Analytical methods for assessing metal bioaccessibility in airborne particulate matter: A scoping review

Green and blue infrastructure as model system for emissions of technology-critical elements

Over the recent decades, technological advancements have led to a rise in the use of so-called technology-critical elements (TCEs). Environmental monitoring of TCEs forms the base to assess whether this leads to increased anthropogenic release and to public health implications. This study employs an exploratory approach to investigate the distribution of the TCEs Li, Be, V, Ga, Ge, Nb, Sb, Te, Ta, Tl, Bi and the REYs (rare-earth elements including yttrium) in urban aerosol in the city of Vienna, Austria. Leaf samples (n = 292) from 8 plant species and two green facades and water samples (n = 18) from the Wienfluss river were examined using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). Surface dust contributions were assessed by washing one replicate of each leaf sample and analysing the washing water (n = 146). The impacts of sampling month, plant species and storey level on elemental distribution were assessed by statistical tools and generative deep neural network modelling. Higher TCE levels, including Li, V, Ga, Ge, Tl, Bi, and the REYs, were found in the winter months, likely due to the use of de-icing materials and fossil fuel combustion. A. millefolium and S. heufleriana displayed the highest levels of Li and Ge, respectively. In addition, increased elemental accumulation at lower storeys was observed, including Be, Sb, Bi and the REYs, indicating greater atmospheric dust deposition and recirculation closer to ground level. The results suggest a broad association of TCE levels with urban dust. This study enhances the current understanding of TCE distribution in urban settings and underscores the importance of their inclusion in pollution monitoring. It highlights the complex interplay of human activities, urban infrastructure, and environmental factors, offering valuable insights for managing urban environmental health risks and underlining the need for comprehensive urban ecosystem studies.

Characterization of the inhalable fraction (< 10 μm) of soil from highly urbanized and industrial environments: magnetic measurements, bioaccessibility, Pb isotopes and health risk assessment

Soil in urban and industrial areas is one of the main sinks of pollutants. It is well known that there is a strong link between metal(loid)s bioaccessibility by inhalation pathway and human health. The critical size fraction is < 10 μm (inhalable fraction) since these particles can approach to the tracheobronchial region. Here, soil samples (< 10 μm) from a highly urbanized area and an industrialized city were characterized by combining magnetic measurements, bioaccessibility of metal(loids) and Pb isotope analyses. Thermomagnetic analysis indicated that the main magnetic mineral is impure magnetite. In vitro inhalation analysis showed that Cd, Mn, Pb and Zn were the elements with the highest bioaccessibility rates (%) for both settings. Anthropogenic sources that are responsible for Pb accumulation in < 10 μm fraction are traffic emissions for the highly urbanized environment, and Pb related to steel emissions and coal combustion in cement plant for the industrial setting. We did not establish differences in the Pb isotope composition between pseudo-total and bioaccessible Pb. The health risk assessment via the inhalation pathway showed limited non-carcinogenic risks for adults and children. The calculated risks based on pseudo-total and lung bioaccessible concentrations were identical for the two areas of contrasting anthropogenic pressures. Carcinogenic risks were under the threshold levels (CR < 10-4), with Ni being the dominant contributor to risk. This research contributes valuable insights into the lung bioaccessibility of metal(loids) in urban and industrial soils, incorporating advanced analytical techniques and health risk assessments for a comprehensive understanding.

Size-segregated source identification of water-soluble and water-insoluble metals and trace elements of coarse and fine PM in central Los Angeles

In this study, the water-solubility and sources of metals and trace elements in both fine and coarse particulate matter (PM) were investigated in Central Los Angeles. Sampling was performed in the winter, spring, and summer of 2022 at the Particle Instrumentation Unit (PIU) of the University of Southern California located in the proximity of I-110 freeway. Both fine and coarse PM samples were collected using Personal Cascade Impactors (PCIS) and chemically analyzed to determine their water-soluble and water-insoluble metal content. Principal Component Analysis (PCA) and Multiple Linear Regression (MLR) were used to determine the sources of soluble and insoluble metals and obtain their contributions to total metal concentration. Our results indicate that the water-solubility of most of the metals is higher in the fine size fraction compared to the coarse fraction. Seasonal variations in the water solubility of selected metals for both coarse and fine fractions were observed, with higher water-soluble metal concentrations in summer for several species (e.g., Fe , S, Pb, Cu, La, Ni, and Al ), possibly due to higher photochemical processing, while in winter, almost all species exhibited higher insoluble fraction concentrations. The PCA and MLR analyses results showed that tire and brake wear was the most significant contributor to the total metals for both fine soluble and insoluble portions, accounting for 35% and 75% of the total metals, respectively. Combustion sources also contributed substantially to water-soluble metals for fine and coarse size ranges, representing 40% and 32% of the total metal mass, respectively. In addition, mineral dust and soil and re-suspended dust were identified as the highest contributors to coarse metals. The MLR analysis also revealed that secondary aerosols contributed 11% to the fine water-soluble metals. Our results suggest that non-tailpipe emissions significantly contribute to both coarse and fine PM metals in the Central Los Angeles region.

Oxidative stress indices induced by industrial and urban PM2.5-bound metals in A549 cells

The detrimental effects of atmospheric fine particulate matter (PM_2.5) on human health are of major global concern. PM_2.5-bound metals are toxic compounds that contribute to cellular damage. To investigate the toxic effects of water-soluble metals on human lung epithelial cells and their bioaccessibility to lung fluid, PM_2.5 samples were collected from both urban and industrial areas in the metropolitan city of Tabriz, Iran. Oxidative stress indices, including proline content, total antioxidant capacity (TAC), cytotoxicity, and DNA damage levels of water-soluble components of PM_2.5, were evaluated. Furthermore, an in vitro test was conducted to assess the bioaccessibility of various PM_2.5-bound metals to the respiratory system using simulated lung fluid. PM_2.5 average concentrations in urban and industrial areas were 83.11 and 97.71 μg/m³, respectively. The cytotoxicity effects of PM_2.5 water-soluble constituents from urban areas were significantly higher than in industrial areas and the IC₅₀ was found to be 96.76 ± 3.34 and 201.31 ± 5.96 μg/mL for urban and industrial PM_2.5 samples, respectively. In addition, higher PM_2.5 concentrations increased the proline content in a concentration-dependent manner in A549 cells, which plays a protective role against oxidative stress and prevents PM_2.5-induced DNA damage. Also, the partial least squares regression revealed that Be, Cd, Co, Ni, and Cr, were significantly correlated with DNA damage and proline accumulation, which caused cell damage through oxidative stress. The results of this study showed that PM_2.5-bound metals in highly polluted metropolitan city caused substantial changes in the cellular proline content, DNA damage levels and cytotoxicity in human lung A549 cells.

Molecular speciation controls arsenic and lead bioaccessibility in fugitive dusts from sulfidic mine tailings

Communities nearby mine wastes in arid and semi-arid regions are potentially exposed to high concentrations of toxic metal(loid)s from fugitive dusts deriving from impoundments. To assess the relation between potentially lofted particles and human health risk, we studied the relationship between pharmacokinetic bioaccessibility and metal(loid) molecular speciation for mine tailings dust particulate matter (PM), with elevated levels of arsenic and lead (up to 59 and 34 mmol kg-1, respectively), by coupling in vitro bioassay (IVBA) with X-ray absorption spectroscopy (XAS). Mine tailing efflorescent salts (PMES) and PM from the surface crust (0-1 cm, PMSC) and near surface (0-25 cm) were isolated to <10 μm and <150 μm effective spherical diameter (PM10 and PM150) and reacted with synthetic gastric and lung fluid for 30 s to 100 h to investigate toxic metal(loid) release kinetics. Bioaccessible (BAc) fractions of arsenic and lead were about 10 and 100 times greater in gastric than in lung fluid simulant, respectively, and 10-100% of the maximum gastric BAc from PM10 and PM150 occurred within 30 s, with parabolic dissolution of fine, highly-reactive particles followed by slower release from less soluble sources. Evaporite salts were almost completely solubilized in gastric-fluid simulants. Arsenate within jarosite and sorbed to ferrihydrite, and lead from anglesite, were identified by XAS as the principal contaminant sources in the near surface tailings. In the synthetic lung fluid, arsenic was released continuously to 100 h, suggesting that residence time in vivo must be considered for risk determination. Analysis of pre- and post-IVBA PM indicated the release of arsenic in lung fluid was principally from arsenic-substituted jarosite, whereas in synthetic gastric fluid arsenic complexed on ferrihydrite surfaces was preferentially released and subsequently repartitioned to jarosite-like coordination at extended exposures. Lead dissolved at 30 s was subsequently repartitioned back to the solid phase as pyromorphite in phosphate rich lung fluid. The bioaccessibility of lead in surface tailings PM was limited due to robust sequestration in plumbojarosite. Kinetic release of toxic elements in both synthetic biofluids indicated that a single IVBA interval may not adequately describe release dynamics.

