Abstract
Direct measurement of the n-octanol partition coefficients (K(OW)) for highly hydrophobic organic chemicals is extremely difficult because of the extremely low concentrations present in the water phase. n-Butanol/water partition coefficients (K(BW)) are generally much lower than K(OW) due to the increased solubility of solute in the alcohol saturated aqueous phase, and therefore become easier to measure. We measured the K(BW) for 25 neutral organic chemicals having measured log K(OW)s ranging from 2 to 9 and 4 additional highly hydrophobic chemicals, with unmeasured K(OW)s, having estimated log K(OW)s ranging from 6 to 18. The measured log K(BW) and log K(OW) values were linearly related, r(2) = 0.978, and using the regression developed from the data, K(OW)s were predicted for the 4 highly hydrophobic chemicals with unmeasured K(OW)s. The resulting predictions were orders of magnitude lower than those predicted by a variety of computational models and suggests the estimates of K(OW) in the literature for highly hydrophobic chemicals (i.e., log K(OW) greater than 10) are likely incorrect by several orders of magnitude.