Crude Tall Oil (CTO) is obtained from the wood pulping industry. It is a dark brown viscous liquid extracted and processed from softwoods and hardwoods. CTO has a complex composition of fatty acids, resin acids, and neutrals.

Partition coefficient

Description of key information

log Kow (constituents of the substance): 3.4 - 8.0 (QSAR)

Additional information

The study does not need to be conducted because the partition coefficient of a UVCB substance of this nature should be evaluated on the basis of the properties of its constituents. A result for the whole substance is not meaningful scientifically for the purpose of assessment of exposure or risk. It is therefore not appropriate to conduct or propose a test for this endpoint. The needs associated with a sound understanding of partition coefficient are adequately met by the available data on constituents. Reliable partition coefficient data are characterised by quantitative structure activity relationships (QSARs) for constituents of the substance.

The individual constituents of the substance has predicted log Kow values in the range 3.4 - 8.0 using a validated QSAR estimation method. A maximum log Kow value of 8 has been used for assessment purposes where the predicted log Kow is greater than 8; this is because log Kow above 8 is not scientifically meaningful. CTO is a UVCB substance with about 80 constituents including fatty acids, resin acids, neutrals such as alcohols and high molecular weight polymeric compounds. For environmental risk assessment, the properties of the substance are assessed using the 'block approach'. The log Kow of each 'block' has been determined based on the weighted average of each constituent in the block. Predicted log Kow of 3.6 - 8.0 was determined for all 'blocks' in CTO. In other supporting study conducted according to OECD 117, a partition coefficient value of seven and nine constituents at pH 2.0 and pH 5 - 6 was 4.9 - 7.7 and 3.2 - 6.8 respectively.