2H-Azepin-2-one, hexahydro-, polymer with 1,6-diisocyanatohexane

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics in vitro / ex vivo

Type of information:

other: Assessment, based on physico-chemical properties of the compound and on toxicological data. Experimental toxicokinetic studies were not performed.

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The assessment of the toxicokinetik of 2H-Azepin-2-one, hexahydro-, polymer with 1,6-diisocyanatohexane is based on physico-chemical properties of the compound and on toxicological data. Experimental toxicokinetic studies were not performed.

Principles of method if other than guideline:

Assessment on toxicokinetics

The remarks on the toxicokinetics of 2H-Azepin-2-one, hexahydro-, polymer with 1,6-diisocyanatohexane are based on physico-chemical properties of the compound and on toxicological data. Experimental toxicokinetic studies were not performed.

Description of key information

There were no studies available in which the toxicokinetic properties (absorption, distribution, metabolism, elimination) of hexamethylene diisocyanate, oligomerisation product, blocked with caprolactam were investigated. Based on the molecular structure, molecular weight, water solubility, and octanol-water partition coefficient significant oral, inhalative and dermal absorption is not expected. In fact, the available data give no indications for systemic availability, since no systemic toxicity could be concluded from the animal studies at all.

Additional information

Hexamethylene diisocyanate, oligomerisation product, blocked with caprolactam (CAS No. 26776 -30 -7); Information/Assumptions regarding toxicokinetics

The following remarks on the toxicokinetics of hexamethylene diisocyanate, oligomerisation product, blocked with caprolactam are based on physiochemical properties of the compound and on toxicological data. Experimental toxicokinetic studies were not performed.

The test substance is a colourless resinous solid having a molecular weight of >= 844 g/mol (The molecular weight is determined by the molecular weight of the main component (hexamethylene diisocyanate, oligomerization product (n = 3), blocked with caprolactam) in the test substance. It has an extremely low vapour pressure (3.8 * 10^-9hPa at 20°C; Smeykal, 2011) and is practically insoluble in water (370 µg/l at 20 °C; Lange, 2012) under normal ambient conditions. The partition coefficient octanol/water was determined as log Kow = 4.4 at 23.3 °C (Goller, 2012) and calculated as log Kow = 10.55 indicating a lipophilic character of the substance. In a preliminary hydrolysis test, less than 10% of the substance was observed to hydrolyse at 50°C at pH 4,7 and 9 after 120 hours (Lange, 2012). In the molecular structure of hexamethylene diisocyanate, oligomerisation product, blocked with caprolactam no functional groups with relevant acidic or basic character can be found. Therefore, no significant dissociation is expected at physiological pH values and beyond. The site of blocking is known to be physically stable. Only at elevated temperatures of > 90 °C a de-blocking occurs and reactive groups are released.

Oral and GI absorption: Due to a very high hydrolysis half-life of the test substance, it is not expected that the substance is significantly hydrolysed in the gastro-intestinal tract. Furthermore, due to the relatively high molecular weight and the very low water solubility of the substance oral absorption is not expected. In fact, the acute oral toxicity is low with a LD₅₀(rat) of > 1800 mg/kg bw (NOTOX, 2003). No mortality occurred. The body weight gain shown by the animals over the study period was considered to be normal. No abnormalities were found at macroscopic post mortem examination of the animals.

Dermal absorption: Dermal penetration of hexamethylene diisocyanate, oligomerisation product, blocked with caprolactam could not be excluded based on a log Kow that shows a high lipophility. Otherwise, due to the high molecular weight a significant dermal absorption is not expected. In fact, no signs of systemic toxicity were observed in an acute dermal irritation/corrosion study (NOTOX, 2003). No indications for a dermal uptake could be concluded from two skin sensitization tests (LLNA (Bayer AG, 2003 and 2007) and guinea pig maximization test (RTC, 2000)), since no skin sensitization potential was detected.

Respiratory absorption: Due to the very low vapour pressure of the substance significant respiratory absorption via vapour is not expected. Furthermore, highly lipophilic compounds (log Kow > 4), particular those that are poorly soluble in water (1 mg/l or less), are expected to be poorly absorbed. In fact, there are no indications of systemic toxicity and systemic availability after inhalative exposure of the aerosol for 14 days. Only mild and non-specific, poorly soluble particle-like effects were observed in this study. Mortality did not occur (Bayer AG, 2013).

Distribution: The physico-chemical information (high molecular weight, low vapour pressure, lipophilicity and low water solubility) indicates that hexamethylene diisocyanate, oligomerisation product, blocked with caprolactam could be distributed only to a low amount.

Accumulative potential: Bioaccumulation potential could not be excluded based on the physico-chemical data (e.g. log Pow). However, no indications of systemic availability could be concluded from the available animal studies, and therefore an accumulation potential for the substance seems to be questionable.

Excretion: No data are available regarding the excretion of absorbed hexamethylene diisocyanate, oligomerisation product, blocked with caprolactam.

Based on the results of several in vitro genotoxicity tests (Bayer AG, 2007 and LPT, 2012; all performed with and without metabolic activation) it is concluded that DNA-reactive metabolites of the ets substance will not be generated in mammals in the course of hepatic biotransformation.

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