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Description of key information

DPDP is not anticipated to be readily absorbed through the skin due to its high Pow and very low water solubility.

Key value for chemical safety assessment

Absorption rate - dermal (%):
50

Additional information

There are no specific studies on the dermal absorption potential of DPDP. However, there are multiple sources of guidance that indicate for substances with a log Kow (Pow) above 5 or 6 that the potential for dermal absorption will be minimal/negligible, including:

REACH TGD Chapter R.7C, Table R.7.12-3:  [For Log Kow] “a bove 6, the rate of transfer between the stratum corneum and the epidermis will be slow and will limit absorption across the skin. Uptake into the stratum corneum itself may be slow”.

ECOTOC TRA manual (Technical Report No. 93, p. 31:Substances that are unlikely to constitute any dermal risk through absorption due to their physico-chemical properties are not considered. Such cases are when the substance has either high hydrophobicity (log Kow > 5), high hydrophilicity (log Kow < -1) or a high molecular weight (>1,000)

DPDP has a Log Kow of 8.52, and therefore it seems appropriate to consider an absorption rate of less than 100%, which would obviously over-estimate the dermal absorption. EC guidance recommends a dermal absorption rate of 10% for substances with high Kow's and molecular weights (EC Health & Consumer Protection DG 2004). Hydrolysis product (phenol) information was considered for the oral and inhalation routes, though it is not clear that the potential for hydrolysis is as great via the dermal route as it would be for the oral and inhalation routes, especially since DPDP is a skin sensitiser and therefore resident time on the skin is likely to be short. Phenol's dermal absorption rate is 80% (ECB 2006). Based on the various considerations, an absorption rate of 50% is used in the assessment. This is believed to be sufficiently conservative given the potential for hydrolysis, though also recognising the likelihood of limited dermal uptake based on DPDP’s high Kow.

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