Research articleVariation of the chemical composition of street dust in a highly industrialized city in the interval of ten years
Introduction
Street dust that is inhaled by humans near roads causes a wide range of health risks. Resuspension of street dust (repeated lifting) is the main source of particles PM2.5 and PM10 in the urban environment, which can have a significant impact on human health. Street dust represents a heterogeneous mixture of particles of various sizes and composition. Dust particles can be of biogenic or mineral origin. In addition, substantial amounts of these particles are formed by anthropic processes (Ayrault et al., 2013). Composition of street dust is, therefore, very variable, and it is influenced by climatic conditions, soil environment, bedrock and anthropic activity (Fedotov et al., 2014). In Zurich, the origin of particles in street dust was identified as follows: 21% tyre wearing, 38% material from the road surface, 41% particles from exhaust gases (Bukowiecki et al., 2010). Emissions of PM from exhaust gases of engines are decreasing as a result of the lowered limits. On the other side, the importance increases for emissions from resuspension and wear (brakes, tyres and road surface).
The tyre wear and tear particle size distributions are dependent on many factors such as type of pavement, temperature, speed, age and composition of the tyre (Grigoratos and Martini, 2015). Another source of contamination is represented by wearing brake pads, which contain binders (phenol-formaldehyde resins), fibres (copper, steel, brass, potassium titanate, glass, organic material and Kevlar), fillers (barium and antimony sulphate, magnesium and chromium oxides, silicates, ground slag, stone and metal powders), lubricants (graphite, ground rubber, metallic particles, carbon black, cashew nut dust and antimony trisulphide) and abrasives (aluminium oxide, iron oxides, quartz and zircon). Counterparts can be cast iron and sometimes composites (Kole et al., 2017).
Street dust can contain up to 60% of particles originated in soil: quartz, feldspars (albite, microcline and others), clay minerals, chlorite and muscovite. Up to 30% of street dust is formed by the amorphous phase, which differs from the amorphous phase common in soils and originates apparently in transport activities (Gunawardana et al., 2012). The main minerals released from pavement wear are biotite, hornblende, K-feldspar, quartz, plagioclase, chlorite and other, mostly Fe-rich minerals (Kupiainen et al., 2016).
An essential part of street dust in regions with the production of iron and steel can also be formed by metallurgical slags that are used as a construction material (landscape shaping, filling of depressions). Steel slag could be utilized in its raw state as a subgrade or subbase material for the construction of roads or in asphalt mixtures (Sas et al., 2015). Asphaltic concrete contains approximately 20% of blast furnace slag, 12% of steel slag while for road bases and surfaces usually 40% of blast furnace slag and 46% of steel slag is used (Piatak et al., 2015). Slags are also often used for the production of construction materials, e.g. clinker (Van Oss, 2019). Their massive utilization leads to their increased transport and possible leakage from trucks.
Main sources of Zn and Fe is tire wearing; brake wearing for Ba, Cu, Fe, Pb and Zr (Urrutia-Goyes et al., 2018), Sb (Juda-Rezler et al., 2011) and Sn (Alves et al., 2018). A source of Zn can also be the galvanized steel in the road structures, and the weathering of asphalt and concrete (Calvillo et al., 2015). Zinc, in the form of ZnO, is added as an activator during the vulcanizing process, comprising from 0.4% to 4.3% of the resulting tyre tread (Adachi and Tainosho, 2004). Concentrations of Cu in the non-asbestos brake pads reach up to 15%, and emissions of copper can reach from 0.3 to 2.7 mg/km (van Der Gon et al., 2007). Nickel and chromium can also originate from corrosion of cars and chromium plating of some motor vehicle parts (Zhang et al., 2012).
Elements Fe, Ti, Cr, V, Mn and Mg most likely have mixed origins, i.e. natural and related to iron and steel production, and in the case of Cu also coke production (Ordóñez et al., 2015). An important source of Fe (13.6%), Ca (5.2%), Zn (1.88%), Pb (0.29%), Na (0.45%), K (0.92%), Cl (2.9%), Cd (72 mg/kg) and Cu (106 mg/kg) is dust from blast furnaces (Lanzerstorfer and Kröppl, 2014). The most important source of Zn, Pb, Cr and Ni in iron processing is an electric arc furnace that for 1 tonne of the product releases 35 g Zn, 2.7 g Pb, 1.5 g Cr and 0.61 g Ni (Wang et al., 2016). Metallurgical dust from steel production contains mostly oxidic phases rich in Fe, Cr, Ca, Zn, Mg, Mn and Ni, with minor amounts of phases containing alkali metals (K and Na) and halogens (Cl and F), and also Si, Mo, Pb and S. The most problematic element is Zn present in the metallurgical dust in the form of zincite (ZnO) or franklinite (ZnFe2O4) (Stefanova et al., 2013).
