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EC number: 219-799-4
CAS number: 2536-05-2
The available data indicate that all substances of the MDI category are of low toxicity by the oral route. Following acute oral exposure, the NCO groups present on the substances of the MDI category react with acids within the stomach leading to formation of an insoluble polymerized mass that is excreted in the feces without being absorbed. Acute oral toxicity studies performed on a sufficient representation of category substances define a lack of acute oral toxicity across the category.
The available acute oral toxicity studies are of high reliability and are sufficient for demonstrating the acute oral toxicity of the substances of the MDI category. Reliable chemical composition including NCO content is also available for all substances of the MDI category acting via this common mechanism and provides an adequate basis for predicting read-across between all of them.
All substances of the MDI category share similar chemical features namely that they a) all contain a significant amount of mMDI, and b) contain at least two NCO functional groups per molecule which is bound to an aromatic ring and this ring is connected to a second aromatic ring by a methylene group. It is the NCO value (driven by the bioaccessible groups on monomeric MDI and low molecular weight constituents (e.g. three-ring oligomer) which is responsible for chemical and physiological reactivity and subsequent toxicological profile. As reactive NCO groups are a common feature of all substances of the MDI category, it is predicted that these have a similar reactivity profile and a read across within the category is warranted (detailed information on the Mode of Action is available in Category Justification Document).
This low toxicity is consistent with the overall hypothesis: a) the bioaccessible reactive NCO group drives chemical and biological activity, and b) MDI substances are not systemically absorbed because the NCO groups present on them react with acids within the stomach leading to the formation of an insoluble polymerized mass that is excreted in the feces without being absorbed.
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