Synthetic Lung Fluid Research Articles

Dissolution behavior of stone wool fibers in synthetic lung fluids: Impact of iron oxidation state changes induced by heat treatment for binder removal

Stone wool fiber materials are commonly used for thermal and acoustic insulation, horticulture and filler purposes. Biosolubility of the stone wool fiber (SWF) materials accessed through acellular in vitro dissolution tests can potentially be used in future as an indicator of fiber biopersistence in vivo. To correlate acellular in vitro studies with in vivo and epidemiological investigations, not only a robust dissolution procedure is needed, but fundamental understanding of fiber behavior during sample preparation and dissolution is required. We investigated the influence of heat treatment procedure for binder removal on the SWF iron oxidation state as well as on the SWF dissolution behavior in simulant lung fluids (with and without complexing agents). We used heat treatments at 450 °C for 5 min and 590 °C for 1 h. Both procedures resulted in complete binder removal from the SWF. Changes of iron oxidation state were moderate if binder was removed at 450 °C for 5 min, and there were no substantial changes of SWF’s dissolution behavior in all investigated fluids after this heat treatment. In contrast, if binder was removed at 590 °C for 1 h, complete Fe(II) oxidation to Fe(III) was observed and significant increase of dissolution was shown in fluids without complexing agent (citrate). PHREEQC solution speciation modeling showed that in this case, released Fe(III) may form ferrihydrite precipitate in the solution. Precipitation of ferrihydrite solid phase leads to removal of iron cations from the solution, thus shifting reaction towards the dissolution products and increasing total mass loss of fiber samples. This effect is not observed for heat treated fibers if citrate is present in the fluid, because Fe(III) binds with citrate and remains mobile in the solution. Therefore, for developing the most accurate SWF in vitro acellular biosolubility test, SWF heat treatment for binder removal is not recommended in combination with dissolution testing in fluids without citrate as a complexing agent.

P16-02: In vitro acellular dissolution tests of stone wool fibers: Influence of binder removal techniques on dissolution behavior in synthetic lung fluids

P16-02: In vitro acellular dissolution tests of stone wool fibers: Influence of binder removal techniques on dissolution behavior in synthetic lung fluids

Characterization and Polydispersity of Volcanic Ash Nanoparticles in Synthetic Lung Fluid.

The inhalation of natural nanoparticles (NPs) emitted from volcanic activity may be a risk to human health. However, the literature rarely reports the fate and response of NPs once in contact with lung fluids. In this work, we studied the particle size distribution of ashfall from Popocatépetl volcano, Mexico. The collected ashes (n = 5) were analyzed with scanning electron microscopy (SEM) to obtain the elemental composition and morphology, and to determine the size of the ash particles using ParticleMetric software (PMS). The PMS reported most of the ash to have submicrometric size (<1 μm) and an average equivalent circle of 2.72 μm. Moreover, to our knowledge, this study investigated for the first time the behavior of ash NPs at different times (0 to 24 h) while in contact with in vitro lung fluid, Gamble Solution (GS) and Artificial Lysosomal Fluid (ALF) using dynamic light scattering (DLS). We found a large variability in the hydrodynamic diameter, with values less than 1 nm and greater than 5 μm. Furthermore, aggregation and disaggregation processes were recognized in GS and ALF, respectively. The results of this study increase the knowledge of the interaction between NPs and lung fluids, particularly within the alveolar macrophage region.

Evaluation of altered environmental conditions as a decontamination approach for SARS-CoV-2 when applied to aircraft related materials.

The purpose of this study was to evaluate the effects of altered environmental conditions, specifically elevated temperature at various levels of expected relative humidity (RH), on the inactivation of SARS-CoV-2 when applied to U.S. Air Force aircraft materials. SARS CoV-2 (USA-WA1/2020) was spiked (∼1×105 TCID50) in either synthetic saliva or lung fluid, dried onto porous (e.g. Nylon strap) and nonporous materials (e.g. bare aluminum, silicone, and ABS plastic), placed in a test chamber and exposed to environmental conditions ranging from 40 to 51.7 °C and RH ranging from 0% to 50%. The amount of infectious SARS-CoV-2 was then assessed at various timepoints from 0 to 2 days. Warmer test temperatures, higher RH, and longer exposure duration resulted in higher inactivation rates per material type. Synthetic saliva inoculation vehicle was more readily decontaminated compared to materials inoculated with synthetic lung fluid. SARS-CoV-2 was readily inactivated below limit of quantitation (LOQ) for all materials inoculated using synthetic saliva vehicle within 6 hours when exposed to environmental conditions of 51.7 °C and RH≥25%. Synthetic lung fluid vehicle did not follow the general trend of an increase in RH resulting in increased efficacy. The lung fluid performed best at the 20%-25% RH range to achieve complete inactivation below LOQ.

