The environment as a complex and interconnected system consists of natural, artificial, and social components. Over the years, there has been observed an overall imbalance in the environment. In practice, monitoring especially of anthropogenic pollutants is a complex process. First, the sources and emissions are identified; then the risks are assessed. Critical emissions are controlled and economic aspects are integrated at the same time. Technical field measurements require equipment and are associated with high costs. Among the wide range approaches that make it possible to assess the state of the atmosphere, biological monitoring, i.e., biomonitoring, is increasingly coming to the fore. The complexity and at the same time the relative simplicity of its application make it an ideal tool for the given purpose. Compared to technical monitoring methods, it is inexpensive. Among the organisms used to monitor the state of the atmosphere, bryophytes are one of the most widely used. Mosses do not have a cuticle and root system and thus obtain nutrients in particles or solution directly from atmospheric deposition. They have good bioaccumulation ability, the concentration in the insole reflects the deposition from the atmosphere without being affected by soil concentrations [1
Currently, the most problematic air pollutants in the urban environment are fine dust particles (Particulate matter). Particulate matter is the result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides, which are pollutants emitted from power plants, industries, and automobiles. They are compounds from trace elements such as Cd, Co, Cr, Cu, Fe, Mn, Pb, Sb and Zn [2
] or Al, Sb, As, Cd, Fe, Mn, Ni, Pb, Cu, V, Zn according to [3
]. According to the European Environment Agency (EEA) map representing the average annual concentrations of PM10
in 2016 (Figure 1
), the areas with the highest airborne dust loads are Poland, within the Czech Republic, the Moravian–Silesian Region. Further north Italy, Bulgaria, Macedonia, Greece and Turkey.
Air quality in the Moravian–Silesian Region, especially in the Ostrava and Karviná regions, has been unsatisfactory for a long time. This fact is also evidenced by the map of average annual concentrations of PM10
for the Czech Republic in 2018 (Figure 2
). This is mainly due to the high concentration of industry in a densely populated area, but transport and heating of households also have an impact.
The territory of the city of Ostrava belongs into the area of the Ostrava Basin, which is a slightly warm area with southwest and northeast wind directions. The landscape is open to the north and northeast, which causes a negative effect of northern winds in winter, but also in summer. The territory of Ostrava belongs into a moderately warm climatic region, but differs with certain peculiarities caused by a high concentration of industry, dense construction and specific conditions of the Ostrava Basin.
According to the database of the Register of Emissions and Air Polution Sources (REZZO), it is evident that primary emissions of solid pollutants are from large industrial sources, as well as local heating plants with a share of about 30%. A large share is not attributed to emissions of solids from transport. Total emissions in the Ostrava–Karviná agglomeration are approximately five times higher than in the Prague agglomeration and eight times higher than in the Brno agglomeration [6
]. The Moravian–Silesian Region is characterized by the highest concentrations of PM2.5
and, compared to other regions, high values of benzo(a)pyrene appear. Directly in Ostrava, the limit value for benzene and arsenic is also repeatedly exceeded.
The aim of the paper is the analysis of spatial data obtained by biomonitoring using mosses. Furthermore, on the basis of the performed analyzes, characterization of the regional atmospheric deposition of pollutants in the air on the Czech–Polish border and verification of the suitability of the use of bryophytes as alternative monitors of air quality in small industrial areas. The another aims are identification of the significance of individual groups of sources of pollutant emissions and determination of the extent and location of polluted areas. The study evaluates the measured data and determines whether the elements contained in the samples are of natural origin, i.e., if they are part of the natural background, or whether they are of anthropogenic origin and determines whether the resulting values are of local origin or come from long-distance transmission.
The research was carried out in frame of the dissertation thesis [7
The findings about potential sources in terms of elemental composition, presence of potential emission sources, but also climactic and geomorphologic conditions, which allow the transmission of pollution from its source to the place of deposition, were included in the evaluation. The result of the principal components analysis is represented by the dispersion diagram of the component score (Figure 5
). Based on the rules explaining the dispersion diagram, a map (Figure 12
) of mutually correlated areas was created.
The points included in groups 1 and 2 are found in locations least affected by anthropogenic activity from the studied location. The sampling sites in category 3 are influenced by industrial activity and also local domestic heating and emissions from transportation, whereas the points in group 5 are not affected by emissions from industrial areas to such an extent. According to the analysis, the sites in group 6 are the most different from other sites. These points are located on the Polish side in an area of mining, engineering, and metallurgical industry. At the same time, one point is found near the town Frýdek-Místek where the metallurgical and machine-building industry is well-developed. According to the dispersion diagram, the points in category 12 are the closest to the origin and as such the most typical for the studied area; in this category, there are two points located near the village Kunčičky in the Ostrava region and close to Třinec. Metallurgical companies can be found in both of these localities.