Incorporating oral, inhalation and dermal bioaccessibility into human health risk characterization following exposure to Chromated Copper Arsenate (CCA)-contaminated soils

Exposure to potentially toxic metal(loid)s (PTMs) in soil may happen via ingestion, inhalation, and dermal pathway. A more accurate risk characterization should consider PTM bioavailability. Using ten soil samples collected in the Montreal area (Canada) near CCA-treated utility poles, this study aims to characterize non-carcinogenic and carcinogenic human health risks associated with As, Cr, Cu, Pb, and Zn through a multi-pathway exposure approach. This innovative study incorporates, for the first time, the bioaccessible fraction of the metal(loid)s for three exposure routes and two different scenarios. For the residential and industrial scenarios, the oral and dermal pathways yielded a hazard index (HI) much higher than 1 with and without bioaccessibility considerations (range 1.7 - 349 without bioaccessibility and 0.8-134 with bioaccessibility), whereas the inhalation pathway caused a lower hazard (HI < 1). For the dermal pathway, the hazard quotient was higher when bioaccessibility of field-collected samples was considered due to inherent assumptions from the US EPA soil approach to calculate the dermal dose. For carcinogenic risk, As and Pb were the most significant contributors to risk for the oral pathway, followed by the same elements for the dermal pathway. The overall carcinogenic risk was higher than the acceptable risk ( > 10-4) with and without bioaccessibility considerations (range 1.9E-4 - 9.6E-3 without bioaccessibility and 6.8E-5 - 3.8E-3 with bioaccessibility). Bioaccessibility tests provide a more accurate assessment of exposure to PTMs compared to total concentrations in soils.

Oxidative potential induced by metal-organic interaction from PM2.5 in simulated biological fluids

The oxidative potential (OP) of fine particulate matter (PM_2.5) has recently been proposed as a metric that may prove more indicative of human health effects than the routinely measured PM_2.5 concentration. Observations of exposure to PM_2.5 show most OP are originated from the contribution of transition metals and organics, but the pertinent coupling mechanisms are unclear. Here, we report laboratory observations in four simulated biological fluids (i.e., simulated saliva, surrogate lung fluid, artificial lysosomal fluid, and synthetic serum) that reveal OP of PM_2.5 are significantly induced by prevalent metal complexes formed with nitrogen- and oxygen-containing compounds in low acid environments. Analyses of mass spectra and interaction factors indicate that organic-metal mixture effect in PM_2.5, leading to synergistic, additive to antagonistic effects, which may serve as the dominant mechanism for this OP formation. A metal-organic mixtures origin for OP could explain why PM_2.5 emission controls should emphasize the reduction of key toxic components, rather than just PM_2.5 mass concentration control. SYNOPSIS: This study has investigated the oxidative potential of inhaled atmospheric particulate matter (PM) in four simulated biological fluids, which highlight the importance of metal-organic complexes to the formation of oxidative potential (OP).

Seasonal variation of dissolved bioaccessibility for potentially toxic elements in size-resolved PM: Impacts of bioaccessibility on inhalable risk and uncertainty

The health effects of potentially toxic elements (PTEs) in airborne particulate matter (PM) are strongly dependent on their size distribution and dissolution. This study examined PTEs within nine distinct sizes of PM in a Chinese megacity, with a focus on their deposited and dissolved bioaccessibility in the human pulmonary region. A Multiple Path Particle Dosimetry (MPPD) model was used to estimate the deposited bioaccessibility, and an in-vitro experiment with simulated lung fluid was conducted for dissolved bioaccessibility. During the non-heating season, the dissolved bioaccessible fraction (DBF) of As, Cd, Co, Cr, Mn, Pb and V were greater in fine PM (aerodynamics less than 2.1 μm) than in coarse PM (aerodynamics between 2.1 and 10 μm), and vice versa for Ni. With the increased demand of heating, the DBF of Pb and As decreased in fine particle sizes, probably due to the presence of oxide/silicate compounds from coal combustion. Inhalation health risks based on the bioaccessible concentrations of PTEs displayed the peaks in <0.43 μm and 2.1-3.3 μm particulate sizes. The non-cancer risk was at an acceptable level (95th percentiles of hazard index (HI) was 0.49), but the cancer risk exceeded the threshold value (95th percentiles of total incremental lifetime cancer risk (TCR) was 8.91 × 10^-5). Based on the results of uncertainty analysis, except for the exposure frequency, the total concentrations and DBF of As and Cr in <0.43 μm particle size segment have a greater influence on the uncertainty of probabilistic risk.

Multi-elemental Characterization of Semolina Samples by Inductively Coupled Plasma-Tandem Mass Spectrometry (ICP-MS/MS)

The precise characterization of the elemental composition of cereals and cereal products is becoming crucial to assess their nutritional values, geographical labeling, and also toxicological profile. Inductively coupled plasma-mass spectrometry (ICP-MS) has become popular for the elemental analysis of foods in recent years. Analytical performance of the inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) is improved with a reaction/collision cell that provides an interference-free analysis of most of the elements including phosphorus and sulfur. In this study, an analytical method was optimized for the quantification of 57 elements using ICP-MS/MS technique and validated for 25 elements that were available in certified reference materials (CRMs). Then, the mineral contents of semolina samples obtained from the durum wheat (Triticum durum) cultivars were analyzed according to the validation procedure. Recoveries of the elements were found in the range of 92-108% for the digested CRM. The method was robust for all elements and the results indicated good precision for the analytical method. The inter- and intra-day precision values were found below 5%, and in the range of 0.11-3.31% and 0.09-4.51%, respectively. Analyzed elements showed significant variability among the semolina samples. The variety and growing conditions might have influences on the elemental composition of semolina samples.

Size-dependent in vitro inhalation bioaccessibility of PAHs and O/N PAHs - Implications to inhalation risk assessment

Size segregated samples (<0.49, 0.49-0.95, 0.95-1.5, 1.5-3.0, 3.0-7.2 and > 7.2 μm) of atmospheric particulate matter (APM) were collected at a traffic site in the urban agglomeration of Thessaloniki, northern Greece, during the cold and the warm period of 2020. The solvent-extractable organic matter was analyzed for selected organic contaminants including polycyclic aromatic hydrocarbons (PAHs), and their nitro- and oxy-derivarives (NPAHs and OPAHs, respectively). Mean concentrations of ∑₁₆PAHs, ∑₆NPAHs and ∑₁₀OPAHs associated to total suspended particles (TSP) were 18 ng m^-3, 0.2 ng m^-3 and 0.9 ng m^-3, respectively, in the cold period exhibiting significant decrease (6.4, 0.2 and 0.09 ng m^-3, respectively) in the warm period. The major amount of all compounds was found to be associated with the alveolar particle size fraction <0.49 μm. The inhalation bioaccessibility of PAHs and O/N PAHs was measured in vitro using two simulated lung fluids (SLFs), the Gamble's solution (GS) and the artificial lysosomal fluid (ALF). With both SLFs, the derived bioaccessible fractions (BAFs) followed the order PAHs > OPAHs > NPAHs. Although no clear dependence of bioaccessibility on particle size was obtained, increased bioaccessibility of PAHs and PAH derivatives in coarse particles (>7.2 μm) was evident. Bioaccessibility was found to be strongly related to the logK_OW and the water solubility of individual compounds hindering limited mobilization of the most hydrophobic and less water-soluble compounds from APM to SLFs. The lifetime cancer risk due to inhalation exposure to bioaccessible PAHs, NPAHs and OPAHs was estimated and compared to those calculated from the particulate concentrations of organic contaminants.

Availability, Toxicology and Medical Significance of Antimony

Antimony has been known and used since ancient times, but its applications have increased significantly during the last two centuries. Aside from its few medical applications, it also has industrial applications, acting as a flame retardant and a catalyst. Geologically, native antimony is rare, and it is mostly found in sulfide ores. The main ore minerals of antimony are antimonite and jamesonite. The extensive mining and use of antimony have led to its introduction into the biosphere, where it can be hazardous, depending on its bioavailability and absorption. Detailed studies exist both from active and abandoned mining sites, and from urban settings, which document the environmental impact of antimony pollution and its impact on human physiology. Despite its evident and pronounced toxicity, it has also been used in some drugs, initially tartar emetics and subsequently antimonials. The latter are used to treat tropical diseases and their therapeutic potential for leishmaniasis means that they will not be soon phased out, despite the fact the antimonial resistance is beginning to be documented. The mechanisms by which antimony is introduced into human cells and subsequently excreted are still the subject of research; their elucidation will enable us to better understand antimony toxicity and, hopefully, to improve the nature and delivery method of antimonial drugs.

A tiered approach to investigate the inhalation toxicity of cobalt substances. Tier 1: Bioaccessibility testing

Bioelution tests measure in vitro the release of metal ion in surrogate physiological conditions (termed "bioaccessibility") and estimate the potential bioavailability relative to that of a known reference metal substance. Bioaccessibility of cobalt ion from twelve cobalt substances was tested in three artificial lung fluids (interstitial, alveolar and lysosomal) to gather information about the substances' fate and potential bioavailability in the respiratory tract after inhalation. The results can be used as one line of evidence to support grouping and read-across for substances lacking in vivo data, and where in vivo testing is not readily justifiable. Strong differences were observed in the dissolution behaviour of the substances in the different fluids, with the cobalt substances generally being less soluble in neutral pH fluids and more soluble in the acidic pH fluid. The resulting database, presented with its strengths and limitations, was used to support the formulation of an initial grouping of these cobalt substances into three categories.

