Silicone-water partition coefficients determined by cosolvent method for chlorinated pesticides, musks, organo phosphates, phthalates and more

To further support implementation of monitoring by passive sampling, robust sampler-water partition coefficients (K_pw) are required to convert data from passive sampler into aqueous phase concentrations. In this work silicone-water partition coefficients were determined for ∼80 hydrophobic organic contaminants using the cosolvent method. Partition coefficients (K_pm) were measured in pure water and water-methanol mixtures up to a methanol mole fraction of 0.3 (50% v/v). Subsequently, logK_pw in pure water was determined as the intercept of linear regression of the logK_pm with the corresponding methanol mole fractions. LogK_pw were determined for phthalates, musks, organo phosphorus flame-retardants, chlorobenzenes, pesticides, some PCBs and a number of miscellaneous compounds. The median standard error and 95% confidence interval of the measured logK_pw was 0.06 and 0.13, respectively. The overall relationship between K_pw and K_ow seems insufficient to predict K_pw for unknown compounds. Prediction may work within a group of compounds with similar nature, e.g. homologues but HCH isomers having the same K_ow exhibit K_pw ranging over an order of magnitude. Long alkyl-chain phthalates and tris(2-ethylhexyl) phosphate; all having a molecular volume >400 ų, deviated the most from the K_pw-K_ow relationship.