Bulk Dust Research Articles

Identification of SARS-CoV-2 variants in indoor dust.

Environmental surveillance of pathogens underlying infectious disease is critical to ensure public health. Recent efforts to track SARS-CoV-2 have utilized wastewater sampling to infer community trends in viral abundance and variant composition. Indoor dust has also been used for building-level inferences, though to date no sequencing data providing variant-scale resolution have been reported from dust samples, and strategies to monitor circulating variants in dust are needed to help inform public health decisions. In this study, we demonstrate that SARS-CoV-2 lineages can be detected and sequenced from indoor bulk dust samples. We collected 93 vacuum bags from April 2021 to March 2022 from buildings on The Ohio State University's (OSU) Columbus campus, and the dust was used to develop and apply an amplicon-based whole-genome sequencing protocol to identify the variants present and estimate their relative abundances. Three variants of concern were detected in the dust: Alpha, Delta, and Omicron. Alpha was found in our earliest sample in April 2021 with an estimated frequency of 100%. Delta was the primary variant present from October of 2021 to January 2022, with an average estimated frequency of 91% (±1.3%). Omicron became the primary variant in January 2022 and was the dominant strain in circulation through March with an estimated frequency of 87% (±3.2%). The detection of these variants on OSU's campus correlates with the circulation of these variants in the surrounding population (Delta p<0.0001 and Omicron p = 0.02). Overall, these results support the hypothesis that dust can be used to track COVID-19 variants in buildings.

Characterization of the Emissions and Crystalline Silica Content of Airborne Dust Generated from Grinding Natural and Engineered Stones.

In this study, we systematically characterized the airborne dust generated from grinding engineered and natural stone products using a laboratory testing system designed and operated to collect representative respirable dust samples. Four stone samples tested included two engineered stones consisting of crystalline silica in a polyester resin matrix (formulations differed with Stones A having up to 90wt% crystalline silica and Stone B up to 50wt% crystalline silica), an engineered stone consisting of recycled glass in a cement matrix (Stone C), and a granite. Aerosol samples were collected by respirable dust samplers, total dust samplers, and a Micro-Orifice Uniform Deposit Impactor. Aerosol samples were analyzed by gravimetric analysis and x-ray diffraction to determine dust generation rates, crystalline silica generation rates, and crystalline silica content. Additionally, bulk dust settled on the floor of the testing system was analyzed for crystalline silica content. Real-time particle size distributions were measured using an Aerodynamic Particle Sizer. All stone types generated similar trimodal lognormal number-weighted particle size distributions during grinding with the most prominent mode at an aerodynamic diameter of about 2.0-2.3 μm, suggesting dust formation from grinding different stones is similar. Bulk dust from Stone C contained no crystalline silica. Bulk dust from Stone A, Stone B, and granite contained 60, 23, and 30wt% crystalline silica, respectively. In Stones A and B, the cristobalite form of crystalline silica was more plentiful than the quartz form. Only the quartz form was detected in granite. The bulk dust, respirable dust, and total dust for each stone had comparable amounts of crystalline silica, suggesting that crystalline silica content in the bulk dust could be representative of that in respirable dust generated during grinding. Granite generated more dust per unit volume of material removed than the engineered stones, which all had similar normalized dust generation rates. Stone A had the highest normalized generation rates of crystalline silica, followed by granite, Stone B, and Stone C (no crystalline silica), which likely leads to the same trend of respirable crystalline silica (RCS) exposure when working with these different stones. Manufacturing and adoption of engineered stone products with formulations such as Stone B or Stone C could potentially lower or eliminate RCS exposure risks. Combining all the effects of dust generation rate, size-dependent silica content, and respirable fraction, the highest normalized generation rate of RCS consistently occurs at 3.2-5.6 µm for all the stones containing crystalline silica. Therefore, removing particles in this size range near the generation sources should be prioritized when developing engineering control measures.

