Approaches for estimating PUF-air partitions coefficient for semi-volatile organic compounds: A critical comparison

Partition coefficients between polyurethane foam (PUF) and air (K_PUF-Air) are important when using PUF as a passive air sampler for semi-volatile organic compounds (SVOCs) and when considering the fate of SVOCs indoors where PUF is a common material. Here, K_PUF-Air for selected SVOCs was estimated using published methods, since measured data are unavailable for most of these compounds. Estimates of K_PUF-Air were within one order of magnitude for SVOCs having values of log octanol-air partition coefficient (K_OA) of 5, but differed by nearly three orders of magnitude for SVOCs with log K_OA of 12. Of all the methods, the correlation developed using experimental measurements gave the lowest estimates for the high K_OA compounds, likely because the compounds did not reach equilibrium throughout the PUF sample. The surface area/volume ratio of the PUF sample was shown to influence the observed correlation, a reflection of the equilibration status of the PUF. For quantitative comparison, the poly parameter linear free energy relationship (pp-LFER) model of Kamprad and Goss (2007) was used here as a "surrogate" standard. The correlations developed with vapor pressure and K_OA produced estimates that were closest to those obtained using the pp-LFER model. COSMO-RS theory, in which intimate and unimpeded contact is assumed between the compound in air and PUF molecules, gave lower estimates for low K_OA compounds, but good average agreement for high K_OA compounds. When used in modeling applications, the selection of the method for estimating K_PUF-Air should reflect the configuration of the products containing PUF and the model assumptions regarding compound homogeneity within the PUF.