Stine Eriksen
Hammer
a,
Torunn
Ervik
*a,
Dag G.
Ellingsen
a,
Yngvar
Thomassen
a,
Stephan
Weinbruch
ab,
Nathalie
Benker
b and
Balazs
Berlinger‡
a
aNational Institute of Occupational Health, Gydas vei 8, N-0363 Oslo, Norway. E-mail: torunn.ervik@stami.no
bInstitute of Applied Geosciences, Technical University of Darmstadt, Schnittspahnstrasse 9, D-64287 Darmstadt, Germany
First published on 3rd September 2021
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 (dae). Thermally generated condensation particles dominated the dae 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 dae up to 2.5 μm, and most pronounced in the dae size range between 0.25 and 1.0 μm. Also, a significantly higher bioaccessibility of Mn was found for PM larger than dae of 0.5 μm collected among crane operators compared to tappers in the HC–FeMn smelter.
Environmental significanceAdverse health effects on the central nervous system caused by manganese exposure depend on the exposure dose, chemical composition and bioavailability of manganese. To investigate this in an occupational setting, the bioaccessibility of manganese in particulate matter has been investigated in terms of dissolution in Gamble's solution. The particulate matter was collected and size fractionated in the breathing zone of workers in manganese smelters. Particle size is important for deposition in the respiratory tract. In addition, individual particles collected using stationary equipment were characterised. Knowledge of physical and chemical properties of particles combined with information on the bioaccessibility is fundamental to understanding exposure–response associations. |
Ferro- and silicomanganese (FeMn and SiMn) are essential additives in steelmaking used to provide specific properties of steel.14 High carbon (HC)–FeMn and SiMn are mainly produced in electric submerged arc furnaces with coke to facilitate the reduction of Mn oxide ores. Other raw materials include fluxes such as dolomite, calcite and quartz in SiMn production and lime in FeMn production. In addition, Mn-rich slag from FeMn production is recycled as feedstock in SiMn production.15 Thermally generated fumes are emitted during tapping, refining and casting of the alloys.16
Previous studies on HC–FeMn and SiMn production showed that the abundance of different particle types strongly depends on the size fraction. HC–FeMn tapping fume particles larger than 0.3 μm were dominated by slag particles, and generally particles were composed of different mineral phases.17 A large number of spherical potassium (K)-rich particles with sizes < 1–2 μm as well as irregular fragments of Mn oxides or mixed oxides > 1 μm were observed in HC–FeMn tapping fume.18 The submicron fraction is dominated by agglomerated Mn oxides, mainly MnO. Similar fume particles were reported by Kero et al. (2015),20 where MnO, MnOx-FeOy, and Mn3O4 were identified depending on the temperature and location during formation, e.g. crucible and filter. According to Ervik et al.19 the predominant phase in the submicron fraction was Mn3O4. In SiMn production, fume from the casting process is composed of slag particles and slag mixed with C-rich particles dominating the size fraction above 0.3 μm.17,18 The submicron fraction was found to be dominated by agglomerated Mn–Si phases.18 Kero et al.20 investigated the size distribution and found that agglomerated spheres dominate the aerodynamic diameter (dae) size range from 0.09 to 0.94 μm. The majority of the SiMn fume particles consisted of Mn, Si and O. Furthermore, SiMn fume thermally generated in a laboratory scale experiment was studied by Ma et al.21 The particle types generated depended on the melt temperature and on the collection position inside their experimental furnace setup. Also, a mixture of Mn– and Mn–Si oxides in both crystalline and amorphous states was observed by X-ray diffraction.
