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EC number: 905-806-4
CAS number: -
The 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.
All substances of the MDI category possess aromatic isocyanate functional groups which are known to rapidly hydrolyse and polymerise to polyurea when added to water. Biodegradation is therefore not a relevant transformation process for the category substances. Nevertheless, biodegradation screening tests for the three boundary substances of the MDI category, 4,4’-MDI, pMDI and 4,4’-MDI/DPG/HMWP have been conducted. When biodegradation studies are conducted on MDI substances, these substances are expected to be rapidly hydrolysed/polymerised to their transformation products (mainly insoluble polyurea) immediately after the initiation of the biodegradation studies. Therefore, the biodegradation study results for MDI substances reflect the biodegradability of their transformation products and not necessarily of the MDI substance constituents themselves. The main common (transformation) compounds (i.e. polyurea) are chemically “inert” and are not expected to be biodegradable in the environment. The minor common (transient) transformation compound MDA is shown in various simulation tests to be not persistent in soil and aquatic/sediment systems. Biodegradability of 4,4’-MDI and 4,4’-MDA mono-ureas was also tested. Both substances were not readily biodegradable.Read-across is used to predict the biodegradability outcome of other MDI substances on the basis that biodegradation is not a relevant pathway for the MDI category substances. This hypothesis is supported with high confidence by reliable biodegradation data available for the three source substances as well as the hydrolysis products.
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