Transformation of zinc oxide nanoparticles in synthetic lung fluids.

Surface coatings, including paints, stains, and sealants, have recently become a focus of “nano-enabled” consumer product engineering. Specifically, zinc oxide (ZnO) nanoparticles (NPs) have been introduced to surface coatings to increase UV resistance. As more “nano-enabled” products are made available for purchase, questions arise regarding their long-term environmental and human health effects. This study tracked the transformation of NP additives commonly added to consumer paints and stains using ZnO NPs as a model system. During product application and use, there is a risk of inhalation of aerosolized ZnO NPs. To investigate the potential chemical interactions and transformations that would occur after inhalation, ZnO NPs were incubated in two synthetic lung fluids (SLFs). Initial studies utilized ZnO NPs dispersed in Milli-Q water (control), or a commercially available deck stain. Additionally, two commercially available products advertising the inclusion of ZnO NP additives were evaluated. Subsamples were taken throughout incubation and analyzed via atomic absorption spectroscopy to determine both the total (including particulate) zinc concentration and dissolved (non-particulate) zinc concentration. Results indicate that the vast majority of ZnO transformation takes place within the first 24 h of incubation and is primarily driven by SLF pH and composition complexity. Significant dissolution of ZnO NPs was observed when incubated in Gamble’s solution (between 25 and 68% depending on the matrix. Additionally, all ZnO solutions saw near immediate dissolution (~ 98–100%) within 3 h of incubation in artificial lysosomal fluid. Results illustrate potential for NPs in consumer products to undergo significant transformation during use and exposure over short time periods. Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s11051-022-05527-y.

The dissolution of stone wool fibers with sugar-based binder and oil in different synthetic lung fluids

The biopersistence of fiber materials is one of the cornerstones in estimating potential risk to human health upon inhalation. To connect epidemiological and in vivo investigations with in vitro studies, reliable and robust methods of fiber biopersistence determination and understanding of fiber dissolution mechanism are required. We investigated dissolution properties of oil treated stone wool fibers with and without sugar-based binder (SBB) at 37 °C in the liquids representing macrophages intracellular conditions (pH 4.5). Conditions varied from batch to flow of different rates. Fiber morphology and surface chemistry changes caused by dissolution were monitored with scanning electron microscopy and time-of-flight secondary ion mass spectrometry mapping. Stone wool fiber dissolution rate depends on liquid composition (presence of ligands, such as citrate), pH, reaction products transport and fibers wetting properties. The dissolution rate decreases when: 1) citrate is consumed by the reaction with the released Al cations; 2) the pH increases during a reaction in poorly buffered solutions; 3) the dissolution products are accumulated; 4) fibers are not fully wetted with the fluid. Presence of SBB has no influence on dissolution rate if fiber material was wetted prior to dissolution experiment to avoid poorly wetted fiber agglomerates formation in the synthetic lung fluids.

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, PM2.5 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 PM2.5 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 PM2.5 showed diverse bioaccessibility in different human organs. The PM2.5 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.

Bioaccessibility of nickel and cobalt in synthetic gastric and lung fluids and its potential use in alloy classification

This study investigated nickel and cobalt ion release from the metals and several alloys in synthetic gastric, as well as interstitial and lysosomal lung fluids. Results were used to calculate the relative bioaccessible concentrations (RBCs) of the metals. Nickel release from SS 316L powder in gastric fluid was >300-fold lower than from a simple mixture of powders of the same bulk composition. Gastric bioaccessibility data showed 50-fold higher metal releases per gram of sample from powder than massive forms. RBCs of nickel and cobalt in the alloy powders were lower, equal, or higher in all fluids tested than their bulk concentrations. This illustrates the fact that matrix effects can increase or decrease the metal ion release, depending on the metal ingredients, alloy type, and fluid, consistent with research by others. Acute inhalation toxicity studies with cobalt-containing alloy powders showed that the RBC of cobalt in interstitial lung fluid predicted acute toxicity better than bulk concentration. This example indicates that the RBC of a metal in an alloy may estimate the concentration of bioavailable metals better than the bulk concentration, and the approach may provide a means to refine the classification of alloys for several human health endpoints.