Soil organic carbon stabilization in permafrost peatlands

In permafrost peatlands, the degradation of permafrost soil can raise soil temperature and alter moisture conditions, which increases the rate of loss of soil organic carbon (SOC). Here we selected three typical permafrost types that have very different active layer thicknesses but with soil originating from the same vegetation and which exist under comparable climatic conditions in the Da Xing'an mountain range: continuous permafrost, island permafrost, and island melting permafrost. To quantify the relative importance of control elements on SOC stabilization in these different permafrost types, we used correlation analysis to assess the relationship between organic carbon, physical and chemical properties and microorganisms, and explored the contribution of these factors to the accumulation of organic carbon. This study shows that the interaction between clay or silt, iron oxides and microorganisms have an important influence on the stability of organic carbon in permafrost peatlands.

Nitrated monoaromatic hydrocarbons (nitrophenols, nitrocatechols, nitrosalicylic acids) in ambient air: levels, mass size distributions and inhalation bioaccessibility

Nitrated monoaromatic hydrocarbons (NMAHs) are ubiquitous in the environment and an important part of atmospheric humic-like substances (HULIS) and brown carbon. They are ecotoxic and with underresearched toxic potential for humans. NMAHs were determined in size-segregated ambient particulate matter collected at two urban sites in central Europe, Ostrava and Kladno, Czech Republic. The average sums of 12 NMAHs (Σ12NMAH) measured in winter PM10 samples from Ostrava and Kladno were 102 and 93 ng m-3, respectively, and 8.8 ng m-3 in summer PM10 samples from Ostrava. The concentrations in winter corresponded to 6.3-7.3% and 2.6-3.1% of HULIS-C and water-soluble organic carbon (WSOC), respectively. Nitrocatechols represented 67-93%, 61-73% and 28-96% of NMAHs in PM10 samples collected in winter and summer at Ostrava and in winter at Kladno, respectively. The mass size distribution of the targeted substance classes peaked in the submicrometre size fractions (PM1), often in the PM0.5 size fraction especially in summer. The bioaccessible fraction of NMAHs was determined by leaching PM3 samples in two simulated lung fluids, Gamble's solution and artificial lysosomal fluid (ALF). More than half of NMAH mass is found bioaccessible, almost complete for nitrosalicylic acids. The bioaccessible fraction was generally higher when using ALF (mimics the chemical environment created by macrophage activity, pH 4.5) than Gamble's solution (pH 7.4). Bioaccessibility may be negligible for lipophilic substances (i.e. log KOW > 4.5).

Particle characterisation and bioaccessibility of manganese in particulate matter in silico- and ferromanganese smelters

The aim of this study was to characterise particulate matter (PM) collected in the furnace area during SiMn and high carbon (HC)-FeMn production in terms of single particle analysis and to determine the bioaccessibility of Mn in the PM in a simulated lung fluid. Airborne PM was collected with Sioutas cascade impactors and respirable cyclones in the breathing zone of tappers and crane operators. Stationary samples were collected from the furnace area with a nanoMOUDI cascade impactor and an ESPnano electrostatic particle collector. Individual particles were characterised by scanning and transmission electron microscopy. Bioaccessibility of Mn was studied in terms of the dissolution of Mn in Gamble solution (24 hours leaching at 37 °C) relative to total Mn. Slag particles, alloy fragments, Mn and Fe oxides as well as carbonaceous particles were observed in the size fraction > 1 μm aerodynamic diameter (d_ae). Thermally generated condensation particles dominated the d_ae size range of 0.18-1 μm collected from the tapping fumes, while carbonaceous particles dominated the fraction below 0.18 μm. Condensation generated particles from the furnace area of HC-FeMn production were coated with an amorphous Si-O rich surface layer which seemed to hold primary particles together as aggregates. In the same size range, the particles from the furnace area of SiMn production were dominated by spherical condensation particles rich in Si, Mn and O, but without a Si-O rich surface layer. Instead, the Mn oxides were enclosed in an amorphous Si-O rich matrix. The bioaccessibility of Mn was low to moderate (<30%), but higher for SiMn furnace workers (highest median = 23%) than HC-FeMn furnace workers (highest median = 12%). This difference in bioaccessibility was significant for PM with d_ae up to 2.5 μm, and most pronounced in the d_ae size range between 0.25 and 1.0 μm. Also, a significantly higher bioaccessibility of Mn was found for PM larger than d_ae of 0.5 μm collected among crane operators compared to tappers in the HC-FeMn smelter.

Tracing the sources of bioaccessible metal(loid)s in urban environments: A multidisciplinary approach

Understanding the links between sources of magnetic particles and bioaccessibility of metal(loids) in environmental sampling media is crucial for better evaluating human health risks, although relevant information in the scientific literature is scarce. Here, soil, road and house dust samples from a heavy industrial area in Greece were characterized in a multidisciplinary study combining magnetic measurements, SEM/EDS analyses, bioaccessibility measurements and Pb isotopic analyses of bioaccessible Pb. The oral and inhalable bioaccessible fractions of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were assessed by applying simulated gastric and lung solutions. SEM/EDS analysis revealed the abundant presence of anthropogenic Fe-containing spherules of industrial origin in all sampling media, often containing minor contents of Cr, Cu, Mn, Pb and Zn. The inhalation bioaccessibility (%) in all environmental compartments was higher than the oral one for most elements analyzed in the present study. Clear associations between magnetic susceptibility and bioaccessible amounts of most of analyzed elements were encountered for the soil and road dust. The isotopic analyses of bioaccessible Pb showed that there are significant differences in the isotopic ratios between total and bioaccessible Pb. We conclude that Pb solubilized by the simulated gastric and lung extractions is principally anthropogenic, representing a mixture of industrial Pb and Pb related to the past usage of leaded petrol. Low values of ²⁰⁶Pb/²⁰⁷Pb were accompanied by high bioaccessible contents of Cd, Pb and Zn indicating that anthropogenic (mostly industrial) sources exert influence on the bioaccessible forms of these metals. Coupling magnetic and bioaccessibility measurements with stable isotopic technique of bioaccessible Pb is more reliable for determining Pb and other metal sources with high oral and inhalation bioaccessibility.

Effect of filter extraction solvents on the measurement of the oxidative potential of airborne PM2.5

Solvent extraction of PM_2.5 samples collected on the filter is a preliminary step for assessing the PM_2.5 oxidative potential (OP) using cell-free assays, as the dithiothreitol (DTT) and the ascorbic acid (AA) assays. In this study, we evaluated the effect of the solvent choice by extracting ambient PM_2.5 samples with different solvents: methanol, as organic solvent, and two aqueous buffers, i.e., phosphate buffer (PB) and Gamble's solution (G), as a lung fluid surrogate solution. Both the measured volume-based OP_V^DTT and OP_V^AA responses varied for the different extraction methods, since methanol extraction generated the lowest values and phosphate buffer the highest. Although all the tested solvents produced intercorrelated OP_V^DTT values, the phosphate buffer resulted the most useful for OP^DTT assessment, as it provided the most sensible measure (nearly double values) compared with other extractions. The association of the measured OP_V values with PM chemical composition suggested that oxidative properties of the investigated PM_2.5 samples depend on both transition metals and quinones, as also supported by additional experimental measurements on standard solutions of redox-active species.

In vitro assessments of bioaccessibility and bioavailability of PM2.5 trace metals in respiratory and digestive systems and their oxidative potential

Air pollution is a serious environmental issue. As a key aerosol component, PM_2.5 associated toxic trace metals pose significant health risks by inhalation and ingestion, but the evidences and mechanisms were insufficient and not well understood just by their total environmental concentrations. To accurately assess the potential risks of airborne metals, a series of in vitro physiologically based tests with synthetic human lung and gastrointestinal fluids were conducted to assess both the bioaccessibility and bioavailability of various PM_2.5 bound metals in the respiratory and digestive systems from both urban and industrial areas of Nanjing city. Moreover, the chemical acellular toxicity test [dithiothreitol (DTT) assay] and source analysis were performed. Generally, the bioaccessibility and bioavailability of investigated metals were element and body fluid dependent. Source oriented metals in PM_2.5 showed diverse bioaccessibility in different human organs. The PM_2.5 induced oxidative potential was mainly contributed by the bioaccessible/bioavailable transition metals such as Fe, Ni and Co from metallurgic dust and traffic emission. Future researches on the toxicological mechanisms of airborne metals incorporating the bioaccessibility, bioavailability and toxicity tests are directions.

