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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The key value is the geometric mean of the Koc for soil determined according to OECD Guideline 106 (von Oepen, Kördel and Klein, 1991). 

Key value for chemical safety assessment

Koc at 20 °C:
25.53

Additional information

A publication is available about a batch-equilibrium method according to OECD Guideline 106, whereby the test substance was investigated beside 49 substances (von Oepen, Kördel and Klein, 1991). Three types of soil were used: Podzol with an organic carbon content of 4.85 %, Alfisol with 1.25 % organic carbon and Sediment with 1.58 % organic carbon, respectively. The sorption equilibrium was reached within 16 hours and it was reversible to a great extent. The mass balance resulted in a recovery of greater than 80 %. For hydrophobic compounds, variation in the Koc-values of different sorbents is within one order of magnitude. For more polar compounds (like amines), the variation in sorption coefficients is up to two orders of magnitude. The sorption of amino-groups to clay-minerals or pH-dependent sorption of acids play a key role. Although several interactions contributing to the sorption process are known, it was not possible to determine the quantitative contribution of each sorption mechanism. For the test substance, the Koc values were reported as followed for Podzol, Alfisol and Sediment: 4, 163 and 508, respectively. Therefore, the geometric mean of the Koc for soil is determined as 25.53.

As supporting information, the computer tool EPIWIN calculates the soil adsorption coefficient also concerning the MCI method, which gave a Koc of 8.158 L/kg (Chemservice S.A., 2010).

The adsorption coefficients for Montmorillonite, Kaolinite, and marine sediment were determined in a batch equilibrium experiment by Wang and Lee (1993). Beside the different adsorption coefficients (please refer to table 9 Overview of studies on adsorption / desorption), the scientists presented the following statements: Adsorption of amines by Montmorillonite and Kaolinite is consistent with control by electrostatic attraction as well as by van der Waals forces and this could be an important control on the distribution of these organic compounds in sediment porewaters. Adsorption of amines by clays and also by FP sediment is essentially a reversible process.

In a study conducted by Wang and Lee in former times (1990), the adsorption coefficient of marine sediment was determined as 2.4 - 4.7, whereby salinity will significantly reduce the adsorption of amines onto freshwater sediments. Beside the soil adsorption procedure, removal of amines from uncontaminated seawater can occur by bacterial uptake (incorporation plus respiration). In relationship to the organic and clay mineral content, the exchangeable and fixed dimethylamine concentration will vary among different sediments. In Flax point sediment seasonal variations were observed for the concentrations of dimethylamine.

[LogKoc: 1.41]