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The following remarks on the toxicokinetics of 3-Isocyanatomethyl-3,5,5-trimethylcyclohexyl-isocyanate (IPDI) oligomers, allophanate type, are based on physicochemical properties of the substance and on toxicological data. Experimental toxicokinetic studies were not performed.

 

IPDI oligomers, allophanate type, is a white organic solid (Currenta GmbH & Co. OHG, 2010) which has a melting range starting at approximately 205 °C (Currenta, 2012) and a very low vapour pressure under normal ambient conditions (0.00017 Pa, BTS, 2012). The water solubility is low (3.1 mg/L at 20 °C and pH 7, Currenta GmbH & Co. OHG, 2011), moreover, the substance is hydrolytically unstable (a degradation of approx. 50 % within 24 hours can be estimated; Currenta GmbH & Co OHG, 2013). Therefore experimental data such as pH, pKa, log Pow cannot be obtained for IPDI oligomers, allophanate type.

 

Due to the low vapour pressure inhalation exposure via vapour is not to be expected. Wherever aerosolization occur inhalation exposure is possible. There are no indications of systemic availability after inhalative exposure to the substance (Pauluhn, 2012, OECD 412), because no substance-related toxicity on organs other than the respiratory tract was found up to the maximum concentration examined. Adverse changes were confined to portal-of-entry related local irritant effects on respiratory tract. These effects most probably are related to the chemical nature of the isocyanate-groups of the substance. 

Oral and dermal absorption of IPDI oligomers, allophanate type, is assumed to be very low, due to the physico-chemical properties of the substance, i.e. low water solubility, hydrolysis in water and reaction with nucleophiles e.g. OH-, NH-, SH-groups. In fact, no systemic signs at all could be observed after oral exposure to the limit dose of 2000 mg/kg (Gillissen, 2010, OECD TG 423). 

A skin sensitizing potential is indicated for IPDI oligomers, allophanate type, on the basis of a LLNA (Vohr, 2011, OECD TG 429), thus indicating that a dermal uptake and subsequent systemic availability, even though small, can occur.

 

Based on the results of several in vitro genotoxicity tests (Nern, 2011, OECD TG 471; Hall, 2011, OECD TG 476; Nern, 2011, OECD TG 473; all performed with and without metabolic activation) it is concluded that DNA-reactive metabolites of IPDI oligomers, allophanate type, will not be generated in mammals in the course of hepatic biotransformation.