The legacy environmental footprints of manufactured capital.

The foundations of today's societies are provided by manufactured capital accumulation driven by investment decisions through time. Reconceiving how the manufactured assets are harnessed in the production-consumption system is at the heart of the paradigm shifts necessary for long-term sustainability. Our research integrates 50 years of economic and environmental data to provide the global legacy environmental footprint (LEF) and unveil the historical material extractions, greenhouse gas emissions, and health impacts accrued in today's manufactured capital. We show that between 1995 and 2019, global LEF growth outpaced GDP and population growth, and the current high level of national capital stocks has been heavily relying on global supply chains in metals. The LEF shows a larger or growing gap between developed economies (DEs) and less-developed economies (LDEs) while economic returns from global asset supply chains disproportionately flow to DEs, resulting in a double burden for LDEs. Our results show that ensuring best practice in asset production while prioritizing well-being outcomes is essential in addressing global inequalities and protecting the environment. Achieving this requires a paradigm shift in sustainability science and policy, as well as in green finance decision-making, to move beyond the focus on the resource use and emissions of daily operations of the assets and instead take into account the long-term environmental footprints of capital accumulation.

Multiplexable and Scalable Aqueous Synthesis Platform for Oleate-Based, Bilayer-Coated Gold Nanoparticles.

Despite gold-based nanomaterials having a unique role in nanomedicine, among other fields, synthesis limitations relating to reaction scale-up and control result in prohibitively high gold nanoparticle costs. In this work, a new preparation procedure for lipid bilayer-coated gold nanoparticles in water is presented, using sodium oleate as reductant and capping agent. The seed-free synthesis not only allows for size precision (8-30 nm) but also remarkable particle concentration (10 mm Au). These reaction efficiencies allow for multiplexing and reaction standardization in 96-well plates using conventional thermocyclers, in addition to simple particle purification via microcentrifugation. Such a multiplexing approach also enables detailed spectroscopic investigation of the nonlinear growth process and dynamic sodium oleate/oleic acid self-assembly. In addition to scalability (at gram-level), resulting gold nanoparticles are stable at physiological pH, in common cell culture media, and are autoclavable. To demonstrate the versatility and applicability of the reported method, a robust ligand exchange with thiolated polyethylene glycol analogues is also presented.

Assessing the Progress toward a Water-Efficient Economy in the United States from 1985 to 2015.

United Nations Sustainable Development Goal 6 tackles the long-neglected economic dimension of water utilization by monitoring nations' water use efficiency (WUE). However, it is imperative to emphasize the need for consistent spatial-temporal subnational WUE estimates, rather than relying solely on recent national trends, which can obscure crucial water use concerns and improvement opportunities. Here, a time series analysis of national, state, and sectoral (e.g., industrial, service, and agriculture) WUE from 1980 to 2015 was developed by compiling the most comprehensive and disaggregated water and economic data from 3243 US counties and 50 US states. The US total WUE increased by 181% from 16.2 (1985) to 45.6 USD/m3 (2015), driven by service sector WUE enhancements. The increased industry and service WUEs in most states were more strongly correlated with decreased per capita water withdrawal than with economic growth. Simultaneously, reductions in agriculture WUE were observed in 18 states potentially because of the complicated interaction of diverse factors specific to local communities. Expanding WUE gaps between affluent and less affluent states, and persisting WUE gaps between water-abundant andwater-scarce states highlight the need to advance policies to support under-resourced communities in effective water planning and water pricing for advancing equitable development.

Toward Property-Based Regulation.

An expanding web of adverse impacts on people and the environment has been steadily linked to anthropogenic chemicals and their proliferation. Central to this web are the regulatory structures intended to protect human and environmental health through the control of new molecules. Through chronically insufficient and inefficient action, the current chemical-by-chemical regulatory approach, which considers regulation at the level of chemical identity, has enabled many adverse impacts to develop and persist. Recognizing the link between fundamental physicochemical properties and hazards, we describe a new paradigm─property-based regulation. By regulating physicochemical properties, we show how governments can delineate and enforce safe chemical spaces, increasing the scalability of chemical assessments, reducing the time and resources to regulate a substance, and providing transparency for chemical designers. We highlight sparse existing property-based approaches and demonstrate their applicability using bioaccumulation as an example. Finally, we present a path to implementation in the United States, prescribing roles and steps for government, nongovernmental organizations, and industry to accelerate this transition, to the benefit of all.

