A Preliminary Study Of The Solid Phase Microextraction Theory And Its Application In Assessment Of The Bioaccessiblilty Of Hydrophobic Organic Contaminants In Sediment Porewater

The theory for sorption of very hydrophobic organic chemicals (VHOCs) into poly(dimethyl)siloxane (PDMS) coated solid-phase microextraction (SPME) fiber and the feasibility for application of SPME in assessing the bioaccessibility of hydrophobic organic chemicals (HOCs) in sediment porewater have yet to be fully examined. The purpose of this study was to address these two issues. The main results are summarized as follows:A static SPME procedure combined with liquid-liquid extraction (LLE) was used to determine the PDMS-water partition coefficients (K_fw) for polychlorinated biphenyls with different hydrophobicities. The accuracy for the measurements of analyte concentrations in the aqueous phase was ensured with a one-to-one recovery correction strategy employing one ¹³C-labeled PCB counterpart as a surrogate standard for each native PCB congener. To verify the accuracy of K_fw values measured with the above procedure, a ¹⁴C-radioactivity approach combined with the static SPME procedure was also successfully developed to determine the K_fw values of several ¹⁴C-labeled HOCs and analyze the relative distribution among various matrix, including water, glassware/stir, and SPME coating.The measured log K_fw values using the two methods mentioned above were consistent with those reported in the literature. The effects of coating thickness were significant only on heavily chlorinated biphenyls, and sample sizes had no significant effect on the measured K_fw for any targhet analytes. The total recoveries before and after SPME of using the ¹⁴C-radioactivity technique (80%-120%) were better than those using native HOCs combined with the LLE procedure (53%-106%). A nonlinear relationship between log K_fw and log K_ow was found for PCB congeners representing all isomeric homologs with the cut-off occurring at log K_ow > -7-7.5, which was attributed to the difference between the structures of PDMS coating and octanol. This explanation can also be used to describe the physical origin of the nonlinear relationship between log BCF (bioconcentration factor) and log K_ow.Two governing equations were derived to predict what experimental parameters are appropriate to satisfy the conditions for the application of SPME in assessing the bioaccessibility of HOCs in sediment. To verify the ultimate utility of this modeling framework, sediment spiked with several ¹⁴C-labeled HOCs combined with disposable PDMS-coated SPME fibers was applied to verify the consistency between the theoretical predications and experimental results. The results indicated that the theoretical predications can be used effectively to guide future experiment designs, and no matrix effect was found in the measurement of SPME. Finally, an in situ sampler based on SPME was successfully developed to examine the feasibility of assessing the bioaccessibility of HOCs in sediment porewater.