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Physical & Chemical properties

Water solubility

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Link to relevant study record(s)

Description of key information

In a weight-of evidence appraoch  three water solubility studies were evaluated. The complex composition of the substance has been identified to be the limiting factor for the determination of an exact value for the water solubility. Only a small portion (less than 0.1 %) of the substance is considered to be soluble in water, indicating a water solubility of about or below 1 mg/L.

Key value for chemical safety assessment

Water solubility:
1 mg/L
at the temperature of:
23 °C

Additional information


A water solubility value of 24 mg/L was given in the report based on gravimetric detection. In the raw data the very low mass difference of 1.2 mg was obtained by two weightings of the relatively heavy evaporating dish before and after evaporation of the water: 34.2583 g – 34.2571 g = 0.0012 g. It is obvious that even with a good and modern analytical balance a high uncertainty of the result is expected. This was the reason why the study director mentioned in the study report: “Information on the water solubility can only be achieved with limitations.”

As the analytical method was not precise enough for the determination of the water solubility, the result should be handled only as a rough estimation indicating that the substance has a low water solubility.


A water solubility value of 2.5 mg/L (pH5) and 3.2 mg/L (pH9) was given in the report based on HPLC detection. Due to the difficulty in analysis of the substance and uncertainty of the composition, the authors stated: “Values of the aqueous solubilities should be considered estimates and not true values. These values will be higher than the true solubilities by an amount that depends on the degree of impurities present”. For this reason the Registrant has evaluated the water solubility as <2.5 mg/L or <3.2 mg/L.


This study is a GLP water solubility test performed according to OECD 105 (column elution method). The water solubility of 2,2,4-Trimethyl-6-(2,2,4-trimethyl-1,2,3,4-tetrahydroquinolin-4-yl)-1,2-dihydroquinoline (“TMQ dimer”) from a matrix of 1,2-Dihydro-2,2,4-trimethylquinoline, oligomers was investigated. TMQ dimer is the main single component in the UVCB substance with a concentration range of 10 to 25%. The sample used in the study contained about 29.9% TMQ dimer. The water solubility was analysed using a HPLC method yielding a result of <0.2 mg/L TMQ dimer. The study director stated a water solubility of <1.0 mg/L for the sum of oligomers.

Each of the three studies has some limitations concerning precision of the analytical method, the limit of quantitation required for low water solubility. Moreover, the chemical composition of the UVCB substance was a source of uncertainty. Nevertheless, the studies were evaluated in a weight-of evidence approach finally leading to the conclusion, that only a small portion (<0.1%) of the substance may be soluble in water. Aniline has been found to be present in a concentration range of 0 to 0.2% in the original UVCB substance. According to the physico-chemical properties of Aniline (e.g. water solubility = 35 g/L) it is suggested that this might be a constituent of the water soluble fraction.

The water solublity is estimated to be around or below 1 mg/L.