Cobalt trihydroxide

Dermal absorption

Administrative data

Endpoint:

dermal absorption in vitro / ex vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 2008-09-08 till 2009-04-16

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline conform study, conducted and documented under the principles of GLP.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2010

Report date:

2010

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 428 (Skin Absorption: In Vitro Method)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: OECD Environmental Health and Safety Publications Series on Testing and Assessment No. 28. Guidance Document for the Conduct of Skin Absorption Studies (2004).

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed by UK GLP Monitoring Authority (2009-09-07)

Test material

Test material information

Constituent 1

Reference substance name:

Cobalt dichloride hexahydrate

IUPAC Name:

Cobalt dichloride hexahydrate

Details on test material:

- Name of test material (as cited in study report): Cobalt dichloride hexahydrate (CAS 7791-13-1)- Molecular formula (if other than submission substance): CoCl2 * 6H2O - Molecular weight (if other than submission substance): 237.93 g/mol - Substance type: pure active substance - Physical state: solid, powder- Storage condition of test material: The test item is stored at ambient temperature in the dark. - Water solubility: approx. 870 g/L (~ 215 g Co/L).

Radiolabelling:

no

Test animals

Species:

human

Details on test animals or test system and environmental conditions:

not applicable

Administration / exposure

Type of coverage:

open

Vehicle:

water

Duration of exposure:

8 hours exposure followed by 64 hours post-exposure monitoring (continued collection of receptor fluid).

Doses:

- Nominal doses: 100 μg/cm² and 1000 μg/cm² of the test material (equivalent to Cobalt concentrations of ca. 31.9 μg/cm² and ca. 319 μg/cm², respectively).- Target Concentration of the test item: 10 mg/mL and 100 mg/mL- Actual Concentration of dosing solutions (test item by weight): 9.95 mg/mL and 100.14 mg/mL - Application Rate of Test Preparation: 10 µL/cm² - Actual doses of cobalt (by ICP-MS): 29 µg/cm² and 318 µg/cm².

No. of animals per group:

not applicable

Details on study design:

5 pieces of full thickness human skin samples (1 breast and 4 abdominal skin samples) were obtained from patients (aged 36 to 45 years old), who gave informed consent for their skin to be taken for scientific research purposes, prior to undergoing routine surgery. Split-thickness human skin membranes (400 µm (Split-Thickness Skin); 1200 to 2200 µm (Full-Thickness Skin)) were mounted into flow-through diffusion cells. The surface area of exposed skin within the cells was 0.64 cm². The receptor chamber volume was 0.25 mL. The peristaltic pumps were adjusted to maintain a flow-rate of ca 1.5 mL/hour. Receptor fluid, physiological saline (sodium chloride, 0.9%, w/v) containing streptomycin (0.1 mg/mL) and penicillin G (100 units/mL), was pumped underneath the skin at a flow rate of ca 1.5 mL/hour. The skin surface temperature was maintained at ca 32°C throughout the experiment. A tritiated water barrier integrity test was performed and any human skin sample exhibiting a kp value greater than 3.5 x 10-³ cm/hour was excluded from subsequent absorption measurements.Cobalt dichloride hexahydrate was applied to human skin at two different application rates: ca 100 µg/cm² and ca 1000 µg/cm². The two test preparations were prepared with final concentrations of Cobalt dichloride hexahydrate (by weight) of ca. 10 mg/mL and 100 mg/mL. These test preparations were applied to the skin mounted in flow through diffusion cells at an application rate of 10 µL/cm².Percutaneous absorption was assessed by collecting receptor fluid in fractions every 4 hours from 0 to 24 hours and every 8 hours from 24 to 72 hours post application. At 8 hours post application, exposure was terminated by washing the skin surface with a concentrated commercial soap followed by rinsing with a dilute soap solution and drying the skin surface with tissue paper (tissue swabs). At 72 hours post application (i.e. after a 64-hour post exposure monitoring period), the underside of the skin was rinsed with receptor fluid. This rinse was added to the 64-72 hours receptor fluid collection sample. The skin was then removed from the flow-through diffusion cells, dried and the stratum corneum removed with 20 successive tape strips. The tape strips were pooled in groups of 5 (1-5, 6-10, 11-15 and 16-20, respectively). These samples were despatched to Scientific Limited where they were analysed by inductively coupled plasma-mass spectroscopy (ICP-MS). The laboratory Charles River then calculated the results from the mass of samples collected and the amount of Cobalt in each sample measured by Scientifics.