Based on the hierarchical clustering on principal components analysis (HCPC), the sample points were divided into three clusters (Figure 8
). From the clusters, we can identify areas affected by the industry, areas not significantly affected by the industry but containing a large concentration of domestic heating, and areas least affected by anthropogenic activity.
The division of elements into five factors according to the factor analysis and also the spatial distribution of the factor loadings of individual factors can be explained by the following description. Factor 1 is composed of a large number of elements (Na, Mg, Al, Sc, Ti, V, Co, Ni, As, Ba, La, Ce, Nd, Sm, Tb, Tm, Hf, Ta, Th, and U). Elements of natural origin can be influenced by the deposition from industrial sources based on the localization of the highest values of the load factor. Another source could be dust/soil particles. As described by Shetekauri et al. [28
], V and Ni are the dominant elements in areas with metallurgical and mining industries. Simultaneously, the aforementioned authors attribute the natural crustal origin of elements to factor 1, which in their case also contains Ti, V, Ni, Co, As, Th, and U. Zinicovscaia et al. [27
] states a combination of geogenic and anthropogenic associations in relation to Co and U as elements belonging to factor 1. Apparently, the measured results may have been affected by soil particles.
The most prominent elements in factor 2 are represented by Mn, Zn, As, and Br. Identical elements were also identified in one of the factors in the study of Olise et al. [42
]. The authors note that coal impurities emitted at high temperatures contain As, Rb, As, Br, Mn, and Cr. This fact is also confirmed by other authors [53
According to the graph of component weights (Figure 6
), the element I can also be added to this group. All above-mentioned elements except for As do not show mutual correlations with other elements (Figure 9
). In the calculation of all factors, manganese came out as the element least affected by anthropogenic activity. Both iodine and bromine have negative values of the geoaccumulation factor; as such, they can be considered elements of natural origin. Due to its origin, arsenic stands apart from the group as it enters the air practically only due to human activity, particularly by burning fossil fuels and wood conserved with arsenic-containing products. According to the Korzekwa et al. [29
] who utilize the method of biomonitoring using mosses in Poland, another source of As besides burning fossil fuels can be represented by pesticides or products used for wood curing; this is because in their case, higher concentrations of As were found in forests or close to agricultural areas. Metallurgical companies processing copper, lead, and other metals containing arsenic in their ore are considered to be a source, too. However, the values of the contamination factor of arsenic reach the “moderate” category at maximum, and they only do so in two points (Figure 13
One point is located in a part of Ostrava called Polanka nad Odrou where the moss was collected in a place with the following activity: Buyout and processing of alloy steel waste, processing of construction materials, selling of solid fuels and metallurgical materials, and manufacturing of asphalt mixes. The second point with its contamination factor in the “moderate” category is located in the town of Wodzisław Śląski where there are long-term issues with emissions originating from fuel burning in home boilers, undesirable technical conditions, and energetic efficiency. Other issues are also represented by the low quality of fuel burned and the burning of waste. Higher values of the contamination factor, up to the category “severe”, are displayed by four points in the case of zinc. The points described can be found in the area around the municipalities Strahovice, Pszów, Marklowice, and Żory. Significant anthropogenic sources of zinc are represented by mining, zinc, lead, and cadmium refining, steelmaking, burning of coal and other organic fuels, ore mining and processing, and utilization of zinc-containing fertilizers. Zinc is utilized to a large extent (up to 40% of production) as an anti-corrosive protective material for iron and its alloys.