Bioaccessibility is the fraction of a compound released from its matrix becoming available for absorption in the body.22 Bioaccessibility of Mn in the respirable aerosol fraction is of interest since it is a measure of the amount of Mn available for absorption into the systemic circulation via the lungs. In laboratory studies, the bioaccessibility depends on the choice of simulated lung fluid.23 In such studies, different simulated lung fluids have been used, with Gamble solution (pH 7.4) being the most used simulated interstitial lung fluid.24 Gamble solution25 consists of an electrolyte composition simulating the human interstitial fluid,26 but lacks phospholipids which are the most abundant components of the alveolar lining fluid.27
The bioaccessibility of Mn in airborne PM from HC–FeMn or SiMn production has to our knowledge been sparsely investigated. In a study of ambient air in a heavily industrialised area, the bioaccessibility of metals in PM collected near an FeMn smelter and steel making plant was moderate (20–40%) for Mn.28 Bioaccessibility of Mn at work places was studied for welding fume29–31 and in PM from other hot processes.32 It was shown that the bioaccessibility of Mn was generally low (<20%) to moderate, depending on the origin of exposure and the simulated lung fluid used. Even when the bioaccessible fraction of Mn was low in welding fume, a correlation with the Mn concentration in the urine of the welders was found.30
Particle mass size distributions of workplace aerosols in Mn alloy smelters were investigated by Berlinger et al.33 using personal respirable cyclones and a 5-stage cascade impactor. As a follow up study, the chemical composition and bioaccessibility of Mn in terms of dissolution in Gamble solution are investigated in the present paper. Special emphasis is placed on the apparent dissolution of Mn as a function of the production process, particle size distribution and work task. Particles collected at different workplaces in the two smelters were studied in detail by scanning and transmission electron microscopy (SEM and TEM) to better understand the dissolution of Mn in size fractionated PM using Gamble solution.
In a second sampling campaign conducted only in Smelter 1, stationary air samples were collected for 10 minutes with a 13-stage nanoMOUDI cascade impactor (MSP Corporation, Shoreview, Minnesota, USA) during tapping of both HC–FeMn and SiMn furnaces. The samples were collected around eight meters from the tapping hole. The 50% dae cut-off for each stage was: 10, 5.6, 3.2, 1.8, 1.0, 0.56, 0.32, 0.18, 0.1, 0.056, 0.032, 0.018 and 0.010 μm. Particles with dae < 0.010 μm are collected by filtration on an end-filter. Cu TEM grids with holey carbon films (EMresolution, Sheffield, UK) were affixed to the surface of polyvinyl chloride membrane filters used as substrates in all impactor stages, except for the end-filter. TEM grids were not attached to the end-filter because the predominant mass on this stage is bounce off particles from the previous impaction stages.34 In addition, a TSI Scanning Mobility Particle Sizer (SMPS) instrument (model 3034, TSI Inc., Shoreview, MN, USA) with flow rate 1 L min−1 was running for six hours for each furnace in Smelter 1 during the second sampling campaign. The SMPS was placed next to nanoMOUDI, around eight metres from the tapping hole.
Reproducibility of the leaching procedure was assessed by use of SiMn and HC–FeMn in-house quality control material. This material is dust collected from the furnace emission electrostatic filters and sieved through 45 μm mesh to remove coarse particles. The total Mn concentrations obtained with the current method were comparable to results obtained by a previously validated method.38 The precision of the method is defined as the relative standard deviation of n = 14 SiMn and n = 16 FeMn in-house samples. The precision of Mn was on average 22% for SiMn (∼18% Mndissolved) and 13% for HC–FeMn (∼27% Mndissolved), respectively. All measured Mn concentrations were above the limit of detection. The limit of detection was calculated as three times the standard deviation of ten blank samples, respectively, 40 ng per filter for acid digested and 7.5 ng per filter for Gamble dissolved.
Extraction time is important in PM dissolution testing.24 Berlinger et al.29 studied the solubility of Mn and other elements using Gamble and Hatch solutions in different welding fumes with extraction times between 30 minutes and 24 hours. Further dissolution ceased after 8 hours. Caboche et al.40 suggested that 24 hours is sufficient for dissolution testing of Mn based on ambient air PM of different origins. Based on these two studies, a 24 hour extraction time was chosen in this study.
The solid-to-liquid ratio (S/L ratio) should not be too low in order to avoid unnecessary agglomeration of the PM which may result in a smaller surface area.39–41 Pelfrêne et al.41 concluded that the S/L ratio influences the PM dissolution when applying Gamble solution. We used a somewhat higher ratio in our study (average: 0.0003, min: 0.00005 max: 0.005 g/10 mL Gamble solution) than what has been found to give the highest bioaccessibility.39 As the ratio was higher, pronounced agglomeration during the leaching procedure was not expected.