Respiratory bioaccessibility and solid phase partitioning of potentially harmful elements in urban environmental matrices

Studies regarding the role of geochemical processes in urban environmental matrices (UEM) and their influence on respiratory bioaccessibility in humans are scarce in humid tropical regions, especially in Brazil. Contaminated UEM are potentially hazardous to humans if particles <10 μm in diameter are inhaled and reach the tracheobronchial region. In this study, we evaluated samples collected in Brazilian UEMs with a large environmental liability left by former mining industries and in a city with strong industrial expansion. UEM samples were classified into soil, sediment and mine tailings according to the characteristics of the collection sites. The respiratory bioaccessibility of potentially harmful elements (PHE) was evaluated using artificial lysosomal fluid (ALF, pH 4.5), and the BCR-sequential extraction was performed to evaluate how the respiratory bioaccessibility of the PHE was related to the solid phase partitioning. The bioaccessible fraction (BAF) ranged from 54 to 98% for Cd; 21-89% for Cu; 46-140% for Pb, 35-88% for Mn and; 41-84% for Zn. The average BAF of the elements decreased in the following order: Soil: Cd > Pb > Mn > Zn > Cu; Tailing: Pb > Cd > Zn > Mn > Cu; and Sediments: Pb > Mn > Cd > Zn > Cu. BCR-fractions were useful to predict the PHE bioaccessibility (R² = 0.79-0.98), thus suggesting that particle geochemistry and mineralogy can influence PHE behaviour in the pulmonary fluid. Therefore, this approach provides a combination of quantitative and qualitative data, which allows us to carry out a more realistic assessment of the current situation of the potentially contaminated site and possible alternatives for decision making by the stakeholders.

Understanding how methodological aspects affect the release of trace metal(loid)s from urban dust in inhalation bioaccessibility tests

The bioaccessibility of metal(loid)s in ambient particulate matter (PM) has been recently used to represent the risk of inhalation exposure. Nevertheless, different methodological factors affect the bioaccessibility values; among these, the type and composition of surrogate biological fluids and the liquid to solid ratio have been revealed to be the most important. To better understand how these methodological aspects affect the bioaccessibility, a reference material corresponding to urban dust (SRM1648a) was contacted with synthetic biological fluids commonly used in the literature representing surrogate fluids that may interact with fine (Gamble's solutions, artificial lysosomal fluid (ALF)) and coarse particles (gastric fluid), for liquid to solid (L/S) ratios ranging from 500 to 20,000. Visual MINTEQ 3.1. was used to enhance the discussion on how the solubility of metals in the leaching solution depends on the composition of the simulated fluids and the speciation of metals. The results obtained indicate that a small change in the composition of Gamble's solution (the presence of glycine) may increase significantly the bioaccessibility at a L/S ratio of 5,000. The highest bioaccessibility of most of the studied metal(loid)s at a L/S ratio of 5,000 was found for ALF fluid. The study of the effect of the L/S ratio showed that metal(loid)s bioaccessibility in Gamble's fluid increased logarithmically with increasing L/S ratio, while it remained practically constant in ALF and gastric fluid. This different behavior is explained assuming that the leaching of metal(loid)s in Gamble's solution is solubility-controlled, while in ALF and gastric fluid is availability-controlled.

Thoracic Fraction (PM10) of Resuspended Urban Dust: Geochemistry, Particle Size Distribution and Lung Bioaccessibility

A fluidized bed aerosol generator was connected to a 13-stage cascade impactor (nanoMOUDI) for the size fractionation of urban dust (<10 µm), followed by the gravimetric analysis of loaded PTFE filter samples. This method was used to characterize the PM10 (thoracic) fraction of road dust sampled from expressways, arterial roads and local roads in Toronto, Canada. The fine particle fractions (<1.8 µm) of all the studied samples accounted for 51–72% of the resuspended PM10 (by weight). Elemental analysis using ICP-MS and ICP-OES revealed an overall trend of element enrichment in the <1.8 µm fraction compared to the coarse fraction (1.8–10 µm) of the road dust. By contrast, archived house dust samples displayed the reverse trend for most elements. The lung bioaccessibility of target elements (Al, B, Ba, Co, Cr, Fe, La, Mn, Mo, Sb, Sr, Ti, V and Zn) was assessed for each road dust fraction using 0.1 M ammonium citrate (pH 4.4) to simulate intracellular fluid and Gamble solution (pH 7.2) to simulate interstitial lung fluid. The <1.8 µm fraction of local road dust displayed significantly higher bioaccessibility (p < 0.05) for Zn when using Gamble solution, and for seven out of the 14 target elements when using ammonium citrate. These results show the importance of characterizing the fine fraction of road dust.

Bioaccessibility of potentially toxic metals in soil, sediments and tailings from a north Africa phosphate-mining area: Insight into human health risk assessment

The risk assessment of phosphate mining/processing industrial activities on the environment and human health is crucial to properly manage and minimize the risks over time. In this work, we studied the inhalation and dermal bioaccessibility of potentially toxic metals (PTM) in different particle-size fractions of urban soil, sediments and tailings from Gafsa-Metlaoui phosphate mining area, to assess afterwards the non-carcinogenic (NCR) and carcinogenic (CR) risks for the health of local citizens and workers constantly exposed to airborne particulate matter (PM) originating from these sources of contamination. Samples were separated in particle-size fractions by centrifugation and consecutive cycles of sedimentation and decanting. The pseudo-total concentrations and bioaccessible fractions of PTM were extracted by aqua regia and in vitro bioaccessibility tests, respectively. Both sediments and tailings showed higher-than-background concentrations of PTM (mainly Cd, Zn and Cr), with a tendency to accumulate these metals in fine particles (<10 μm). In urban soil, only Cd was above the background concentration. The bioaccessibility of PTM via inhalation was significantly higher in artificial lysosomal fluid (ALF) than in simulated epithelial lung fluid (SELF): basically, Cd was the most bioaccessible metal (relative bioaccessibility up to 80%), followed by the medium-to-high bioaccessible Zn (47%), Pb (46%) and Cu (39%), and the least bioaccessible Cr (16%). In synthetic skin surface liquid (NIHS 96-10), only Cd was bioaccessible at worrying extent (20-44%). On the basis of US.EPA risk assessment, the exposure to PTM bioaccessible fractions or pseudo-total concentrations would not cause serious NCR and CR risks for human health. Significant health risks (Hazard Index >1 and CR > 10^-4), especially for children, can occur if ingestion route is also considered. The findings underline the need for adequate protection of contaminated soil, sediments and mine tailings laying nearby urban agglomerates, to reduce the health risks for inhabitants and workers of Gafsa-Metlaoui mining area.

Reusable Filters Augmented with Heating Microfibers for Antibacterial and Antiviral Sterilization

Numerous threats to human health and ecosystems on earth exist due to air pollution and the spread of fatal diseases. Airborne pollutants and particulate matter (PM) pose serious public health risks. In addition, the emergence and spread of bacterial and viral diseases constantly threaten public health and safety. Although various approaches have been implemented thus far to protect humans from air pollution and exposure to diseases, several challenges remain to be addressed. In this study, we developed a hybrid air filter consisting of filtration, heating, and thermal insulation layers. The air filtration layer can effectively capture airborne PM₁ particles (less than 1.0 μm in diameter). Furthermore, the heating layer enables the hybrid air filter to generate temperatures above 100 °C, and the insulation layer prevents the heat from being transferred to the other side (e.g., the human skin, if the hybrid air filter is used in a facemask). Since several bacteria and viruses are incapacitated under high temperatures, this hybrid air filter holds great promise for antibacterial and antiviral protection.

Health risk assessment of construction workers from trace metals in PM2.5 from Kolkata, India

Construction activities have long been recognized as a pertinent source of PM_2.5 though limited information exists regarding chemical characteristics of aerosols generated during building demolition/construction. A comprehensive investigation was carried out to assess the physical (SEM analysis) and chemical (ICP MS analysis) properties of PM_2.5 in a building demolition and construction site and compared with background. Average concentrations of PM_2.5 at both the sites exceeded the National Ambient Air Quality Standards (NAAQS). Overall trend of the total metal concentrations of PM_2.5 followed the order of (Na, Ca, Al, Mg, Fe, Zn) > (Ti, Sr, Cd, Ba, Pb, V, Cr, Mn, Co, Ni, Cu) in both the sites. Sr, Ba, Mg, Zn, Ti, Cd, Al, Cr, Fe, Co, Mn, V, Ni, Ca, and Zn showed a ∼1.3-3.0 fold increase, and Pb showed the highest increase of almost >3.5 times when compared to the background concentrations. Health risk estimates based on the bio-available concentration of metals indicated that hazard quotient (HQ) values for non-carcinogenic metals were within the prescribed limit (HQ ≤ 1). However, the excess lifetime cancer risk (ELCR) for the carcinogenic metals Pb, Ni, Cd, and Cr(VI) were higher than the guideline limits of USEPA.

