Isocyanic acid, polymethylenepolyphenylene ester, 2-ethyl-1-hexanol-blocked

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

Conclusion for the P criterion

All components of MDI MT possess aromatic isocyanate functional groups which are known to rapidly hydrolyse under homogeneous conditions of an OECD 111 test. Under the conditions of a ready biodegradation test of the OECD 301 series, the substance polymerises to polyurea when added to water. Biodegradation is therefore not a relevant transformation process for the substances. Nevertheless, a biodegradation screening tests for the substance has been conducted. The biodegradation study for MDI MT reflect the biodegradability of the transformation products and not necessarily of the MDI MT constituents themselves. Based on experimental hydrolysis half-lives, the substance is not considered to be persistent in the environment and is identified as not P.

 

Conclusion for the B criterion

Direct measurement of a BCF according the definite criteria is not possible as MDI MT hydrolyses quickly in water with half-lifes < 5  minutes. The same is true for the screening criteria, i.e. logPow. Estimated values for NCO terminated components of MDI MT using QSAR are not expedient for the same reason. The main hydrolysis products polymeric ureas is insoluble in water and cannot be taken up by fish due to their high molecular weight. The trace hydrolysis product MDA is not B/vB according to screening criteria.

 

Conclusion for the T criterion

The acute aquatic toxicity potential of MDI MT was measured in three acute tests in fish, daphnia and algae. The lowest EL50 was found in daphnia as 2 mg/L. Thus the substance does not fulfill the T criterion for aquatic toxicity. However, according to Annex I of 67/548/EEC MDI is classified as STOT RE cat. 2, which automatically triggers a T. Based on this classification the MDI MT is identified as T.

 

Overall conclusion:

Generally, diisocyanates are known to hydrolyze readily in water to yield a carbamic acid intermediate, which decarboxylates to produce CO₂ and an amine; the latter immediately reacts with an additional isocyanate group to yield a di-substituted urea as primary reaction product [Ullmann’s Encyclopedia of Industrial Chemistry]. The kinetically- and probability-favored urea formation reactions of this nature result in formation of polyurea solids which have high molecular weight, and are insoluble and non-reactive in the environment. Furthermore, and to a much lesser degree, also Mono-ureas of MDI (both NCO- and Amino-ended) are formed. This reaction dominates the environmental fate of diisocyanates, and therefore also impacts the hazardous properties of these substances as tested in the laboratory, and as observed in the environment. The probability for the formation of MDA is low and such traces were found to be < 0.5%. Approximated amounts in which the hydrolysis products of the MDI category members are occurring are: 

 

Polyurea incl. Mono-urea of MDI (both NCO- and Amino-ended)	> 90%
CO2	approx. 8%
Methylenedianiline (MDA)	< 0.5%

Consequently, separate PBT assessments are provided for the following, relevant hydrolysis products: 

1. Polyurea 

2. Mono-ureas of MDI (both NCO- and Amino-terminated) 

3. Methylenedianiline (MDA) 

No such assessment is performed for CO₂, which is a naturally occurring gas. A PBT assessment is not required for those type of substances under Regulation (EC) No 1907/2006 (REACH). 

As demonstrated by the individual assessments of the hydrolysis products of MDI MT provided in the subsections under the PBT section, none of these reaction products is considered a PBT / vPvB substance.