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Environmental fate & pathways

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It has to be considered, that based upon its pKa-values, dicarboxylic acids are mostly present as anions (i. e. deprotonated) under environmental pHs. As anions are neither subject to volatilization nor to adsorption, the hydrosphere is also the target compartment for the deprotonated molecule.

As no data on adsorption and volatilisation are available for the mixture, adipic acid is applied for read-across approach to describe the transport and distribution behaviour for dicarboxylic acids. Additional calculations for the other two acids will lead to results in the same order of magnitude, based upon the similarity to physico-chemical properties of the compounds.

Due to the low vapour pressure of 0.097 hPa and the low Henry´s law constant of 0.0616 Pa m³/mole, adipic acid is expected to be distributed mainly to the aqueous compartment if released to the environment.

The estimated Koc values for adipic acid, using different accepted calculation methods are 2.4, 5.3 and 21.5 (Currenta, 2009), indicating that the substance is not expected to adsorb neither to suspended solids and sediment in water nor to soil.

In order to describe the distribution of dicarboxylic acids in a ”unit world” calculation is performed according to the Mackay fugacity model level I (Currenta, 2009a) based on the physico-chemical properties of adipic acid. The main target compartment for adipic acid is water with 97.9 %, followed by air with 2.1 %.

Due to its low vapour pressures and its low Henry´s law constants, each constituent is expected to be distributed mainly to the aqueous compartment if released to the environment.