Selective Extraction of Critical Metals from Spent Lithium-Ion Batteries.

Selective and highly efficient extraction technologies for the recovery of critical metals including lithium, nickel, cobalt, and manganese from spent lithium-ion battery (LIB) cathode materials are essential in driving circularity. The tailored deep eutectic solvent (DES) choline chloride-formic acid (ChCl-FA) demonstrated a high selectivity and efficiency in extracting critical metals from mixed cathode materials (LiFePO4:Li(NiCoMn)1/3O2 mass ratio of 1:1) under mild conditions (80 °C, 120 min) with a solid-liquid mass ratio of 1:200. The leaching performance of critical metals could be further enhanced by mechanochemical processing because of particle size reduction, grain refinement, and internal energy storage. Furthermore, mechanochemical reactions effectively inhibited undesirable leaching of nontarget elements (iron and phosphorus), thus promoting the selectivity and leaching efficiency of critical metals. This was achieved through the preoxidation of Fe and the enhanced stability of iron phosphate framework, which significantly increased the separation factor of critical metals to nontarget elements from 56.9 to 1475. The proposed combination of ChCl-FA extraction and the mechanochemical reaction can achieve a highly selective extraction of critical metals from multisource spent LIBs under mild conditions.

Microalgae Commercialization Using Renewable Lignocellulose Is Economically and Environmentally Viable.

Conventional phototrophic cultivation for microalgae production suffers from low and unstable biomass productivity due to limited and unreliable light transmission outdoors. Alternatively, the use of a renewable lignocellulose-derived carbon source, cellulosic hydrolysate, offers a cost-effective and sustainable pathway to cultivate microalgae heterotrophically with high algal growth rate and terminal density. In this study, we evaluate the feasibility of cellulosic hydrolysate-mediated heterotrophic cultivation (Cel-HC) for microalgae production by performing economic and environmental comparisons with phototrophic cultivation through techno-economic analysis and life cycle assessment. We estimate a minimum selling price (MSP) of 4722 USD/t for producing high-purity microalgae through Cel-HC considering annual biomass productivity of 300 t (dry weight), which is competitive with the conventional phototrophic raceway pond system. Revenues from the lignocellulose-derived co-products, xylose and fulvic acid fertilizer, could further reduce the MSP to 2976 USD/t, highlighting the advantages of simultaneously producing high-value products and biofuels in an integrated biorefinery scheme. Further, Cel-HC exhibits lower environmental impacts, such as cumulative energy demand and greenhouse gas emissions, than phototrophic systems, revealing its potential to reduce the carbon intensity of algae-derived commodities. Our results demonstrate the economic and environmental competitiveness of heterotrophic microalgae production based on renewable bio-feedstock of lignocellulose.

Synthetic cooling agent in oral nicotine pouch products marketed as 'Flavour-Ban Approved'.

BACKGROUND: US sales of oral nicotine pouches (ONPs) have rapidly increased, with cool/mint-flavoured ONPs the most popular flavour category. Restrictions on sales of flavoured tobacco products have either been implemented or proposed by several US states and localities. Zyn, the most popular ONP brand, is marketing Zyn Chill and Zyn Smooth as 'Flavour-Ban Approved' or 'unflavoured', probably to evade flavour bans and increase product appeal. At present, it is unclear whether these ONPs are indeed free of flavour additives that can impart pleasant sensations such as cooling. METHODS: Sensory cooling and irritant activities of 'Flavour-Ban Approved' Zyn ONPs, Chill and Smooth, along with minty varieties (Cool Mint, Peppermint, Spearmint, Menthol), were analysed by Ca2+ microfluorimetry in HEK293 cells expressing the cold/menthol (TRPM8) or menthol/irritant receptor (TRPA1). Flavour chemical content of these ONPs was analysed by gas chromatography/mass spectrometry. RESULTS: Zyn Chill ONP extracts robustly activated TRPM8, with much higher efficacy (39%-53%) than the mint-flavoured ONPs. In contrast, mint-flavoured ONP extracts elicited stronger TRPA1 irritant receptor responses than Chill extracts. Chemical analysis demonstrated that Chill exclusively contained WS-3, an odourless synthetic cooling agent, while mint-flavoured ONPs contained WS-3 together with mint flavourants. CONCLUSIONS: ONP products marketed as 'Flavour-Ban Approved' or 'unflavoured' contain flavouring agents, proving that the manufacturer's advertising is misleading. Synthetic coolants such as WS-3 can provide a robust cooling sensation with reduced sensory irritancy, thereby increasing product appeal and use. Regulators need to develop effective strategies for the control of odourless sensory additives used by the industry to bypass flavour bans.

