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Environmental Science and Pollution Research

, Volume 26, Issue 3, pp 2950–2959 | Cite as

Settled iron-based road dust and its characteristics and possible association with detection in human tissues

  • Kristina ČabanováEmail author
  • Kamila Hrabovská
  • Petra Matějková
  • Kateřina Dědková
  • Vladimír Tomášek
  • Jana Dvořáčková
  • Jana Kukutschová
Research Article
  • 93 Downloads

Abstract

Settled road dust was examined to detect the presence of non-airborne submicron and nano-sized iron-based particles and to characterize these particles. Samples were collected from a road surface near a busy road junction in the city of Ostrava, Czech Republic, once a month from March to October. The eight collected samples were subjected to a combination of experimental techniques including elemental analysis, Raman microspectroscopy, scanning electron microscopy (SEM) analysis, and magnetometry. The data thereby obtained confirmed the presence of non-agglomerated spherical nano-sized iron-based particles, with average sizes ranging from 2 down to 490 nm. There are several sources in road traffic which generate road dust particles, including exhaust and non-exhaust processes. Some of them (e.g., brake wear) produce iron as the dominant metallic element. Raman microspectroscopy revealed forms of iron (mainly as oxides, Fe2O3, and mixtures of Fe2O3 and Fe3O4). Moreover, Fe3O4 was also detected in samples of human tissues from the upper and lower respiratory tract. In view of the fact that no agglomeration of those particles was found by SEM, it is supposed that these particles may be easily resuspended and represent a risk to human health due to inhalation exposure, as proved by the detection of particles with similar morphology and phase composition in human tissues.

Keywords

Iron-based particles Magnetic character Environmental aspects Road traffic Road dust Brake wear 

Introduction

Natural particles consist partly (60%) of minerals from the soil, of which 40–50% are quartz and approximately only 2% are organic matter. On average, approx. 30% of settled road dust is made up of potentially toxic substances. These include products of fuel combustion, brake wear, tire wear, and particulates from road surface abrasion (Thorpe and Harrison 2008; Gunawardana et al. 2012). These potentially toxic substances are emitted by anthropogenic sources—mainly by road traffic, but also by industrial and domestic heating systems (Jeleńska et al. 2017). As a result of the global rise in the number of road motor vehicles and the increasing density of road traffic, the quantity of particulates emitted by road motor vehicles is also increasing. These metal particles include complex mixtures of metals (Apeagyei et al. 2011). According to Adachi and Tainosho (2004), brake dust contains primarily Fe-rich particles, as well as Ti, Cu, Sb, Zr, and Ba particles and also heavy minerals (Y, Zr, La, and Ce). Dust from tire wear also contains Zn. The Fe content in brake pad materials and emitted brake dust (suspended and sedimented fractions) can be up to 63.7% and 53.7% respectively (Thorpe and Harrison 2008). In most large cities, trams also form part of the public transport system. It is therefore likely that settled road dust also contains wear particles generated by friction between tram wheels and rails; steel tram wheels and rails produce especially iron-based particles (Okagata 2013). The detection of iron-based particles produced as a consequence of rail transport has also been confirmed by Lyu et al. (2015). Additionally, a study by Moreno et al. (2015) has presented the results of the detection of nano-sized and submicron iron-based particles on underground railway platforms. Besides chemical composition, other significant information includes the size of the particles present in sedimentary dust. Particles resulting from non-combustion processes in transport can reach very small dimensions. Often their diameters are in the hundreds of nanometers, but they can sometimes reach tens of nanometers (Kukutschová et al. 2011). Due to this size, they can enter the body relatively easily via inhalation exposure, especially when settled road dust is resuspended due to different weather conditions or turbulence caused by traffic (Thomas 2013; Chen and Lippmann 2015). In the USA, the EPA uses a classification which defines inhalable coarse particles as particles ≤ 10 μm but ≥ 2.5 μm in diameter, and fine particles as particles < 2.5 μm (US EPA 2018). The average adult breathes between 10,000 and 20,000 dm3 of air per day, and it is assumed that the airspace load is approx. 10 μg/m3 and the daily mass of inhaled particles is approx. 100 μg (Bascom et al. 1996). Due to their properties, solid particles present in settled road dust can also contribute to systemic oxidative stress and multiple disorders as a consequence of the presence of smaller particle size fractions attached to the larger particles/clusters (Adamiec 2017).