Results and discussion

Signs and symptoms of toxicity:

not specified

Dermal irritation:

not specified

Total recovery:

- Recovery of applied dose acceptable: yes (ca. 85%). The resulting data was normalised to account for this lower than originally calculated recovery.

Percutaneous absorption

Percutaneous absorption 1

Dose:

100 µg/cm²

Parameter:

percentage

Absorption:

0.38 %

Remarks on result:

other: 72 hours (8 hours exposure + 64-hour post-exposure monitoring)

Remarks:

Potentially absorbable dose: the sum of the absorbed dose, skin and stratum corneum tape strips 6 to 20.

Percutaneous absorption 2

Dose:

1000 µg/cm²

Parameter:

percentage

Absorption:

1.08 %

Remarks on result:

other: 72 hours (8 hours exposure + 64-hour post-exposure monitoring)

Remarks:

Potentially absorbable dose: the sum of the absorbed dose, skin and stratum corneum tape strips 6 to 20

Any other information on results incl. tables

Summary of the mean results after normalisation:

Test preparation	1		2
Target [test item] Actual [test item] by weight	10 mg/mL 9.95 mg/mL		100 mg/mL 100.14 mg/mL
Target [Cobalt] Actual [Cobalt] by weight Actual [Cobalt] by ICP-MS	31.9μg/cm^2 31.7μg/cm^2 29.0μg/cm^2		319μg/cm^2 319μg/cm^2 318 µg/cm^2
Application rate of the test preparation	10 µL/cm²		10 µL/cm²
Distribution of Cobalt	% Applied Dose	μg/cm²	% Applied Dose	μg/cm²
Dislodgeable dose 8 hours Unabsorbed dose Absorbed dose Dermal delivery Potentially absorbable dose Mass balance	99.51 99.71 0.15 0.29 0.38 100	28.83 28.89 0.04 0.08 0.11 28.97	98.83 99.01 0.87 0.99 1.08 100	313.79 314.37 2.77 3.15 3.44 317.52

Dislodgeable dose 8 hours = skin wash + tissue swab

Unabsorbed dose = dislodgeable dose 8 hours + stratum corneum

Absorbed dose = cumulative receptor fluid

Dermal delivery = skin + absorbed dose

Potentially absorbable dose = dermal delivery + stratum corneum tape strips 6 to 20

Mass balance = unabsorbed dose + dermal delivery

Applicant's summary and conclusion

Conclusions:

For the purposes of risk assessment, the potentially absorbable dose (the sum of the absorbed dose, skin and stratum corneum tape strips 6 to 20) may be used. In order to provide the most conservative value for the risk assessment, the values obtained following normalisation have been selected. This corresponds to 0.38% for the low exposure scenarios (ca 31.9 μg Co/cm²) and 1.08% for the high exposure scenarios (ca 319 μg Co/cm²). These values also account for part of the material associated with the stratum corneum and the test was conducted with a highly water soluble form of Cobalt in an aqueous solution. Thus, these values are considered to represent a conservative estimate.

Executive summary:

As part of the safety evaluation of Cobalt and its compounds, this study was required to assess the rate and extent of absorption of Cobalt following topical application of a soluble Cobalt substance to human skin in vitro. As a candidate, the salt Cobalt dichloride hexahydrate was selected for testing two exposure scenarios to human skin (high and low exposure). The test item was applied to human skin at two different application rates: ca 100 μg/cm² and ca 1000 μg/cm² (equivalent to Cobalt concentrations of ca 31.9 μg/cm² and 319 μg/cm², respectively). The two test preparations had Cobalt salt concentrations of ca 10 mg/mL and ca 100 mg/mL applied to the skin at 10 μL/cm². The test preparations were exposed to the skin for 8 hours after which time they were washed off. This was followed by a ca 64 hours post exposure monitoring period.

For Test Preparations 1 and 2, the absorbed dose of Cobalt was 0.15 and 0.87%, respectively. The dermal delivery of Cobalt was 0.29% and 0.99%, respectively. The majority of the applied dose was removed during the washing process with 99.51% and 98.83% removed at 8 hours post dose from Test Preparations 1 and 2, respectively. For the purposes of risk assessment, the potentially absorbable dose (the sum of the absorbed dose, skin and stratum corneum tape strips 6 to 20) may be used. In order to provide the most conservative value for the risk assessment, the values obtained following normalisation have been selected. This corresponds to 0.38% for the low exposure scenarios (ca 31.9 μg Co/cm²) and 1.08% for the high exposure scenarios (ca 319 μg Co/cm²). These values also account for part of the material associated with the stratum corneum and the test was conducted with a highly water soluble form of Cobalt in an aqueous solution. Thus, these values are considered to represent a conservative estimate.