Abstract  Considering the grave concerns caused by conventional per- and polyfluorinated substances (PFAS), production and use of fluoroalkylether compounds (ether-PFAS) have been on the rise. These ether-PFAS are deemed as PFAS replacement chemicals. To understand distribution of ether-PFAS in plant-soil systems, we investigated plant uptake of five selected ether-PFAS (i.e., PFMOPrA, PFMOBA, GenX, ADONA, F53B) by Carex comosa (longhair sedge) and the fractionation of these compounds in soil. Our results demonstrated that all five ether-PFAS in this study were taken up by C. comosa and translocated to plant shoots to different extents. Exposure concentration and time both positively affected plant uptake of ether-PFAS. Unlike the other four ether-PFAS, F53B with the longest carbon chain length and a sulfonic functional group was largely accumulated in C. comosa roots with limited translocation to plant shoots. Results from sequential extractions revealed that the five ether-PFAS had different distributions in soil with regard to extractable by water, basic methanol, acidic methanol and non-extractable. Concentration of ether-PFAS in water-soluble fraction increased with decreasing carbon chain length and logKow values and had a positive linear relationship with the mass of ether-PFAS in plant shoots (R2 = 0.64) and in whole plants (R2 = 0.94). Our results also indicated that the aging process could facilitate ether-PFAS to become non-extractable, hence reducing their mobility in soil and bioavailability to plants.

Abstract  This paper reports a MEMS capacitive pressure sensor (CPS) based on the operating principle of touch mode. The CPS was designed and fabricated using wafer-level self-packaged MEMS processes. The variable capacitance sensing structure was vacuum-sealed in a cavity using the Si-glass anodic bonding technique, and the embedded Al feedthrough lines at the Si-glass interface were used to realize the electrical connections between the parallel plate electrodes and the electrode pads through Al vias. The optimal design of the CPS structure was performed to trade-off the performance and reliability using finite element simulation. The CPS based on a circular-shaped diaphragm with a radius of 2000 µm and a thickness of 40 µm exhibits good comprehensive performance with a sensitivity of 52.3 pF/MPa and a nonlinearity of 2.7%FS in the pressure range of 100-500 kPa when the ambient temperature is less than 50 °C.

Abstract  Novel per- and polyfluoroalkyl substances (PFAS) were recently identified in drinking water sources throughout North Carolina. These include the perfluoroether acids (PFEAs) perfluoro-2-methoxyacetic acid (PFMOAA), perfluoro-2-methoxypropanoic acid (PFMOPrA), and perfluoro-4-methoxybutanioc acid (PFMOBA). Little toxicological data exist for these PFEAs. Therefore, the present study described signs of toxicity and immunotoxicity following oral exposure. Adult male and female C57BL/6 mice were exposed once/day for 30 days to PFMOAA (0, 0.00025, 0.025, or 2.5 mg/kg), PFMOPrA, or PFMOBA (0, 0.5, 5, or 50 mg/kg). A dose of 7.5 mg/kg of perfluorooctanoic acid (PFOA) was used as a positive control. Terminal body weights, and absolute liver, spleen, or thymus weights did not differ by dose for any compound; exposure to 50 mg/kg of PFMOBA increased relative liver weights in males. Changes in splenic cellularity were observed in males exposed to PFMOPrA and decreased numbers of B and natural killer (NK) cells were observed in males and females exposed to PFMOBA. Exposure did not alter NK cell cytotoxicity or T cell-dependent antibody responses at doses administered. Our results indicate that these "understudied" PFAS have toxicological potential but require additional investigation across endpoints and species, including humans, to understand health effects via drinking water exposure.

Abstract  Per- and polyfluoroalkyl substances (PFAS) are emerging contaminants widely used in a variety of industrial and consumer applications. Due to phasing out legacy PFAS, some manufacturers developed short-chain alternatives like perfluoroalkyl ether carboxylic acids (PFECA). Published liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods cover a wide range of these replacement chemicals including PFMPA (perfluoro-3-methoxypropanoic acid) and PFMBA (perfluoro-4-methoxybutanoic acid). However, many methods do not monitor for their branched isomers, PMPA (perfluoro-2-methoxypropanoic acid) and PEPA (perfluoro-2-ethoxypropanoic acid), respectively. Although these isomers are chromatographically separable under certain conditions, using the common MS/MS transitions for PFMPA (m/z 229 → 85) and PFMBA (m/z 279 → 85) can yield low or no detection signals for PMPA and PEPA, thus leading to underestimated values or nondetects. We compared various MS/MS transitions for these isomers and determined the optimal transitions for PMPA (m/z 185 → 85) and PEPA (m/z 235 → 135). We applied the developed method to water sampled near two chemical manufacturing plants and observed these analytes, plus a suspected third isomer. Using these MS/MS transitions will ensure all isomers are detected and will lead to better monitoring and exposure estimates of PFECA in humans and the environment.

Abstract  We have synthesized small silver clusters in aqueous microemulsion droplets in supercritical carbon dioxide (sc-CO2) solutions with fluorinated surfactants; ammonium carboxylate perfluoropolyether, PFPE-1, PFPE-2 and PFPE-3. Irradiation of water-in-sc-CO2 (w/c) microemulsions of PFPE-1 containing concentrated AgClO4 Solution within the water core (local concentration [AgClO4] = 5.0 M) at P = 36.3 MPa and T = 311 K with weak UV light resulted in the appearance of a broad absorption band in the lambda = 320-400 nm range with a small peak around X = 330 nm and a shoulder around lambda = 370 nm in the UV-vis absorption spectra. Irradiation of the w/c microemulsions of PFPE-2 containing [AgClO4] = 5.0 M with intense UV light brought about the development of almost the same absorption band at the early stage. Then a single broad peak bearing the absorbance as large as about 3.0 around X = 340 nm developed after prolonged irradiation. Those spectral features would demonstrate the formation of small Ag clusters, Ag-n, due to photoreduction of Ag+ ions inside of water core of the w/c microemulsions. Although the absorption spectrum gradually changed during dark storage at P = 30 MPa and T = 311 K, there was no indication of the surface plasmon band even after 20 h storage, indicating that the growth of colloidal Ag nanoparticles, Ag-c, by agglomeration of small Ag clusters does not proceed because microemulsions are separated each other in the sc-CO2. These observations would suggest that the w/c microemulsion is an excellent "nanoreactor" to confine the reaction field on the nanometer scale. (C) 2008 Elsevier B.V. All rights reserved.