The aim of this study is to characterize iron-based solid particles with micron and nano-size present in settled road dust. The article also assesses the relationship between road transport (especially through braking of road motor vehicles and trams) and the presence of these iron-based particles in road dust. The study also suggests possible links between iron-based particles from settled road dust and iron-based particles found in human tissues.

Materials and methods

Sample preparation

Samples were obtained from the surface of an urban road junction in the Poruba district of the city of Ostrava (Czech Republic). The Poruba district is a typical urban location with minimal direct influence from the iron- and steel-making industrial complexes or other major point sources which contribute to environmental pollution in the rest of the city of Ostrava (Vossler et al. 2016). The sampling site is in the vicinity of a busy road junction and pedestrian crossing; hence, vehicle braking is common. Dust samples were collected from 1 m2 of the road surface; the dust was swept into a glass sample container using a sampling set. Samples were collected once per month (from March to October = samples 1–8), between 9:00 and 10:00 a.m. The date of the sampling was selected depending on the meteorological conditions: sampling was performed only on rainless days after at least a 2-day period without wet precipitation. Eight samples (450–500 g per sample) were collected. According to the local municipal road maintenance authority, road cleaning at the sampling site is carried out only twice a year, on an irregular basis—usually after the winter season (March) and then in the summer period (August). Each sample was homogenized in a rotary mill (Fritsch Pulverisette) at 250 rpm for 15 min and was then passed through a sieve with 200-μm mesh. Grain size was selected according to the standard operating procedure used by the accredited laboratory of the Nanotechnology Centre at the VŠB-Technical University of Ostrava, Czech Republic. The levels of road dust reported worldwide vary significantly depending on the particle size sampled, traffic conditions, tire types, road types, road maintenance practices, and climate (Denby et al. 2018 in Amato 2018). A unified experimental control is therefore very difficult to define.

Methods used for sample characterization

A MicroSense Vibration Sample Magnetometer (VSM) EV9 was used to measure the magnetization curves of the samples. VSM is able to analyze liquid, powder, solid, bulk, and thin-film samples with the sensitivity of the magnetic moment up to 1 × 10−10 A m2. The magnetometer detects magnetic properties from the entire sample volume, and its results cannot be directly compared with local surface-sensitive methods (e.g., Raman microspectroscopy, EDAX analysis). This experimental technique is based on the principle that a vibrating sample placed in an external magnetic field generated by an electromagnet induces a voltage which is sensed by the detection coils and whose magnitude is directly proportional to the magnetic moment or magnetization of the measured sample. In our case, the powder samples (approximate mass 0.1 g) were placed in a cylindrical non-magnetic sample holder. The magnetization curves measured at room temperature show the dependence of the sample magnetization (magnetic moment divided by the sample mass) on the external magnetic field ranging between – 1600 kA m−1 and + 1600 kA m−1.

An eXplorer PSEM scanning electron microscope (ASPEX, Delmont, USA) equipped with a secondary electron (SE) detector, a quadrupole backscattered electron (BSE) detector, and energy-dispersive X-ray microanalysis (EDX) was used for the characterization of the samples. The samples were fixed to adhesive conductive carbon tape attached to the pin stubs, and accelerating voltage 20 keV was used during the analysis. The BSE mode provides material contrast according to the elemental composition of a sample, and therefore this mode was selected for the study of the settled road dust in order to clearly show the difference in the particle composition. The double-sided adhesive conductive carbon tape (discs, SPI Supplies) was kept in a closed plastic box, and the tape had protection on both sides. The top protection was not removed until the sample was ready to be mounted, thus reducing possible contamination. The surface of the tape was checked and was found to be free of solid particles.