Oral and inhalation bioaccessibility of metal(loid)s in chromated copper arsenate (CCA)-contaminated soils: Assessment of particle size influence

Soil samples adjacent to ten CCA-treated utility poles were collected, sieved into four fractions (<2 mm, 250-90 μm, 90-20 μm and <20 μm), and characterized for their total metal(loid) (As, Cu, Cr, Pb, and Zn) content and physico-chemical properties. Oral bioaccessibility tests were performed using In Vitro Gastrointestinal (IVG) method for fractions 250-90 μm and 90-20 μm. Inhalation bioaccessibility tests were performed in particle size fraction <20 μm using two simulated lung fluids: artificial lysosomal fluid (ALF) and Gamble's solution (GS). The total concentration of metal(loid)s increased with decreasing particle size. Oral As bioaccessibility (%) increased with increasing particle size in 9 out of 10 soils (p < .05), but oral As bioaccessibility expressed in mg/kg was not significantly different for both particle size. Oral Cu bioaccessibility (% and mg/kg) was not influenced by particle size, but oral Cr bioaccessibility (% and mg/kg) increased when reducing particle size (p < .05), although Cr bioaccessibility was very low (< 8%). Oral bioaccessibility (%) of metal(loid)s decreased in the order: Cu > As > Pb > Zn > Cr. Bioaccessibility (%) in simulated lung fluids decreased in the order: Cu > Zn > As > Pb ≈ Cr using ALF, and As > Cu using GS solution. For all elements, inhalation bioaccessibility (% and mg/kg) using ALF was higher than oral bioaccessibility, except for Pb bioaccessibility (mg/kg) in two samples. However, solubility of metal(loid)s in GS presented the lowest values. Copper showed the highest oral and inhalation bioaccessibility (%) and Cr showed the lowest. Moreover, organic matter content and cation exchange capacity in particle size 90-20 μm were negatively correlated with Cu and Pb oral bioaccessibility (%).

Health risk assessment of metal(loid)s in soil and particulate matter from industrialized regions: A multidisciplinary approach

In this study, samples of soil and particulate matter obtained from the highly industrialized region of Ostrava, Czech Republic, are used for the toxicity evaluation of the selected metal(loid)s (Cd, Cr, Cu, Ni, Pb, Zn, As). We investigated the samples from sites supposedly affected the most by the local pollution sources using mineralogical techniques (XRD, SEM/EDS) to understand the solid speciation of the contaminants as the crucial factor affecting their release. Although the bulk composition was defined by common silicates and oxides that are rather resistant to leaching, the presence of tiny Ni, Pb, and/or Zn sulfate-like droplets indicated a potential increase of the solubility of these metals. In vitro tests simulating gastric and lung fluids were used to assess the exposure risk for humans, as well as metal(loid) bioaccessibility. Based on the results, the potential risk for the observed age group (3-year-old children) could be recognized, particularly in the cases of As, Pb and Cd for both oral and inhalation exposure. Arsenic exhibits high bioaccessibility (7.13-79.7%, with the median values of 10.6 and 15.6 for SGL and SLF, respectively), high daily intake (1.4- to 8.5-fold higher than the tolerable daily intake) and high concentrations in atmospheric PM₁₀ (2.5 times the tolerable concentration in air). In contrast, Ni exceeded tolerable concentrations in the atmosphere up to 20-fold, but its bioaccessibility remained relatively low (0.1-22%), and Ni did not pose a major threat to human health. Cadmium, Pb and As originating from industrial activities and domestic heating have been suggested to be the most important pollutants (tolerable daily intake was exceeded by up to 74-, 34- and 8-fold for Cd, Pb and As, respectively).

Metal bioaccessibility, particle size distribution and polydispersity of playground dust in synthetic lysosomal fluids

Inhalation of playground dust-derived fine particles in schoolyards poses a risk from exposure to metal(oids) and minerals. In this work, we obtained the total concentration and bioaccessibility of metal(oids) with Gamble Solution (GS) and Artificial Lysosomal Fluid (ALF) synthetic solutions, simulating the extracellular neutral pH environment of the lung and the intracellular conditions of the macrophage, respectively. Scanning Electron Microscope (SEM), and Dynamic Light Scattering analysis (DLS) techniques were used to characterize particles with a size smaller than 2.5 μm, which can be assimilated by macrophages in the deep part of the lung. Arsenic (As), lead (Pb), copper (Cu), manganese (Mn), zinc (Zn), and iron (Fe) showed concentrations of 39.9, 147.9, 286, 1369, 2313, 112,457 mg·kg^-1, respectively. The results indicated that all studied elements were enriched when compared to (i) local geochemical background and (ii) findings reported in other cities around the world. Bioaccessibility of metal(oids) in GS was low-moderate for most studied elements. However, in ALF assays, bioaccessibility was high among the samples: for lead (Pb = 34-100%), arsenic (As = 14.7-100%), copper (Cu = 17.9-100%), and zinc (Zn = 35-52%) possibly related to hydrophobic minerals in dust. SEM and DLS image analysis showed that playground dust particles smaller than 2.5 μm are dominant, particularly particles with a size range of 500-600 nm. The polydispersity detected in these particle sizes showed that most of them might be crystalline compounds (elongated shapes) forming agglomerates instead of combustion particles (spheres). Moreover, the circularity detected varies from 0.57 to 0.79 (low roundness), which corroborates this finding. The presence of agglomerates of ultrafine/nanoparticles containing highly bioaccessible metals in playground sites may have severe implications in children's health. Therefore, further studies are required to characterize the size distribution, structure, shape and composition of such minerals which are essential factors related to the toxicology of inhaled dust particles.

Formation of metal-organic ligand complexes affects solubility of metals in airborne particles at an urban site in the Po valley

Metals in atmospheric aerosols play potentially an important role in human health and ocean primary productivity. However, the lack of knowledge about solubility and speciation of metal ions in the particles or after solubilisation in aqueous media (sea or surface waters, cloud or rain droplets, biological fluids) limits our understanding of the underlying physico-chemical processes. In this work, a wide range of metals, their soluble fractions, and inorganic/organic compounds contained in urban particulate matter (PM) from Padua (Italy) were determined. Metal solubility tests have been performed by dissolving the PM in water and in solutions simulating rain droplet composition. The water-soluble fractions of the metal ions and of the organic compounds having ligand properties have been subjected to a multivariate statistical procedure, in order to elucidate associations among the aqueous concentrations of these PM components in simulated rain droplets. In parallel, a multi-dimensional speciation calculation has been performed to identify the stoichiometry and the amount of metal-ligand complexes theoretically expected in aqueous solutions. Both approaches showed that the solubility and the aqueous speciation of metal ions were differently affected by the presence of inorganic and organic ligands in the PM. The solubility of Al, Cr, and Fe was strongly correlated to the concentrations of oxalic acid, as their oxalate complexes represented the expected dominant species in aqueous solutions. Oxalates of Al represented ∼98% of soluble Al, while oxalates of Cu represented 34-75% of the soluble Cu, and oxalates of Fe represented 76% of soluble Fe. The oxidation state of Fe can strongly impact the speciation picture. If Fe is present as Fe(II) rather than Fe(III), the amount of Cr and Cu complexed with diacids can increase from 75% to 94%, and from 32% to 53%, respectively. For other metals, the solubility depended on the formation of soluble aquo-complexes, hence with a scarce effect of the organic ligands. An iron-oxalate complex was also directly detected in aerosol sample extracts.

Metal(loid)s inhalation bioaccessibility and oxidative potential of particulate matter from chromated copper arsenate (CCA)-contaminated soils

Field-collected chromated copper arsenate (CCA)-contaminated soils and associated particulate matter (PM) were characterized for their total metal(loid)s content (As, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and physicochemical properties. Copper, Ni, Pb and Zn fractionation (using sequential extraction) and inhalation bioaccessibility (using two lung fluids) of trace elements were assessed in PM samples. In Gamble's solution (GS), low average bioaccessibility (up to 12%) was observed for As, Cu, Mn, and Ni. A strong correlation (r = 0.92, p < 0.005, n = 9) between the soluble and exchangeable fraction (F1) and bioaccessibility in GS was observed for Cu. Inhalation bioaccessibility in artificial lysosomal fluid (ALF) was higher for Cu (avg. 78.5 ± 4.2%), Mn (avg. 56.8 ± 12.1%), Zn (avg. 54.8 ± 24.5%) and As (avg. 45.4 ± 18.8%). Strong correlations between inhalation bioaccessibility in ALF and the mobile (i.e. F1+F2) metal fraction were observed for all tested metals (i.e. (Cu (r = 0.95, p < 0.005), Ni (r = 0.79, p < 0.05), Pb (r = 0.92, p < 0.005) and Zn (r = 0.98, p < 0.005)), n = 9). The oxidative potential (OP) of PM was also assessed using an ascorbate (AA) depletion assay (OP_AA). Mobile Cu fractions were deemed to be the main factor influencing OP_AA ((F1 (r = 0.99, p < 0.005), F2 (r = 0.97, p < 0.005)), n = 9) in PM samples. A strong correlation (r = 0.94, p < 0.005, n = 10) was also observed between Cu bioaccessibility in GS and OP_AA.