Characterization of Saharan and Sahelian dust sources based on geochemical and radiogenic isotope signatures

Mineral dust can significantly impact climate and biogeochemical cycles on Earth. To understand dust provenance, an accurate characterization of dust sources and emission regions is required. In this study, we combine rare-earth element patterns, elemental ratios, and radiogenic Sr-Nd-Pb isotopes to discriminate dust sources from key regions in North Africa responsible for ∼55% of the total dust load emitted annually on Earth. This new dataset, based on fifty-nine analyses of deflatable fine soil material, improves our current knowledge about North African dust sources, especially those underrepresented in Saharan-Sahelian regions. Six potential source areas (PSA) – Libya-Algeria-Mali (PSALAM), Libya-Egypt (PSALE), Bodélé Depression (PSABD), Mali Center (PSAMC), West African Coast (PSAWAC) and Mauritania (PSAMa) – are defined based on several lithogenic tracers as well as on the geological subdivision of North African geological provinces, providing a unique chemical and isotope fingerprint for each PSA. For example, the PSABD – the main dust activation area in North Africa – is clearly distinguished from western African sources using Pb isotopes. Major elements show a large variability within each PSA and are not alone diagnostically useful. Comparison of the newly defined PSA with aerosols collected in remote locations over the North Atlantic shows that their sources are predominantly from western African regions (PSALAM and PSAWAC). Bodélé-derived dust has a limited impact on the bulk dust transported over the tropical North Atlantic, regardless of the season and altitude of dust transport. The low impact of the Bodélé Depression can be explained by a high deposition rate (wet and dry) of aerosols along its southwestward trajectory. A detailed analysis of dust collected over South America during winter will be essential to confirm this observation at a global scale. The present dataset can be efficiently used to track modern dust emissions as well as their changes at the scale of glacial/interglacial cycles or during the development of African Humid Periods as stored in sedimentary archives.

Composition and Cr- and Fe-speciation of dust generated during ferrochrome production in a DC arc furnace

A potential hazard associated with ferrochrome production is the unintentional generation of Cr(VI) in the off-gas dusts produced during smelting. Cr(VI) is a well-known environmental toxin and genotoxic carcinogen. Although Cr(VI) has been identified in baghouse dusts associated with submerged-arc furnaces, its occurrence in DC-arc-furnace dusts has not been previously investigated. In this study, we report the bulk composition and phase make-up, as well as the surface and bulk speciation of Cr and Fe of dusts generated during smelting of chromite ore under basic slag conditions in a pilot-scale DC arc smelter. Dusts are captured from both within the DC furnace as well as along the off-gas handling stream, after passing through the afterburner. The dusts primarily comprise feed material (chromite, flux, reductant), aerosolized slag, and glassy spherules, interpreted as off-gas condensates. Dusts collected from within the furnace, known as freeboard dusts, are dominated by feed materials, with elevated amounts of flux (lime) and lesser amounts of slag and spherules. In contrast, spherules dominate dusts collected along the off-gas handling stream by dust separators that capture the increasingly fine-grained fraction of dust, with the highest proportion of spherules occurring in baghouse dusts. Chromite is the primary host of Cr in all dust samples, whereas the spherules have low Cr contents. Cr(VI) was identified by X-ray photoelectron spectroscopy in the surfaces of dust collected from all parts of the smelter system considered, including from the furnace freeboard, despite the overall reducing conditions present therein. Cr(VI) concentrations are sufficiently high in dusts collected from the off-gas handling stream (post-afterburner, cyclone, and baghouse) to be detected in the bulk dust samples by X-ray absorption spectroscopy. The higher concentration of Cr(VI) in the finer-grained off-gas dusts, especially the baghouse dusts, is consistent with the increased abundance of spherules, the major Cr(VI)-hosting phase, in these samples. Fe is similarly more oxidized in dusts collected down the off-gas handling stream compared to dusts collected from within the furnace, which are dominated by Fe(II). Fe(III) hosted by FeOOH is predominate in dusts collected from all locations along the off-gas handling stream. These results demonstrate that there is sufficient oxygen ingress and sufficiently high temperatures in the closed DC furnace for Cr(VI) to be generated in the freeboard off-gas dusts. Cr(VI) is associated with the finest grained fraction of dusts, underlining the importance of ensuring the continual improvement of dust-capture systems, especially in terms of their ability to target increasingly finer fractions of dust. • Cr(VI) can form in a closed DC arc furnace. • Cr(VI) forms up to about one-third of the Cr species present on particle surfaces. • Fine-grained dusts captured by the baghouse host the highest proportion of Cr(VI). • Spherules are the major Cr(VI)-bearing phase in off-gas dust. • Chromite is the major source and host of Cr in smelter dusts.

