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Environmental fate & pathways

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The distribution generated using fugacity level III model of EPIWEB 4.1 indicates that C16 TMAC is likely to partition mostly to the soil (64.61%) and sediment (23.21%) compartments and to a lesser extent to water (12.09%) and air (0.11%) (US EPA, 2012c). However, considering its ready biodegradability, toxicokinetic data and low BCF value (i.e., 71 L/kg ww), C16 TMAC is not expected to persistent in the environment. The low vapour pressure (5.8 x10–3 Pa at 25°C) together with a low Henry’s law coefficient of 2.92 x 10-5 Pa-m3/mole and the percent distribution data from the Level III fugacity modelling, further supports the expected low potential for C16 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) indicate that the read-across substance C12-16 ADBAC will adsorb to soil, does not easily desorb and can be considered immobile. Cationic surfactants adsorb to soil mainly due to ionic interaction with negatively charged surfaces. This means that there will be a poor correlation with organic carbon in soil and that sorption should not be normalized to the organic matter content in soil. Rather, the average Kd values should be used to estimate the solids-water partition coefficient in soil. When organic matter is not a determining factor in 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 the solids-water partition coefficients in sediment and suspended sediment are both equal to 13,630 L/kg.