Incorporating bioaccessibility into health risk assessment of heavy metals in particulate matter originated from different sources of atmospheric pollution

Rapid industrialization and urbanization have resulted in widespread pollution of airborne particulate matter (PM) containing various heavy metals with adverse human-health effects. Health risk assessment of PM calls for accurate evaluation of the bioaccessibility, instead of the total content, of heavy metals in PM. Here, we demonstrated that the leachable fraction of particle-bound As, Pb, Cr, Mn, Cd, Cu, Ni and Zn in lung fluid within the typical retention duration of particles in human lungs varied drastically among particles originated from different air pollution sources, including coal combustion, biomass combustion, fugitive dust, road dust, construction dust, cement and soil. Moreover, bioaccessibility of heavy metals, particularly in biomass combustion, cement and soil particles, was strongly dependent on pollution sources, and the particulate Cu, Ni, Pb and Cd appeared to be the primary indicators of the source dependence of heavy metal bioaccessibility. Using total rather than bioaccessible concentrations of particle-bound heavy metals not only led to overestimation of the health risk of source particles, but more importantly, inaccurate identification of the high-risk pollution sources and the priority metal pollutants in the source particles. When considering bioaccessibility of particle-bound heavy metals examined in this study, coal combustion products exhibited the highest carcinogenic and noncarcinogenic risks among all source particles, whereas cement particles would be the source with highest risk based on total metal content. As and Mn appeared to be the main drivers for the noncarcinogenic risks of source particles, while As, Ni and Cr were the major contributors to the carcinogenic risks of source particles, significantly different from those based on total contents. This research underlines the importance of incorporating bioaccessibility into health risk indexes of frequently occurring particle-bound heavy metals from specific air pollution sources, which will facilitate risk-based assessment of source contribution and hence effective source regulation of airborne PM.

A quick and simple in vitro assay to predict bioavailability of actinides following accidental exposure

Physicochemical properties of actinides highly influence internal intake and biodistribution. An a priori knowledge of the dissolution properties of compounds involved in accidental exposure would be of great help in early dose assessment. However, this information is rarely available, leading to difficulties in interpreting excretion data from contaminated victims. We developed an in vitro acellular assay to predict in vivo bioavailability of actinides and improve medical handling of the victims. Various actinides of different physicochemical properties were used to validate the reliability of the assay to mimic in vivo behavior of the contaminants. Our assay was designed as a dynamic muticompartmental system in which an agarose gel represents the retention compartment of actinides and a dynamic phase the transfer compartment. Relevant physiological conditions were obtained by introducing various components both in the static and dynamic phases. The proposed model may provide a good prediction of in vivo behavior and could be used as a first assessment to predict the fraction of actinides that could be potentially transferred from retention compartments, as well as the fraction available to chelating drugs.

Pulmonary bioaccessibility of trace metals in PM2.5 from different megacities simulated by lung fluid extraction and DGT method

Atmospheric fine particulate matters (PM_2.5) pose significant risks to human health through inhalation, especially in the rapidly developing China due to air pollution. The harmful effects of PM_2.5 are determined not only by its concentrations and hazardous components from diverse sources, but more by their bioavailable fractions actually absorbed by human body. To accurately estimate the inhalation risks of airborne metals, a physiologically based bioaccessibility method combining Simulated Lung Fluid (SLF) extraction and Diffusive Gradients in Thin-films (DGT) approaches was developed, representing the dissolution of particulate metals into lung fluid and the subsequent lung absorption of free metal cations in solution, respectively. The new method was used to compare the lung bioaccessibility of typical trace metals in PM_2.5 from three China megacities (Shanghai and Nanjing in the east, Guangzhou in south) during heavy pollution seasons. Generally, the SLF bioaccessibility (%) simulating the solubility of particulate metals in alveolar lung fluid was in order of Ni > Cd > Mn » Pb, while the succeeding DGT bioaccessibility representing labile metal fractions in solution phase absorbed directly by lung was lower and ranked as Ni ∼ Mn > Cd » Pb, thus Ni and Cd posed relatively higher potential risks owing to their high air pollution level and higher pulmonary bioaccessibility. Due to varied particle sources such as coal combustion and traffic emissions, some airborne metal concentrations (Pb, Ni) showed inconsistent spatial patterns with bulk PM_2.5 concentrations, and also varied bioaccessibility in different regions. The framework for PM_2.5 pollution risk assessments should be refined by considering both aerosol components and associated pollutants' bioaccessibility.

In vitro inhalation bioaccessibility for particle-bound hydrophobic organic chemicals: Method development, effects of particle size and hydrophobicity, and risk assessment

Bioaccessibility of particle-bound hydrophobic organic contaminants and related particle size effects are significant for assessing the potential human health risk via inhalation exposure, but have not been clearly evaluated. To fill this knowledge gap, the present study developed an in vitro method to estimate the inhalation bioaccessibility of particulate polycyclic aromatic hydrocarbons (PAHs) using simulated human lung fluids, i.e., a modified Gamble's solution (MGS) and artificial lysosomal fluid (ALF) with Tenax as the absorption media. Assay parameters, namely incubation time (10 d) and influence of filter use, were optimized for establishing the in vitro method. The results showed that the bioaccessibility of PAHs increased with increasing particle size, but other factors, such as total organic carbon and chemical hydrophobicity, also played a large role in the fate of these compounds. The results from this portion of the present study were then used to evaluate human health risk, which showed that the risk of these particle-bound PAHs by incorporating size-dependent PAHs bioaccessibility and deposition efficiency in the human respiratory tract into inhalation exposure risk calculations was reduced by >90% when compared to using total concentration. This suggested that the inhalation bioaccessibility and deposition efficiency of hydrophobic organic chemicals should be included in human health risk assessment.

Methodological factors influencing inhalation bioaccessibility of metal(loid)s in PM2.5 using simulated lung fluid

In this study, methodological factors influencing the dissolution of metal(loid)s in simulated lung fluid (SLF) was assessed in order to develop a standardised method for the assessment of inhalation bioaccessibility in PM_2.5. To achieve this aim, the effects of solid to liquid (S/L) ratio (1:100 to 1:5000), agitation (magnetic agitation, occasional shaking, orbital and end-over-end rotation), composition of SLF (artificial lysosomal fluid: ALF; phagolysosomal simulant fluid: PSF) and extraction time (1-120 h) on metal(loid) bioaccessibility were investigated using PM_2.5 from three Australian mining/smelting impacted soils and a certified reference material. The results highlighted that SLF composition significantly (p < 0.001) influenced metal(loid) bioaccessibility and that when a S/L ratio of 1:5000 and end-over-end rotation was used, metal(loid) solubility plateaued after approximately 24 h. Additionally, in order to assess the exposure of metal(loid)s via incidental ingestion of surface dust, PM_2.5 was subjected to simulated gastro-intestinal tract (GIT) solutions and the results were compared to extraction using SLF. Although As bioaccessibility in SLF (24 h) was significantly lower than in simulated GIT solutions (p < 0.05), Pb bioaccessibility was equal to or significantly higher than that extracted using simulated GIT solutions (p < 0.05).

An assessment of the inhalation bioaccessibility of platinum group elements in road dust using a simulated lung fluid

Metal enrichment of road dust is well characterized but available data on the bioaccessibility of metals in particle size fractions relevant to human respiratory health remain limited. The study goal was to investigate the bioaccessibility of platinum group elements (PGE), which are used as catalysts in automotive exhaust converters, in the inhalable fraction of road dust. Street sweepings were provided by the City of Toronto, Canada, collected as part of its Clean Roads to Clean Air program.The particle size relevance of road dust for inhalation exposures was confirmed using a laser diffraction particle size analyzer (mean Dx(50): 9.42 μm). Total PGE were determined in both bulk and inhalable fractions using nickel sulfide (NiS) fire-assay and instrumental neutron-activation analysis (INAA). PGE lung solubility was examined for the inhalable fraction using Gamble's extraction. Sample digests were co-precipitated with Te-Sn, to pre-concentrate and isolate PGE, prior to their measurement using inductively coupled plasma mass spectrometry (ICP-MS).Total PGE concentrations were enriched in the inhalable fraction of road sweepings. Geomean concentrations in the inhalable fraction were: palladium (Pd) (152 μg/kg), platinum (Pt) (55 μg/kg), rhodium (Rh) (21 μg/kg) and iridium (Ir) (0.23 μg/kg). Osmium (Os) concentrations were below the limit of detection (LOD). Bioaccessible PGEs (n = 16) using Gamble's solution were below LOD for Ir and ruthenium (Ru). For the remainder, the geomean % bioaccessibility was highest for platinum (16%), followed by rhodium (14%) and palladium (3.4%). This study provides evidence that PGE in road dust are bioaccessible in the human lung.

