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Per‐ and poly‐fluoroalkyl substances (PFAS) are ubiquitous in the environment and are detected in wildlife and humans. With respect to human exposure, studies have shown that ingestion is the primary route of exposure; however, in certain settings, exposure via inhalation could also be a significant source of exposure. While many studies examined toxicity of PFAS via ingestion, limited information is available for PFAS toxicity via the inhalation route, translating into a lack of exposure guidelines. Consequently, this article examined whether route‐to‐route extrapolation to derive guidelines for inhalation exposure is appropriate for PFAS. Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) were used as exemplary PFAS given the abundance of toxicity data for these two compounds. Our evaluation determined that available toxicity and toxicokinetic data support route‐to‐route extrapolation for PFAS in order to derive inhalation‐based standards. Results from this analysis suggest that an air concentration of 7.0 × 10−5 mg/m3 (or 0.07 μg/m3) would be an appropriate RfC for PFOA and PFOS assuming the 2016 EPA RfD of 0.00002 mg/kg‐day, whereas use of the interim RfDs proposed in 2022 of 1.5 × 10−9 and 7.9 × 10−9 mg/kg would yield much lower RfCs of 5.25 × 10−9 and 2.77 × 10−8 mg/m3 (or 5.25 × 10−6 and 2.77 × 10−5 μg/m3) for PFOA and PFOS, respectively. [ABSTRACT FROM AUTHOR]

Thermogravimetric methods with internal polymer standards have successfully quantified environmental tire and road wear particle (TRWP) concentrations. However, TRWP quantification in environmental matrices via pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) using butadiene rubber (BR) and styrene-butadiene rubber (SBR) marker 4-vinylcyclohexene (4-VCH; 1,4-butadiene-1,4-butadiene dimer) may be uncertain because of variable polymer compositions and BR and SBR microstructures. To determine if tire polymer microstructure is contributing to potentially over- or underestimating TRWP in the environment in py-GC-MS analyses, SBR materials (n = 8) commonly found in tire tread with varying microstructure were quantified via py-GC-MS, using 4-VCH and the deuterated internal standard d-4-VCH to provide a response ratio for each polymer. The response ratios of the dimer response to the total polymer quantity (instrument response slope) varied up to 6.8-fold for SBR, with a reduction to a 3.6-fold range when the polymer quantity was expressed as 1,4-butadiene mass rather than total polymer mass. Variability was reduced further when considering the polymerization method for emulsion-SBRs (n = 3; 1.4-fold range), but not solution-SBRs (n = 5; 2.7-fold range), which reflects the random versus structured heterosequencing of the two rubber types, respectively. Our findings suggest that py-GC-MS response should be interpreted based on empirical analysis of an appropriate number of regionally representative tire tread materials, rather than individual rubbers, because of the lack of methods available for determining unknown average microstructure in environmental samples. [ABSTRACT FROM AUTHOR]

To mitigate the spread of COVID-19, face masks, including fabric face coverings, have been encouraged or mandated. To meet demand, traditional clothes-making fabrics have been redirected to face covering manufacture. It has been reported that phthalates may be present in textiles, posing a health risk consideration for the industry; however, the potential presence of and exposure to phthalates in fabric face coverings have not been evaluated. Consequently, this study 1) estimated the concentrations of phthalates in fabric face coverings, 2) estimated the potential consumer exposures, and compared them to health guidance values (HGVs), and 3) advised on voluntary phthalate testing in textiles and/or face coverings. Precautionary upper-bound phthalate mass in face coverings was estimated from phthalate concentrations in clothing articles. Exposure to phthalates was predicted to occur predominantly via inhalation and direct dermal contact; however, for both routes, the doses were below HGVs, indicating that, based on the limited materials characterized in the literature, a health risk was unlikely. Further, the limit of 0.1% (w/w) set for individual or sum of phthalates in child care articles in the U.S. and other countries was deemed protective for children and adult face coverings. We conclude that the establishment of industry-wide voluntary phthalate quality specifications and test data for commercial face coverings or textiles used to manufacture them is advisable to substantiate product safety given the limited data. [ABSTRACT FROM AUTHOR]

