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Environmental fate & pathways

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A bioaccumulation study on MDI PIR is waived because exposure to aquatic compartment is unlikely. This is because the rapid hydrolysis of MDI with a t1/2 of 20 hours.

Other data can be considered alongside the fundamental data waiver.

Log Pow for MDI

Degradation products of the hydrolysis

Mesocosm study of MDI (Heimbach 1993)

Bioconcentration study on MDI (CERI 2002)

It is recognised that there is a measured log Pow value of 4.51 for monomeric MDI. This log Pow value is of somewhat theoretical as MDI is very unstable in aqueous media (see Section 5.1.2: Hydrolysis). The determination was by an hplc method and comparison to reference chemicals.

MDI reacts with water to form predominantly high molecular weight, inert polyureas and trace amounts of 4,4’-methylenedianiline (MDA). This MDA is considered as the only degradation product of significance, and it has a log Pow value of 1.55. Its measured BCF is < 14 (at 0.2 mg/L) in Cyprinus carpio (EU Risk Assessment Report: 4,4’-methylenedianiline). So, it is concluded that degradation products of MDI do not bioaccumulate.

There is a mesocosm study on PMDI (Heimbach 1993 PMDI dossier 6.1.2a) study, carried out over 112 days, at a loading of 10,000 mg PMDI/L. MDI was detected neither in the water (detection limit 0.005 mg/l) nor in fish (detection limit 0.51 mg/kg). A numeric BCF can not be calculated from these non-detects, but clearly these results show in a practical way that MDI does not accumulate in fish.

A BCF study (III report 11564) carried out according to guideline principles with [14C] radiolabelled 4,4’-MDI and Cyprinus carpio, derives BCF values of 92 and 200 for concentrations of 0.8 and 0.08µg MDI/l. The reported BCF values are highly questionable given the known rapid hydrolysis of MDI under these conditions. Liquid scintillation counting was the method of analysis for all water and fish samples and no analyses of 4,4’-MDI itself were carried out during the course of the study. A BCF value of 200 indicates low potential for bioaccumulation, but it must be recognised that this value probably reflects the bioconcentration of water soluble hydrolysis products which most likely include 4,4’-MDA and low molecular weight ureas. So, again, it is concluded that degradation products of MDI do not bioaccumulate.

Lastly, a BCF value of 439 for 4,4’-MDI may be estimated using the BCFBAFTM (v 3.00) model, a part of the Estimation Program Interface Suite of QSAR tools. An estimated BCF value of 439 for 4,4’-MDI suggests low potential for bioaccumulation.

To summarise, bioaccumulation study is waived due to the unlikely exposure due to rapid hydrolysis of MDI. Supporting data including a mesocosm study, modelling and assessment of degradation products all indicate no potential for significant bioaccumulation.