Phosphoric acid, mono- and bis(branched and linear pentyl) esters

Partition coefficient

Description of key information

One reliable key study is available on the registered mixture. The experimental value of Log Pow  have been determinated on the two main components of the test item to be <-2.07 for the monoester and -0.235 for the diester at 22.5°C and a pH of 5 (corresponding to the maximum partition coefficient under environmental conditions). The weighted average of both values to the composition rates have been calculated to be - 0.93 for the purposes of chemical risk assessment, classification and labelling and PBT assessment.

Key value for chemical safety assessment

Log Kow (Log Pow):

-0.93

at the temperature of:

22.5 °C

Additional information

The determination of the partition coefficient was measured on the two main components of the registered mixture, the monoester and the diester, using an HPLC estimation method, according to the method A8 Partition Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008 and the method 107 of the OECD Guidelines for testing of Chemicals, 13 April 2004 and compliant with GLP. No deviation from the guidelines were observed.

A preliminary assessment of the partition coefficient was calculated using KOWWIN model. The definitive test was performed with the experimental shake flask method at pH 5. Based on the acidic profile of the two dominant components present in the test item, this pH resulted in maximum possible partition coefficient values within the environmentally relevant pH range of 5 to 9.

Six partitions were performed by inversion of the flasks and aliquots of both phases were taken for analysis by HPLC-MS. Calculations were performed individually for the monoester and the diester component peaks of the test item by interpolation from the relevant calibration curve. 

The values obtained at 22.5°C by shake flask method were log Pow -2.07 for the monoester component and -0.235 for the diester component.

Regulatory guidance documents raise caution for the use of the shake-flask method for the determination of partition coefficient for surface active substances due to possible interferences. However no evidence of micelle formation or emulsification was observed in either the water solubility or partition coefficient test, phase separation was achieved with ease and the consistency of the phase concentrations on analysis and the mean mass balance recoveries of 104 and 97.3% for the monoester and diester components respectively also demonstrated that no significant concentration of test item had accumulated at the phase boundary. Final supportive evidence for the validity of the experimental partition coefficient was obtained from the consistency with the computer estimated values of partition coefficient at pH 5 of log₁₀P_ow<-1.94 and log₁₀P_ow0.08 for the monoester and the diester components, respectively.

Based on the weighted average with the composition rates of its two main components, a partition coefficient value of -0.93 at 22.5°C was assessed for the registered mixture for chemical risk assessment, classification and labelling and PBT assessment purposes.