What to Expect When Expecting in Lab: A Review of Unique Risks and Resources for Pregnant Researchers in the Chemical Laboratory.

Pregnancy presents a unique risk to chemical researchers due to their occupational exposures to chemical, equipment, and physical hazards in chemical research laboratories across science, engineering, and technology disciplines. Understanding "risk" as a function of hazard, exposure, and vulnerability, this review aims to critically examine the state of the science for the risks and associated recommendations (or lack thereof) for pregnant researchers in chemical laboratories (labs). Commonly encountered hazards for pregnant lab workers include chemical hazards (organic solvents, heavy metals, engineered nanomaterials, and endocrine disruptors), radiation hazards (ionizing radiation producing equipment and materials and nonionizing radiation producing equipment), and other hazards related to the lab environment (excessive noise, excessive heat, psychosocial stress, strenuous physical work, and/or abnormal working hours). Lab relevant doses and routes of exposure in the chemical lab environment along with literature and governmental recommendations or resources for exposure mitigation are critically assessed. The specific windows of vulnerability based on stage of pregnancy are described for each hazard, if available. Finally, policy gaps for further scientific research are detailed to enhance future guidance to protect pregnant lab workers.

Synthetic Cooling Agents in US-marketed E-cigarette Refill Liquids and Popular Disposable E-cigarettes: Chemical Analysis and Risk Assessment.

INTRODUCTION: Menthol, through its cooling and pleasant sensory effects, facilitates smoking and tobacco product initiation, resulting in the high popularity of mint/menthol-flavored E-cigarettes. More recently, E-cigarette vendors started marketing synthetic cooling agents as additives that impart a cooling effect but lack a characteristic minty odor. Knowledge about content of synthetic coolants in US-marketed E-cigarette products and associated health risks is limited. AIMS AND METHODS: E-liquid vendor sites were searched with the terms "koolada", "kool/cool", "ice", or WS-3/WS-23, denoting individual cooling agents, and relevant refill E-liquids were purchased. "Ice" flavor varieties of Puffbar, the most popular disposable E-cigarette brand, were compared with non-"Ice" varieties. E-liquids were characterized, and synthetic coolants quantified using GC/MS. Margin of exposure (MOE), a risk assessment parameter, was calculated to assess the risk associated with synthetic coolant exposure from E-cigarette use. RESULTS: WS-3 was detected in 24/25 refill E-liquids analyzed. All Puffbar flavor varieties contained either WS-23 (13/14) or WS-3 (5/14), in both "Ice"- and non-"Ice" flavors. Modeling consumption of WS-3 from vaped E-liquids, resulted in MOEs below the safe margin of 100 for most daily use scenarios. MOEs for WS-23 were <100 for 10/13 Puffbar flavors in all use scenarios. Puffbar power specifications are identical to Juul devices. CONCLUSIONS: Synthetic cooling agents (WS-3/WS-23) were present in US-marketed E-cigarettes, at levels that may result in consumer exposures exceeding safety thresholds set by regulatory agencies. Synthetic coolants are not only found in mint- or menthol-flavored products but also in fruit- and candy-flavored products, including popular disposable E-cigarette products such as Puffbar. IMPLICATIONS: Synthetic cooling agents are widely used in "kool/cool"- and "ice"-flavored E-liquids and in E-liquids without these labels, both as a potential replacement for menthol or to add cooling "notes" to nonmenthol flavors. These agents may be used to bypass current and future regulatory limits on menthol content in tobacco products, and not just E-cigarettes. Because synthetic cooling agents are odorless, they may not fall under the category of "characterizing flavor", potentially circumventing regulatory measures based on this concept. Regulators need to consider the additional health risks associated with exposure to synthetic cooling agents.