According to the graph of component weights (Figure 6
), Ca and Mo are more correlated with each other when compared to the pair of Cr and Fe. Based on the values of the contamination factor, calcium appears as an element included in the natural background; similarly, molybdenum belongs to the essential microelements necessary for plant development. However, Korzekwa et al. [29
] states the origin of molybdenum to be the metallurgical plant. In line with this statement, higher values of the contamination factor of molybdenum correspond with the distribution of residences, pointing to anthropogenic sources such as fossil fuels burning, metallurgy, but also mining and the electrotechnical industry. In the case of Ca, the drawing of the element can occur from soil substrate according to a number of sources [42
Higher concentrations of chromium can be found in the regions of Ostrava, Třinec, and the surrounding areas of the town Wodzisław Śląski where the mining, metallurgical, and engineering industries are well-developed. A contamination factor of the “moderate” category is also spread around smaller residencies and this reality can be caused by the burning of fossil fuels (in the form of Cr3+
). Other sources can be represented by cement plants, communal waste incinerators, exhaust gases from automobiles with a catalyst, emissions from air-conditioning cooling towers using compounds of chromium as corrosion inhibitors, and flying asbestos from automobile brakes. High values of the contamination factor of Cr and Fe are also apparent on the north side of the Beskids Protected Landscape Area near the municipalities Řeka, Vyšní Lhoty, and Komorní Lhotka where the industry concentration is not so dense but where the massive of the Moravian–Silesian Beskids begins. Therefore, pollution is likely brought by the blowing wind from the north and its fallout and capture take place on the windy side of the massive. Iron and chromium interfere and their main sources are found in the agglomeration of Ostrava/Karviná/Frýdek Místek and in the vicinity of iron foundries. A particular affinity to absorption and accumulation of dust particles was also confirmed by Pandey et al. [60
] and Olise et al. [42
], who also confirms Fe as the dominant element in moss samples in the vicinity of iron and steel plants.
Factor 4 is made up of elements Se, Cd, and W. On one hand, according to the geoaccumulation factor, selenium can be considered an element of geogenic origin. This is also indicated by the scatter of its higher concentrations in the regions of the Beskids Protected Landscape Area on both the Czech and the Polish sides, the Poodří Protected Landscape Area, Oderské vrchy Natural Park, and the Cysterskie Kompozycje Krajobrazowe Rud Wielkich Protected Landscape Area. On the other hand, according to the contamination factor, selenium is “suspected of contamination”, which corresponds with the higher concentrations in the vicinity of the towns Rydyłtowy and Rybnik where the main emission sources of selenium are thermal power plants and plants of metallurgical and chemical industry. In the case of cadmium, the situation is questionable. The scatter of higher concentrations and higher levels of contamination factor of cadmium is particularly apparent in the peripheral parts of the studied area where clean locations without industry or dense settlement are found. Based on The Integrated pollution register [61
], the anthropogenic emissions of cadmium are approximately eight times higher than the emissions from natural sources. One of the explanations of such scatter of concentrations is the long-distance transmission of emissions; in areas of immediate proximity of emission sources, the deposition of other substances prevails and cadmium is transported into more distant locations. Higher concentration could be caused also by transport. The points located in agricultural areas can be affected by using phosphate fertilizers with cadmium ingredients and loading waste treatment plant sewage into the fields. In the case of cadmium, it is necessary to admit an error in the analysis of the samples using the neutron activation analysis. It is evident that higher values occur only in the samples collected in the year 2016. Therefore, differences between the results from the years 2015 and 2016 can be counted on.
The differences between the elements from factor 4 and 5 and the elements from other factors are also confirmed by the results of the PCA depicted in the graph of components weights (Figure 6
) where Cd, Se, Mn, and Rb show an obvious positive mutual correlation paired with a negative correlation towards Cl and K. In the case of K, intake from soil substrate can occur [56
]. According to the PCA result, none of these elements correlates with other examined elements. This fact is confirmed by the results of the correlation matrix (Figure 9
) where the elements Au, Cl, K, W, Se, Cd, Rb, Cs, Zn, Sb, Mn, Br, and I do not correlate with a greater group of other examined elements. The last element of the group, tungsten, came out to be in the category among the elements meaning contamination in all factors (CF, Igeo, EF) and as such coming from anthropogenic activity. The contamination factor of W belongs to the “moderate” and “severe” categories across the entire studied area except for peripheral areas where protected landscape areas are found. Tungsten is a part of coal and given its high density and difficult melting properties, it is widely used in a number of industrial sectors. For example, it is used in the production of lightbulb threads and W electrodes, the utilization as an ingredient in alloys to increase the hardness and mechanical and heat resistance (fast speed steel), and the production of penetration projectiles or materials for radiation shielding [62
]. The contamination factor in the “moderate” category appears almost everywhere across the inhabited area. This fact can be caused by domestic heating where coal burning takes place. Higher concentrations are located in the vicinity of Třinec, Český Těšín and Cieszyna, Ostrava, Rybnik, Rydułtowy, and Wodzisław Śląski where the metallurgical industry is well-developed.