Derivation of indoor dust screening concentrations for the protection of human health (DSCHH) for inorganic elements

Few guidelines, screening standards, or benchmarks exist for the assessment of wipe sampling results and bulk dust concentrations for indoor dust screening, and the existing guidelines are limited in their application or number of analytical parameters. To address this gap, guidelines – as indoor dust screening concentrations (DSCHH) – were derived for 33 inorganic elements, following guidance for risk assessment of indoor dust, and using toxicological reference values from Canada or the U.S. The guidelines were developed on a surface area basis (for the assessment of wipe samples) and for bulk dust. The derived bulk dust DSCHH’s were higher than most existing soil quality guidelines, suggesting that for all elements except bismuth, chromium (Cr), mercury, lead (Pb), nickel, and thallium, the soil quality guidelines are protective. Baseline values (background concentrations) obtained from a literature review were lower than most derived DSCHH ’s. The exceptions were antimony, Pb, and vanadium surface area baseline values that were higher than the toddler DSCHH in a residential scenario, and arsenic, Pb, and Cr bulk dust baseline concentrations that were higher than toddler DSCHH’s. If these elements are a concern in a risk assessment, the practitioner should be aware that baseline values may need to be examined closely, which may include measuring local baseline conditions.

Indoor Dust as a Matrix for Surveillance of COVID-19.

ABSTRACTOngoing disease surveillance is a critical tool to mitigate viral outbreaks, especially during a pandemic. Environmental monitoring has significant promise even following widespread vaccination among high-risk populations. The goal of this work is to demonstrate molecular severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) monitoring in bulk floor dust and related samples as a proof of concept of a noninvasive environmental surveillance methodology for coronavirus disease 2019 (COVID-19) and potentially other viral diseases. Surface swab, passive sampler, and bulk floor dust samples were collected from the rooms of individuals positive for COVID-19, and SARS-CoV-2 was measured with quantitative reverse transcription-PCR (RT-qPCR) and two digital PCR (dPCR) methods. Bulk dust samples had a geometric mean concentration of 163 copies/mg of dust and ranged from nondetects to 23,049 copies/mg of dust detected using droplet digital PCR (ddPCR). An average of 89% of bulk dust samples were positive for the virus by the detection methods compared to 55% of surface swabs and fewer on the passive sampler (19% carpet, 29% polystyrene). In bulk dust, SARS-CoV-2 was detected in 76%, 93%, and 97% of samples measured by qPCR, chip-based dPCR, and droplet dPCR, respectively. Detectable viral RNA in the bulk vacuum bags did not measurably decay over 4 weeks, despite the application of a disinfectant before room cleaning. Future monitoring efforts should further evaluate RNA persistence and heterogeneity in dust. This study did not measure virus infectivity in dust or potential transmission associated with dust. Overall, this work demonstrates that bulk floor dust is a potentially useful matrix for long-term monitoring of viral disease in high-risk populations and buildings.IMPORTANCE Environmental surveillance to assess pathogen presence within a community is proving to be a critical tool to protect public health, and it is especially relevant during the ongoing COVID-19 pandemic. Importantly, environmental surveillance tools also allow for the detection of asymptomatic disease carriers and for routine monitoring of a large number of people as has been shown for SARS-CoV-2 wastewater monitoring. However, additional monitoring techniques are needed to screen for outbreaks in high-risk settings such as congregate care facilities. Here, we demonstrate that SARS-CoV-2 can be detected in bulk floor dust collected from rooms housing infected individuals. This analysis suggests that dust may be a useful and efficient matrix for routine surveillance of viral disease.

