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Sediment toxicity

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A Koc value of 2,658,608 L/kg for C12-C16 ADBAC indicates a high potential for adsorption to sediment. However C12-C16 ADBAC is ready biodegradable and has a low measured BCF value of 79 and therefore C12-C16 ADBAC has a low potential for exposure to sediment organisms.Nevertheless, the equilibrium partitioning method was calculated and used to assess the hazard for sediment organisms.

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Based on the experimentally determined Koc values of 282,624 and 2,658,608 (log Koc: 5.5 to 6.4) C12-C16 ADBAC 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 narcotic substances. They adsorb mainly due to ionic interaction with the negatively charged surfaces in soil. Therefore that 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. However, considering the ready biodegradability in water and low BCF value (i.e., 79), C12-C16 ADBAC can be expected to have a low potential for exposure to the sediment organisms. Nevertheless, the sediment PNEC value of 0.267mg/kg d.w was determined with the equilibrium partitioning method using the equation: PNECsediment freshwater = (0.783 + 0.0217 x Kd) x PNECwater. The sediment marine water PNEC value of 0.0267 mg/kg d.w. was determined with the equilibrium partitioning method using the equation: PNECsediment marine water = (0.783 + 0.0217 x Kd) x PNECwater (ECHA guidance document R10, May, 2008).