal absorption/percutaneous penetration of [14C]-radiolabelled ammonium thioglycolate out of a representative permanent hair waiving formulation (13% in the formulation, pH 9.5) was studied on the clipped excised skin of four Landrace large white cross pigs. The pig skin, dermatomed to a mean thickness of 0.80 mm, was used because it shares essential penetration characteristics with human skin. The dermal absorption/percutaneous penetration of the test substance was investigated for the open application of about 20 mg formulation per cm² pig skin. Therefore the resulting dose of ammonium thioglycolate was approximately 2.63 mg/cm² skin (equivalent to 2.1 mg thioglycolic acid/cm²). Skin discs of about 3.14 cm² were exposed to the formulations for 30 min., terminated by gently rinsing with a commercial shampoo solution diluted with water. The amount of ammonium thioglycolate systemically available (epidermis/dermis plus receptor fluid) was found to be 19.83 µg/cm² (0.77%), corresponding to 16.74 µg/cm² when calculated for thioglycolic acid (Toner, 2007).

In vivo study

Three groups of rats (5/sex; ~200 g) received on the clipped dorsal skin approximately 300 mg of ammonium14C-thioglycolate (radiochemical purity 97.6%) as an 11% solution (equivalent to 165 mg a. i./kg bw or 133 mg/kg bw as thioglycolic acid) at pH 6, pH 7, and pH 8 for 30 minutes followed by a washing of the site. The test site was then neutralized with 0.3 ml of a “natural styling solution” containing 2.1% hydrogen peroxide for 10 minutes followed by a washing of the site. These applications were to mimic human exposure to hair waving products. After the second wash, the test sites were covered with four layers of gauze and the rats were placed into metabolism cages for 72 hours. Following the observation period, the animals were sacrificed. The test sites and surrounding skin were excised and dissolved in Soluene-350 for radioactivity analysis. The radioactivity of the waste wash water, urine, and feces as well as the carcasses was also measured. The results of the radioactivity count are presented in the following Table.

Recovery of the radioactivity after dermal administration of ammonium14C-thioglycolate to rats

Analysed sample

14C-activity in % of applied dose,
mean (SD)

pH 6

pH 7

pH 8

Rinsings

96.8 (1.2)

96.7 (2.1)

96.1 (1.4)

Adsorption
(application site)

0.82 (0.43)

0.57 (0.24)

0.60 (0.34)

Urine (0-72 h)

0.11 (0.12)

0.091 (0.073)

0.11 (0.11)

Faeces (0-72 h)

0.029 (0.032)

0.028 (0.025)

0.027 (0.025)

Carcass

0.126 (0.087)

0.116 (0.076)

0.121 (0.089)

Total recovery

97.9 (1.1)

97.5 (2.1)

97.0 (1.5)

Cutaneous absorption[1]

1.09

0.81

0.86

[1]total of urine, feces, adsorption at the application site and carcass14C recovery.

Most of the14C was removed from the rat skin during washing of the test material and neutralization solution (mean 96.1 - 96.8%). The mean14C recovered in urine and feces in the pH 6, pH 7, and pH 8 exposure groups was 0.139%, 0.119%, and 0.137%, respectively. The mean14C-content of the skin at the application site for the pH 6, pH 7, and pH 8 exposure groups was 0.82%, 0.57%, and 0.60%, respectively. The mean cutaneous absorption for 11% Ammonium14C-thioglycolate at pH 6, pH 7, and pH 8 was 1.09%, 0.81%, and 0.86%, respectively. Cutaneous absorption and14C concentrations in urine, feces, and carcasses were higher in males than females, but it was determined that this was not statistically significant (Reindl, 1993).

The urinary excretion of an ammonium thioglycolate solution (0.6 N, pH 9.3) was evaluated in rabbits (2.3-3.0 kg, strain not stated). A single application (1.0 ml/kg, equivalent to 65.5 mg/kg bw) of the solution containing 0.10 to 0.20 µCi of 35S was made via a syringe to a clipped area (15% of body surface) on an animal's right side (apparently without occlusion and rinsing). At 24 hours, 16.22 ± 0.55 % of the labeled sulphur had been excreted in the urine, while in the following 48 hours 6.46% was excreted. When the same volume was applied on 4 successive days, approximately 35-40% of the total35S had been excreted in the urine within this time (Gershbein, 1979).

The range finding study of an in vivo micronucleus test (Haddouk, 2006)) showed that pH can significantly affect the systemic toxicity of thioglycolic acid after a dermal application to mice. No mortality and no clinical signs were observed at 1491 mg thioglycolate/kg/day at pH 7 for 2 days. In contrast, 2 out of 3 males died after the first treatment with 1500 mg thioglycolate/kg/day at pH 4. Thus, it seems that the dermal penetration of thioglycolic acid is pH-dependent, the more the pH is acidic, the less the molecule is ionized and more it is absorbed.