Segregation of respirable dust for chemical and toxicological analyses

Respirable dust can pass beyond ciliated airways of the respiratory tract and influence adverse health effects. Health effects can be studied using samples generated from bulk dust segregation. Because previous segregation methods diverge from size-selection criteria of the international convention for respirable particles (ICRP), a method was developed to approximate the ICRP. The method was compared to an ideal sampler by measuring the sample collection bias. The comparison shows that the uncertainty due to the bias was 0.10 based on European Standard EN13205:2014 criteria, which indicates that the segregator effectively follows the ICRP. Respirable particle size distributions were confirmed by an aerodynamic particle sizer and by computer-controlled scanning electron microscopy. Consequently, a systematic way to generate respirable powders for health effects studies and chemical analyses was developed.

Characterization of Silica Exposure during Manufacturing of Artificial Stone Countertops.

Artificial stone is increasing in popularity in construction applications, including commercial and residential countertops. Eco-friendliness, durability, and resistance to staining, make artificial stone attractive to consumers. Health concerns have arisen during manufacturing of artificial stone due to increased incidence of silicosis after relatively short exposure. Three artificial stone samples (A, B, and C) and one natural granite sample were subjected to cutting and grinding in a controlled environment. Gravimetric analysis, X-Ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy were employed to determine crystalline silica concentrations and particle morphology of bulk and respirable particles. Silica content of bulk dust from artificial samples A and B was 91%, sample C was <10%, while granite was 31%. Silica percent in the respirable fraction for samples A and B was 53% and 54%, respectively, while sample C was <5% and granite was 8%. Number concentrations for samples A and B were mainly in the nano-fraction, indicating potential for translocation of silica particles to other organs outside of the lungs. Respirable dust concentrations inside the chamber were well above Occupational Safety and Health Administration standards for all materials, indicating that confined-space exposures require ventilation to lower risks of acute silicosis regardless of the nature of the stone.

Origin and evolution of the Galactic inventories of interstellar dust and its composition

ABSTRACTInterstellar dust is a significant component of matter in the galaxies. The dust owns its origin and reprocessing in a wide range of astrophysical environments. In order to understand the origin and evolution of the distinct types of interstellar dust grains, we have attempted a comprehensive correlated study of the thermodynamics condensation of dust grains in distinct stellar environments with the Galactic chemical evolution of the Milky Way Galaxy. The Galaxy is evolved in terms of elemental evolution resulting from stellar nucleosynthetic contributions of several generations of stars. Based on the elemental composition of the evolving Galaxy, the relative abundances of the major constituents of interstellar dust are assessed. The major aim is to redistribute the various condensable elements at any epoch during the evolution of the Galaxy into various grain constituents and understand their abundance evolution based on a mass-balance formalism. We also performed thermodynamical equilibrium condensation calculations to understand the stellar origin of various grain constituents that could carry the isotopic signatures of the various stellar nucleosynthetic sources. This is perhaps a novel attempt to estimate the bulk dust mass budget in the evolving Galaxy. The normalized mass of the Galactic dust is predicted to decrease with the increase in distance from the Galactic centre. It increases over time. The supernovae SNe Ia are predicted as the most prominent sources of Fe-dust mass, the supernova SN II+Ib/c produces oxides- and silicate-dust mass, and the AGB stars contribute to carbonaceous dust mass.

