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Adsorption/desorption

At typical soil pH (i.e. pH 5 to 9) the ionisable components (pKa = 3.4) would be largely dissociated and as such, the most environmentally relevant log Koc values are those determined for the dissociated forms.

Log Koc values for three ionisable components of the test material (C14-, C16- and C18-components) were estimated by HPLC and also using chemical modelling software. The HPLC method was equivalent to OECD Guideline 121 (with acceptable deviations), and to GLP. Isocratic elutions of test and reference compounds from a cyanopropyl column with 55 % methanol/45 % citric acid buffer (pH 6) mobile phase were performed. Under the circumneutral pH conditions of the column the test material components were in their dissociated forms and had high affinity for the solid phase resulting in their non-elution after injection. A log Koc value of >5.6 was assigned to all three test material components.

Estimation of log Kow of the dissociated test material components was performed using KOWWIN chemical modelling software, giving values of 5.1 to 7.0 respectively. The KOWWIN log Kow values were fitted to an equation defining the relationship between log Kow and log Koc for organic acids, giving log Koc values of 2.9 to 3.8 for their dissociated conjugates.