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Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

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.


 


The substances of the MDI category have in common their high reactivity and unique combination of physico-chemical properties, which dictate a high degree of uniformity in their environmental fate and ecotoxicological effects. The same uniformity in reactivity and in physical-chemical properties will also govern their potential to bioaccumulate in the category substances represent the highest potential for exposure and mobility in the environment because of their lowest molecular weight and calculated octanol-water partition coefficient values of all possible constituents. Yet, studies of their bioconcentration in fish and mobility in soil show very low or no potential for accumulation and mobility in the environment.
The assessment of bioaccumulation potential for the constituents of the substances of the MDI category and the transformation products of their constituents requires an understanding of all the preceding aspects of their physical-chemical properties and reactivity. Bioaccumulation of any MDI substance is implausible, as these substances will react with water at their point of introduction to any body of water (e.g. wastewater). Fish bioconcentration studies with 14C-radiolabeled 4,4’-MDI and the minor degradation product 4,4’-MDA support this conclusion. The most water-soluble and lowest molecular weight polyurea species (diamino-monourea of MDA) has also been assessed using a QSAR with incorporates results from an in vitro fish metabolism study, showing that the polyurea, being the main common (transformation) compound have very low bioaccumulation potential. Hence, data of the source substances and the supporting data on diamino-monourea of MDA can be used to cover the bioaccumulation endpoint. 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. With half-lives of less than five minutes, as determined in OECD 111 studies, stable concentrations cannot be achieved as required by guidelines for bioaccumulation. However, a bioaccumulation study with the source substances 4,4'-MDI and a mesocosm study with pMDI have been performed. The MDI substances could not be monitored due to its extremely rapid hydrolysis, hence a bioaccumulation factor (BCF) of the parent compound could not be measured indicating that MDI has no bioaccumulation potential in the aquatic biota. No data are available on terrestrial bioaccumulation on any of the MDI substances of the category, but it is not a requirement under REACH. The reactivity of MDI substances with water, the low measured BCF in fish and the evidence of the mesocosm study, suggest that the MDI substances have a low potential to bioaccumulate in terrestrial food chains. Since all substances of the MDI category show a similar behaviour in the aquatic environment (rapid hydrolysis, rapid formation of polyurea, no biodegradation), it can be concluded that none of the MDI substances within the category will show a bioaccumulation potential. This is supported with high confidence by reliable data available on two source substances of the category and on the common (transformation) compounds. As such, the substances of the MDI category can be regarded as not meeting the bioaccumulative/very bioaccumulative (B/vB) screening criteria under REACH. 


However based on the outcome of the soil biodegradation studies the registrant may propose bioaccumulation studies at a later stage.

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