Engineering Design and Analysis of the CFETR Divertor Remote Maintenance System

A China Fusion Engineering Testing Reactor (CFETR) will be built to test and verify the feasibility of engineering and technology in practice for the future fusion reactor. Long pulse and steady-state operation will be demonstrated with duty cycle time more than 30%–50%. Because of the beta and gamma activation of the component bulk and surface dust (beryllium, carbon, and tungsten), special remote handling (RH) techniques will be required during machine maintenance periods. The divertor cassettes’ remote replacement is one of the key maintenance operations for the CFETR to meet the requirements of duty cycle time. RH maintenance strategies will have a significant impact on the layout of the machine and design of components. In this article, an overview of the CFETR divertor components’ remote maintenance strategy and the description of the maintenance process of the divertor cassettes were introduced. The engineering design features of the divertor RH systems (DHRSs) were described to meet the requirements such as high efficiency and reliability. Preliminary assessment of the divertor RH system is done in order to successfully and efficiently carry out RH maintenance tasks.

Threshold Behavior of Volume Dust Cluster Untwisting in a Magnetic Field

The action of a magnetic field on the behavior of a bulk dust cluster formed in the strata of a glowing discharge has been studied. The cluster that consists of seven chains of particles and is a hexagonal cell in the horizontal cross-section has been studied. It has been found that the rotation of a dust cluster arises in nonzero magnetic field unlike the dusty structure containing many particles in the horizontal cross-section. Moreover, it has been found that the threshold behavior of the occurrence of rotation in the cluster is affected by the discharge current and plasma-forming gas pressure. The enhancement of the ionization inside a dust cluster is suggested as an interpretation. The radial ion flux that moves in the longitudinal magnetic field from the dusty structure to the discharge tube wall additionally twists the structure with the negative projection of an angular velocity on the magnetic induction vector.

Analysis of coal dust source strength in open storage yard of coal port area of Huanghua Port

Starting in 2017, the Ministry of Ecology and Environment began to implement a pollution permit system nationwide, in which environmental protection authorities issue permits to enterprises and institutions and supervise them in accordance with the permits. The accounting results of pollutant emissions are an important basis for the issuance of emission permits. At present, the air pollutant accounting methods for emissions from fixed emission facilities are mature and reliable, while there is no mature calculation method for coal dust emission in open storage yard. In this paper, based on the data of area, volume and coal nature of open storage yard in the coal port area of Huanghua Port, the author calculated the strong dust source under different wind speed by using the calculation formula of bulk dust amount in large ports, so as to provide technical support for the forecast study of atmospheric environmental impact in the coal port area of Huanghua Port and the calculation of total atmospheric particulate emission by the environmental management department.

Fingerprints of the Protosolar Cloud Collapse in the Solar System. I. Distribution of Presolar Short-lived 26Al

Abstract The short-lived radionuclide 26Al is widely used to determine the relative ages of chondrite components and timescales of physical and thermal events that attended the formation of the solar system. However, an important assumption for using 26Al as a chronometer is its homogeneous distribution in the disk. Yet, the oldest components in chondrites, the Ca–Al-rich inclusions (CAIs), which are usually considered as time anchors for this chronometer, show evidence of 26Al/27Al variations independent of radioactive decay. Since their formation epoch may have been contemporaneous with the collapse of the parent cloud that formed the disk, this suggests that 26Al was heterogeneously distributed in the cloud. We model the collapse of such a heterogeneous cloud, using two different 26Al distributions (monotonic and nonmonotonic), and follow its redistribution in the first condensates and bulk dust that populate the forming disk. We find that CAIs inherit the 26Al/27Al ratio of the matter infalling at the time of their formation, so that variations of 26Al/27Al among primordial CAIs can be accounted for, independently of radioactive decay. The prevalence of a canonical ratio among them and its necessity for the differentiation of the first planetesimals suggest a (monotonic) scenario where 26Al sharply rose relatively close to the center of the protosolar cloud and essentially remained at a high level outward (rather than decreased since). As the 26Al abundance would be relatively homogeneous after cessation of infall, this would warrant the use of the Al–Mg chronometer from the formation of “regular” CAIs onward, to chondrules and chondrite accretion.

Silicosis in rhinestone-manufacturing workers in South China.

