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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption to the solid soil phase is not to be expected.

Key value for chemical safety assessment

Additional information

Since no studies on the adsorption potential of reaction mass of bis(2-hydroxyethanaminium) sulfite and 2-(methylamino)ethanol - oxosulfane oxide (1:1) the

assessment has been performed with the substance’s dissociation products.

For 2 -aminoethanol a logKoc of 0.067 has been calculated based on estimates from MCI [BASF SE, KOCWIN v2.00, 2011]. The molecule is not expected to adsorb to suspended solids and sediment based upon the logKoc as calculated for the uncharged molecule. However, a pKa value of 9.5 indicates that the molecule will exist primarily as a cation in the environment and cations generally adsorb stronger to soils containing organic carbon and clay than their neutral counterparts. Hence, the PCKOC-model may underestimate adsorption to organic carbon since it does not consider the ionic structure of the molecule. Under environmental conditions (pH from 5 to 9) 2 -aminoethanol is almost completely present in its charged form (as calculated by the formula: % ionised = 100/(1+10(pKa - pH)): 97% at a pH of 8, 100% at lower pH values). To consider the pH-dependent molecule speciation, the calculated logKoc was therefore pH-corrected by a calculation method developed by Franco & Trapp (2008) which resulted in a logKoc of 1.16 for pH 7.

Considering the low logPow (-0.91) the adsorption / desorption won´t be an important environmental fate for the substance N-Methylethanolamine. In additon, the chemical is readily biodegradable. Due to this assumption, experimental data are not necessary for this endpoint. A calculation was performed with the help of the US-EPA computer tool EPIWIN (software KOCWINv2.00) to receive a first indication for the adsorption / desorption properties of N-Methylethanolamine. The MCI method gives a Koc value of 1.303 L/kg, whereby the traditional method shows a value of 0.8915 L/kg. The MCI method is taken more seriously into account, due to the fact that it uses correction factors. The traditional method is an estimation from the logPow value. The data of this calculation tool refer to the uncharged molecule. Since N-Methylethanolamine possess a pKa value of 9.95, it will exist almost completely as a cation in the environment. Cations generally adsorb stronger to soil containing organic carbon and clay than their neutral counterparts. Hence, the KOCWIN model may underestimeate adsorption to organic carbon since ist does not consider the ionic structure of the molecule.

For this reason another calculation approach was used: according to Franco and Trapp the logKoc (as well as the Koc) value will not change at a range from pH 5 to pH 9. This indicates that for the substance N-Methylethanolamine the surrounding pH will not have a great influence on its adsorption coefficients.

Simple inorganic salts like the read-across substance sodium sulphite with high aqueous solubility will exist in a dissociated form in an aqueous solution. Such a substance has a low potential for adsorption.

Conclusively, adsorption of

Reaction mass of bis(2-hydroxyethanaminium) sulfite and 2-(methylamino)ethanol - oxosulfane oxide (1:1)

to the solid soil phase is not expected.

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