Equilibrium Partition Coefficients of Diverse Polar and Nonpolar Organic Compounds to Polyoxymethylene (POM) Passive Sampling Devices

Abstract

Equilibrium passive samplers (EPS) based on polyoxymethylene (POM) are increasingly used for determining freely dissolved water and pore water concentrations of hydrophobic organic compounds in the environment. Unlike other polymeric materials commonly used as EPS, namely poly(dimethylsiloxane) (PDMS) and low-density polyethylene (PE), POM is a polar polymer, containing repeating H-bond accepting ether units. Thus, POM is expected to be a more sensitive EPS than PDMS and PE for polar, H-bond donating compounds, such as many hormones, pharmaceuticals, and biocides. To better characterize the sorption capacity of POM for diverse polar and apolar compounds, equilibrium POM-water partition coefficients, K(POM/w), were measured for 56 compounds, including several classes of polar compounds and organochlorine pesticides. Using this data set and literature data, various POM-partitioning models were calibrated and validated for their ability to predict K(POM/w). The best performing models tested were an Abraham descriptor based polyparameter linear free energy relationship (PP-LFER) (SD = 0.24 log units) and COSMOthermX (SD = 0.37 log units). The performance of SPARC (SD = 0.61 log units) and log-log correlations with K(ow) (SD = 0.49 log units) were lower. A comparison with PDMS and PE confirmed expectations that POM exhibits a higher sensitivity for H-bond donating polar compounds than PDMS and PE do for these compounds. These findings expand the domain of chemicals for which POM can be used as an EPS sampler, and demonstrate that POM is as suitable a passive sampler for many polar organic compounds as it is for hydrophobic organic compounds.