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EC number: 701-173-1
CAS number: -
test substance is covered by the category approach of methylenediphenyl
diisocyanates (MDI). Hence, data of the category substances can be used
to cover this endpoint. The read-across category justification document
is attached in IUCLID section 13. It is important to note that the MDI
category approach for read-across of environmental and human hazards
between the MDI substances belonging to the MDI category is work in
progress under REACH. Therefore the read-across document should be
considered a draft.
The test substances of the methylenediphenyl isocyanate category react
quickly with water and hence will be rapidly hydrolysed upon contact
with water, soil, sediment, etc.. The half-life for hydrolysis under
heterogeneous reaction conditions is estimated to be 20 hours and in
homogeneous solution is on the order of seconds. Hence, hydrolysis is
considered to be the main removal mechanism in the different
compartments. However, MDI is hydrophobic and poorly soluble in water
and thus the heterogeneous reaction with water or soil is less rapid.
The major product of such a reaction is a solid, insoluble polyurea.
Under conditions typical of many types of environmental contact, i. e.
with relatively poor dispersion of the denser isocyanate, the
interfacial reaction leads to the formation of a solid crust encasing
partially or unreacted material. This crust restricts ingress of water
and egress of amine, and hence slows and modifies hydrolysis.
Due to the relatively low vapour pressures, and thus, low magnitude of
vapour emission, for the MDI substances, atmospheric emission and
degradation of vapour is considered to be of low importance for MDI
substances. The half-life of 4,4'-MDI, based on predicted reaction with
photochemically-generated hydroxyl redicals, has been estimated to be
Phototransformation in water and soil for the test substance was assumed
to be a negligible removal mechanism, compared to the predominant
hydrolytic degradation pathways.
Biotic degradation is not considered to be the main removal mechanism.
Due to the rapid reaction with water (hydrolysis T1/2 = 20 days), any
attempt with biodegradation test to measure biological removal, will
measure the biodegradation of the hydrolysis products. In an attempt
with an inherent biodegradation test, it was found that PMDI (and mainly
its hydrolysis products) is not readily biodegradable.
Due to the high reactivity of the substances of the MDI category with
water, bioaccumulation tests can in principle not be performed with
these substances. However, one bioaccumulation test (OECD 305E) with
4,4'-MDI and a mesocosm study with PMDI with an indication of
bioaccumulation potential have been performed showing that MDI has no
bioaccumulation potential in the aquatic environment.
No data are available on terrestrial bioaccumulation on any of the MDIs
of the category approach. The reactivity of MDI with water, the low
measured BCF in fish and the evidence of the mesocosm study, suggest
that MDI has a low potential to bioaccumulate in terrestrial food-chains.
Due to the transient existence of MDI substances, only estimated values
for water solubility and octanol-water partition coefficient (log Kow)
can be determined and these numbers have little scientific value or
relevance. This has been demonstrated for Toluenediisocyanate (TDI)
which is similar to the MDI substances in structure and reactivity. A
sensitivity analysis of the Level III fugacity model outputs for TDI
showed that wide variation in model inputs such as water solubility ,
log Kow had negligible impact on the predicted environmental
distribution and inter-media transport of such a reactive substance.
This modeling analysis showed that, regardless of whether TDI (or in
this case, MDI substances) are emitted directly to air, water, or soil,
> 99.5% of the emission will remain and be degraded within the
compartment to which emissions were made. Hence, the transport and
distribution of the MDI substances are governed by their reactivity in
environmental media, and properties such as water solubility, log Kow,
and soil adsorption coefficient are of no real value and cannot be
determined properly. No accumulation of the MDI substances is expected
in any compartment.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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