The air samples were collected according to size onto filters. This may lead to increased uncertainty of the estimates of dissolution as the particles are packed onto each other on the filter, and the surface area available for the dissolution is hence reduced. To minimize this effect, shaking of the samples is applied in dissolution testing,24,39 but would most probably not release all particles from the filters as they are incorporated deep into the filter material or closely packed on the filter surface. However, in our study this effect will most probably not result in significant relative differences in Mndissolved between SiMn and HC–FeMn production (Smelter 1) or tapper and crane operators (Smelter 2), as we discuss the same size fractions separately. Also, the respirable samples (Table 3) are compared between plant and occupational groups separately from the cascade impactor samples (Fig. 4). The in-house standards of SiMn and HC–FeMn were directly weighed onto the filters and the PM is not packed as the air samples. These samples may therefore have a larger surface area in contact with the Gamble solution. Even in this case, a similar difference in the percentage of Mndissolved as the collected air samples was observed, 29% for SiMn and 5% for HC–FeMn, respectively.
All statistical calculations were performed in R studio version 4.0.4.,42 and all figures were produced with the package ‘ggplot2’ version 3.3.2.43 Wilcoxon rank sum test was calculated with the package ‘ggpubr’ version 0.4.0.999.44
Process | Particle types |
---|---|
a Categories of particle abundance: >50% = dominating; >10% = often; <10% = some. | |
Tapping SiMn furnace | Dominated by condensation particles rich in Mn–Si–O (some particles also have minor amounts of Mg, K and Na) and mixed particles of Mn–O rich crystalline phases surrounded by a Si–O rich amorphous phase. The particles occur as both, individual particles and agglomerates/aggregates. The different particle types were often found in the same agglomerate/aggregate |
Tapping HC–FeMn furnace | Dominated by spherical condensation particles of crystalline Mn oxides. These occur as single particles or as aggregates/agglomerates, with primary particle sizes between a few nm and 500 nm. All particles were coated with a few nm thick Si–O-rich surface layer (most likely SiO2), which holds the primary particles as aggregates |
Fig. 2 TEM image of a particle collected from the SiMn tapping fume in Smelter 1 (left) and STEM-EDX elemental distribution images for Mn, O, Si (right). |
The HC–FeMn tapping fume was dominated by spherical primary condensation particles of Mn oxides, which occur as aggregates/agglomerates with sizes up to several μm, or as single particles with a size range from a few nm up to 500 nm. A selection of about 100 primary Mn oxide particles was investigated by SEM-EBSD. Most particles were identified as Mn3O4 (hausmannite) and some particles were identified as MnO (manganosite). The hausmannite phase was confirmed by applying TEM-SAED on a few selected particles. Typical particles collected during tapping of the HC–FeMn furnace are shown in Fig. 3. An amorphous Si–O rich surface layer (presumably SiO2) seems to hold the primary particles together as aggregates (Fig. 3 lower left and lower right). A STEM-EDX elemental line scan for Mn, Si and O of such a particle is shown in Fig. S3.† Please note that the term aggregate will be used for such particles, as the primary particles are held together by chemical forces. When discussing the findings in general or the particles collected from SiMn furnace area (i.e., without a surface layer covering the primary particles), the term agglomerate/aggregate is used. Agglomerates may consist of primary particles and/or aggregates, and it is not always possible to discriminate between agglomerates and aggregates.
Stages (dae cut size) | Particle type |
---|---|
a d ae = aerodynamic diameter. Categories of particle abundance were: dominating > 50%, often > 10%, some < 10%, rare < 2%. | |
SiMn | |
1–4 (10.0–1.8 μm) | Dominating: irregular mixed slag particles and Fe and Mn oxides |
Some: slag particles mixed with coke | |
5–8 (1.0–0.18 μm) | Dominating: condensation particles rich in Si and Mn oxides (larger condensation particles have minor amounts of Mg), which may co-exist with angular Mn-rich phases identified as hausmannite (Mn3O4) and manganosite (MnO) enclosed in a Si–O rich matrix |
Often: slag particles mixed with oxides of Mn and Fe in stages 5 and 6 | |
9–13 (0.10–0.010 μm) | Dominating: carbonaceous particles (most likely soot) |
Often: volatile K and/or S rich particles | |
Some: single particles or small aggregates of particles rich in Si and Mn oxides in stage 9 and 10 | |
Rare: single particles or small aggregates of Mn–Si oxides in stages 11, 12 and 13 | |
HC–FeMn | |
1–4 (10.0–1.8 μm) | Dominating: spherical particles with high content of K, Na, chlorine (Cl) and O often with high zinc (Zn) and Mn contents, and irregular slag particles with high MnO content |
Often: large agglomerates/aggregates of Mn oxides in stage 4 | |
Some: large agglomerates/aggregates of Mn oxides stage 1–3 | |
Some: alloy fragments of Mn, Si and Fe | |
5–8 (1.0–0.18 μm) | Dominating: condensation particles of Mn oxides occurring as aggregates/agglomerates consisting primarily of Mn3O4 and MnO. The MnO particles show a Si–O-rich surface layer of a few nm thickness |
Often: carbonaceous particles (most likely soot) | |
9–13 (0.10–0.010 μm) | Dominating: carbonaceous particles (most likely soot) |
Some: single particles or small aggregates of Mn oxides were found in stage 8 and 9 | |
Rare: single particles or small aggregates of Mn oxides in stage 10–13 |
In the furnace area of SiMn production, the first four stages (dae cut size: 10.0–1.8 μm) were dominated by irregular mixed slag particles, Mn and Fe oxides and coke particles. The slag particles were rich in Si, calcium (Ca), aluminium (Al) and O, with minor amounts of Mg and Mn. The slag particles in the SiMn furnace area had much lower Mn contents than slag particles in the HC–FeMn furnace area. Most particles are inhomogeneous and consist of several phases. An example of a typical particle is shown in the ESI (Fig. S4†).