A SPECTRO XEPOS energy-dispersive XRF spectrometer (SPECTRO A. I., Kleve, Germany) was used to estimate elemental composition. The samples were dried at room temperature and then milled in an agate planetary mill. Four grams of the sample was mixed with 0.9 g of Hoechst wax C micropowder and a pellet was made using a hydraulic press. A 50-W Pd end-window tube operating at max. Fifty kilovolts was used for the excitation of the samples. The target changer (with polarization and secondary targets) offers many different excitation conditions ensuring optimum determination of most elements from Na to U. Measurements were performed in a He atmosphere. A silicon drift detector with Peltier cooling achieves a spectral resolution of less than 160 eV for Mn K-α; the maximum count rate is 120 kcps. A special SPECTRO TurboQuant method for pellets was used for analysis evaluation.

Raman spectra were obtained using the XploRA™ Smart Raman microscopy system (HORIBA Jobin Yvon, France) in the entire range of wavenumbers from 100 to 4000 cm−1. A lens with magnification × 100 and a laser of 532 nm (20–25 mW) were used. The laser spot diameter was approximately 0.5 μm, enabling a particle/aggregate spot analysis. The intensity of the laser beam ranged from 10 to 25%. The grid was set to 1200 grooves/mm.

Results and discussion

XRFS analysis (Table 1) confirmed Si and Al to be the predominant elements in the settled road dust. These elements are most likely present in the form of quartz and aluminum silicates and are obviously of natural origin. Other dominant metals detected were iron, manganese, and titanium. Their quantity varied slightly depending on the month of sampling. The highest iron value was found in April and then during the summer period, in July and August. Other elements are present in significantly smaller quantities (Table 1).
Table 1

Contents of elements detected by XRFS in the settled dust from the road surface (mg/kg). Dust samples were collected from March (No. 1) to October (No. 8)

Element (mg/kg)

Sample

1

2

3

4

5

6

7

8

Al

58,400

61,400

63,700

59,100

60,100

60,800

64,200

64,300

Ba

600

654

666

668

669

667

694

668

Bi

< 1

< 1

< 1

< 1

< 1

< 1

< 1

< 1

Ce

< 2

< 2

< 2

63

60

< 2

< 2

< 2

Cr

550

537

399

531

633

519

757

454

Cu

71

130

100

96

91

134

95

94

Fe

36,000

48,700

43,800

45,100

47,000

43,300

40,800

41,900

La

< 2

< 2

< 2

22

5.2

< 2

< 2

18

Mn

18,010

1550

1520

1830

1830

1470

1300

1150

Ni

27

31

31

31

27

27

30

31

Pb

25

29

33

30

34

36

26

28

Sb

4.2

6.4

5.6

2.6

1.9

3.0

5.2

6.4

Si

272,000

270,000

282,000

279,000

284,000

283,000

278,000

281,000

Sn

7.5

3.1

7.6

4.7

2.0

3.9

2.5

4.5

Ti

2820

2970

3410

2870

2910

3060

2890

3040

V

69

67

76

69

72

71

66

63

Zn

218

298

290

235

251

307

236

280

SEM-EDX analyzed micron and submicron particles/clusters, and elements such as Si, Al, Mg, Ca, K, P, S, and O (which are commonly found in soils) were detected in all samples of the settled road dust. Moreover, iron was also detected in all evaluated dust samples. Some metal-based elements (Ba, Bi, Ce, Cr, Cu, La, Mn, Ni, Pb, Sb, Sn, Ti, V, and Zn) were detected only in some of the samples. The elements Ce and La were detected only in samples 4, 5, and 8; their presence in these samples was also confirmed by XRFS (Table 1). These elements may be released into the environment by rail welding processes, in which they may be used as additional alloying elements in welding electrodes. It can be assumed that rail welding occurs predominantly in the summer period (Naboychenko et al. 2005). Road dust can also be enriched by traces of La and Ce from road vehicle catalysts (Moreno et al. 2008).