Ingestion and inhalation of metal(loid)s through preschool gardening: An exposure and risk assessment in legacy mining communities

Children residing in mining towns are potentially disproportionately exposed to metal(loid)s via ingestion and dust inhalation, thus, increasing their exposure when engaging in school or home gardening or playing outside. This citizen science study assessed preschool children’s potential arsenic (As), cadmium (Cd), and lead (Pb) exposure via locally grown produce, water, incidental soil ingestion, and dust inhalation at four sites. Participants were trained to properly collect water, soil, and vegetable samples from their preschools in Nevada County, California. As, Cd, and Pb concentrations in irrigation sources did not exceed the U.S. EPA’s maximum contaminant and action levels. In general, garden and playground As and Pb soil concentrations exceeded the U.S. EPA Regional Screening Level, CalEPA Human Health Screening Level, and California Department of Toxic Substances Control Screening Level. In contrast, all Cd concentrations were below these recommended screening levels. Dust samples (<10 μm diameter) were generated from surface garden and playground soil collected at the preschools by a technique that simulated windblown dust. Soil and dust samples were then analyzed by in-vitro bioaccessibility assays using synthetic lung and gastric fluids to estimate the bioaccessible fraction of As, Cd, and Pb in the body. Metal(loid) exposure via grown produce revealed that lettuce, carrot, and cabbage grown in the preschool gardens accumulated a higher concentration of metal(loid) than those store-bought nation-wide. None of the vegetables exceeded the respective recommendation maximum levels for Cd and Pb set by the World Health Organization Codex Alimentarius Commission. The results of this study indicate that consumption of preschool-grown produce and incidental soil ingestion were major contributors to preschool-aged children’s exposure to As, Cd, and Pb. Traditionally, this level of site- and age-specific assessment and analyses does not occur at contaminated sites. The results of this holistic risk assessment can inform future risk assessment and public health interventions related to childhood metal(loid) exposures.

Dissolution of Stone Wool Fibers with Phenol-urea-formaldehyde Binder in a Synthetic Lung Fluid.

Mineral wool products, composed of stone wool fibers and organic binder, are used in many construction applications. Among all their beneficial properties, the most important requirement is safety for human health, such as when fibers are inhaled. For determining long-term toxicity, biosolubility and biopersistence studies in vitro and in vivo are essential. In vitro fiber dissolution rate, which depends on the medium, fiber composition, and the surface available for dissolution, is a key parameter in determining biopersistence of the material in vivo. We investigated how organic binder (phenol-urea-formaldehyde), which can partially shield fiber surfaces from the solution, influences fiber dissolution kinetics in synthetic lung fluid (modified Gamble's solution) at pH 4.5 and temperature 37 °C, in vitro. Dissolution experiments were made in batch and continuous flow using stone wool fibers with typical insulation product binder amounts (0-6 wt %), applied by the standard industrial process. Dissolution rates were determined from element concentrations in the reacted solution, and changes in fiber surface composition and morphology were monitored. Stone wool fiber dissolution was close to stoichiometric and was similar, whether or not the material contained binder. The high dissolution rate (508 ng of fiber/cm2/h) is explained by Al and Fe complexing agents, that is, citrate and tartrate, in the synthetic lung fluid. The organic binder mainly forms micrometer-sized discrete droplets on the fiber surfaces rather than a homogeneous thick coating. During in vitro tests, fibers with organic binder preferentially dissolved in the areas free of binder, forming cavities, whereas the untreated fibers dissolved homogeneously. Propagation of cavities undermined the binder droplets, leading to complete fiber dissolution. Thus, presence of organic binder on stone wool fibers, produced by the standard industrial process, had no measurable effect on dissolution rate in synthetic lung fluid containing Al and Fe complexing agents.

Development of tracheobronchial fluid for in vitro bioaccessibility assessment of particulates-bound trace elements

This study was piloted to evaluate bioaccessibility of particulate-bound trace elements using synthetic epithelia lung fluid; in which dipalmitoylphophatidylcholine was substituted with locus bean gum (LBSFL). The resulting data reveal that no significant change in physicochemical characteristics of the stimulated lung fluid compare with similar synthetic fluids; pH value of 7.3, density (0.998gcm−3), conductivity (13.9 mS m-1), surface viscosity (1.136 × 10-12 pas) and surface tension (50.6 mN m-1). To prove the potential applicability of the fluid in in vitro bioaccessibility test, we compared bioaccessibility of particulates-bound trace elements using this fluid with those of stimulated epithelial lung fluid. Bioaccessibility were relatively low values (<30%) in locus bean substituted lung fluid and stimulated epithelial lung fluid. Specifically, As and Cd had significantly higher bioaccessibility values in locus bean substituted lung fluid than stimulated epithelial lung fluid. The data demonstrate that fluid formulated and used in this study can provide a suitable means of evaluate bioaccessibility of trace elements-bound to airborne particulates.•The fluid was used for assessing bioaccessibility of particulate matters-bound trace elements•The formulated fluid can be applied to study in toxicity assessment•The data can be used for inter-laboratory comparison of bioaccessibility of particulate -bound trace element and could stimulate environmental concerns on the impacts of airborne particulates.

