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Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional 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.

MDI is not predicted to occur in appreciable concentrations in water, sediment, soil and air. Biotic degradation is not considered to be the main removal mechanism. Due to the rapid reaction with water (hydrolysis T1/2 = 20 days), any attempt with biodegradation test to measure biological removal, will measure the biodegradation of the hydrolysis products.

In a study based on the principles of the OECD 307 guideline, the abiotic degradation of 4,4`-MDI in 4 soil types was monitored. Best fit for "double first order in parallel (DFOP)" indicated two different reaction mechanisms. The kinetic model yielded overall DT50 values in the range of 0.036 to 0.285 d at 22°C resulting in anarithmetic average of 0.12 d (2.9 h). Arithmetic averages for the rate constants of 40 d-1for k1 and 0.73 d-1for k2 are used for further assessment. The more conservative average rate constant average value of 0.73 d-1will be used for environmental assessments of 4,4’-MDI. This average first order rate constant value of 0.73 d-1corresponds to a half-life of 1 day (24h).

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