Silicosis is caused by long-term exposure to silica dust. Crystal rhinestone workers can be exposed to high levels of silica dust and are at risk of silicosis. To explore silicosis cases, silica dust exposure and control measures in a rhinestone factory in South China. We extracted and analysed data on new silicosis cases reported to China's occupational disease and occupational health information monitoring system between 2006 and 2012 from a rhinestone factory in South China. We measured the quartz content of bulk dust, static total and respirable dust samples. Ninety-eight silicosis cases were reported between 2006 and 2012. The mean duration of silica dust exposure was 9.2 years (range 3-16). Drilling and polishing workers accounted for 96 (98%) of cases. We collected 1479 static samples including 690 total dust and 789 respirable dust samples. Mean dust levels for drilling were 1.01 mg/m3 (range 0.20-3.80) for total dust and 0.51 mg/m3 (range 0.04-1.70) for respirable dust. Mean dust levels for polishing were 0.59 mg/m3 (range 0.20-2.10) for total dust and 0.28 mg/m3 (range 0.08-0.71) for respirable dust. Over a third [289/789 (37%)] of total dust samples and 129/690 (19%) respirable dust samples exceeded the national permissible exposure limit. Exposure to silica dust, ineffective dust control measures and inefficient health surveillance may have contributed to the incidence of silicosis in the factory we studied. Identification of silica dust exposure and effective dust control measures would reduce the risk of silicosis in rhinestone workers.

From hatch to egg grading: monitoring of Salmonella shedding in free-range egg production systems

Human cases of salmonellosis are frequently liked with the consumption of contaminated table eggs. Recently, there has been an increase in consumer demand for cage-free eggs precipitating the need for a greater understanding of Salmonella dynamics in free-range production systems. A longitudinal study was conducted to determine the points in production where birds are most likely to be exposed to Salmonella and where the risk of egg contamination is highest. In this study, two free-range flocks were sampled from hatch to the end of production. At hatch, all chicks were Salmonella negative and remained negative during rearing. During production, the proportion of positive samples was low on both farms. Salmonella positive samples were detected intermittently for Flock A. Dust, nest box, and egg belt swabs had the highest proportion of positive samples and highest overall loads of Salmonella. The egg grading floor was swabbed at different points following the processing of eggs from Flock A. Only the suction cups that handle eggs prior to egg washing tested positive for Salmonella. Swabs collected from machinery handling eggs after washing were Salmonella negative. During production, positive samples from Flock B were observed at only single time point. Dust has been implicated as a source of Salmonella that can lead to flock to flock contamination. Bulk dust samples were collected and tested for Salmonella. The proportion of positive dust samples was low and is likely due to physical parameters which are not likely to support the survival of Salmonella in the environment.

Seasonal evaluation of chemical compositions of dust fall at motor parks in a Nigerian university campus

Bulk dust fall was collected from three different motor parks in University of Ilorin using an open-bucket sampler for 5 months of dry and wet season periods. The collected bulk dust fall was separated by filtration to obtain a filtrate and a residue. The filtrate pH and conductivity were determined as well as concentrations of $${\text{SO}}_{4}^{2 - }$$ , $${\text{NO}}_{3}^{ - }$$ and $${\text{NH}}_{4}^{ + }$$ using a Beckman UV/visible spectrometer, Cl− titrimetrically with silver nitrate while Na+ and K+ ions by flame photometer (FP 640). Atomic absorption spectrometry (Buck Scientific 210/211VGP) was used to determine Mg2+ and Ca2+ in the filtrate and heavy metals (Mn2+, Cd2+, Cu2+, Fe3+ and Zn2+) in the residue. The pH for both season periods was slightly less than 7 at all the sites except for PK2 in dry season period, while EC was higher in the dry season than in the wet season period at all sites. There were high concentrations of anions during the wet season period, but cations were more during the dry season. The abundance of parameters generally followed the order of Cl− > $${\text{NO}}_{3}^{ - }$$ > $${\text{SO}}_{4}^{2 - }$$ for anions, Na+ > $${\text{NH}}_{4}^{ + }$$ > K+ > Ca2+ > Mg2+ for cations in filtrate, while heavy metals generally followed Fe3+ > Zn2+ > Mn2+ > Cu2+ > Cd2+ in residue. The metal pollution index of residue for heavy metals showed that all the sites were polluted with heavy metals in both seasons. A very wide seasonal variation was generally observed which was due to metrological conditions and vehicular density.