In vitro inhalation/ingestion bioaccessibility, health risks, and source appointment of airborne particle-bound elements trapped in room air conditioner filters

The airborne particle-bound elements (Ca, Fe, Al, Mg, K, Na, Zn, Mn, P, Pb, Cu, Sr, Ti, Ba, Cr, Ni, As, Sb, Cd, Co, and V) trapped in room air conditioners' filters (filter dusts) during recirculating indoor air from different types of rooms were analyzed, and the objectives of this study were to assess the potential sources of those elements and their potential health risks via inhalation/ingestion exposure. Main crustal elements such as Ca, Fe, Al, Mg, and K with an average value of 60.6, 17.9, 11.3, 7.58, and 6.90 mg g^-1, respectively, are the preponderant elements, and the mean values of main toxic elements were 2230, 344, 508, 85.7, 71.5, 36.0, 8.02, and 16.9 mg kg^-1 for Zn, Cu, Pb, Cr, Ni, As, Cd, and Sb, respectively. The enrichment factors indicated the significant enrichment of Cd, Pb, Cr, Cu, Sb, and Zn in the filter dusts. Four potential sources with the contributions of 33.5, 29.1, 22.6, and 14.8%, respectively, were identified by absolute principal component scores-multiple linear regression analysis (APCS-MLR). Enrichment factor and APCS-MLR model reveal the outdoor input of toxic elements. In vitro inhalation and ingestion bioaccessibility of toxic elements showed elemental and in vitro procedure dependence. There are potential carcinogenic risks via ingestion exposure and no non-carcinogenic risks to both children and adults based on bioaccessible contents of toxic elements. This study reveals the potential health risks posed by the particle-bound elements.

Size Distribution, Bioaccessibility and Health Risks of Indoor/Outdoor Airborne Toxic Elements Collected from School Office Room

20 sets of indoor and outdoor size-segregated aerosol (SSA) samples (180 foils) were collected synchronously by using two 8 Stage Non-Viable Cascade Impactor from an office room in the central region of the megacity-Nanjing, China in winter and spring in 2016. The mass size distribution of SSAs was bimodal for outdoor SSAs and unimodal for indoor in both winter and spring. The crustal elements, such as K, Ca, Mg and Fe, were mainly distributed in the coarse fractions of SSAs while toxic elements such as As, Cd, Pb and Sb were enriched more in the fine fractions in both winter and spring. Moreover, indoor/outdoor (I/O) concentration ratios of SSAs and inorganic elements indicated the penetration of outdoor fine fractions of SSAs into indoor air. As, Pb, V and Mn showed higher inhalation bioaccessibility extracted by the artificial lysosomal fluid (ALF); while V, As, Sr and Cd showed higher inhalation bioaccessibility using the simulated lung fluid (SLF), suggesting differences in elemental inhalation bioaccessibility between ALF and SLF extraction. There were similar potential carcinogenic and accumulative non-carcinogenic risks via inhalation exposure to indoor and outdoor particle-bound toxic elements based on their bioaccessible concentrations. Therefore, the potential health risks to human posed by toxic elements in office rooms cannot be neglected via inhalation exposure of the fine airborne particles.

Metal(loid) bioaccessibility and inhalation risk assessment: A comparison between an urban and an industrial area

The content of metal(loid)s in particulate matter (PM) is of special concern due to their contribution to overall (PM) toxicity. In this study, the bioaccessibility and human health risk of potentially toxic metal(loid)s associated with PM₁₀ were investigated in two areas of the Cantabrian region (northern Spain) with different levels of exposure: an industrial area mainly influenced by a ferromanganese alloy plant; and an urban area consisting mainly of residential and commercial activities, but also affected, albeit to a lesser extent by the ferroalloy plant. Total content and bioaccessible fractions in simulated lung fluids (SLFs) of Fe, Mn, Zn, Ni, Cu, Sb, Mo, Cd and Pb were determined by ICP-MS. Gamble's solution and artificial lysosomal fluid (ALF) were used to mimic different conditions inside the human respiratory system. A health risk assessment was performed based on the United States Environmental Protection Agency's (USEPA) methodology. Most metal(loid)s showed moderate and high bioaccessibility in Gamble's solution and ALF, respectively. Despite the high variability between the samples, metal(loid) bioaccessibility was found to be higher on average at the industrial site, suggesting a greater hazard to human health in the proximity of the main metal(loid) sources. Based on the results of the risk assessment, the non-carcinogenic risk associated with Mn exposure was above the safe limit (HQ> 1) under all the studied scenarios at the industrial site and under some specific scenarios at the urban location. The estimated carcinogenic inhalation risk for Cd exposure at the industrial site was found to be within the range between 1.0 × 10^-6 to 1.0 × 10^-4 (uncertainty range) under some scenarios. The results obtained in this study indicate that Mn and Cd inhalation exposure occurring in the vicinities of the studied areas may pose a human health risk.

An inhalation-ingestion bioaccessibility assay (IIBA) for the assessment of exposure to metal(loid)s in PM10

Although metal(loid) bioaccessibility of ambient particulate matter, with an aerodynamic diameter of <10μm (PM₁₀), has recently received increasing attention, limited research exists into standardising in-vitro methodologies using simulated lung fluid (SLF). Contradictions exist regarding which assay parameters should be adopted. Additionally, potential continuation of metal(loid) dissolution once PM₁₀ is cleared from the lungs and passed through the gastro-intestinal tract (GIT) has rarely been addressed. The objective of this study was to assess parameters that influence inhalation bioaccessibility in order to develop a conservative assay that is relevant to a human inhalation scenario. To achieve this aim, the effect of solid to liquid (S/L) ratio, extraction time, agitation and five major SLF compositions on the bioaccessibilities of arsenic (As) and lead (Pb) was investigated using PM₁₀ from three Australian mining/smelting impacted regions. Using the biologically relevant parameters that resulted in the most conservative outcomes, bioaccessibility of metal(loid)s in PM₁₀ was assessed in SLF, followed by simulated GIT solutions. Results from this study revealed that fluid composition and S/L ratio significantly affected metal(loid) dissolution (p<0.05). The highest Pb bioaccessibility resulted using simulated lung-gastric solution, while that of As resulted using simulated lung-gastric-small intestinal tract solutions. Compared to SLF alone, metal(loid) dissolution using the inhalation-ingestion bioaccessibility assay (IIBA) was significantly higher (p<0.05) for all PM₁₀ samples.

In vitro assessment of arsenic mobility in historical mine waste dust using simulated lung fluid

Exposure studies have linked arsenic (As) ingestion with disease in mining-affected populations; however, inhalation of mine waste dust as a pathway for pulmonary toxicity and systemic absorption has received limited attention. A biologically relevant extractant was used to assess the 24-h lung bioaccessibility of As in dust isolated from four distinct types of historical gold mine wastes common to regional Victoria, Australia. Mine waste particles less than 20 µm in size (PM₂₀) were incubated in a simulated lung fluid containing a major surface-active component found in mammalian lungs, dipalmitoylphosphatidylcholine. The supernatants were extracted, and their As contents measured after 1, 2, 4, 8 and 24 h. The resultant As solubility profiles show rapid dissolution followed by a more modest increasing trend, with between 75 and 82% of the total 24-h bioaccessible As released within the first 8 h. These profiles are consistent with the solubility profile of scorodite, a secondary As-bearing phase detected by X-ray diffraction in one of the investigated waste materials. Compared with similar studies, the cumulative As concentrations released at the 24-h time point were extremely low (range 297 ± 6-3983 ± 396 µg L^-1), representing between 0.020 ± 0.002 and 0.036 ± 0.003% of the total As in the PM₂₀.

Toxicity of the readily leachable fraction of urban PM2.5 to human lung epithelial cells: Role of soluble metals

Fine airborne particulate matter (PM_2.5) has been repeatedly associated with adverse health effects in humans. The PM_2.5 soluble fraction, and soluble metals in particular, are thought to cause lung damage. Literature data, however, are not consistent and the role of leachable metals is still under debate. In this study, Winter and Summer urban PM_2.5 aqueous extracts, obtained by using a bio-compatible solution and different contact times at 37 °C, were used to investigate cytotoxic effects of PM_2.5 in cultured lung epithelial cells (A549) and the role played by the leachable metals Cu, Fe, Zn, Ni, Pb and Cd. Cell viability and migration, as well as intracellular glutathione, extracellular cysteine, cysteinylglycine and homocysteine concentrations, were evaluated in cells challenged with both PM_2.5 extracts before and after ultrafiltration and artificial metal ion solutions mimicking the metal composition of the genuine extracts. The thiol oxidative potential was also evaluated by an abiotic test. Results demonstrate that PM_2.5 bioactive components were released within minutes of PM_2.5 interaction with the leaching solution. Among these are i) low MW (<3 kDa) solutes inducing oxidative stress and ii) high MW and/or water-insoluble compounds largely contributing to thiol oxidation and to increased homocysteine levels in the cell medium. Cu and/or Ni ions likely contributed to the effects of Summer PM_2.5 extracts. Nonetheless, the strong bio-reactivity of Winter PM_2.5 extracts could not be explained by the presence of the studied metals. A possible role for PM_2.5 water-extractable organic components is discussed.