The characterization, mobility, and persistence of roaster-derived arsenic in soils at Giant Mine, NWT

Approximately 20,000 tonnes of arsenic (As)-bearing emissions from roasting gold (Au)-bearing arsenopyrite ore were aerially released from 1949 to 1999 at Giant Mine, near Yellowknife, Canada. Soil samples collected within 4 km of the former roaster from sites undisturbed by mining or other human activity contain up to 7700 mg/kg total As. Total As concentrations are highest within a few cm of the surface, and particularly enriched in soil pockets on rock outcrops. Scanning electron microscopy and synchrotron microanalysis show that roaster-derived arsenic trioxide (As2O3) has persisted in shallow soils in the area. Roaster-generated maghemite and hematite are also present. These anthropogenic forms of As are much more common in near-surface soils than natural As-bearing minerals. Comparison of the proportions of As, Sb, and Au concentrations in outcrop soil samples and historic As2O3-rich dust captured by emission controls suggest most of the roaster-derived As in soils at Giant was likely deposited before 1964. Topographic restriction by rock outcrops and a dry, cold climate likely contribute to the persistence of As2O3 in outcrop soils.Limited post-depositional mobility of roaster-generated As is evident from textural relationships in thin section, the presence of As in weathering products, the variation of As:Sb with depth, and the elevated As concentrations in soil pore waters sampled by suction lysimeters. Synthetic gastric and lung fluids extracted an average of 34% and 18% of the total As in three adjacent soil samples. Given that As2O3 is one of the most toxic and bioaccessible forms of As, the persistence of roaster-generated As in shallow soils may be a human health risk at this site.

Determination of the bioaccessible fraction of metals in urban aerosol using simulated lung fluids

Determination of the bioaccessible fraction of metals in atmospheric aerosol is a significant issue with respect to air pollution in the urban environment. The aim of this work was to compare of metal bioaccessibility determined according to the extraction yields of six simulated lung fluids. Aerosol samples of the PM1 fraction were collected in Brno, Czech Republic. The total contents of Cd, Ce, Cr, Cu, Fe, Mn, Ni, Pb, V, and Zn in the samples were determined and their enrichment factors were calculated. The bioaccessible proportions of elements were determined by means of extraction in Gamble’s solution, Gamble’s solution with dipalmitoyl phosphatidyl choline (DPPC), artificial lysosomal fluid, saline, water, and in a newly proposed solution based on DPPC, referred to as “Simulated Alveoli Fluid” (SAF). The chemical composition and surface tension of the simulated lung fluids were the main parameters influencing extraction yields. Gamble’s solutions and the newly designed solution of SAF exhibited the lowest extraction efficiency, and also had the lowest surface tensions. The bioaccessibility of particulate metals should be assessed by synthetic lung fluids with a low surface tension, which simulate better the behavior and composition of native lung surfactant. The bioaccessibility of metals in aerosol assessed by means of the extraction in water or artificial lysosomal fluid can be overestimated.

Dissolution rates of five inorganic mine ore inorganic elements in synthetic lung fluid

Inhalation of dust generated in the mining process exposes workers to many health hazards. The inorganic elements nickel, copper, arsenic, cadmium, and lead have been found in some mine ore and have suspected relationships to adverse health effects. Dissolution rates for copper, arsenic, lead, cadmium, and nickel in respirable sized particles of a selected mine ore were determined in synthetic lung fluid at two different pH levels. Synthetic lung fluid with a pH of 7.2 was used to simulate extracellular lung fluid and synthetic lung fluid with a pH of 4.5 was used to simulate intracellular lung fluid. The synthetic lung fluid samples and quality assurance and quality control samples were continuously agitated for a 25-day period. A ten-milliliter sample was removed from each solution on days 0, 1, 2, 3, 4, 5, 6, 7, 10, 14, 18, 21, and 25. Each sample was analyzed for dissolved nickel, copper, arsenic, cadmium, and lead concentrations using inductively coupled plasma mass spectrometry. Analytical results show that all inorganic elements investigated dissolved at a higher rate in the 4.5 pH synthetic lung fluid than in the 7.2 pH synthetic lung fluid throughout the 25-day sampling period. In summary, it was observed that the dissolution rates for all inorganic elements in synthetic lung fluid were significantly different in the solutions at the two different pH levels. Maximum concentration of each inorganic element was higher in the 4.5 pH synthetic lung fluid solution. Results of this study show the five inorganic elements investigated are more likely to dissolve in intracellular lung fluid than in extracellular lung fluid.