The Composition of Emissions from Sawing Corian®, a Solid Surface Composite Material.

We conducted detailed analyses of the composition of emissions from sawing Corian®, a solid surface composite material, in a laboratory testing system. The analyses included the aluminum content of size-selective dust samples, semivolatile organic compounds (SVOCs) in respirable dust samples, and volatile organic compounds (VOCs). The normalized respirable dust generation rate found using a Micro-Orifice Uniform Deposit Impactor was 5.9 milligrams per gram (mg g-1) suggesting that 0.59% of the mass removed from sawing Corian® becomes respirable dust. The alumina trihydrate content of the dust was consistently above 85% in most parts of the respirable size range, verifying an earlier finding that it is the dominant composition of the airborne particles of all sizes, including ultrafine particles. VOC analyses revealed that methyl methacrylate (MMA) was the most abundant compound, with a generation rate of 6.9 mg g-1 (0.69% of the mass removed from sawing Corian® became MMA vapor). The SVOC analysis only found a small amount of MMA (0.55%) in the bulk dust.

Distributions of organophosphate flame retardants (OPFRs) in three dust size fractions from homes and building material markets

The distributions of organophosphate flame retardants (OPFRs) in various size fractions of indoor dust samples from homes (H; n = 18) and building material markets (B; n = 7) in the Rhine/Main region of Germany were investigated. Three particle size fractions (F1: 150–200 μm, F2: 63–150 μm, and F3: <63 μm) and bulk dust (BD) subsamples (<200 μm) of each sample were analyzed for 10 OPFRs. On average, the total OPFR concentrations (∑10OPFR) in bulk dust and all three size fractions from building material markets were 133, 153, 196, and 88.0 μg/g in subsamples B-BD, B-F1, B-F2, and B-F3. These concentrations were at least five times higher than those in bulk dust and all three size fractions from homes, with values of 19.3, 17.2, 19.5, and 18.7 μg/g for subsamples H-BD, H-F1, H-F2, and H-F3, respectively. Tris(2-chloroisopropyl)phosphate (TCIPP) was the dominant congener in dust from building material markets, contributing over 91% to the ∑10OPFR of B-BD and all particle size fractions. Meanwhile, both tris(2-butoxyethyl)phosphate (TBOEP) and TCIPP were abundant in dust from homes, respectively contributing 28%–41% and 31%–43% to the ∑10OPFR of H-BD and all particle size fractions. Most of the OPFR concentrations showed no consistent trend with particle size. However, TCIPP was more likely to be enriched in F2. Microscopic examination indicated that TCIPP in indoor dust mainly originated from abraded fragments of commercial products. In contrast, TBOEP accumulated in F3, related to direct transfer of floor-care products to fine dust particles. The concentrations of OPFRs were not significantly correlated with total organic carbon contents in any particle size fraction. However, evaluation of their mass contributions showed that more than 85% of OPFRs accumulated in particles smaller than 150 μm, indicating that this particle size fraction is most suitable for monitoring of OPFRs.

New comprehensive approach for airborne asbestos characterisation and monitoring.

