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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

The substance is characterised by estimated bioconcentration factors between 1.1 and 25920 covering BCF values of the parent compounds (isocyanate groups) and possible hydrolysis products (amine groups), respectively (Currenta, 2010d).
Due to the chemical nature of the parent compounds (isocyanate groups) only the corresponding amines and further transformation products, resulting from the reaction of isocyantes with amines, will be found in the aqueous phase having BCF values between 1.1 and 3.2. Based on these BCF values, presenting the environmental relevant structures, the substance and transformation products can be scored as having only a low potential for bioaccumulation.

Key value for chemical safety assessment

Additional information

According to the Guidance Document R.7c (ECHA, 2008), the use of alternative information is recommended in the absence of measured data, before new vertebrate tests are conducted. Furthermore, an experimental determination of the bioaccumulation potential is hampered due to the poor water solubility of the test item, its heterogeneous reaction with water paralleled by the formation of numerous hydrolysis products and the lack of a feasible analytical method to determine test item concentrations either in the aqueous phase or in biota. Therefore, the bioaccumulation potential of the substance was solely estimated by the means of calculated BCF values.

The test substance is a UVCB substance characterized by the presence of 2,4-/2,6-TDI as well as a plurality of unresolved structures. An exact determination of the identity is not possibly, but they all have in common the presence of biuret structures, which were built through the heterogeneous reaction of formed amines with unreacted isocyanates. BCF values were thus estimated for the main substance components as well as possible reaction/ hydrolysis products.

BCF values for the isocyanates (2,4/2,6-TDI) account for 151.4 being only of a theoretical interest due to the rapid hydrolysis of these compounds. 2,4-/2,6-TDA are the corresponding amines possibly formed through the hydrolysis and characterized by a BCF value of 3.16. But amines will only be formed to a minor extent due to side reactions with unreacted isocyanate functions. During these reactions, biuret structures with a variable molecular size are formed. Two example structures of different molecular size were developed and BCF values were calculated for (i) structures containing the unreacted isocyanate functions, and (ii) the corresponding amine structures. For the isocyanate containing structures, BCF values of 25290 and 2251 were calculated, whereas the corresponding amine compounds have BCF values of 3.2 and 1.1, respectively. Concluding, theoretical possible structures, initially contained (isocyanates) are characterized by high BCF values indicating a high potential for bioaccumulation, but these values are only of theoretical interest due to the rapid reaction of these compounds. BCF values of the corresponding amines in turn indicate only a low potential for bioaccumulation.

Accordingly, initially present compounds might have a high potential for bioaccumulation but are furthermore characterized by instability in aqueous media and thus a rapid disappearance thereof. The so formed degradation products are again characterized by a low potential for bioaccumulation.