In Section 12 of the safety data sheets, you can frequently encounter phrases such as “log Kow”, “log Pow” or “log pOW” in connection with the bioaccumulation potential. What is behind these values? Which ones are used and when? What are the implications of these values for the bioaccumulation potential?


“log Kow” is a ratio value without a unit and is normally used in the decadic logarithm (“log” in log Kow). This value stands for the octanol/water partition coefficient. The test substance is added to N-octanol (“O” in log Kow) and water (“W” in log Kow) to determine the value. Since N-octanol is nonpolar and water is polar, the two liquids do not really mix and are present in two phases. The result is the concentration of the test substance in N-octanol in relation to the concentration in water. This means that the smaller the log Kow, the more soluble the substance is in water. Consequently, this means the higher the log Kow, the more soluble the substance is in fatty (nonpolar) substances.


The use of log Kow, log Pow or log pOW is merely a way of specifying different abbreviations for the same value. All abbreviations stand for the decadic logarithm of the octanol/water partition coefficient.

The octanol/water partition coefficient together with the bioconcentration factor (BCF) are stated in the Regulation (EC) No. 1907/2006 (REACH Regulation) as possible test results for the assessment of the bioaccumulation potential. The abbreviation used for the partition coefficient in the English language version is Kow.

Effects of log Kow on the bioaccumulation potential

The octanol/water partition coefficient can be used to predict how quickly the tested chemical will accumulate in living organisms.

The following applies:

  • The more fat-soluble the chemical, the more it will accumulate in living organisms (fatty tissue) and therefore in the environment.
  • Water-soluble substances are more readily eliminated and generally have a lower bioaccumulation potential.

Sources: Regulation (EC) No. 1907/2006, consolidated version, as of 11/10/2016