Tetrakis(phenylmethyl)thioperoxydi(carbothioamide)

Endpoint summary

Description of key information

Short description of key information on bioaccumulation potential result: 
Based on its high molecular weight, low water solubility and other physico-chemical parameters the bioavailability of TBzTD is expected to be low. Absorption via the oral, inhaltory and dermal route is estimated to be about 10% each.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

Oral

The octanol/water partition coefficient of TBzTD, being 3.4-3.7, is favourable for absorption. However, the water solubility of TBzTD is very low (below 0.01 mg/L at 20°C). In general, a compound needs to be dissolved before it can be taken up from the gastro-intestinal tract after oral administration (1). The absorption will furthermore be lowered by the relatively large molecular weight of the compound (MW>500), limiting the passage through biological membranes. Overall, it is expected that TBzTD will be absorbed to a limited extend in the gastro-intestinal tract. For risk assessment purposes the oral absorption of TBzTD is set at 10%. The results of the toxicity studies do not provide reason to deviate from this proposed oral absorption. After absorption of TBzTD from the gastro-intestinal tract, metabolism may occur in the liver (3). Excretion of TBzTD will mainly occur via faeces, due to the low water solubility and relative high molecular weight of the substance. As a consequence of the relative high molecular weight of TBzTD, excretion in bile is considered not relevant.

Inhalation

The relatively low vapour pressure / high boiling point indicate that the substance will not be available for inhalation as a vapour. In the absence of data on particle size distribution, absorption resulting from exposure via inhalation cannot be excluded, and is therefore assumed to take place. Particles with a size <100 μm have the potential to be inhaled. Particles with a diameter >5 μm will deposit in the nasopharyngeal region and subsequently be coughed or sneezed out of the body or swallowed. Particles below 5 μm might reach the tracheobronchial or pulmonary regions. TBzTD, being a lipophilic substance (log Pow 3.4-3.7) has the potential to be absorbed directly. However, based on its low water solubility (below 0.01 mg/L at 20°C) TBzTD will not dissolve into the mucus lining of the respiratory tract. For risk assessment purposes, the inhalation absorption for TBzTD is set at 10%, based on the low water solubility of TBzTD. Dermal TBzTD being a solid with a relative high molecular weight has no real potential for dermal absorption. Furthermore, its low water solubility does not facilitate dermal absorption. However, the criteria for 10% dermal absorption as given in the TGD (2) (IV1W>500 and log Pow >4) are not met, and therefore 100% dermal absorption of TBzTD should be considered for risk assessment purposes. It is, however, generally accepted that dermal absorption is lower compared to oral absorption. The 100% dermal absorption derived from physical/chemical properties of the substance should therefore be considered as a non-realistic assumption, and for risk assessment purposes a lower dermal absorption of e.g. 10% might be considered more appropriate. Based on the present available data, no additional conclusions can be drawn on the distribution, metabolism and excretion of TBzTD after dermal absorption