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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption to solid soil phase is expected.

Key value for chemical safety assessment

Koc at 20 °C:
10 000

Additional information

The Adsorption/desorption screening analysis using the HPLC method cannot technically be performed on the members of the Stilbene Fluorescent Whitening Agents category because of their interaction with silica.

Traditional estimation methods rely upon the octanol/water partition coefficient or related parameters, but the first-order molecular connectivity index (MCI) was used successfully to predict Koc values for hydrophobic organic compounds (Sabljic, 1984, 1987; Bahnick and Doucette, 1988). The original KOCWIN program (PCKOC) used MCI and a series of group contribution factors to predict Koc (Meylan et al., 1992). This group contribution method was shown to outperform traditional estimation methods based on octanol/water partition coefficients and water solubility.

Two adsorption studies are available for the assessment of the adsorption potential of the substances belonging to the Stilbene Fluorescent Whitening Agents category.They were performed on CAS 16090-02-1 (morpholino derivative, disulphonate) and on CAS 16470-24-9 (the analogous dihydroxyethylamino tetrasulphonated salt). These two tested substances are different in terms of solubility and log Kow, but their adsorption potential to soil does not change sensibly, demonstrating that the property is related to the whole structure, geometry and organic functional groups. Furthermore, both studies indicate that the substances belonging to this category possess a medium to high adsorption potential all along the category which indicates that the tested substances bind to soils and sediments.

The measured values on the tested substances are compared with the estimation values and the following results are obtained:

13863-31-5 16090-02-1 16470-24-9

Cation

2 Na+ 2 Na+ 4 Na+

Log Koc measured

RA 2.93 - 3.35 3.45- 4

Log Koc estimated (KocWIN)

8.20 (A) – 8.57 (Na) 9.96 (Na) - 10.11 (A) 11.32 (A) – 11.55 (Na)

(A): estimation based on the acid form; (Na): estimation based on the bound [Na] form

It can be seen that the calculated Koc of the substance under registration (CAS 13863 -31 -5) is below the other two substances, therefore the value of log Koc of 4 has been taken as representative for the substance CAS 13863-31-5.

[LogKoc: 4.0]