Copper Recycling Flow Model for the United States Economy: Impact of Scrap Quality on Potential Energy Benefit.

Is recycling a means for meeting the increasing copper demand in the face of declining ore grades? To date, research to address this question has generally focused on the quantity, not the quality of copper scrap. Here, the waste input-output impact assessment (WIO-IA) model integrates information on United States (US) economy-wide material flow, various recycling indicators, and the impact of material production from diverse sources to represent the quantity and quality of copper flows throughout the lifecycle. This approach enables assessment of recycling performance against environmental impact indicators. If all potentially recyclable copper scrap was recycled, energy consumption associated with copper production would decrease by 15% with alloy scrap as the largest contributor. Further energy benefits from increased recycling are limited by the lower quality of the scrap yet to be recycled. Improving the yield ratio of final products and the grade of diverse consumer product scrap could help increase copper circularity and decrease energy consumption. Policy makers should address the importance of a portfolio of material efficiency strategies like improved utilization of copper products and lifetime extension in addition to encouraging the demand for recycled copper.

Electrocatalysis for Chemical and Fuel Production: Investigating Climate Change Mitigation Potential and Economic Feasibility.

The manufacture of goods from oil, coal, or gas to everyday consumer products comprises in more or less all cases at least one catalytic step. Compared to conventional hydrothermal catalysis, electrocatalysis possesses the advantage of mild operational conditions and high selectivity, yet the potential energy savings and climate change mitigation have rarely been assessed. This study conducted a life cycle assessment (LCA) for the electrocatalytic oxidation of crude glycerol to produce lactic acid, one of the most common platform chemicals. The LCA results demonstrated a 31% reduction in global warming potential (GWP) compared to the benchmark (bio- and chemocatalytic) processes. Additionally, electrocatalysis yielded a synergetic potential to mitigate climate change depending on the scenario. For example, electrocatalysis combined with a low-carbon-intensity grid can reduce GWP by 57% if the process yields lactic acid and lignocellulosic biofuel as compared to a conventional fossil-based system with functionally equivalent products. This illustrates the potential of electrocatalysis as an important contributor to climate change mitigation across multiple industries. A technoeconomic analysis (TEA) for electrocatalytic lactic acid production indicated considerable challenges in economic feasibility due to the significant upfront capital cost. This challenge could be largely addressed by enabling dual redox processing to produce separate streams of renewable chemicals and biofuels simultaneously.

Quantification of Flavorants and Nicotine in Waterpipe Tobacco and Mainstream Smoke and Comparison to E-cigarette Aerosol.

INTRODUCTION: Waterpipe use remains popular among youth with the availability of flavored shisha tobacco being one of the main drivers of waterpipe use. Although waterpipe mainstream toxicant emissions are well understood, less is known about the carryover of flavorants such as vanillin, benzaldehyde, and eugenol. In this study, flavored waterpipe tobacco was analyzed for flavorants and nicotine, and subsequent carryover to mainstream smoke. METHODS: Flavorants vanillin, benzaldehyde, and eugenol, and nicotine were quantified in vanilla-, cherry-, and cinnamon-flavored shisha tobacco by gas chromatography/flame ionization detector and subsequently in waterpipe mainstream smoke generated by a smoking machine. The setup allowed for sampling before and after the water-filtration step. RESULTS: Flavorant and nicotine content in smoke was reduced 3- to 10-fold and 1.4- to 3.1-fold, respectively, due to water filtration. Per-puff content of filtered waterpipe mainstream smoke ranged from 13 to 46 µg/puff for nicotine and from 6 to 55 µg/puff for flavorants. CONCLUSIONS: Although water filtration reduced flavor and nicotine content in waterpipe mainstream smoke, the detected flavorant concentrations were similar or higher to those previously reported in e-cigarette aerosol. Therefore, users could be drawn to waterpipes due to similar flavor appeal as popular e-cigarette products. Absolute nicotine content of waterpipe smoke was lower than in e-cigarette aerosol, but the differential use patterns of waterpipe (>100 puffs/session) and e-cigarette (mostly <10 puffs/session, multiple session throughout the day) probably result in higher flavorant and nicotine exposure during a waterpipe session. Strategies to reduce youth introduction and exposure to nicotine via waterpipe use may consider similar flavor restrictions as those for e-cigarettes. IMPLICATIONS: Although waterpipe mainstream smoke is well characterized for toxicants content, little is known about carryover of molecules relevant for appeal and addiction: flavorants and nicotine. This study shows that flavorant content of waterpipe mainstream smoke is comparable or higher than e-cigarette aerosol flavorant content. Regulatory action to address tobacco use behaviors targeting the availability of flavors should also include other tobacco products such as flavored shisha tobacco.

