Per- And Polyfluoroalkyl Substances In The Soil Environment: Sorption, Bioaccumulation And Biotransformation

Per- and polyfluoroalkyl substances (PFASs) are man-made chemicals, widely used in both industries and daily lives, such as in non-stick cookware, waterproof clothing, and painting materials. Researchers have investigated PFASs for about two decades, but most of the studies focus on perfluoroalkyl substances with very limited information available on polyfluoroalkyl substances. In this research, we investigated the sorption/desorption mechanisms perfluorooctanoic acid (PFOA) and its two cationic and zwitterionic precursor compounds, perfluorooctanesulfonamido ammonium salt (PFOSAmS) and perfluorooctaneamido betaine (PFOAB) in a group of soil. We also studied the bioaccumulation and bioconcentration of these chemicals along with perfluorooctane sulfonate (PFOS) and its cationic and zwitterionic precursor compounds, perfluorooctanesulfonamido ammonium salt (PFOSAmS) and perfluorooctanesulfonamido betaine (PFOSB), in earthworm (Lumbricus terrestris). Chapter 2 of this thesis presents the sorption and desorption results of PFOA, PFOAB, and PFOAAmS in five soils. The Freundlich model was fitted to the sorption and desorption data. The value of the distribution coefficient (Kd) was computed and used to compare the adsorption and desorption of different PFAS compounds. The result showed that Kd values of PFOAB and PFOAAmS were much higher than PFOA, with the ranked order of PFOAAmS \u3e PFOAB \u3e PFOA. Soil properties, especially including the soil organic matter, the cation exchange capacity, and the BET surface area, were found to affect the adsorption of these chemicals. The sorption-desorption hysteresis of the zwitterionic PFAS (PFOAB) was found in soils with a relatively low soil organic matter. The desorption hysteresis index was calculated and employed to assess the degree of hysteresis. The sorption study could help to understand and predict the fate and transport of cationic and zwitterionic poly-PFASs in the soil environment. Chapter 3 presents the bioaccumulation and biotransformation results of all the six PFAS compounds in earthworm. Earthworms were exposed to a PFAS in a loamy soil for up to 28 days and in water for up to 21 days. The bioaccumulation factors were calculated, and the bioaccumulation factor (BAF) of PFOS was observed the highest one in all the experiments. The order of BAF values was PFOAB \u3e PFOSB \u3e PFOSAmS \u3e PFOAAmS in the first bioaccumulation experiment. The results also demonstrate the generation of PFOA and PFOS from their cationic and zwitterionic precursor compounds in earthworm

Power Loss and Efficiency Analysis of a Four-level π-type Converter

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Evaluation of the off-state base-emitter voltage requirement of the SiC BJT with a regenerative proportional base driver circuit and their application in an inverter

A strong candidate device for use in high-efficiency and high-density power converters is the SiC bipolar junction transistor, which requires a continuous gate (base) current to maintain its on-state. A base driver circuit with regenerative collector current feedback using a current transformer, and a negative off-state base-emitter voltage is presented in this article. The off-state base-emitter voltage required to prevent simultaneous conduction of a commercially available device when subjected to dv/dt's is assessed. The device is then utilized in a three-phase dc-To-Ac power converter where the efficacy of using the proposed base driver is evaluated. The off-state base-emitter voltage used is informed by the dv/dt tests. The converter is supplied from a 600-V dc rail, switches at 50 kHz and supplies a 4.1-kW load at a modulation index of 0.9. An efficiency of 97.4% was measured

Electron bifurcation and fluoride efflux systems implicated in defluorination of perfluorinated unsaturated carboxylic acids by Acetobacterium spp.

Enzymatic cleavage of C─F bonds in per- and polyfluoroalkyl substances (PFAS) is largely unknown but avidly sought to promote systems biology for PFAS bioremediation. Here, we report the reductive defluorination of α, β-unsaturated per- and polyfluorocarboxylic acids by Acetobacterium spp. The microbial defluorination products were structurally confirmed and showed regiospecificity and stereospecificity, consistent with their formation by enzymatic reactions. A comparison of defluorination activities among several Acetobacterium species indicated that a functional fluoride exporter was required for the detoxification of the released fluoride. Results from both in vivo inhibition tests and in silico enzyme modeling suggested the involvement of enzymes of the flavin-based electron-bifurcating caffeate reduction pathway [caffeoyl-CoA reductase (CarABCDE)] in the reductive defluorination. This is a report on specific microorganisms carrying out enzymatic reductive defluorination of PFAS, which could be linked to electron-bifurcating reductases that are environmentally widespread

Tunable positions of Weyl nodes via magnetism and pressure in the ferromagnetic Weyl semimetal CeAlSi

The noncentrosymmetric ferromagnetic Weyl semimetal CeAlSi with simultaneous space-inversion and time-reversal symmetry breaking provides a unique platform for exploring novel topological states. Here, by employing multiple experimental techniques, we demonstrate that ferromagnetism and pressure can serve as efficient parameters to tune the positions of Weyl nodes in CeAlSi. At ambient pressure, a magnetism-facilitated anomalous Hall/Nernst effect (AHE/ANE) is uncovered. Angle-resolved photoemission spectroscopy (ARPES) measurements demonstrated that the Weyl nodes with opposite chirality are moving away from each other upon entering the ferromagnetic phase. Under pressure, by tracing the pressure evolution of AHE and band structure, we demonstrate that pressure could also serve as a pivotal knob to tune the positions of Weyl nodes. Moreover, multiple pressure-induced phase transitions are also revealed. These findings indicate that CeAlSi provides a unique and tunable platform for exploring exotic topological physics and electron correlations, as well as catering to potential applications, such as spintronics