Determination of polyoxymethylene-water partition coefficients for diverse organophosphate esters (OPEs) and prediction of the free-dissolved OPEs in OPE-contaminated soil

Increasing attention on the estimation of bioavailability of organophosphate esters (OPEs) in soil or sediment has urged the development of techniques to measure soil-/sediment-associated porewater concentrations of OPEs. In this study, we investigated the sorption dynamics of 8 OPEs to polyoxymethylene (POM) spanning one order of magnitude of aqueous OPE concentrations and proposed POM-water partitioning coefficients (K-pom/(w)) for OPEs. The results showed that the K-pom/w values were mainly affected by the hydrophobicity of OPEs. OPEs with high solubility preferentially partitioned into the aqueous phase indicated by the low log K-pom/w values; while lipophilic OPEs were observed to be taken up by POM. The concentration of lipophilic OPEs in the aqueous phase had a strong impact on their sorption dynamics on POM, with higher aqueous concentrations accelerating the sorption dynamics and shortening the time for equilibration. We proposed that the required time to reach equilibration for targeted OPEs should be 42 d. The proposed equilibration time and Kpom/w values were further validated by applying POM to soil artificially contaminated with OPEs to measure OPEs soil-water partitioning coefficients (K-s). The variations of Ks among soil types implied the need to elucidate the effects of soil properties and chemical properties of OPEs on their distribution between soil and water in the future.