Dispersion in porous media has been postulated as a mechanism that can increase particle transport, but the magnitude of increased transport predicted using analytical models of column experiments is a function of the boundary conditions chosen for the models. To date, insufficient attention has been paid to the implications of these boundary conditions for column or field simulations of particle transport. In order to assess the potential effect of particle dispersion on bacterial transport during bioremediation using bioaugmentation, we review the most frequently applied boundary conditions and models used in particle transport modeling. Using a finite-difference model written in MATLAB to simulate a column experiment, we demonstrate that for boundary conditions typically employed in short (approximately 10 cm) laboratory columns, hydrodynamic dispersion in such systems does not appreciably alter the calculation of bacterial stickiness or overall transport. However, dispersion is known to increase with distance, resulting in dispersivities on the order of one to several hundred meters over distances of 100 m. Using boundary conditions appropriate for field tests (a semi-infinite domain), and increasing dispersivity in proportion to transport distance, it was similarly demonstrated that dispersion would not appreciably increase the distance of particle travel (defined as the distance prior to a 2-log reduction in bacteria concentration) in field situations. Thus, it is concluded that dispersion can be neglected in calculating particle collision efficiencies in both laboratory and field experiments.

Few studies have evaluated airborne exposures to benzene, toluene, ethylbenzene, and xylenes (BTEX) during operation of two-stroke and four-stroke small engines, such as those in lawn maintenance equipment. Full-shift, 8-hour personal samples were collected during a simulation study to characterize yard maintenance activities including mowing, trimming, and fueling. Short-term, 15-minute personal samples were collected to separately evaluate mowing and trimming exposures. Mean 8-hour time weighted average (TWA) BTEX concentrations were 2.3, 5.8, 0.91, and 4.6 ppb, respectively (n = 2). Mean 15-minute TWA BTEX concentrations were 1.6, 1.8, 0.22, and 1.3 ppb, respectively, during mowing and 1.2, 3.6, 0.68, and 3.3 ppb, respectively, during trimming (n = 3 per task). Measured BTEX concentrations during fueling were 20–110, 61–310, 8–41, and 40–203 ppb, respectively (n = 2, duration 2–3 minutes). These exposure concentrations were well below applicable US occupational exposure limits. [ABSTRACT FROM AUTHOR]

Abstract: Advantages of second‐generation metal‐on‐metal (MoM) hip implants include low volumetric wear rates and the release of nanosized wear particles that are chemically inert and readily cleared from local tissue. In some patients, edge loading conditions occur, which result in higher volumetric wear. The objective of this study was to characterize the size, morphology, and chemistry of wear particles released from MoM hip implants during normal (40° angle) and edge‐loading (65° angle with microseparation) conditions. The mean primary particle size by volume under normal wear was 35 nm (range: 9–152 nm) compared with 95 nm (range: 6–573 nm) under edge‐loading conditions. Hydrodynamic diameter analysis by volume showed that particles from normal wear were in the nano‐ (<100 nm) to submicron (<1000 nm) size range, whereas edge‐loading conditions generated particles that ranged from <100 nm up to 3000–6000 nm in size. Particles isolated from normal wear were primarily chromium (98.5%) and round to oval in shape. Edge‐loading conditions generated more elongated particles (4.5%) (aspect ratio ≥ 2.5) and more CoCr alloy particles (9.3%) compared with normal wear conditions (1.3% CoCr particles). By total mass, edge‐loading particles contained approximately 640‐fold more cobalt than normal wear particles. Our findings suggest that high wear conditions are a potential risk factor for adverse local tissue effects in MoM patients who experience edge loading. This study is the first to characterize both the physical and chemical characteristics of MoM wear particles collected under normal and edge‐loading conditions. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 986–996, 2018. [ABSTRACT FROM AUTHOR]