The iron-based spherical particles/clusters exhibited sizes in the range from 1 to 50 μm. However, particles/clusters smaller than 1 μm were also found (see Fig. 2).

Figure 1 shows examples of spherical submicron iron-based particles/clusters detected in the settled road dust. The particle diameters in Fig. 1a are 0.67 μm, 0.49 μm, and 1.91 μm, and in Fig. 1b, the particle diameter is 0.57 μm. Due to the regular shape of these particles, it can be assumed that they consist of a single particle rather than a cluster of very fine particles. Figure 2 shows a spherical micron-sized particle of diameter 5.9 μm and its corresponding EDX spectrum. Due to the presence of relatively large amounts of oxygen in the EDX spectrum, these micron and submicron particles are probably composed of iron oxides. Raman microspectroscopy confirmed the presence of iron oxides in the settled road dust samples, including magnetite Fe3O4 and hematite Fe2O3 (see Fig. 3). In view of the observed individual spectra, it can be confirmed that these compounds are the above-mentioned iron oxides (Hanesch 2009). It can be assumed that such spherical and symmetrical particles are formed to a large extent by high-temperature processes. Road traffic is undoubtedly one of these processes (Chen et al. 2006; Liati et al. 2015; Mitchell and Maher 2009).
Fig. 1

SEM images of submicron iron-based particles/clusters. The particle diameters in image a are 0.67 μm (A), 0.49 μm (B), and 1.91 μm (C); the particle diameter in image b is 0.57 μm

Fig. 2

Example of a typical iron-based particle of spherical shape, with its corresponding EDX spectrum

Fig. 3

Examples of Raman spectra of the detected iron oxides found in almost all the samples of settled road dust

Magnetization curves were also measured for all samples. The results of the magnetic measurements are shown in Fig. 4 and Table 2. It can be seen that almost all the samples are saturated at a magnetic field of 1600 kA m−1. The similar submicron size fractions (Fig. 1) of the samples, including fine particles, are responsible for small changes in the values of the coercive field, typically tens of units of kiloampere per meter. The low values of remanent magnetization indicate that each particle of the powder has its own magnetic anisotropy with a random direction of easy magnetization axis. This fact is proved by the ratio of Mr/M1600, which is practically the same for all the samples. The obtained values of magnetization at a magnetic field of 1600 kA m−1 (M1600) correspond well with the amount of iron contained in the samples (see Table 1). However, in our case, we observed relatively low values of magnetization at a magnetic field of 1600 kA/m and coercive fields of approx. 4 kA/m. We assume that such behavior corresponds mainly with magnetite (the low value of magnetization is connected with low quantities of Fe in the samples) or with the presence of iron oxides containing both magnetite and hematite. These values can be influenced by magnetite and hematite particle size. Similar shapes of hysteresis loops were measured in (Ahmadzadeh et al. 2018; Luňáček et al. 2016). Moreover, both above-mentioned assumptions were confirmed by the measurements of Raman spectra (Fig. 3).
Fig. 4

Magnetization curves of road dust samples 1–8 after removal of the diamagnetic background of the plastic container

Table 2

Main magnetic parameters from VSM magnetization curves. M1600, magnetization at a magnetic field of 1600 kA m−1; Hc, coercive field; Mr, remanent magnetization

 

Sample

1

2

3

4

5

6

7

8

M1600 (A m2/kg)

0.5517

2.3246

0.9628

1.0320

1.1530

1.0697

0.8460

0.7088

Hc (kA/m)

3.939

3.939

3.939

3.143

0.974

3.939

3.939

8.674

Mr (Am2/kg)

0.0372

0.1693

0.0741

0.0876

0.0476

0.0858

0.0679

0.0639

Mr/M1600 (−)