Selective adsorption of arsenic over phosphate by transition metal cross-linked chitosan.

The ability of transition metal chitosan complexes (TMCs) of varying valence and charge to selectively adsorb As(III) and As(V) over their strongest adsorptive competitor, phosphate is examined. Fe(III)-chitosan, Al(III)-chitosan, Ni(II)-chitosan, Cu(II)-chitosan, and Zn(II)-chitosan are synthesized, characterized via Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR) and X-ray Diffractometry (XRD), and their selective sorption capabilities towards As(III) and As(V) in the presence of phosphate are evaluated. It was found that the stability of the metal-chitosan complexes varied, with Al(III)- and Zn(II)-chitosan forming very unstable complexes resulting in precipitation of gibbsite, and Wulfingite and Zincite, respectively. Cu(II)-, Ni(II)-, and Fe(III)-chitosan formed a mixture of monodentate and bidentate complexes. The TMCs which formed the bidentate complex (Cu(II)-, Ni(II)-, and Fe(III)-) showed greater adsorption capability for As(V) in the presence of phosphate. Using the binary separation factor ∝t/c, it can be shown that only Fe(III)-chitosan is selective for As(V) and As(III) over phosphate. Density Functional Theory (DFT) modeling and extended X-ray adsorption fine structure (EXAFS) determined that Fe(III)-chitosan and Ni(II)-chitosan adsorbed As(V) and As(III) via inner-sphere complexation, while Cu(II)-chitosan formed mainly outer-sphere complexes with As(V) and As(III). These differences in complexation likely result in the observed differences in selective adsorption capability towards As(V) and As(III) over phosphate. It is hypothesized that the greater affinity of Fe(III)- and Ni(II)-chitosan towards As(V) and As(III) compared to Cu(II)-chitosan is due to their forming less-stable, more reactive chitosan complexes as predicted by the Irving Williams Series.

Toward Realizing Multifunctionality: Photoactive and Selective Adsorbents for the Removal of Inorganics in Water Treatment.

Persistent and potentially toxic inorganic oxoanions (e.g., arsenic and selenium) are one class of contaminants of concern in drinking water for which treatment technologies must be improved. Effective removal of these oxoanions is made difficult by the varying adsorption affinity of the different oxidation states, as well as the presence of background ions with similar chemical structure and behavior that strongly compete for adsorption sites, greatly reducing removal efficiencies. Recent studies pointing to the negative health effects of inorganic oxoanion contaminants have resulted or are expected to result in new regulations lowering their allowable maximum concentration level (MCL) in drinking water. While these regulations are intended to protect human and environmental health, they must also allow for balanced economic costs. As such, the MCLs are often set at levels that are not as health protective due to high treatment costs that continue to present a significant challenge for small (500-3300 people) to very small (25-500 people) communities. In this Account, we focus on the development of novel cost-effective, sustainable, and efficient multifunctional and selective adsorbents that offer solutions to the above challenges through two platforms: nanoenabled and transition-metal cross-linked chitosan (TMCC) and crystal facet engineered nanometal oxides (NMO). These complementary platforms offer treatment solutions at different scales and flow rates (e.g., in a point-of-use device versus a small-scale community system). Multifunctional adsorbents combine processes that traditionally require multiple steps offering the potential for reducing treatment time and costs. Development of selective adsorbents can greatly increase removal efficiencies of target contaminants by either promoting their adsorption or hindering adsorption of competitive ions. The following sections describe (1) synthesis of novel nanoenabled waste sourced bioadsorbents; (2) development of multifunctional adsorbents to simultaneously photo-oxidize arsenite and adsorb arsenate; (3) development of a selective adsorbent for removal of arsenate and selenite over phosphate; (4) investigations of the conventional wisdom that increased surface area yields increased oxoanion removal using selenium sorption on nanohematite as a case study; and (5) crystal engineering of nanohematite to promote selenite adsorption. The novel technologies developed through these research efforts can serve as templates for the creation of future adsorbents tailored for use targeting other oxoanion contaminants of interest.

