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Environmental fate & pathways

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The percent distribution generated using fugacity level III model of EPIWEB 4.1 indicates that C16-18 TMAC is likely to partition mostly to the soil (51.72%) and sediment (40.37%) compartments and to a lesser extent to water (7.87%) and air (0.06%). However, considering its ready biodegradability and low BCF value (i.e., 71 L/kg ww), it can be assumed that C16-18 TMAC will not be persistent or bioaccumulate in soil or other environmental compartments. Furthermore, the low vapour pressure (2.9 x10 - 6Pa at 25°C) together with low Henry’s law coefficient of 4.27x 10 -5Pa-m3/mole further supports the expected low potential for C16 -C18 TMAC to distribute into the atmospheric compartment.

The experimentally determined Koc values of 282,624 and 2,658,608 (log Koc: 5.5 to 6.4) indicated that the read-across substance 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. This means that there will be a very poor correlation with organic carbon in soil. This also means that sorption should not be normalized to the organic matter content in soil but instead it is better to use the average Kd value and enter this 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 for the C16 -C18 TMAC, the solids-water partition coefficient in sediment and suspended sediment are also 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 C16 -C18 TMAC based on the adopted read-across approach.