Factor 5 is made of elements Cl and K. The highest values appeared particularly in agricultural areas. Based on the result of Igeo, CF, and EF, potassium is a part of the natural background; it is a biogenic element and therefore, a vegetal origin can be expected. For instance, Olise et al. [42
] identified crustal/soil dust as a source. In the case of CF, chlorine is classified into the slight contaminated category. By comparing the distribution of its concentrations with the distribution of the corresponding CF values, locations where high values are a part of the natural background are eliminated (Figure 14
Most of the locations with higher CF values are found in the vicinity of agricultural areas and an influence through the use of potassium fertilizers, whose basic component is potassium chloride (KCl) or potassium sulfate (K2SO4), can be assumed. Higher values in the areas surrounding Ostrava, Frýdek Místek, and the Polish city Skoczów can originate from chlorine and hydrogen chloride leaks from the industry, specifically from their production and processing, the burning of chloride-containing fuels such as coal, or the leakage of hydrochloric acid during steel processing.
Regarding the rate of excessive of the concentration of heavy metals in the natural environment calculated using the Tomlinson Pollution Load Index (PLI) based on the division of values into categories greater or less than one, expressing if given concentrations in a given location are nearing the value of the background or indicating pollution, the results identified nearly the entire studied area (except for six points in the southern mountainous part) as affected by anthropogenic activity. Similar results were also reached by Shirani et al. [13
]. For that reason, a map with PLI values divided into six categories (Figure 11
) was created. Higher PLI values correspond with the distribution of industrial centers on both the Czech and the Polish side. High values are also located to the west and south-west of the cities Frýdek-Místek and Paskov, reaching into the Poodří Protected Landscape Area where higher concentration of industry is not found. This reality can be caused by the north-east drift from industrial areas or domestic heating together with transportation emissions. In this location, an airport can also be found. However, none of the performed statistical analyses determined the link between higher concentrations of individual heavy metals and the vicinity of the airport. Moderately elevated PLI values are observed on the north windy side of the Beskids. Except for typical industrial areas in the studied location, high PLI values are also found in the area surrounding Dolní Benešov where the engineering industry and a foundry are located. A high index also appears in the north part of the Opava region in the Sudice-Třebom promontory. Despite the absence of heavy industry, high concentrations of a number of elements (As, Br, Mn, Zn, Ca, Cr, Fe, Mo, Cd, W, Sc, and Cl) can be found there. This fact can be affected by the surface gypsum mine located in the land registry of the municipality Koběřice where the subsequent processing of natural gypsum also takes place. Another influence in this area can come from domestic heating, particularly in the town Třebom where according to the results of the 2011 census of persons, houses, and flats [63
], heating with solid fuels, particularly with coal, coke, or coal briquettes, prevails. Additionally, transmission of emissions to this area from the Polish side probably takes place.
During the years 2015, 2016, 99 samples of moss were collected, the results of which were processed as part of the presented work. After eliminating unsuitable samples, 93 samples were included in the analyses. The samples were analyzed using the instrumental neutron activation analysis. The result was represented by 38 variables, the chemical elements.
A partial goal of this work was to evaluate the measured data and determine if the elements contained in the samples were of natural or anthropogenic origin. To reach this goal, multi-criteria analysis of data was used. Hierarchical clustering on principal components and factor analysis were conducted. Through the principal component analysis, locations most typical for the studied area were determined; these were the locations in the immediate vicinity of metallurgical plants. From the results of this partial goal, it can be assumed that the dominant polluter of the area of interest likely is the metallurgical industry. By hierarchical clustering, the area was divided, according to the type of pollution, into three groups composed of an industry-influenced group, a group with prevailing emissions from domestic heating and also industrial emissions from long-distance transmission, and a so-called clean group.
The distinction between elements with their concentrations near the natural background and elements which can indicate pollution was performed using a number of factors, namely the contamination, geoaccumulation, and enrichment factor and the pollution load index. An intersection of a set of elements Sm, W, U, Tb, and Th, which were determined to be the elements causing pollution and whose concentrations do not near the natural background of the studied locations, took place in all factors. The elements are emitted among others by the metallurgical industry. Sm and Th are applied in a number of chemical industries. Tb is used moreover by electronic industry. W and U are substantial compound of coal. High concentrations in samples coming from areas with no local sources of pollution can be associated with a climactic standpoint, particularly for the prevailing direction of the wind, and long-distance transmission of pollute.
Moss sampling in the study was carried out in an exceptional dense network of sampling sites. Based on the results of the paper, it is possible to propose a dense sampling of the entire region of the Czech Republic as biomonitoring with the use of mosses gives us the ability to detect regional sources of air pollution in a sufficiently dense network yet at acceptable costs.