CRISPR-Generated Nrf2a Loss- and Gain-of-Function Mutants Facilitate Mechanistic Analysis of Chemical Oxidative Stress-Mediated Toxicity in Zebrafish.

The transcription factor Nrf2a induces a cellular antioxidant response and provides protection against chemical-induced oxidative stress, as well as playing a critical role in development and disease. Zebrafish are a powerful model to study the role of Nrf2a in these processes but have been limited by reliance on transient gene knockdown techniques or mutants with only partial functional alteration. We developed several lines of zebrafish carrying different null (loss of function, LOF) or hyperactive (gain of function, GOF) mutations to facilitate our understanding of the Nrf2a pathway in protecting against oxidative stress. The mutants confirmed Nrf2a dependence for induction of the antioxidant genes gclc, gstp, prdx1, and gpx1a and identified a role for Nrf2a in the baseline expression of these genes, as well as for sod1. Specifically, the 4-fold induction of gstp by tert-butyl hydroperoxide (tBHP) in wild type fish was abolished in LOF mutants. In addition, baseline gstp expression in GOF mutants increased by 12.6-fold and in LOF mutants was 0.8-fold relative to wild type. Nrf2a LOF mutants showed increased sensitivity to the acute toxicity of cumene hydroperoxide (CHP) and tBHP throughout the first 4 days of development. Conversely, GOF mutants were less sensitive to CHP toxicity during the first 4 days of development and were protected against the toxicity of both hydroperoxides after 4 dpf. Neither gain nor loss of Nrf2a modulated the toxicity of R-(-)-carvone (CAR), despite the ability of this compound to potently induce Nrf2a-dependent antioxidant genes. Similar to other species, GOF zebrafish mutants exhibited significant growth and survival defects. In summary, these new genetic tools can be used to facilitate the identification of downstream gene targets of Nrf2a, better define the role of Nrf2a in the toxicity of environmental chemicals, and further the study of diseases involving altered Nrf2a function.

Toward Less Hazardous Industrial Compounds: Coupling Quantum Mechanical Computations, Biomarker Responses, and Behavioral Profiles To Identify Bioactivity of SN2 Electrophiles in Alternative Vertebrate Models.

Sustainable molecular design of less hazardous chemicals promises to reduce risks to public health and the environment. Computational chemistry modeling coupled with alternative toxicology models (e.g., larval fish) present unique high-throughput opportunities to understand structural characteristics eliciting adverse outcomes. Numerous environmental contaminants with reactive properties can elicit oxidative stress, an important toxicological response associated with diverse adverse outcomes (i.e., cancer, diabetes, neurodegenerative disorders, etc.). We examined a common chemical mechanism (bimolecular nucleophilic substitution (SN2)) associated with oxidative stress using property-based computational modeling coupled with acute (mortality) and sublethal (glutathione, photomotor behavior) responses in the zebrafish (Danio rerio) and the fathead minnow (Pimephales promelas) models to identify whether relationships exist among biological responses and molecular attributes of industrial chemicals. Following standardized methods, embryonic zebrafish and larval fathead minnows were exposed separately to eight different SN2 compounds for 96 h. Acute and sublethal responses were compared to computationally derived in silico chemical descriptors. Specifically, frontier molecular orbital energies were significantly related to acute LC50 values and photomotor response (PMR) no observed effect concentrations (NOECs) in both fathead minnow and zebrafish. This reactivity index, LC50 values, and PMR NOECs were also significantly related to whole body glutathione (GSH) levels, suggesting that acute and chronic toxicity results from protein adduct formation for SN2 electrophiles. Shared refractory locomotor response patterns among study compounds and two alternative vertebrate models appear informative of electrophilic properties associated with oxidative stress for SN2 chemicals. Electrophilic parameters derived from frontier molecular orbitals were predictive of experimental in vivo acute and sublethal toxicity. These observations provide important implications for identifying and designing less hazardous industrial chemicals with reduced potential to elicit oxidative stress through bimolecular nucleophilic substitution.

