PFOS dominates PFAS composition in ambient fine particulate matter (PM2.5) collected across North Carolina nearly 20 years after the end of its US production.

Contamination of drinking water by per- and polyfluoroalkyl substances (PFASs) emitted from manufacturing plants, fire-fighting foams, and urban waste streams has received considerable attention due to concerns over toxicity and environmental persistence; however, PFASs in ambient air remain poorly understood, especially in the United States (US). We measured PFAS concentrations in ambient fine particulate matter (PM2.5) at 5 locations across North Carolina over a 1 year period in 2019. Thirty-four PFASs, including perfluoroalkyl carboxylic, perfluoroalkane sulfonic, perfluoroalkyl ether carboxylic and sulfonic acids were analyzed by UHPLC/ESI-MS/MS. Quarterly averaged concentrations ranged from <0.004-14.1 pg m-3. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) ranged from <0.18 to 14.1 pg m-3, comparable to previous PM2.5 measurements from Canada and Europe (<0.02-3.5 pg m-3). Concentrations above 1 pg m-3 were observed in July-September at Charlotte (14.1 pg m-3, PFOA), Wilmington (4.75 pg m-3, PFOS), and Research Triangle Park (1.37 pg m-3, PFOS). Notably, PM2.5 has a short atmospheric lifetime (<2 weeks), and thus, the presence of PFOS in these samples raises questions about their sources, since PFOS production was phased out in the US ∼20 years ago. This is the first US study to provide insights into ambient PFAS concentrations in PM2.5.

Determination of ambient ethanol concentrations in aqueous environmental matrixes by two independent analyses.

A new method for the determination of ethanol in aqueous environmental matrixes at nanomolar concentrations is presented and compared to an existing method that has been optimized for low-level alcohol determinations. The new analysis is based upon oxidation of ethanol by the enzyme alcohol oxidase obtained from the yeast Hansenula sp. which quantitatively produces acetaldehyde after reaction for 120 min at 40 °C and pH 9.0. The acetaldehyde reacts with 2,4-dinitrophenylhydrazine forming a hydrazone that is separated from interfering substances and quantified by high-performance liquid chromatography (HPLC) with UV detection at 370 nm. Comparison of initial acetaldehyde concentration with that after enzymatic oxidation yields the ethanol concentration with a corresponding detection limit of 10 nM. Analytical results were verified by intercomparison with a completely independent technique utilizing a solid-phase microextraction (SPME) Carboxen/PDMS SPME fiber. A 12 mL aqueous phase sample was heated at 50 °C for 10 min prior to loading onto the SPME fiber. Extraction of ethanol was performed by introducing the fiber into the headspace above a pH 4.4 buffered sample containing 30% NaCl for 20 min. Samples were agitated during heating and extraction by magnetic stirring at a rate of 750 rpm. The fiber was thermally desorbed for 1 min at 230 °C in the injection port of a gas chromatograph equipped with a flame ionization detector (FID) set at 250 °C. The resulting ethanol detection limit is 19 nM. Results of an intercomparison study between the enzymatic and SPME analyses produced a trend line with a slope of unity demonstrating that methods produced statistically equivalent ethanol concentrations in several natural waters including rainwater, fresh surface waters, and sediment pore waters.

A molecular dynamics study of densification mechanisms in calcium silicate glasses CaSi2O5 and CaSiO3 at pressures of 5 and 10 GPa.

Molecular dynamics is used to obtain models of (CaO)(x)(SiO(2))(1-x) glasses, with compositions CaSi(2)O(5) (x=0.33) and CaSiO(3) (x=0.50), at pressures of 5 and 10 GPa. At 5 GPa there are increases in Ca and Si coordinations for x=0.33, whereas for x=0.50 there is distortion of CaO(N) polyhedra but no substantial change in coordination. At 10 GPa the Ca coordination increases by approximately 20% for x=0.33 and by approximately 10% for x=0.50. This increase is due to increased Ca bonds to bridging oxygens (O(b)), since nonbridging oxygens (O(nb)) are already highly bonded to Ca, and the proportion of O(nb) is decreasing due to changes in the silica network. At 10 GPa there are approximately 20% of fivefold and a few percent of sixfold coordinated Si. Since the new Si-O bonds involve the conversion of O(nb) to O(b), there is a corresponding increase in the network connectivity. The x=0.50 glass is more resistant to deformation because there is less possibility to convert O(nb) to O(b) due to lower Si content. The changes in Ca-O, Si-Ca, and Ca-Ca correlations are predicted to produce changes in the x-ray diffraction structure factor S(Q), including a shift of the first sharp diffraction peak to higher Q values.

Modulation of elicited behavior by a fixed-interval schedule of electric shock presentation.

Responding elicited in the squirrel monkey by electric shocks presented every 60 seconds was gradually altered in temporal patterning, especially when the shock was also produced by responses under a 30-second fixed-interval schedule. The initially elicited pattern of maximal responding just after each shock was altered by the recurrent shock and by the added fixed-interval schedule to a pattern of maximal responding just before each shock. Most shocks were produced by responses and the response pattern was maintained for several months, but little responding occurred when shocks were omitted.