High concentrations of airborne asbestos in the ambient air are still a serious problem of air quality in numerous localities around the world. Since 2002, elevated concentrations of asbestos minerals of unknown origin have been detected in the ambient air of Pilsen, Czech Republic. To determine the asbestos fibre sources in this urban air, a systematic study was conducted. First, 14 bulk dust samples were collected in Pilsen at nine localities, and 6 bulk samples of construction aggregates for gravel production were collected in a quarry in the Pilsen-Litice district. The quarry is the largest quarry in the Pilsen region and the closest quarry to the built-up urban area. X-ray diffraction of the asbestos minerals revealed that monoclinic amphibole (MA, namely actinolite based on subsequent SEM-EDX analysis) in the bulk samples accounted for < 1-33% of the mass and that the highest values were found in the bulk dust samples from the railway platform of the Pilsen main railway station. Simultaneously, 24-h samples of airborne particulate matter (PM) at three localities in Pilsen were collected. Actinolite was identified in 40% of the PM samples. The relationship between the meteorology and presence of actinolite in the 24 PM10 samples was not proven, probably due to the long sampling integration time. Therefore, highly time-and-size-resolved PM sampling was performed. Second, sampling of size-segregated aerosols and measurements of the wind speed (WS), wind direction (WD), precipitation (P) and hourly PM10, PM2.5 and PM1 were conducted in a suburban locality near the quarry in two monthly highly time-resolved periods (30, 60, 120min). Three/eight PM size fractions were sampled by a Davis Rotating-drum Uniform-size-cut Monitor (3/8DRUM) and analysed for the presences of asbestos fibres by scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX). Asbestos fibre detection in highly time-resolved PM samples and current WD and WS determination allows the apportionment directionality of asbestos fibre sources. The number of critical actinolite asbestos fibres (length ≥ 5μm and width < 3μm, 3:1) increased with the PM1-10/PM10 and PM2.5-10/PM10 ratios, WS > 2ms-1 and precipitation < 1mm. Additionally, the number of critical actinolite asbestos fibres was not related to a specific WD. Therefore, we conclude that the sources of airborne critical actinolite asbestos fibres in Pilsen's urban area are omnipresent. Frequent use of construction aggregates and gravel from the metamorphic spilite quarries in the Pilsen region and in many localities around the urban area is a plausible explanation for the omnipresence of the critical actinolite asbestos fibres concentration in Pilsen's ambient air. Mitigation strategies to reduce the concentrations of critical actinolite asbestos fibres must be developed. Continuous monitoring and performing SEM-EDX analysis of highly time-and-size-resolved PM samples, correlated with fast changing WS and WD, seems to be a strong tool for efficiently controlling the mitigation strategies of critical actinolite asbestos fibres.

Exceedance of environmental exposure limits to crystalline silica in communities surrounding gold mine tailings storage facilities in South Africa

BackgroundUnlike occupational silica exposures, the association between non-occupational silica exposures and adverse health effects is not well researched, despite its occurrence in communities close to dust-generating sources such as tailings storage facilities (TSFs). Recent studies have shown that communities surrounding TSFs in South Africa often complain about the onset of dust-related health effects. Even though international interim non-occupational crystalline silica limits have been established, South Africa is yet to enforce its own limits for residential areas close to TSF sites. ObjectiveThe objective of the study was to assess the need to enforce non-occupational crystalline silica limits for South Africa. MethodsThe methods involved (1) Quantifying the silica polymorph content in bulk dust collected from TSFs in South Africa; (2) Assessing the possibility of the dust to reach surrounding communities through ambient and personal filter sampling and; (3) Conducting risk characterisation for both cancer and non-cancer endpoints. ResultsAll bulk dust samples consisted mostly of crystalline silica (73.14–87.09%). Large percentages of nanoparticles were identified in all bulk samples (66.8–70.7%) indicating the possibility of the dust to lodge deep within the lungs. The crystalline silica levels obtained from ambient PM10 sampling and personal PM4 sampling all exceeded the international crystalline silica interim limits and reached maximum levels of 90 and 50.9μg·m−3, respectively. For three TSFs, sampling sites close to the TSFs showed higher PM4 silica levels compared to sites further from TSFs. Risk characterisation revealed the possibility of cancer and non-cancer health effects when chronically exposed to silica levels recorded during the study. ConclusionThe results indicate unacceptable crystalline silica exposures in surrounding communities and the need for enforcement of an ambient silica limit for South Africa.