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Environmental fate & pathways

Biodegradation in soil

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Annex IX states that this study need not be conducted if direct or indirect exposure to soil is unlikely (column 2).
MDI is rapidly hydrolysed in aqueous solution. 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 insoluble polyurea.
In the production of PMDI the formation of insoluble polyurea would cause abrasion problems and blockage of valves and pipes and therefore releases of PMDI to effluents are expected to be non-existent. Since production is performed in closed systems, releases to soil and sediment are also expected to be negligible. Furthermore, the EUSES program has been used to calculate PEC values based on measured emission data provided by PMDI producers and processors, including polyurethane producers (EU MDI Risk Assessment Report: methylenediphenyl diisocyanate (MDI)).
Calculated PEC values were 1.4 x 10-6 mg/l for water, 6.9x 10-5 mg/kg for sediment and ranged from 4.2 x 10-5 to 7.2 x 10-4 mg/kg for
soils/grassland. The corresponding PEC/PNEC ratios would be extremely small and less than 1.
Taking into account the scientific and exposure arguments, it appears appropriate to waiver the long-term fish/plant/soil and sediment toxicity studies.

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