Exploring the Mechanisms of Selectivity for Environmentally Significant Oxo-Anion Removal during Water Treatment: A Review of Common Competing Oxo-Anions and Tools for Quantifying Selective Adsorption.

Development of novel adsorbents often neglects the competitive adsorption between co-occurring oxo-anions, overestimating realistic pollutant removal potentials, and overlooking the need to improve selectivity of materials. This critical review focuses on adsorptive competition between commonly co-occurring oxo-anions in water and mechanistic approaches for the design and development of selective adsorbents. Six "target" oxo-anion pollutants (arsenate, arsenite, selenate, selenite, chromate, and perchlorate) were selected for study. Five "competing" co-occurring oxo-anions (phosphate, sulfate, bicarbonate, silicate, and nitrate) were selected due to their potential to compete with target oxo-anions for sorption sites resulting in decreased removal of the target oxo-anions. First, a comprehensive review of competition between target and competitor oxo-anions to sorb on commonly used, nonselective, metal (hydr)oxide materials is presented, and the strength of competition between each target and competitive oxo-anion pair is classified. This is followed by a critical discussion of the different equations and models used to quantify selectivity. Next, four mechanisms that have been successfully utilized in the development of selective adsorbents are reviewed: variation in surface complexation, Lewis acid/base hardness, steric hindrance, and electrostatic interactions. For each mechanism, the oxo-anions, both target and competitors, are ranked in terms of adsorptive attraction and technologies that exploit this mechanism are reviewed. Third, given the significant effort to evaluate these systems empirically, the potential to use computational quantum techniques, such as density functional theory (DFT), for modeling and prediction is explored. Finally, areas within the field of selective adsorption requiring further research are detailed with guidance on priorities for screening and defining selective adsorbents.

Chemical Adducts of Reactive Flavor Aldehydes Formed in E-Cigarette Liquids Are Cytotoxic and Inhibit Mitochondrial Function in Respiratory Epithelial Cells.

INTRODUCTION: Flavor aldehydes in e-cigarettes, including vanillin, ethyl vanillin (vanilla), and benzaldehyde (berry/fruit), rapidly undergo chemical reactions with the e-liquid solvents, propylene glycol, and vegetable glycerol (PG/VG), to form chemical adducts named flavor aldehyde PG/VG acetals that can efficiently transfer to e-cigarette aerosol. The objective of this study was to compare the cytotoxic and metabolic toxic effects of acetals and their parent aldehydes in respiratory epithelial cells. AIMS AND METHODS: Cell metabolic assays were carried out in bronchial (BEAS-2B) and alveolar (A549) epithelial cells assessing the effects of benzaldehyde, vanillin, ethyl vanillin, and their corresponding PG acetals on key bioenergetic parameters of mitochondrial function. The potential cytotoxic effects of benzaldehyde and vanillin and their corresponding PG acetals were analyzed using the LIVE/DEAD cell assay in BEAS-2B cells and primary human nasal epithelial cells (HNEpC). Cytostatic effects of vanillin and vanillin PG acetal were compared using Click-iT EDU cell proliferation assay in BEAS-2B cells. RESULTS: Compared with their parent aldehydes, PG acetals diminished key parameters of cellular energy metabolic functions, including basal respiration, adenosine triphosphate production, and spare respiratory capacity. Benzaldehyde PG acetal (1-10 mM) increased cell mortality in BEAS-2B and HNEpC, compared with benzaldehyde. Vanillin PG acetal was more cytotoxic than vanillin at the highest concentration tested while both diminished cellular proliferation in a concentration-dependent manner. CONCLUSIONS: Reaction products formed in e-liquids between flavor aldehydes and solvent chemicals have differential toxicological properties from their parent flavor aldehydes and may contribute to the health effects of e-cigarette aerosol in the respiratory system of e-cigarette users. IMPLICATIONS: With no inhalation toxicity studies available for acetals, data from this study will provide a basis for further toxicological studies using in vitro and in vivo models. This study suggests that manufacturers' disclosure of e-liquid ingredients at time of production may be insufficient to inform a comprehensive risk assessment of e-liquids and electronic nicotine delivery systems use, due to the chemical instability of e-liquids over time and the formation of new compounds.

