A review of sample collection and analytical methods for detecting per- and polyfluoroalkyl substances in indoor and outdoor air.

Per- and polyfluoroalkyl substances (PFAS) are a unique class of chemicals synthesized to aid in industrial processes, fire-fighting products, and to benefit consumer products such as clothing, cosmetics, textiles, carpets, and coatings. The widespread use of PFAS and their strong carbon-fluorine bonds has led to their ubiquitous presence throughout the world. Airborne transport of PFAS throughout the atmosphere has also contributed to environmental pollution. Due to the potential environmental and human exposure concerns of some PFAS, research has extensively focused on water, soil, and organismal detection, but the presence of PFAS in the air has become an area of growing concern. Methods to measure polar PFAS in various matrices have been established, while the investigation of polar and nonpolar PFAS in air is still in its early development. This literature review aims to present the last two decades of research characterizing PFAS in outdoor and indoor air, focusing on active and passive air sampling and analytical methods. The PFAS classes targeted and detected in air samples include fluorotelomer alcohols (FTOHs), perfluoroalkane sulfonamides (FASAs), perfluoroalkane sulfonamido ethanols (FASEs), perfluorinated carboxylic acids (PFCAs), and perfluorinated sulfonic acids (PFSAs). Although the manufacturing of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) has been largely phased out, these two PFAS are still often detected in air samples. Additionally, recent estimates indicate that there are thousands of PFAS that are likely present in the air that are not currently monitored in air methods. Advances in air sampling methods are needed to fully characterize the atmospheric transport of PFAS.

Quantifying functional group compositions of household fuel-burning emissions.

Globally, billions of people burn fuels indoors for cooking and heating, which contributes to millions of chronic illnesses and premature deaths annually. Additionally, residential burning contributes significantly to black carbon emissions, which have the highest global warming impacts after carbon dioxide and methane. In this study, we use Fourier transform infrared spectroscopy (FTIR) to analyze fine-particulate emissions collected on Teflon membrane filters from 15 cookstove types and 5 fuel types. Emissions from three fuel types (charcoal, kerosene, and red oak wood) were found to have enough FTIR spectral response for functional group (FG) analysis. We present distinct spectral profiles for particulate emissions of these three fuel types. We highlight the influential FGs constituting organic carbon (OC) using a multivariate statistical method and show that OC estimates by collocated FTIR and thermal-optical transmittance (TOT) are highly correlated, with a coefficient determination of 82.5 %. As FTIR analysis is fast and non-destructive and provides complementary FG information, the analysis method demonstrated herein can substantially reduce the need for thermal-optical measurements for source emissions.

Tubing material considerably affects measurement delays of gas-phase oxygenated per- and polyfluoroalkyl substances.

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental pollutants associated with negative health impacts. Assessments of tubing-related measurement bias for volatile PFAS are lacking, as gas-wall interactions with tubing can delay quantification of gas-phase analytes. We use online iodide chemical ionization mass spectrometry measurements to characterize tubing delays for three gas-phase oxygenated PFAS - 4:2 fluorotelomer alcohol (4:2 FTOH), perfluorobutanoic acid (PFBA), and hexafluoropropylene oxide dimer acid (HFPO-DA). Perfluoroalkoxy alkane and high-density polyethylene tubing yielded relatively short absorptive measurement delays, with no clear dependence on tubing temperature or sampled humidity. Sampling through stainless steel tubing led to prolonged measurement delays due to reversible adsorption of PFAS to the tubing surface, with strong dependence on tubing temperature and sample humidification. Silcosteel tubing afforded shorter measurement delays than stainless steel due to diminished surface adsorption of PFAS. Characterizing and mitigating these tubing delays is crucial for reliable quantification of airborne PFAS.Implications: Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants. Many PFAS are sufficiently volatile to exist as airborne pollutants. Measurements and quantification of airborne PFAS can be biased from material-dependent gas-wall interactions with sampling inlet tubing. Thus, characterizing these gas-wall interactions are crucial for reliably investigating emissions, environmental transport, and fates of airborne PFAS.

Characterization of PFAS air emissions from thermal application of fluoropolymer dispersions on fabrics.

