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Environmental fate & pathways

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Due to the transient existence of MDI substances in the environment, only estimated values for water solubility, octanol-water partition coefficient (log Kow), soil adsorption coefficient (log Koc), and other inter-media partitioning parameters can be determined; and these numbers have little scientific value or relevance. This has been demonstrated by West (2008) for Toluenediisocyanate (TDI), which is similar to the MDI substances in structure and reactivity. A sensitivity analysis of the Level III fugacity model outputs for TDI showed that wide variation in model inputs such as water solubility and log Kow had negligible impact on the predicted environmental distribution and inter-media transport of such a reactive substance. This modeling analysis showed that, regardless of whether TDI (or in this case, MDI substances) are emitted directly to air, water, or soil, > 99.5% of the emission will remain and be degraded within the compartment to which emissions were made. Hence, the transport and distribution of the MDI substances are governed by their reactivity in environmental media, and properties such as water solubility, log Kow, and soil adsorption coefficient are of no real value and cannot be determined properly. No accumulation or inter-media exchange of the MDI substances is expected in the environment.

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