Potentially Harmful Elements Content in Soil and Stream Sediments in Southwestern Districts of Katowice (Southern Poland) – Geochemical Record of Historical Industrial Plants’ Activity

The research area is located in southern Poland in the Upper Silesian Coal Basin (USCB). It is a part of the Palaeozoic Variscan structure, which is cut by numerous faults. The stratigraphic section is represented by the Triassic, Neogene, and Quaternary systems [Wyczółkowski, 1957; Buła et al. 2008].

The soils in the study area developed on a bedrock of Carboniferous, Triassic and Quaternary deposits. The northern part of the region is composed of Carboniferous claystones, sandstones, and conglomerates with hard coal [Wyczółkowski 1957], which in some places are covered by Quaternary glacial loams (Fig. 2). In the southern region (in the Kokociniec estate and the Ligota and Ochojec districts), there are Quaternary glacial formations (sands and gravels), and locally, outcrops of Triassic carbonaceous formations (limestones, dolomites and marls) are exposed. Quaternary lake sands and aeolian deposits occur in some small areas. The valleys of the Kłodnica River, the Ślepotka River and other smaller watercourses are filled with Holocene river deposits (muds, clays and sands).

Figure 2.

The condition of the natural environment and the spatial development of the analysed part of the city were influenced primarily by the exploitation of hard coal deposits, as well as metallurgy. Historically, in the northern part of the area under discussion, near the Kłodnica River valley, there has been a zinc smelter („Victor”) and an iron smelter („Ida”) [Degenhardt 1870] (Fig. 3).

Figure 3.

Within the settlement of Katowicka Hałda, the zinc smelter “Henrietta” and the coal mine “Beate” were active in the first half of the 18th century [Szaraniec 1984; Grzegorek et al. 2017]. The north-eastern part of the area under analysis is home to the shafts of the hard coal mine KWK (“Wujek”), which has been in operation since 1900 [Chmielewska 2010]. The most intensive development of mining and exploitation of hard coal in the Upper Silesian Coal Basin took place in the 1960s and 1970s [Frużyński 2012].

Limonite has been mined in the area of Załęska Hałda since the Middle Ages. The zinc smelter “Victor” operated in the years 1840–1877, later merging with the “Oheim” mine (currently referred to as the “Wujek” coal mine) [Chmielewska 2010; Grzegorek et al. 2017]. In the same district, in the Johanka colony, the “Johanna” zinc-works operated at the former site of the “Saeman” glassworks [Borowy 1997].

The Kokociniec colony was founded around a hammer forge built in 1650 near the Kłodnica River valley. This was the predecessor of the “Ida” ironworks, which operated from 1845–1948 on the border of today’s Panewniki and Ligota districts. This ironworks had two coal-fired furnaces, an iron foundry, and a boiler room [Degenhardt 1870; Szaraniec 1984; Złoty 2008].

Other industrial branches also had plants in Ligota, such as the Upper Silesian Paint Factory, the “Silesia” Chemical Factory, the Ligocka Chemical Factory (refinery), and the Upper Silesian Wood Impregnation Plant [Krukowiecka-Brzęczek 2016].

Sampling of soils and stream sediments was carried out in accordance with the methodology developed for the geochemical survey of Upper Silesia [Lis, Pasieczna 2005]. A total 271 topsoil samples (ranging 0.0–0.3 m in depth) were collected based on a regular grid measuring 250x250 m (16 samples per km²). Soil samples (approx. 500 g), collected with a hand auger, 60 mm in diameter, were placed in canvas bags labeled with appropriate numbers, and pre-dried on wooden pallets in a field storage facility. Sediment samples (58 in total) were collected from the Kłodnica and Ślepotka rivers, smaller streams and ditches. The distance between sampling sites along watercourses was about 250 m. Sediment samples weighing approx. 500 g (and of the finest possible fraction) were taken from the banks of water bodies using the aluminum scoop and placed in 500 ml plastic containers, marked with appropriate numbers.

The soil samples were air-dried and sieved through a 2-mm mesh, and the resulting fraction was pulverized in agate planetary ball mills to a grain size of < 0.06 mm. Sediment samples were air-dried and sieved through a 0.2-mm mesh. After digestion of the samples with hot aqua regia, their Ag, As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, P, Pb, S, Sr and Zn content was determined using the ICP-AES method. The concentration of Hg was determined using the CV-AAS method with FIAS-100, with a flow injection system. The pH of the soil samples was determined with the potentiometric method.