Effect of lactate, glycine, and citrate on the kinetics of montmorillonite dissolution

The montmorillonite dissolution in saline solutions that mimic synthetic lung fluids (SLF) was investigated to gain knowledge on the clearance mechanisms of inhaled clay particles. Dissolution rates were measured at pH 4 (macrophages) and 7.5 (interstitial fluids) at 37 °C in flow-through reactors. The effect of organic acids was investigated through the addition of lactate, citrate, and glycine (0.15, 1.5, and 15 mmol/L). Lactate or glycine does not markedly affect the montmorillonite dissolution rates at pH 4, but at pH 7.5 there exists a slight inhibitory effect of lactate on the dissolution, probably due to a reduction in the number of reactive surface sites caused by lactate adsorption. Citrate enhances the dissolution rate by 0.5 order of magnitude at pH 4 and more than 1 order of magnitude at pH 7.5, thus indicating the prevalence of the ligand-promoted over the proton-promoted dissolution mechanism under these experimental conditions. The kinetic data were used to estimate the reduction in size of an inhaled clay particle. At pH 7.5, a particle 500 nm in diameter could be reduced 25% in the presence of citrate, whereas the reduction in saline solution would only be 10% after 10 years.

Dissolution and nanoparticle generation behavior of Be-associated materials in synthetic lung fluid using inductively coupled plasma mass spectroscopy and flow field-flow fractionation

Various Be-containing micro-particle suspensions were equilibrated with simulated lung fluid (SLF) to examine their dissolution behavior as well as the potential generation of nanoparticles. The motivation for this study was to explore the relationship between dissolution/particle generation behaviors of Be-containing materials relevant to Be-ore processing, and their epidemiologically indicated inhalation toxicities. Limited data suggest that BeO is associated with higher rates of beryllium sensitization (BS) and chronic beryllium disease (CBD) relative to the other five relevant materials studied: bertrandite-containing ore, beryl-containing ore, frit (a processing intermediate), Be(OH) 2 (a processing intermediate), and silica (control). These materials were equilibrated with SLF at two pH values (4.5 and 7.2) to reflect inter- and intra-cellular environments in lung tissue. Concentrations of Be, Al, and Si in SLF increased linearly during the first 20 days of equilibration, and then rose slowly, or in some cases reached a maximum, and subsequently decreased. Relative to the other materials, BeO produced relatively low Be concentration in solution at pH 7.2; and relatively high Be concentration in solution at pH 4.5 during the first 20 days of equilibration. For both pH values, however, the Be concentration in SLF normalized to Be content of the material was lowest for BeO, demonstrating that BeO was distinct among the four other Be-containing materials in terms of its persistence as a source of Be to the SLF solution. Following 149 days of equilibration, the SLF solutions were fractionated using flow-field flow fractionation (FlFFF) with detection via ICP-MS. For all materials, nanoparticles (which were formed during equilibration) were dominantly distributed in the 10–100 nm size range. Notably, BeO produced the least nanoparticle-associated Be mass (other than silica) at both pH values. Furthermore, BeO produced the highest Be concentrations in the size range corresponding to < 3 kDa (determined via centrifugal ultrafiltration), indicating that in addition to persistence, the BeO produced the highest concentrations of truly dissolved (potentially ionic) Be relative to the other materials. Mass balance analysis showed reasonable sample recoveries during FFF fractionation (50–100%), whereas recoveries during ICP-MS (relative to acidified standards) were much lower (5–10%), likely due to inefficiencies in nebulizing and ionizing the nanoparticles.