During thermal processes utilized in affixing fluoropolymer coatings dispersion to fibers and fabrics, coating components are vaporized. It is suspected that per- and polyfluoroalkyl substances (PFAS) from the dispersions may undergo chemical transformations at the temperatures used, leading to additional emitted PFAS thermal byproducts. It is important to characterize these emissions to support evaluation of the resulting environmental and health impacts. In this study, a bench-scale system was built to simulate this industrial process via thermal application of dispersions to fiberglass utilizing relevant temperatures and residence times in sequential drying, baking, and sintering steps. Experiments were performed with two commercially available dispersions and a simple model mixture containing a single PFAS (6:2 fluorotelomer alcohol [6:2 FTOH]). Vapor-phase emissions were sampled and characterized by several off-line and real-time mass spectrometry techniques for targeted and nontargeted PFAS. Results indicate that multiple PFAS thermal transformation products and multiple nonhalogenated organic species were emitted from the exit of the high temperature third (sintering) furnace when 6:2 FTOH was the only PFAS present in the aqueous mixture. This finding supports the hypothesis that temperatures typical of these industrial furnaces may also induce chemical transformations within the fluorinated air emissions. Experiments using the two commercial fluoropolymer dispersions indicate air emissions of part-per-million by volume (ppmv) concentrations of heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether (Fluoroether E1), as well as other PFAS at operationally relevant temperatures. We suspect that E1 is a direct thermal decomposition product (via decarboxylation) of 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoic acid (commonly referred to as HFPO-DA) present in the dispersions. Other thermal decomposition products, including the monomer, tetrafluoroethene, may originate from the PFAS used to stabilize the dispersion or from the polymer particles in suspension. This study represents the first researcher-built coating application simulator to report nontargeted PFAS emission characterization, real-time analyses, and the quantification of 30 volatile target PFAS.Implications: Thermal processes used to affix fluoropolymers to fabrics are believed to be a source of PFAS air emissions. These coating operations are used by many large and small manufacturers and typically do not currently require any air emissions control. This research designed and constructed a bench-scale system that simulates these processes and used several off-line and advanced real-time mass spectroscopy techniques to characterize PFAS air emissions from two commercial fluoropolymer dispersions. Further, as the compositions of commercial dispersions are largely unknown, a model three-component solution containing a single PFAS was used to characterize emissions of multiple PFAS thermal transformation products at operationally relevant conditions. This research shows that fluoropolymer fabric coating facilities can be sources of complex mixtures of PFAS air emissions that include volatile and semivolatile PFAS present in the dispersions, as well as PFAS byproducts formed by the thermal transformation of fluorocarbon and hydrocarbon species present in these dispersions.

The role of aspartic acid residues 405 and 416 of the kidney isotype of sodium-bicarbonate cotransporter 1 in its targeting to the plasma membrane.

The NH(2) terminus of the sodium-bicarbonate cotransporter 1 (NBCe1) plays an important role in its targeting to the plasma membrane. To identify the amino acid residues that contribute to the targeting of NBCe1 to the plasma membrane, polarized MDCK cells were transfected with expression constructs coding for green fluorescent protein (GFP)-tagged NBCe1 NH(2)-terminal deletion mutants, and the localization of GFP-tagged proteins was analyzed by confocal microscopy. Our results indicate that the amino acids between residues 399 and 424 of NBCe1A contain important sequences that contribute to its localization to the plasma membrane. Site-directed mutagenesis studies showed that GFP-NBCe1A mutants D405A and D416A are retained in the cytoplasm of the polarized MDCK epithelial cells. Examination of functional activities of D405A and D416A reveals that their activities are reduced compared with the wild-type NBCe1A. Similarly, aspartic acid residues 449 and 460 of pancreatic NBCe1 (NBCe1B), which correspond to residues 405 and 416 of NBCe1A, are also required for its full functional activity and accurate targeting to the plasma membrane. In addition, while replacement of D416 with glutamic acid did not affect the targeting or functional activity of NBCe1A, substitution of D405 with glutamic acid led to the retention of the mutated protein in the intracellular compartment and impaired functional activity. These studies demonstrate that aspartic acid residues 405 and 416 in the NH(2) terminus of NBCe1A are important in its accurate targeting to the plasma membrane.

Sequence- or position-specific mutations in the carboxyl-terminal FL motif of the kidney sodium bicarbonate cotransporter (NBC1) disrupt its basolateral targeting and alpha-helical structure.

