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Description of key information

A toxicokinetic assessment has been performed based on available physico-chemical properties and toxicological data of the substance.

Key value for chemical safety assessment

Absorption rate - oral (%):
50
Absorption rate - dermal (%):
10
Absorption rate - inhalation (%):
100

Additional information

As no partition coefficient could be determined, this parameter cannot be used in the prediction of toxicokinetics of B508.

Generally, a solid has to be dissolved before it can be absorbed. The relatively high molecular weight (>500 g/mol) and the low water solubility (<0.967 mg/L) of B508 predict absorption in the gastro-intestinal tract by passive diffusion to be unlikely. In the 28-day study urine was not discoloured due to the test substance, but faeces were. Therefore, for risk assessment purposes, the oral absorption of B508 is set at 50%. The results of the toxicity studies do not provide reason to deviate from this proposed oral absorption percentage.

Based on the relatively high molecular weight and low water solubility B508 is expected to have a limited distribution once absorbed. Accumulation in the lungs may occur as was demonstrated in the acute inhalation study by blue foci in the lungs. As no partition coefficient could be determined no further prediction of bioaccumulation can be made. Absorbed B508 may be metabolised and/or conjugated. The conjugates are expected to be excreted via the faeces as they are relatively high molecular weight compounds.

The low vapour pressure (<8.40´10-7Pa) indicates that B508 is not available for inhalation as a vapour. At least 50% of particles is small enough to be inhaled and more than 10% is expected to reach the alveolar region of the respiratory tract. The low water solubility (<0.967 mg/L) enhances penetration to the lower parts of the respiratory tract where B508 might be taken up by micellular solubilisation. For risk assessment purposes the inhalation absorption of B508 is set at 100%. The result of the acute inhalation study does not provide reason to deviate from this proposed inhalation absorption percentage.

A solid has to dissolve into the surface moisture of the skin before uptake can occur. The high molecular weight and the low water solubility indicate a low expected dermal absorption of B508. According to the criteria given in the REACh guidance: 10% dermal absorption will be considered in case MW >500 and log Pow <-1 and >4, otherwise 100% dermal absorption should be used. Therefore, for risk assessment purposes, 10% dermal absorption of B508 is proposed.

 

Based on the present data, no additional conclusions can be drawn on the distribution, metabolism and excretion of B508 after dermal and inhalatory absorption.