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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The range for Koc of key components in wash oil is estimated to be between 1300 and 10300 (log Koc between approx. 3.1 and 4) at 20°C. Log Koc for wash oil is calculated as mean of the six major components (typical concentration above 5 %). This mean value (log Koc = 3.632) relates to a Koc of 4280.

Key value for chemical safety assessment

Koc at 20 °C:
4 280

Additional information

Adsorption Coefficient

Due to the complex composition of creosote oil, acenaphthene fraction (wash oil), a single Koc value cannot be determined for the substance. Main components (all PAH) will have their individual Koc values. An extract is presented in the following paragraphs.

Koc values of PAH have been estimated by calculations based on Pow/log Pow values using different relations between log Pow/Pow and log Koc/Koc. Well established is the equation by Karickhoff et al. (1979) derived from experimental data: log Koc = log Pow - 0.21 (or Koc = 0.63 Kow). Log Koc/Koc data reported for wash oil constituents will originate from this equation. Koc data derived using this equation have also been used in the EU Risk Assessment Report for Coal-tar pitch, high temperature (European Union 2008).

Overall properties of wash oil will best be represented by the range of log Koc/Koc values corresponding to the PAH present in wash oil (naphthalene to anthracene, see Chapter 1.). The estimated adsorption coefficients for these constituents extend from approx. log Koc ca. 3.1 for naphthalene to approx. 4.5 for anthracene (Koc range from ca. 1300 - 30000).

Substances with typical concentration above 5 % are naphthalene (11 – 13 % w/w), 1-methylnaphthalene (7 – 9 % w/w), 2 -methylnaphthalene (17 – 20 % w/w), biphenyl (5 – 6 % w/w), fluorene (4 – 5 % w/w), acenaphthene (13 – 15 % w/w). They amount to ca. 60 % of total wash oil. Their log Koc values range from 3.13 (naphthalene) to 4.01 (fluorene) (Koc = ca. 1300 to 10230).

Taking into account the log Koc values of these six substances, a mean log Koc value for wash oil can be calculated. Accordingly, the mean log Koc value is estimated to 3.632 for the six major components of wash oil. This value is very close to the Log Koc values of 1- and 2- methylnaphthalene, acenaphthene and biphenyl accounting for almost 50% of wash oil. Koc is calculated to 4280. This value is considered to represent best the properties of wash oil by a single Koc value as required for risk assessment.

Adsorption to Soil

Depending on their log Koc, adsorption of individual wash oil components to soil organic matter will differ: Mainly naphthalenes and other two-ring aromatic constituents will tend to be mobile and migrate into the water phase.

Adsorption to Air Particles

Based on vapour pressure, the majority of volatile wash oil components are expected in the gas phase rather than bound to air particulates.

[LogKoc: 3.632]