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Sediment toxicity

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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. It is important to note that the MDI category approach for read-across of environmental and human hazards between the MDI substances belonging to the MDI category is work in progress under REACH. Therefore the read-across document should be considered a draft.

No sediment toxicity data is available for the test substance. 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).

Key value for chemical safety assessment

Additional information

The test substances of the methylenediphenyl isocyanate (MDI) category react quickly with water and hence will be rapidly hydrolysed in contact with aqueous media (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 10-3 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 acute and long-term toxity test to sediment organisms.