Doctor of Philosophy (PhD)
This research focuses on the environmental fate of particle associated pollutants such as Polybrominated Diphenyl Ethers (PBDEs), Polyaromatic Hydrocarbons (PAHs), and Environmentally Persistent Free Radicals (EPFRs) with a special emphasis on their transformation due to interaction with a matrix or co-pollutants. It encompasses two approaches to the stated problems: analysis of samples collected in the environment and laboratory simulation of the molecular transformations.
The PBDE studies relied on the ambient air Particulate Matter (PM) samples collected from Bangkok, Thailand. Results showed the presence of various PBDE homologs from tri- to hepta-PBDEs on both PM2.5and Total Suspended Particle (TSP) samples. Sample comparison based on distance from reclamation site indicated elevated levels of PBDEs in close proximity to the e-waste site. Interestingly, a shift in the congener pattern was observed with lower brominated PBDEs being more prevalent on nearby e-waste sites samples.
Overall, a clear trend can be observed indicating a debromination of PBDEs during the reclamation process and later during air transport. The results show PBDEs were translocated from treated materials to ambient air PM, and thermal treatment methods produced congener transformation as well as increased emissions of toxic PBDEs.
This dissertation presents the impacts EPFR-laden particles have on the transformation of PAHs into oxy-/hydroxy-PAHs based on the laboratory simulation of the model molecule 1-Methylnaphthalene (1-MN). We found that for PM surrogates suspended in aqueous media, the presence of EPFRs resulted in the oxidation of 1-MN and formation of the several oxygenated PAHs products. EPFRs have been shown to produce .OH in the redox cycle when transferred to aqueous media. Produced .OH can reach other PM constituents, changing PM chemistry and potential exposure characteristics. Differences were observed in oxidation product yields, depending on whether EPFRs and PAHs were cohabiting or present on separate PM. This effect is attributed to the .OH concentration gradient as a factor in the oxidation process, further strengthening the hypothesis of EPFRs’ role in the PAH oxidation process.
We propose that EPFRs on PM increase the risk associated with PAHs exposure, increase PAHs transformation to an aqueous medium, thus increasing their bioavailability.
Ghimire, Ajit, "Fate of Selected Pollutants of Concern on Particulate Matter (PM) Surface" (2019). LSU Doctoral Dissertations. 4863.
Available for download on Tuesday, March 15, 2022