Differences in flavourant levels and synthetic coolant use between USA, EU and Canadian Juul products.

BACKGROUND: 'Juul' is the dominant US e-cigarette brand and was recently introduced to Canada, UK, France, Germany and Italy, with several flavours available across countries. US/Canadian products are sold with 5%, 3% and 1.5% (Canada only) nicotine content, whereas European Union (EU) regulation limits nicotine content to 1.7%. The differential nicotine content raises the question if flavour profiles and Juul device power output differ between countries. METHODS: 'Mint', 'Vanilla' and 'Mango' e-liquids from all six countries were purchased in 2019 and analysed by GC/MS for their principal flavourant and nicotine content. In addition, device power specifications were compared for devices purchased from the respective countries. RESULTS: Compositions of Juul e-liquids from the USA and Canada were identical and differed from the EU-marketed liquids, in which principal flavourant concentrations were significantly lower. EU Juul 'Mint' e-liquids contained a synthetic coolant, N-ethyl-p-menthane-3-carboxamide (WS-3), absent in US/Canadian products. US/Canadian 'Mango' e-liquid contained triethyl-citrate, an emulsifier. Nicotine contents matched label information, and devices had identical power specifications. CONCLUSIONS: Tested US/Canadian Juul e-liquids contained higher flavour concentrations than EU products, likely reflecting adaptation to user preferences. In EU, 'Mint' e-liquid, menthol is partially substituted with the synthetic coolant WS-3 that elicits a cooling effect like menthol but lacks its distinct 'minty' odour. The inhalational safety of WS-3 is unknown. The use of an emulsifier in US/Canadian 'Mango' Juul e-liquid may be necessary to keep the product homogeneous. Similar power specifications of devices between countries suggest that nicotine aerosol delivery is likely proportional to the e-liquid nicotine content.

Formation of flavorant-propylene Glycol Adducts With Novel Toxicological Properties in Chemically Unstable E-Cigarette Liquids.

INTRODUCTION: "Vaping" electronic cigarettes (e-cigarettes) is increasingly popular with youth, driven by the wide range of available flavors, often created using flavor aldehydes. The objective of this study was to examine whether flavor aldehydes remain stable in e-cigarette liquids or whether they undergo chemical reactions, forming novel chemical species that may cause harm to the user. METHODS: Gas chromatography was used to determine concentrations of flavor aldehydes and reaction products in e-liquids and vapor generated from a commercial e-cigarette. Stability of the detected reaction products in aqueous media was monitored by ultraviolet spectroscopy and nuclear magnetic resonance spectroscopy, and their effects on irritant receptors determined by fluorescent calcium imaging in HEK-293T cells. RESULTS: Flavor aldehydes including benzaldehyde, cinnamaldehyde, citral, ethylvanillin, and vanillin rapidly reacted with the e-liquid solvent propylene glycol (PG) after mixing, and upward of 40% of flavor aldehyde content was converted to flavor aldehyde PG acetals, which were also detected in commercial e-liquids. Vaping experiments showed carryover rates of 50%-80% of acetals to e-cigarette vapor. Acetals remained stable in physiological aqueous solution, with half-lives above 36 hours, suggesting they persist when inhaled by the user. Acetals activated aldehyde-sensitive TRPA1 irritant receptors and aldehyde-insensitive TRPV1 irritant receptors. CONCLUSIONS: E-liquids are potentially reactive chemical systems in which new compounds can form after mixing of constituents and during storage, as demonstrated here for flavor aldehyde PG acetals, with unexpected toxicological effects. For regulatory purposes, a rigorous process is advised to monitor the potentially changing composition of e-liquids and e-vapors over time, to identify possible health hazards. IMPLICATIONS: This study demonstrates that e-cigarette liquids can be chemically unstable, with reactions occurring between flavorant and solvent components immediately after mixing at room temperature. The resulting compounds have toxicological properties that differ from either the flavorants or solvent components. These findings suggest that the reporting of manufacturing ingredients of e-liquids is insufficient for a safety assessment. The establishment of an analytical workflow to detect newly formed compounds in e-liquids and their potential toxicological effects is imperative for regulatory risk analysis.