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Sediment toxicity

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Description of key information

Based on Koc data from the read-across substance C12-C16 ADBAC, C12-C18 TMAC is expected to bind strongly to soil and sediment (see Section 4.2.1). However, the substance is ready biodegradable and has a low BCF value (i.e., 67.25 L/kg ww). Therefore, it is not expected to persist in sediment and a study on sediment organisms was not conducted. 

Key value for chemical safety assessment

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Experimentally determined Koc values of 282,624 and 2,658,608 (log Koc: 5.5 to 6.4) for the read-across substance C12-C16 ADBAC demonstrated that the test substance is expected to adsorb onto soil and does not desorb easily and can be classified as immobile. Cationic surfactants do not sorb to soil in a similar way as normal organic substances. They adsorb mainly due to ionic interaction with the negatively charged surfaces in soil. Therefore there will be a very poor correlation with organic carbon in soil. This means that sorption should not be normalized to the organic matter content in soil but instead use the average Kd value as the solids water partition coefficient in soil. When organic matter is not determining the distribution in soil, sediment and suspended sediment there is no difference in adsorption to these three compartments (based on dry weight) as the organic matter content is the only variable. This means that also the solids-water partition coefficient in sediment and suspended sediment are equal to 13630 L/kg. Therefore it was better to use the mean Kd value of 13630 L/kg to further calculate the partition coffecients to soil-water, sediment-water and suspended-sediment matter for C12 -C18 TMAC based on the read-across approach. However, considering the ready biodegradability in water and low BCF value (i.e., 67.25 L/kg ww),

C12 -C18 TMAC can be expected to have a low potential for exposure to the sediment organisms. Nevertheless, the sediment PNEC value of 9.27 mg/kg dw was determined with the equilibrium partitioning method using the equation: PNECsediment freshwater = Ksusp-water * PNECaquatic * 1000 * 1 / RHOsusp (ECHA guidance document R10, May, 2008). The sediment marine water PNEC value of 0.927 mg/kg dw was determined with the equilibrium partitioning method using the equation: PNECsediment marine water = Ksusp-water* PNECmarinewater * 1000 * 1 / RHOsusp (ECHA guidance document R10, May, 2008).