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Ecotoxicological information

Toxicity to soil microorganisms

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Description of key information

No data is available on the test substance for the toxicity to terrestrial microorganisms. As there is no indication of risk to the terrestrial environment, it is not deemed necessary to perform these tests.

Key value for chemical safety assessment

Additional information

Annex X states that this study need not be conducted if the chemical safety assessment does not indicate a need to further investigate the effects on sediment organisms (column 2). The test substances of the methylenediphenyl isocyanate (MDI) category react quickly with water and hence could rapidly be hydrolysed in aqueous solution (T1/2 = 20h). 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 a solid, insoluble polyurea. Under conditions typical of many types of environmental contact, i. e. with relatively poor dispersion of the denser isocyanate, the interfacial reaction leads to the formation of a solid crust encasing partially or unreacted material. This crust restricts ingress of water and egress of amine, and hence slows and modifies hydrolysis. All methylenediphenyl isocyanates are produced in closed systems. Formation of insoluble polyurea due to the presence of water would cause abrasion problems and blockage of valves and pipes. Therefore, production plant releases of MDI to effluents are expected to be non-existent. 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 MDI producers and processors, including polyurethane producers (EU MDI Risk Assessment Report: methylenediphenyl diisocyanate (MDI), 2005). Calculated PEC values were 6.87 x 10-6 mg/L for freshwater, 5.43 x 10-4 for saltwater, negligible for sediment and 0.239 mg/kg for soils/grassland. The corresponding PEC/PNEC ratios would be less than 1. Taking into account the scientific and exposure arguments, it appears appropriate to waive the toxity test to terrestrial microorganisms.