Lithium (C8-C10, branched, C9 rich, alkylnaphthalene sulphonate)

Water solubility

Description of key information

In a study using the flask method (Laus 2014), the water solubility could not be conclusively assessed, due to the inability of the lab to achieve a clear solution. After several-fold dilution, the clear solution contained no detectable amount of the test substance.  A QSAR according to Waternt v1.01 (EPIWIN) showed a water solubility of 4.7E-04 µg/L. This low value indicates that the water solubility of LiDNNSA is similar to the water solubility of the structural analogues DNNSA and BaDNNSA.

Key value for chemical safety assessment

Water solubility:

0.229 mg/L

at the temperature of:

20 °C

Additional information

In the water solubility tests that are available for all three compounds, difficulties to assess an actual value were seen. This is not surprising in view of the complex structure of the substances. The ECHA guidance on Information Requirements indicates for UVCB substances: “solubility of a single substance in water is not applicable to substances which are multi-component, such as multi-constituent or UVCB substances, i.e. complex substances. The usually accepted meaning of ‘solubility’ in such cases is ‘the composition of the aqueous solution formed at equilibrium under a defined set of conditions’. Temperature and the amount of substance added per unit volume of water (i.e. the ‘loading’) are the main factors to consider. It may not always be possible to establish that equilibrium of all components has been achieved; in these cases, time and type of agitation of the test vessels must also be described”. Different components of the UVCB may exhibit different water solubility, so that in practice water solubility is not a single point, but likely to a range. It is noted that for complex substances water solubility may also be dependent on the loading rate. In addition, the analytical method (in all available studies based on a single peak in the chromatogram) may influence the assessed value strongly.

The methods to assess the water solubility of LiDNNSA, BaDNNSA and DNNSA included both column elution and slow stirring approaches. The flask test with LiDNNSA showed that the water solubility could not be conclusively assessed, as the clear solution achieved only after multiple dilutions produced measurements below the LOQ of the test substance. The preparation of an analyzable solution without any dissolved particles was not described in detail in all of the available reports. Problems associated with turbidity of the eluted solutions were not reported in the studies with the source substances, but were seen clearly in the study on the target substance. Nevertheless all studies on the three substances claim that no particles were present in the analyzed samples.

In view of the uncertainties described above, QSARs were run using the Epiwin model for LiDNNSA, although the Epiwin model in principle is not suitable for salts. The structures of LiDNNSA as shown in table 1 can be modelled but do not reflect the actual substance accurately, as this substance is an ionizable salt. Therefore the most reliable estimation for water solubility will be based on the test with the acid, which shows a water solubility of 0.229 mg/L. This value is considered to represent a worst case estimate for use in any risk assessment of the target substance.