0.0670

0.0720

0.0769

0.0849

0.0413

0.0802

0.0802

0.0901

Since the sampling was carried out in an industrial city, the iron particles in the settled dust most probably originated in heavy industry or road traffic. To confirm traffic as one of the most important sources of iron particles detected in the settled road dust, a comparison was performed of the dependence of the iron content on the number of vehicles that passed through the road junction at the sampling point in each month of sampling (Statutory City of Ostrava 2015). A significant correlation was found between the amount of iron in the samples and magnetization (r = 0.795, p = 0.0182), while the correlation between the amount of iron and road traffic intensity (i.e., number of vehicles) at the sampling site was lower and insignificant (r = 0.632, p = 0.0923) as assessed by the Pearson correlation test. Linear regression confirmed a linear dependence of the magnetization on the Fe content (R2 = 0.57, p = 0.018), as apparent from (Fig. 5). An outlier was revealed skewing the linear response of the Fe content depending on the traffic at the sampling site. The peculiar decrease in the Fe content in this sample can be explained by road cleaning work carried out before the March sample was taken (sample 1). When this sample was excluded from the analysis, a significant linear dependence of the Fe content on the sampling site traffic was also apparent (R2 = 0.59, p = 0.045), as apparent from (Fig. 6).
Fig. 5

Magnetization at a magnetic field of 1600 kA/m vs. Fe content in dust samples (1–8)

Fig. 6

Fe content in dust samples (1–8) vs. number of vehicles per month at the selected road junction in 2015 (data on the number of vehicles passing through the collection point were obtained from the Statutory City of Ostrava 2015)

Numerous studies have already confirmed a certain link between iron-based particles in settled road dust and traffic. Magnetite (Fe3O4) has also been found as a dominant metal-based phase in road dust by Bardelli et al. (2011). According to the authors, the detected Fe3O4 compound in the Traforo del San Bernardo highway tunnel may be of anthropogenic origin, i.e., exhaust emissions and de-icing salts (FeCl3). The origin of the chloride compounds is probably related to the salt used to prevent ice formation on the road surface during winter. The presence of FeCl3 enhances heavy metal dispersion by forming volatile metallic chlorides during the combustion process (Bardelli et al. 2011; Wang et al. 2001). Likewise, Verma (2015) evaluated the content of iron and other metals (lead, chromium, and cadmium) in roadside dust samples. Roadside dust was randomly collected from five roundabouts in Damaturu (Nigeria, West Africa). Repeated analyses of dust samples found iron as the most dominant metal, followed by Cd, Cr, and Pb. According to the author, the main sources of these metals are exhaust emissions from vehicles (Verma 2015). Hulskotte et al. (2014) studied elemental composition profiles of brake hardware (pads and discs) used in the Netherlands in 2012 (in total, 65 brake pads and 15 brake discs). They found that Fe, Cu, Zn, and Sn together make up about 80–90% of the metals present in brake pads. Based on their measurements, the average brake pad profile contained 20% Fe, 10% Cu, 4% Zn, and 3% Sn as the dominant metals. The brake discs consisted almost entirely of metal, with iron content > 95% and only traces of other metals (< 1% for individual metals). Non-metallic components in the discs were mainly based on silicon (Hulskotte et al. 2014). The presence of iron-based particles as a consequence of rail transport has also been confirmed by Lyu et al. (2015). Additionally, a study by Moreno et al. (2015) has shown the presence of nano-sized and submicrometric iron-based particles on railway underground platforms.

According to Kukutschová et al. (2009), Thorpe and Harrison (2008), and Matějka et al. (2017), the composition of regular automotive brake pads typically includes several groups of components which serve as reinforcement agents, friction modifiers, fillers, and binders; these ingredients include elemental iron and iron compounds. The most commonly used brake discs are made of cast iron, with its chemical composition approx. 93.6 wt.% of elemental iron (Hulskotte et al. 2014).