The sodium-bicarbonate cotransporter NBC1 is targeted exclusively at the basolateral membrane. Mutagenesis of a dihydrophobic FL motif (residues 1013-1014) in the C-terminal domain disrupts the targeting of NBC1. In the present study, we determined the precise constraints of the FL motif required for basolateral targeting of NBC1 by expressing epitope-tagged wild-type and mutant NBC1 in MDCK cells and RNA-injected Xenopus oocytes and examining their subcellular localization. We assayed the functional activity of the mutants by measuring bicarbonate-induced currents in oocytes. Wild-type NBC1 (containing PFLS) was expressed exclusively on the basolateral membrane in MDCK cells. Reversal of the FL motif (PLFS) had no effect on basolateral targeting or activity. Shifting the FL motif one residue upstream (FLPS) resulted in mistargeting of the apical membrane but the FLPS mutant retained its functional activity in oocytes. Shifting the FL motif one residue downstream resulted in a mutant (PSFL) that did not efficiently translocate to the plasma membrane and was instead colocalized with the ER marker, protein disulfide isomerase (PDI). Analysis of circular dichroism (CD) revealed that a short peptide, 20 amino acid residues, of wild-type NBC1 contained a significant alpha-helical structure, whereas peptides in which the FL motif was reversed or C-terminally shifted were disordered. We therefore propose that the specific orientation and the precise location of the FL motif in the primary sequence of NBC1 are strict requirements for the alpha-helical structure of the C-terminal cytoplasmic domain and for targeting of NBC1 to the basolateral membrane.

Improving public health control of schistosomiasis with a modified WHO strategy: a model-based comparison study.

BACKGROUND: Schistosomiasis is endemic in many low-income and middle-income countries. To reduce infection-associated morbidity, WHO has published guidelines for control of schistosomiasis based on targeted mass drug administration (MDA) and, in 2017, on supplemental snail control. We compared the current WHO guideline-based strategies from 2012 to an alternative, adaptive decision making framework for control in heterogeneous environments, to estimate their predicted relative effectiveness and time to achievement of defined public health goals. METHODS: In this model-based comparison study, we adapted an established transmission model for Schistosoma infection that couples local human and snail populations and includes aspects of snail ecology and parasite biology. We calibrated the model using data from high-risk, moderate-risk, and lower-risk rural villages in Kenya, and then simulated control via MDA. We compared 2012 WHO guidelines with a modified adaptive strategy that tested a lower-prevalence threshold for MDA and shorter intervals between implementation, evaluation, and modification. We also explored the addition of snail control to this modified strategy. The primary outcomes were the proportion of simulations that achieved the WHO targets in children aged 5-14 years of less than 5% (2020 morbidity control goal) and less than 1% (2025 elimination as a public health problem goal) heavy infection and the mean duration of treatment required to achieve these goals. FINDINGS: In high-risk communities (80% baseline prevalence), current WHO strategies for MDA were not predicted to achieve morbidity control (<5% prevalence of heavy infections) in 80% of simulations over a 10-year period, whereas the modified adaptive strategy was predicted to achieve this goal in over 50% of simulations within 5 years. In low-risk and moderate-risk communities, current WHO guidelines from 2012 were predicted to achieve morbidity control in most simulations (96% in low-risk and 41% for moderate-risk), although the proposed adaptive strategy reached this goal in a shorter period (mean reduction of 5 years). The model predicted that the addition of snail control to the proposed adaptive strategy would achieve morbidity control in all high-risk communities, and 54% of communities could reach the goal for elimination as a public health problem (<1% heavy infection) within 7 years. INTERPRETATION: The modified adaptive decision making framework is predicted to be more effective than the current WHO guidelines in reaching 2025 public health goals, especially for high-prevalence regions. Modifications in current guidelines could reduce the time and resources needed for countries who are currently working on achieving public health goals against schistosomiasis. FUNDING: University of Georgia Research Foundation, The Bill & Melinda Gates Foundation, and the Medical Scientist Training Program at Stanford University School of Medicine.

Identification of a novel signal in the cytoplasmic tail of the Na+:HCO3- cotransporter NBC1 that mediates basolateral targeting.

The Na(+):HCO(3)(-) cotransporter NBC1 (SLC4A4, variant A, kidney specific) is located exclusively on the basolateral membrane of epithelial cells, implying that this molecule has acquired specific signals for targeting to the basolateral membrane. A motif with the sequence QQPFLS (positions 1010-1015) in the cytoplasmic tail of NBC1 was recently demonstrated to mediate targeting of NBC1 to the basolateral membrane. Here, we demonstrate that mutating the amino acid F (phenylalanine) or L (leucine) at positions 1013 or 1014 to alanine, respectively, resulted in the retargeting of NBC1 to the apical membrane. Furthermore, mutation of the FL motif to FF showed similar properties as the wild-type; however, mutation of the FL motif to LL showed significant intracellular retention of NBC1. Mutating the amino acids Q-Q-P and S (positions 1010-1011-1012 and 1015) to A-A-A and A, respectively, did not affect the membrane targeting of NBC1. Functional studies in oocytes with microelectrode demonstrated that the apically targeted mutants, as well as basolaterally targeted mutants, are all functional. We propose that the FL motif in the COOH-terminal tail of NBC1 is essential for the targeting of NBC1 to the basolateral membrane but is distinct from the membrane-targeting di-leucine motif identified in other membrane proteins.