The next four impactor stages (dae cut size: 1.0–0.18 μm) are dominated by condensation particles, similar to the particles from the tapping fume (chapter 3.1.1).
The smallest particles (stage 9–13; dae cut size 0.10–0.010 μm) were dominated by carbonaceous particles. In addition, residues of volatile K and S rich particles were observed. The exact composition of these particles was difficult to determine because these particles were volatile under electron bombardment. Some small agglomerates and single particles of Mn–Si oxides were also observed in stage 9 and 10. Mn containing particles were rare in the last four stages (dae cut size: 0.056–0.010 μm).
In the furnace area of HC–FeMn production, the first four stages (dae cut size: 10.0–1.8 μm) were dominated by spherical shaped mixed particles with a high content of K, Na, Cl (often also Zn and Mn) and minor amounts of S and phosphorus (P), as well as irregular shaped particles with a high Mn content. The latter particles often had considerable amounts of Si, Ca and minor amounts of Fe, Al and Mg. The slag in HC–FeMn production is MnO–SiO2–CaO based. An example of a typical particle encountered can be found in the ESI (Fig. S5 and S6†). Some alloy fragments rich in Mn and Si (minor Fe contents) were observed. Large agglomerates/aggregates of Mn oxides were often found in stage 4 (dae cut size 5.6 μm).
The next three impactor stages (dae cut size: 1.0–0.32 μm) were dominated by agglomerates/aggregates of spherical Mn oxides. According to TEM-SAED and SEM-EBSD, these particles primarily consist of hausmannite (Mn3O4) and manganosite (MnO). The MnO particles were observed with a few nm thick Si–O rich surface layer (Fig. 3).
In stage 8 (dae cut size: 0.18 μm) and below, carbonaceous particles dominate and only some Mn-rich particles were found. Below stage 9 (dae cut size: 0.10 μm), Mn-rich particles were rare. In stages 12 and 13 only a few particles were observed (<500).
SiMn | HC–FeMn | |||||
---|---|---|---|---|---|---|
Location | Smelter 1 | Smelter 1 | Smelter 2 | |||
Work task | Crane operators n = 5 | Tappers n = 5 | Crane operators n = 5 | Tappers n = 4 | Crane operators n = 8 | Tappers n = 10 |
Minimum | 7.2 (15) | 6.8 (12) | 17.0 (6) | 21.4 (8) | 12.2 (4) | 26.0 (2) |
Lower quartile | 11.3 (20) | 21.5 (17) | 31.7 (7) | 46.3 (10) | 15.6 (7) | 35.0 (3) |
Median | 14.6 (23) | 23.5 (20) | 39.5 (11) | 55.0 (12) | 24.5 (10) | 40.6 (4) |
Upper quartile | 14.8 (25) | 26.9 (21) | 43.2 (12) | 56.3 (17) | 29.7 (14) | 53.8 (6) |
Maximum | 17.0 (27) | 65.0 (44) | 43.5 (18) | 59.5 (30) | 46.9 (18) | 115.0 (7) |
The median percentage of Mndissolved among SiMn furnace workers is somewhat higher than that among HC–FeMn furnace workers (Table 3). The Mndissolved appears to be independent of the work task in Smelter 1. In contrast, the Mndissolved is significantly higher (p = 0.008) for crane operators compared to tappers in HC–FeMn production of Smelter 2.
