Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The octanol/air partition coefficient (KOA) is a key parameter used to predict the long-range transport potential (LRTP) of volatile and semivolatile organic compounds and their bioaccumulation in terrestrial biota. Despite the enormous importance of this parameter, reliable KOA values are not available for volatile methylsiloxanes (VMS). In this study, a method of syringe headspace analysis was developed to determine KOA values for six common VMS at trace levels. It was found that log KOA values of any given VMS were linearly related to the reciprocal of the environmental temperature (T) from -3 deg C to 40 deg C, whereas at any given T, the log KOA values of different VMS were linearly related to their molecular mass and normal boiling point temperatures (Tb). Based on those findings, empirical models were developed to predict log KOA values of methylsiloxanes using Tb (or molecular mass) and T as the only independent variables. The log KOA values for common VMS at 25 deg C were in the range from 2.98 (for hexamethyldisiloxane) to 5.77 (for dodecamethylcyclohexasiloxane). Judging from the log KOA values, these VMS have little potential for long-range transport and deposition to remote surface media and for bioaccumulation in terrestrial biota.