Determination of Polyoxymethylene (POM) : Water Partition Coefficients for Alkylated Polycyclic Aromatic Hydrocarbons by Use of GC/MS

Abstract: Methods to measure the concentration of freely dissolved PAHs in pore water have been developed and are based on the usage of passive samplers, in this case polyoxymethylene (POM). Spiked samples (containing PAHs with 4-5 rings, methylated PAHs with 2-5 rings and dibenzothiophenes in three different concentrations) were placed on an end-over-end shaker for 28 days, to obtain equilibrium between the amount of PAHs accumulated on the POM strips and the amount of PAHs freely dissolved in the water. Four samples (medium concentration) were removed from the shaker after 7 and 14 days, respectively, and after 28 days were 12 samples (low, medium and high concentrations) removed. The variance of the average log(KPOM) values obtained from medium concentration were statistically tested, and showed that the coefficients for all compounds did not differ significantly over time. The coefficient difference between the three concentrations for the methylated PAHs were greater amongst the more hydrophobic compounds; 7,12-Dimethylbenz(a)anthracene had log(KPOM) of 5.64, 2.77 and 3.71 (low, medium, high). The hydrophilic compounds had coefficients that were more similar in the three concentrations; 1,6-Dimethylnaphthalene had log(KPOM) of 3.80, 2.62, and 3.39 (low, medium, high). Previous studies have determined log(KPOM) for several PAHs, and merged log(KPOM) for alkylated isomeric PAHs. The coefficients from the lowest concentration of serval methylated PAHs and Benzo(e)pyrene were similar to log(KPOM) values obtained for those compounds in an earlier study. The accuracy of risk assessments of PAH contaminated areas will increase when analysing individual methylated PAHs and using individual KPOM values for methylated PAHs, as in this study, instead of merged coefficients.