The percentage of Mndissolved in air samples collected with the Sioutas cascade impactor was determined as a function of particle size among tappers and crane operators in the SiMn and HC–FeMn production (Fig. 4). In air samples collected from HC–FeMn workers in Smelter 1, the percentage of Mndissolved is independent of dae particle size except for a small increase for particles < 0.25 μm. In contrast, in air samples from SiMn furnace workers, Mndissolved increases with decreasing particle size (Fig. 4, Smelter 1). The percentage of Mndissolved is significantly higher for SiMn than in HC–FeMn workers for particle dae sizes up to 2.5 μm. The Mn air concentration in PM collected with the Sioutas cascade impactor is given in the ESI (Fig. S1†).
In the air samples from the HC–FeMn workers in Smelter 2 (Fig. 4, Smelter 2), the percentage of Mndissolved is similar in all size fractions for both crane operators and tappers. However, the percentage of Mndissolved is considerably higher (by a factor of 2–5) with a larger variation within the size fractionated samples among crane operators compared to tappers. In general, the percentage of Mndissolved is low for workers in Smelter 2, and lowest for tappers (Table 3). Tappers have slightly higher air concentrations of Mn in dae size fractions below 2.5 μm compared to crane operators (Fig. S1†).
In general, the percentage of Mndissolved was low to moderate (<30%) in both type of smelters. A significantly higher percentage of Mndissolved was observed in the SiMn furnace area compared to the HC–FeMn furnace area. In the size fractionated samples, this difference was significant for particles between <0.25 and 2.5 μm.
Particles collected during tapping of HC–FeMn in the dae size range 0.18–1 μm were dominated by crystalline Mn oxide particles (MnO and Mn3O4). This is in accordance with the results of Gjønnes et al.,18 except that they additionally observed MnO fibers during tapping of HC–FeMn. Furthermore, Ervik et al.19 analysed particles by SEM-EBSD and identified hausmannite (Mn3O4) as the dominating Mn oxide. Agglomerated spheres of Mn oxides dominated the dae size range from 0.09 to 0.94 μm in particles studied by Kero, Slizovskiy,45 which is in good agreement with the results of our study (Table 2). Our SEM and TEM observations indicate that the primary particles collected in HC–FeMn tapping fume are held together by an amorphous Si–O rich surface layer. The presence of such surface layers may have implications for the behaviour and toxicity of the particles, e.g. such as a higher resistance of breakdown or collapse of the aggregate/agglomerate in the lung.46 Additionally, micrometre sized particles are reported to be phagocytized more easily than nanometre sized particles.47,48
In our study, a complex mix of condensation particles was found in the SiMn fume (e.g. mixture of Mn3O4 and Si–O, as well as amorphous and crystalline Si–Mn–O rich particles). Ma et al.21 observed similar particles in SiMn fume from an experimental setup and identified Mn2SiO4 as well as Mn3O4 in the fume at melting temperatures of 1500–1700 °C. In accordance with their findings, we also observed angular Mn3O4 phases, often mixed with an amorphous Si–O phase. The molten metal will react with oxygen in the air and the observation of various MnSi phases in Gjønnes et al.18 (in, e.g., Mn3Si, Mn6Si and Mn5Si2) from SiMn casting is therefore surprising. Some particles collected during tapping of the SiMn furnace consisted of nanometre sized Mn rich phases enclosed in a Si–O rich matrix (Fig. 1 and 2). A silica precursor has been used in previous investigations as an additive in shielding gas in welding. The resulting amorphous silica formed a coating that encapsulated the welding fume particles49 leading to formation of larger particles that may change the deposition efficiency in the lungs. However, amorphous silica particles have earlier shown to have a low retention in rat lungs explained by a high solubility.50 Considering this in our work, a high solubility of the Si–O rich layer may expose the Mn rich phases.