Dispersion stabilization of silver nanoparticles in synthetic lung fluid studied under in situ conditions

The dispersion stabilization of silver nanoparticles (AgNPs) in synthetic lung fluid was studied to interrogate the effects on colloidal stability due to the principal constituents of the fluid. The colloidal stability of 20 nm citrate-AgNPs dispersed in the presence of each constituent of the synthetic lung fluid (individually, the complete fluid, and without additives) was observed during titration of increasing sodium chloride concentration. A variety of complementary in situ measurement techniques were utilized, including dynamic light scattering, ultraviolet-visible absorption spectroscopy, atomic force microscopy, and small-angle X-ray scattering, which provided a collective set of information that enabled far better understanding of the dispersion behavior in the fluid than any one technique alone. It was observed that AgNPs continued to adsorb bovine serum albumin (BSA) protein from the synthetic lung fluid solution as the sodium chloride concentration increased, until a maximum BSA coating was achieved prior to reaching the physiological sodium chloride concentration of 154 mmol L−1. BSA was determined to be the constituent of the synthetic lung fluid that is required to provide colloidal stability at high salt loadings, though the phospholipid constituent exerts a subtle effect. Additionally, as AgNPs are a distinctly different class of nanoparticles apart from the carbon nanotubes and titanium dioxide nanoparticles initially reported to be dispersible using this fluid, this work also demonstrates the broad applicability of synthetic lung fluid in providing stable dispersions for engineered nanoparticles for use in biological assays.

Comparison of nickel release in solutions used for the identification of water-soluble nickel exposures and in synthetic lung fluids

Chemical speciation of workplace nickel exposures is critical because nickel-containing substances often differ in toxicological properties. Exposure matrices based on leaching methods have been used to ascertain which chemical forms of nickel are primarily associated with adverse respiratory effects after inhalation. Misjudgments in the relative proportion of each of the main fractions of nickel in workplace exposures could translate into possible misattributions of risk to the various forms of nickel. This preliminary study looked at the efficiency of the first step of the Zatka leaching method for accurately assessing the 'water-soluble' fraction of several substances present in nickel production operations, compared to leaching in synthetic lung fluid. The present results demonstrate that for nickel sulfate or chloride, the current Zatka solution is adequate to assess the 'water-soluble' fraction. However, when sparingly water-soluble compounds like nickel carbonates or water-insoluble substances like nickel subsulfide and fine metallic nickel powders are present, the first step of the Zatka method can greatly over estimate the amount of nickel that could be released in pure water. In contrast, the releases of nickel from nickel carbonate, nickel subsulfide, and nickel metal powders in pure water are consistent with their releases in synthetic lung fluid, indicating that deionized water is a better leaching solution to estimate the biologically relevant 'water-soluble' nickel fraction of workplace exposures. Exposure matrices relying mostly on the Zatka speciation method to estimate the main forms of nickel need to be re-evaluated to account for any possible misattributions of risk.

Temperature effect on nickel release in ammonium citrate

Leaching in ammonium citrate has been extensively used to assess the fraction of water-soluble nickel compounds present in nickel producing and using workplace aerosols. Leaching in ammonium citrate according to the first step of the Zatka protocol was found to overestimate the water-soluble nickel fraction by more than ten-fold compared to synthetic lung fluid (37 degrees C), when nickel carbonate and subsulfide were present. These results suggest that exposure matrices based on this method should be reexamined. Leaching studies of refinery particles are needed to further clarify this important issue.

The bioaccessibility of lead from Welsh mine waste using a respiratory uptake test

The objective of this study was to develop an in vitro respiratory uptake test to determine the bioaccessibility of lead derived from mining waste tailings and dusts. Samples were collected from an abandoned mining area in mid-Wales, UK, the < 10 μ m fraction was characterized using SEM and the < 100 μ m fraction using XRD techniques. Gamble's Solution was employed as the synthetic lung fluid and tests were run for 630 hours in a specially designed water bath. The long test duration was specified because of the long duration of particulates in the lung after inhalation. Bioaccessible lead was determined throughout the test and the final values ranged from 15 to 41% of total lead. The extraction profile of the lead could be modeled by: Pb − extracted (M) = b × ln (time, t) + c, where b and c are sample specific constants, M is the mass extracted in mg and t is the time in hours. However, despite acceptable values of R2, the standardised residuals of simple regression suggest that lead extracted is under predicted at early time and over predicted at later time. Clearly from the regression model presented the dissolution rate is declining with time and the dissolution rate decreases by an order of magnitude for the tailings tested over the duration of the test. The explanation for this is the deposition of an insoluble lead phosphate mineral during the extraction onto lead mineral surfaces that effectively limits dissolution. Based on this finding it is suggested that the in vitro extraction method described can provide a conservative estimate of bioaccessible lead for a shorter duration test of 100 hours.