Bioaccessibility and bioavailability of environmental semi-volatile organic compounds via inhalation: A review of methods and models

Semi-volatile organic compounds (SVOCs) present in indoor environments are known to cause adverse health effects through multiple routes of exposure. To assess the aggregate exposure, the bioaccessibility and bioavailability of SVOCs need to be determined. In this review, we discussed measurements of the bioaccessibility and bioavailability of SVOCs after inhalation. Published literature related to this issue is available for 2,3,7,8-tetrachlorodibenzo-p-dioxin and a few polycyclic aromatic hydrocarbons, such as benzo[a]pyrene and phenanthrene. Then, we reviewed common modeling approaches for the characterization of the gas- and particle-phase partitioning of SVOCs during inhalation. The models are based on mass transfer mechanisms as well as the structure of the respiratory system, using common computational techniques, such as computational fluid dynamics. However, the existing models are restricted to special conditions and cannot predict SVOC bioaccessibility and bioavailability in the whole respiratory system. The present review notes two main challenges for the estimation of SVOC bioaccessibility and bioavailability via inhalation in humans. First, in vitro and in vivo methods need to be developed and validated for a wide range of SVOCs. The in vitro methods should be validated with in vivo tests to evaluate human exposures to SVOCs in airborne particles. Second, modeling approaches for SVOCs need to consider the whole respiratory system. Alterations of the respiratory cycle period and human biological variability may be considered in future studies.

Assessment of oral and lung bioaccessibility of Cd and Pb from smelter-impacted dust

Soil and dust contamination by metals engenders significant environmental and health problems in northern France where a lead smelter was in activity for more than a century. This study aims to examine the long-term effects of the smelter, 10 years after its closedown, on the presence of metal in sidewalk dust for a better assessment of the local population's exposure to Cd and Pb. The investigation included: (i) the metal distribution in different dust particle sizes and (ii) the assessment of metal bioaccessibility via ingestion and inhalation of dust. Seventy-two sidewalk dust samples were collected using a dust-sampling vacuum. The samples were sieved to collect different particle sizes from 0.3 to 1000 μm. The unified bioaccessibility method (UBM) was employed to evaluate the oral bioaccessibility of metals in the different particle sizes. The pulmonary bioaccessible fraction of Cd and Pb via the finest particles was extracted with lung-simulating solution (artificial lysosomal fluid). Ten years after the smelter closedown, (i) a strong relationship was observed between the concentrations of metals in dust and the distance to the former smelter, whatever the particle size; (ii) both total and oral bioaccessible concentrations of metals were high in the finest fraction (0.3-5 μm) and decreased when the particle size increased; (iii) a higher oral bioaccessibility of Cd and Pb was measured in the gastric phase (on average 43% for both metals for all particle sizes) and compared to the gastrointestinal phase (on average 16% for both metals for all particle sizes); and (iv) metal bioaccessibility via inhalation of dust was relatively high (on average 74 and 69%, for Cd and Pb, respectively). The results of the present study suggest that this environmental compartment may be a sensitive and effective indicator of anthropogenic metal contamination and the human exposure in urban areas.

Chemical fractionation and health risk assessment of particulate matter-bound metals in Pune, India

The present study deals with the assessment of sequential extraction of particulate matter (PM)-bound metals and the potential health risks associated with them in a growing metropolitan city (Pune) of India. The average mass concentration of both PM_2.5-10 and PM_2.5 exceeded the National Ambient Air Quality Standards. Significant seasonal variation in mass concentration was found for both size fractions of PM with higher values in winter season and lower in monsoon. Chemical species of the studied trace metals in PM exhibited significant differences, due to difference in sources of pollution. Metals such as Cd, Pb, and Cr in both size fractions and Zn and Co in fine fraction were more efficiently extracted in mobile fractions showing their mobile nature while Ni and Fe showed reduced mobility. Fe showed the highest concentrations among all the analyzed elements in both coarse (PM_2.5-10) and fine (PM_2.5) PM, while Cd showed least concentration in both size fractions. PCA identified industrial emissions, vehicular activity, coal combustion, diesel exhaust, waste incineration, electronic waste processing, constructional activities, soil, and road dust as probable contributors responsible for the metallic fraction of PM. All the metals showed varying contamination in PM samples. The contamination was higher for fine particles than coarse ones. The average global contamination factor was found to be 27.0-34.3 in coarse and fine PM, respectively. The hazard quotient (HQ) estimated for Cd, Co, and Ni (both total and easily accessible concentrations) exceeded the safe level (HQ = 1), indicating that these metals would result in non-carcinogenic health effects to the exposed population. The HQ ranged from 9.1 × 10^-5 for Cu (coarse) to 8.3 for Ni (fine) PM. The cancer risk for Cd, Ni, and Cr in both sized PM were much higher than the acceptable limits of USEPA.

The importance of simulated lung fluid (SLF) extractions for a more relevant evaluation of the oxidative potential of particulate matter

Particulate matter (PM) induces oxidative stress in vivo, leading to adverse health effects. Oxidative potential (OP) of PM is increasingly studied as a relevant metric for health impact (instead of PM mass concentration) as much of the ambient particle mass do not contribute to PM toxicity. Several assays have been developed to quantify PM oxidative potential and a widely used one is the acellular dithiothreitol (DTT) assay. However in such assays, particles are usually extracted with methanol or Milli-Q water which is unrepresentative of physiological conditions. For this purpose, OP_DTT measurements after simulated lung fluids (SLF) extraction, in order to look at the impact of simulated lung fluid constituents, were compared to Milli-Q water extraction measurements. Our major finding is a significant decrease of the OP_DTT when the artificial lysosomal fluid (ALF) solution was used. Indeed, ligand compounds are present in the SLF solutions and some induce a decrease of the OP when compared to water extraction. Our results suggest that the effect of ligands and complexation in lining fluids towards PM contaminants probably has been underestimated and should be investigated further.

Is Unpaved Road Dust Near Fairbanks, Alaska a Health Concern? Examination of the Total and Bioaccessible Metal(loid)s

Recent studies highlight the health risks associated with toxic metal(loid)s [e.g., arsenic (As), zinc (Zn), and lead (Pb)] in dust from mining operations, urban settings, and rural roads. To have a deleterious health effect, inhaled or ingested metal(loid)s must dissolve under conditions in the lung or gastrointestinal tract. In this study, we determined total and physiologically-soluble fractions of metal(loid)s in road dust from four sites in east-central interior Alaska. Total As and antimony (Sb) were enriched up to 26.2 and 53.7, respectively in dusts relative to average crustal abundance. Several elements such as nickel (Ni), As, and Sb were highly to moderately soluble in simulated lung fluids (7-80%, 15-51%, and 5-42%, respectively). Nickel and As exceeded the EPA inhalation risk unit, which is an exposure level of minimal risk. Despite several elements being highly soluble in simulated gastric fluids, including Ni, Cu, As, and Pb, only As samples exceeded the oral reference dose for children (based on total elemental concentrations) in some samples. The highest exposure risks identified in this study are inhalation of As and Ni present in road dust and ingestion of As-containing dust, especially by children. Additional studies would be needed to further quantify the health risk posed by road dust in this region.

Particulate metal bioaccessibility in physiological fluids and cell culture media: Toxicological perspectives

According to the literature, tiny amounts of transition metals in airborne fine particles (PM_2.5) may induce proinflammatory cell response through reactive oxygen species production. The solubility of particle-bound metals in physiological fluids, i.e. the metal bioaccessibility is driven by factors such as the solution chemical composition, the contact time with the particles, and the solid-to-liquid phase ratio (S/L). In this work, PM_2.5-bound metal bioaccessibility was assessed in various physiological-like solutions including cell culture media in order to evidence the potential impact on normal human bronchial epithelial cells (NHBE) when studying the cytotoxicity and inflammatory responses of PM_2.5 towards the target bronchial compartment. Different fluids (H₂O, PBS, LHC-9 culture medium, Gamble and human respiratory mucus collected from COPD patients), various S/L conditions (from 1/6000 to 1/100,000) and exposure times (6, 24 and 72h) were tested on urban PM_2.5 samples. In addition, metals' total, soluble and insoluble fractions from PM_2.5 in LHC-9 were deposited on NHBE cells (BEAS-2B) to measure their cytotoxicity and inflammatory potential (i.e., G6PDH activity, secretion of IL-6 and IL-8). The bioaccessibility is solution-dependent. A higher salinity or organic content may increase or inhibit the bioaccessibiliy according to the element, as observed in the complex mucus matrix. Decreasing the S/L ratio also affect the bioaccessibility depending on the solution tested while the exposure time appears less critical. The LHC-9 culture medium appears to be a good physiological proxy as it induces metal bioaccessibilities close to the mucus values and is little affected by S/L ratios or exposure time. Only the insoluble fraction can be linked to the PM_2.5-induced cytotoxicity. By contrast, both soluble and insoluble fractions can be related to the secretion of cytokines. The metal bioaccessibility in LHC-9 of the total, soluble, and insoluble fractions of the PM_2.5 under study did not explain alone, the cytotoxicity nor the inflammatory response observed in BEAS-2B cells. These findings confirm the urgent need to perform further toxicological studies to better evaluate the synergistic effect of both bioaccessible particle-bound metals and organic species.