Carbonaceous particles dominate the dae size fraction below 0.18 μm, both in HC–FeMn and SiMn furnace area, with some single particles and small agglomerates of Mn oxides and Mn–Si oxides. The fact that few nanometre sized Mn containing particles were observed, and instead seem to be bound in aggregates/agglomerates, is an important finding. This is because a change in particle size affects the deposition fate upon inhalation. In addition, translocation of particles to other organs is only relevant for the smallest particles. It should also be noted that even though few particles were observed in the last two stages of the cascade impactor, it is likely that particles of this size exist in large numbers as is shown in the particle size distribution (Fig. S2†) and observed in this industry previously.20,33 Residues of secondary organic particles have been found from combustion in high temperature industrial processes, as was found, for example, in an Al plant.51 Such small secondary particles evaporate under electron bombardment in EM. Secondary organic particles might also exist in the workroom air of Mn smelters. In addition, small soot particles below dae of 30 nm are not easily detected in SEM.
The percentage of Mndissolved was higher in PM collected among SiMn furnace workers compared to HC–FeMn furnace workers. The largest difference in the percentage of Mndissolved was observed for PM with dae between 0.25 and 1.0 μm. This size range is dominated by agglomerates and agglomerates/aggregates of primary particles. Gjønnes et al.18 suggested a higher health risk for workers exposed to Mn in HC–FeMn compared to SiMn production. Their conclusion was based on the assumption that Mn oxides are more soluble than SiMn, as was shown by Thomassen et al.52 We observed a surface layer of amorphous Si–O on MnO-containing particles in the HC–FeMn furnace area holding the primary particles together into agglomerates/aggregates. Such an amorphous layer was not observed for particles in the SiMn fume. Instead, Mn rich crystalline phases were encapsulated in a Si rich amorphous matrix (Fig. 3). Amorphous and crystalline Si–Mn–O rich particles without a surface layer or an additional matrix were also observed. Amorphous SiO2 has been shown to dissolve substantially in Gamble solution.53 The higher percentage of Mndissolved in SiMn fume PM may, thus, be a result of the amorphous Si–O matrix dissolving in Gamble solution and releasing small Mn rich phases.
The air concentration of Mn [μg m−3] in PM was higher in the breathing zone of tappers compared to that of the crane operators (Table 3). This result was not unexpected, as it has been previously shown that the tappers were exposed to a statistically significant higher mass concentration of PM than the crane operators.33 The difference in Mndissolved is, however, only statistically significant between crane operators and tappers in Smelter 2, which only included a HC–FeMn furnace. The largest differences in Mndissolved between tappers and crane operators are observed for PM with dae > 500 nm, representing most of the mass.33 In this size fraction, we found irregular slag particles with high MnO content and particles with higher amount of Mn and Zn, as well as minor amounts of K, Na and Cl. The particle composition in different working areas of the HC–FeMn smelter was also studied by Gunst et al.,17 and a different chemical composition of PM collected among tappers and crane operators was found. Particulate matter collected among tappers contained higher mass fractions of K, Na and Zn than among crane operators. In our study, a dominating fraction of the particles observed in the first stages of the cascade impactor contained K, Na, Cl and Zn together with Mn, but such particles did not dominate in samples collected directly from the tapping fume with the electrostatic sampler. The amount of such particles may explain the difference in the percentage of Mndissolved between tappers and crane operators. The difference from Gunst's17 study may be a result of the composition of the raw material used in the production during sampling. Further investigations are needed to conclude on the observed difference in bioaccessible Mn between tappers and crane operators in the HC–FeMn industry.
Our results show that the concentration of Mn in PM in air was significantly higher for tappers and crane operators, but the Mndissolved was significantly lower for tappers than crane operators. Further research is needed to investigate if this difference in Mndissolved between crane operators and tappers is related to the physicochemical properties of the particles.
In conclusion, the results have shown that connecting the knowledge of particle characteristics and bioaccessibility is important to gain more information on how particles may behave in contact with lung fluids. The physicochemical properties of single particles and Mn bioaccessibility are key factors to be considered in risk assessment. With regards to this, our size resolved data on particle characteristics and bioaccessibility give additional information which can be combined with what is already known about the particle size dependent deposition efficiency in lungs. Furthermore, the results of this study can be applied in future epidemiological studies and toxicological assays.
Footnotes |
† Electronic supplementary information (ESI) available. See DOI: 10.1039/d1em00243k |
‡ Current address: Soos Research and Development Center, University of Pannonia, Zrinyi Miklos str. 18, H-8800 Nagykanizsa, Hungary. |
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