Settled road dust contains solid particles that, due to their size and weight, undergo gravitational settling. However, settled road dust also contains particles of submicron dimensions (Fig. 1). Due to weather conditions and other mechanical influences (passing vehicles), dust is often resuspended (Watanabe et al. 2011). As a result, these particles can re-enter the air, where they can be relatively easily inhaled or swallowed. Inhalation exposure is one of the most effective routes for the unintentional entry of solid particles into the human body (Thomas 2013; Chen and Lippmann 2015). These inhaled or swallowed submicron particles may then enter the entire respiratory tract, where they are deposited. The present study includes an evaluation of human tissues from the upper and lower respiratory tract where such solid iron-based particles have been found (see Fig. 7).
Fig. 7

Example of SEM images and Raman spectra of particles/clusters detected in the lower respiratory tract, i.e., lung tissue of carcinoma (a) and in the upper respiratory tract (tissue from the inferior nasal turbinates with chronic rhinitis) (b)

Figure 7a shows a particle/cluster mainly composed of iron, with size approx. 2.25 μm, found in a human lung carcinoma sample. Figure 7b shows an iron particle, with size approximately 1.89 μm, detected in the tissue of the upper respiratory tract of a person suffering from chronic rhinitis. In accordance with SEM-EDX, Raman microspectroscopy found one Fe phase (i.e., Fe3O4) in the tissue from the inferior nasal turbinates and also in the lung carcinoma tissue. However, the Raman spectrum in Fig. 7b is different due to the presence of other phases, probably based on zinc—which was also detected by SEM-EDX. Both objects appear to be almost spherical in shape. The phase composition of Fe-based solid particles detected in a larger group of these tissue samples has already been presented in the following studies (Čábalová et al. 2015; Čabanová et al. 2015, 2018). Magnetic particles may appear in the human body even under normal circumstances, and they are predominantly of spherical shapes (biogenic magnetite/maghemite in human hippocampal tissue) (Maher et al. 2016; Schultheiss-Grassi et al. 1999; Kirschvink et al. 1992). However, spherical particles can be released also by high-temperature processes in combustion of fuels but also non-exhaust processes (e.g., braking) may generate spheric particles as well (Chen et al. 2006; Liati et al. 2015; Mitchell and Maher 2009; Kukutschová et al. 2011). With regard to the shape of the particles detected, it can be assumed that these metal-based objects may potentially be of exogeneous origin, infiltrated into the organism through inhalation. Nonetheless, it is very difficult to precisely determine the relation between the quantity of inhaled particles and their health effects in humans. Several studies have proved that exposure to higher concentrations of Fe oxide dusts causes a retention of those particles in the lungs rather than an acute toxic response (Lewinski et al. 2013; Teculescu and Albu 1973). Occupational cohort studies provide data on real workplace conditions; however, these studies are often limited due to incomplete exposure assessment, where single chemical compounds cannot be evaluated separately. In clinical studies, investigators have control over the exposure conditions, though these studies are limited to assessing short-term effects (Lewinski et al. 2013). It is evident that experimental results from occupational exposure cannot be easily extrapolated to ambient environment exposure. Despite this fact, there are convincing proofs of the adverse effects of Fe-based solid particles on living organisms. Khiroya and Turner (2015) described the association between iron metabolism and pulmonary disease phenotypes. IREB2 is a gene that produces iron regulatory protein 2 (IRP2), which has a key role in iron homeostasis. Some environmental factors can influence phenotypic variation in respiratory diseases, e.g., inhaled iron from cigarette smoke can be deposited in the lungs and causes tissue damage by altering iron homeostasis (Khiroya and Turner 2015). By inhalation exposure, the lungs may be exposed to iron and other agents (e.g., particles) with a capacity to disrupt the homeostasis of this metal. These exposures may result in increased availability of catalytically reactive iron, and by generating oxidative stress, this metal may contribute to tissue damage (Ghio 2009).

