Direct measurement of octanol–water partition coefficients of some environmentally relevant brominated diphenyl ether congeners

Octanol–water partition coefficients (KOW) of nine environmentally relevant brominated diphenyl ether (BDE) congeners present in two technical mixtures were directly measured using a slow-stir technique. Log KOW values of tri- to heptabrominated BDE congeners ranged from 5.74 to 8.27, and were related to bromine content by the equation logKOW=0.621(#Br)+4.12 (R2=0.970). The directly determined KOW values were generally lower than those calculated using fragment constant methods, particularly at higher levels of bromine substitution. The quasi-experimental approach of using fragment constants to modify a “backbone” compound of known KOW was much more successful than using the fragment constants to “build” the entire molecule. The tri- and tetrabrominated congeners are in the range of optimum bioaccumulation potential.