Magnetic properties of dust particles (PM) are utilized more and more often for identification of various contamination sources in urban soils, street dust and atmospheric particles. The source of magnetic particles in the urban environment is fuel combustion, emissions from vehicles (Yang et al., 2010) and/or from wear and corrosion and from the industry (Zhang et al., 2012). Another important source of magnetic particles in urban areas is considered to be traffic. Magnetic particles from traffic emissions form irregular non-spherical aggregates of magnetic minerals, particularly magnetite (Zhang et al., 2012). Based on the various morphology of particles contained in street dust from Thessaloniki, two groups of ferrimagnetic particles were identified by Bourliva et al. (2016): spherules and angular particles/aggregates with elevated heavy metal content. Technogenic magnetic particles (TMPs) are Fe-rich particles formed at high temperature that can be characterized by high magnetic susceptibility (Rachwał et al., 2015). Technogenic magnetic particles (TMPs) from the high-temperature combustion processes have characteristic spherical shape while TMPs from traffic emissions and iron smelting form irregular non-spherical aggregates (Lu et al., 2016). Technogenic magnetic particles differ markedly from magnetic particles formed by natural processes, especially by morphology, stoichiometric ratios and structure, which can influence magnetic properties (Szuszkiewicz et al., 2015).
The winter maintenance of roads is the last but essential factor influencing the composition of street dust. In the Czech Republic, the road winter gritting consumes annually approximately 168,000 tonnes of salt, 348,000 tonnes of grit and sand and 91,000 tonnes of inert material (slag and cinder) (Melcher, 2001). All these materials must be tested each year for their suitability according to the Technological Conditions TP 116 “Chemical de-icing and gritting materials” valid from July 2015 (Technological Conditions TP 116, 2015). Chemical treatment is usually used for main roads in the winter season while for local roads gritting is used, very often utilizing material from local sources. Gritting material is mostly removed after the end of the winter season. However, the quality of the cleaning can be very variable. From the year 2018, the main roads in the city of Ostrava are cleaned six times per month, and wet cleaning is applied three times per month. The roads with lower traffic are cleaned four times per month, and wet cleaning is applied two times per month. The streets with the lowest traffic load are dry cleaned two times per month, and one wet cleaning is applied per month. The amount of street dust obtained annually from the sweeping of streets in Waco (Texas) ranges around 2000 tonnes (Calvillo et al., 2015). In the city of Ostrava in the year 2019 (Ostrava Magistrate), from sweeping of streets 4402 tonnes of waste were obtained (13.9 kg per person annually) and in Environmental Portal of Prague (2017),1 it was 18,875 tonnes, i.e. 15 kg per person annually (Environmental Portal of Prague, 2017).
The aim of this work is an application of chemical and mineralogical methods to the study of street dust in the industrial region. Verification of the decreasing trend of the environmental load from the deposition was performed within the territory of the city of Ostrava influenced by the production of pig iron and steel. The comparison was performed of the situation in the years 2008 and 2018 after realization of several technological measures for decreasing the environmental load from industry and in the period of the increasing impact of traffic. Enrichment factor for street dust, urban soils and newly also for blast furnace slags and steel slags was used for comparison of differences in the environmental load. On the basis of the mass determination of magnetic particles in street dust, it was estimated proportion of magnetic particles originated from slag and other sources including identification of risk elements from other sources of contamination.
Section snippets
Materials and methods
Street dust collected at the territory of the industrial city was analysed using a combination of chemical analysis and mineralogical methods. Chemical analysis was performed by X-ray fluorescence spectroscopy. Mineralogical methods included determination of magnetic susceptibility and study of individual particles in the scanning electron microscope combined with energy dispersive X-ray spectrometer. The sampling sites were located at the territory of the city of Ostrava. Sampling was
Results
The primary indicator of environmental quality is the amount of street dust per unit area (m2). The minimum amount of dust was indicated in the Ostrava-Jih locality at 47 g/m2, the highest amount was found in O-Vítkovice 1.37 kg/m2, the average value was 229.7 ± 88.97 g/m2 (Fig. 3). Quite different results were obtained for the same sampling procedure for the university City of Olomouc which only has a food industry in its vicinity. In late summer, the smallest amount of dust was 9.88 g/m2, the
Conclusion
The proportion of silt (<0.063 mm) in street dust in the city of Ostrava is 8% at maximum. The amount of silt ranges from 8 to 80 g/m2, and the total dust load is 100–500 g/m2 with a maximum value of 1.3 kg/m2. It has been shown that higher concentrations of Cu, Pb, Zn are present in the class below 0.063 mm, while Ca, Cr, Mn, V are more bound to coarse particles, Fe is distributed evenly between the two phases. For the identification of the polluter – the effect of traffic, the comparison of
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
CRediT authorship contribution statement
Barbora Švédová: Formal analysis, Writing - original draft, Visualization. Dalibor Matýsek: Methodology, Software. Helena Raclavská: Conceptualization, Writing - original draft, Supervision. Marek Kucbel: Formal analysis, Writing - original draft, Writing - review & editing. Pavel Kantor: Methodology, Formal analysis, Visualization. Michal Šafář: Formal analysis, Software. Konstantin Raclavský: Conceptualization, Writing - review & editing, Validation.
Acknowledgement
This paper was supported by the research projects of the Ministry of Education, Youth and Sport of the Czech Republic: SP2019/35 “Identification of combustion processes using composition of street dust”, RRC/10/2018 “Support for Science and Research in the Moravian-Silesian Region 2018”, SP2019/77 “Geology of the eastern margin of the Bohemian Massif and adjacent areas” and TJ7779121/2203 “Identification of dust particles in street dust and technological measures to reduce emitted street dust
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