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EC number: 233-334-2
CAS number: 10124-43-3
Summary of the mean results after normalisation:
Target [test item]
Actual [test item] by weight
Actual [Cobalt] by weight
Actual [Cobalt] by ICP-MS
Application rate of the test preparation
Distribution of Cobalt
% Applied Dose
Dislodgeable dose 8 hours
Potentially absorbable dose
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
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.
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