Reaction Product of Ca(OH)2, MgO and Tall Oil Pitch

Water solubility

Description of key information

The water solubility of the Ca-/Mg-salt of Tall Oil Pitch (TOP) was determined at 20°C according to OECD TG 105 using the flask method.
At an initial weight of 10 g /L and 0.1 g/L, a  water solubility of 0.038 to 0.107g/L test item and < 0.0025 g/L test item, respectively was observed. 

Key value for chemical safety assessment

Water solubility:

107 mg/L

Additional information

As the test item is a UVCB substance, the test design had to be adapted. The flask method was chosen to determine the water solubility of Ca/Mg-salt of Tall-Oil Pitch, as the elution method is not suitable for UVCB substances.

For a complex substance the water solubility strongly fraction depends on the amount of test substance added. Therefore, two loading rates (0.1 g/L and 10 g/L) were tested resulting in a significant higher water solubilty at an initial weighing of 10 g/L compared to concentrations found at initial concentrations of 0.1 g/L. As the substance consists of components with a low as well as a high water solubility, higher loading rates might thus result in the dissolution of higher portions of soluble components. Experiments were evaluated on the basis of the total organic carbon (TOC) content of the aqueous phase (sum parameter), as the quantification based on individual components is not feasible.

Normally, the flasks are stirred up to 72 h to achieve equilibrium between the dissolved and undissolved fraction shown by a constant aqueous concentration throughout the test period. This could not be observed in the present study as the test item concentration in the aqueous phase decreased after 48 h. To determine aqueous concentrations after distinct periods of stirring (24 h, 48 h and 72 h), individual flasks were prepared providing a sample for each time point. As the substance is highly viscous, the substance might not be equally dispersed in the three flasks due to the formation of agglomerates of different sizes. The dissolution behavior might thus be determined by the surface of the formed agglomerates rather than by the substance properties explaining the decreasing aqueous concentration after 48 h.

Concluding, the variable concentrations observed result from the complex substance composition (presence of good soluble components besides poorly soluble ones) as well as the different dispersion of the sample in the individual test flasks. Even so, the study was scored as valid for assessment providing information about the order of magnitude in which the substance will be dissolved in an aqueous medium.