Fe(III) and Fe(II) are naturally frequently occurring forms of iron. Due to the fact that iron can donate or accept free electrons, it participates in the production of free radicals via the Fenton reaction. It has been proved that superoxide radicals originating during the Fenton reaction can damage cells and ultimately result in apoptosis (Khiroya and Turner 2015; Barbusiński 2009). This assumption is supported by the fact that both detected particles were found in damaged, pathological tissues. A possible significant factor affecting toxicity is the presence of metals such as Fe and others (Cu, Zn, Sn, Sb, Cr, and Ni) in road traffic emissions, which may produce reactive oxygen species (ROS) in biological systems and cause damage to these systems. The structures that are most often damaged and influenced by ROS are proteins, DNA, and lipids containing polyunsaturated fatty acids (Rajhelova et al. 2018). Happo et al. (2010) found significant inflammatory response in the lungs of rats exposed to coarse PM in Helsinki, and correlated this with Fe and Cu content. Some MED-PARTICLES project outcomes have suggested a link between Fe and cardiovascular disease in Barcelona and Rome (Amato et al. 2014). In some studies, it has also been shown that iron particles are involved in many diseases. For example, siderite particles (FeCO3) have been found in lung cancer tissue (Čabanová et al. 2018). Anthropogenic magnetic particles in brain tissue were first time detected and described by Maher and co-authors (Maher et al. 2016), whereas the study of relation between Alzheimer’s disease and magnetic particles present in brain tissue has been studied since the 1990s (Dobson and co-authors). Several other studies (Hautot et al. 2003; Pankhurst et al. 2008) revealed biogenic magnetite and its correlation between the amount of nano-sized biogenic magnetite in brain tissue pathologies and the onset and progression of Alzheimer’s disease.

The experimental results presented above suggest a need to thoroughly address the potential risks related to iron-based emissions—not only when evaluating biological materials but also when designing and developing new eco-friendly materials (e.g., friction materials for automotive brake pads) with lower environmental health impacts. Despite the fact that iron is a biogenic element with well-known biological functions within an organism, in specific forms, iron may also pose significant environmental and health risks. Therefore, proper experimental approaches are needed in the process of control and regulation of iron-based particulate emissions released into the environment.

Conclusions

To evaluate the settled road dust composition, a combination of methods was used to determine both the elemental and phase composition as well as the magnetic character of the samples. Iron particles/clusters were found in all the samples of the settled road dust, predominantly in the form of iron-based spherical particles of a size in the range of 1 to 50 μm. Nevertheless, particles smaller than 1 μm were also found. Iron was predominantly identified as a magnetite (Fe3O4) and hematite (Fe2O3). Significant correlation was found between the amount of iron in the sample and magnetization, and the relationship between the amount of iron and traffic (number of vehicles per month) was also observed. Moreover, iron-based particles/clusters of similar composition and particle size were detected in human respiratory tissue samples. In the tissue from the inferior nasal turbinates and from the lung carcinoma tissue, magnetite particles were identified. Based on all the findings, it cannot be stated definitely that a clear link exists between iron-based particles in sedimentary dust and iron-based particles detected in human respiratory tissues. However, road traffic is thus important contributor of the iron pollution in the environment and produces vast amounts of micron and submicron particle sizes of iron with a high probability of inhalation.

Notes

Acknowledgments

The authors thank Dr. Oldřich Motyka for statistical analysis of the experimental data and Mr. Chris Hopkinson for language corrections.

Funding information

This study was supported by Project “Characterization and possible environmental risks of synthetic lanthanide oxides nanoparticles and particles from non-combustion processes in traffic” (number SP2018/81) funded by Ministry of Education, Youth and Sports of the Czech Republic, and by the Project “New Composite Materials for Environmental Applications” (number CZ.02.1.01/0.0/0.0/17_048/0007399) funded by ERDF (European Regional Development Fund)/ESF (European Social Fund).

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Center for Advanced Innovation TechnologiesVŠB-Technical University of Ostrava,OstravaCzech Republic
  2. 2.Department of PhysicsVŠB-Technical University of OstravaOstravaCzech Republic
  3. 3.Nanotechnology CentreVŠB-Technical University of OstravaOstravaCzech Republic
  4. 4.Faculty of MedicineUniversity of OstravaOstravaCzech Republic

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