Indoor Dust/Air Partitioning: Evidence for Kinetic Delay in Equilibration for Low-Volatility SVOCs

Effective modeling of semivolatile organic chemical (SVOC) partitioning between air and indoor dust is investigated by calculating partition ratios for selected SVOCs between air and n-octanol as well as 8 other oligomers similar in chemical structure to common components of household dust. COSMO-RS solvation theory was used to calculate air-oligomer partition ratios, which were converted to estimates for K_OA (octanol-air) and K_dust-air. The results are compared with reported monitored partition ratios with good agreement for the more volatile SVOCs of vapor pressure (VP) exceeding 10^-5 Pa and corresponding calculated log K_dust-air (m³ g^-1) of <5.5 or unitless log K_OA of <11.5. For less volatile SVOCs, reported values of K_DA are significantly lower than predicted, with the deviation increasing with decrease in VP. This effect is attributed to a kinetic delay in which characteristic times for equilibration exceed the dust-air contact time, and equilibrium is not achieved. It is hoped that the approach of computing partition ratios of SVOCs using oligomers selected on the basis of likely dust sources and compositions may improve the estimation of indoor human exposure to SVOCs present in air and dust and assist in exploiting dust samples to monitor and evaluate the fate and exposure of organic chemicals used indoors.