Quality control of the analyses was carried out using duplicate samples (5% of all samples), analyses of laboratory control samples confirming correct instrument calibration (5% of all samples), certified standards (2% of all samples), and blanks. In quality control of the analyses, materials with certified content of the tested elements were used: LOAM 7004, SRM 2709 (NIST) and SRM 2711 (NIST) for soils and SRM 2704 (NIST) and PACS for stream sediments. The expanded uncertainty of results (with an a ssumed probability level 95% coverage factor; k = 2) did not exceed 25%, except the mercury content levels in the soil and sediment samples.

Calculation of statistical parameters for the various elements in the soil and sediment, as well as soil pH (arithmetic mean, geometric mean, median, minimum and maximum values, standard deviation and coefficient of variation), are shown in Table 2 and Table 4. In the case of some elements with elemental content lower than the detection limit for a given analytical method, half the value of this limit was applied in the calculations. The regional geochemical background was calculated based on a database for the Detailed Geochemical Map of Upper Silesia (27,941 soil samples and 5,769 sediment samples). The contamination factor (CF) and geoaccumulation index (Igeo) were used to assess the soil contamination. These indices are widely used for the estimation of geochemical anomalies and the anthropogenic impact on soil chemistry, which refers to the concentration of metal enrichment in the soils under investigation, relative to uncontaminated background levels [Hakanson, 1980; Loska et al. 2004; Barbieri, 2016].

The contamination factor (CF) was calculated as: CF=Csample/Cregional background {\rm{CF}} = {{\rm{C}}_{{\rm{sample}}}}/{{\rm{C}}_{{\rm{regional}}\,{\rm{background}}}} where: C_sample is the chemical element content in the sample, and C_{regional background} is the content of the element in the geochemical background for soil in Upper Silesia Region. This contaminati on factor distinguishes four classes of contamination degree and potential ecological risk for soil and sediments: CF < 1 is considered low, 1 ≤ CF < 3 is moderate, 3 ≤ CF < 6 is considerable, and CF ≥ 6 is very high [Shen et al. 2019].

The geoaccumulation index (I_geo) was originally defin ed and used for assessing metal concentration in sediments [Muller, 1969; Förstner, 1989] but is also used here to determine the condition of the soil. This index is calculated according to the formula: Igeo=log2(A/1.5×B) {{\rm{I}}_{{\rm{geo}}}} = {{\rm log}_2}({\rm{A}}/1.5 \times {\rm{B}}) where: A is the measured concentration of the element in the sample and B is the geochemical background of elements for Upper Silesia (regional background level).

The factor 1.5 in the formula is introduced to reduce the lithology-related variability in the geochemical background. The geoaccumulation index enables the classification of soil and sediments as follows: I_geo < 0 is uncontaminated; 0 ≤ I_geo ≤ 1 is uncontaminated to moderately contaminated; 1 < I_geo ≤ 2 is moderately contaminated; 2 < I_geo ≤ 3 is moderately to heavily contaminate; 3 < I_geo ≤ 4 is heavily contaminated; 4 < I_geo ≤ 5 is heavily to extremely contaminate; I_geo > 5 is extremely contaminated [Loska et al. 2004; Barbieri 2016].

Principal Component Analysis (PCA) of a correlation matrix was carried out to delineate the different sources (lithogenic, anthropogenic or mixed) contributing to the observed pollution. PCA calculations allowed for the separation of groups of closely related chemical elements from the raw data set, which illustrate the variability of the studied set and are called factors. Factors grouping individual chemical elements can often be clearly interpreted as natural and anthropogenic processes that could have led to the observed changes [Dragon 2002; Yammani et al. 2008]. The first factor explains the largest part of the variance, and each subsequent factor explains less and less. Both in the topsoil layer and in stream sediments, four factors of eigenvalues >0.7 were distinguished, this is important for the interpretation of the results [Wieczorkowska, Wierzbiński 2011; Czopek 2013].

Ecotoxicological quality indicators were used to assess the contamination of the examined sediments by determining the threshold value of TEC (Threshold Effect Concentration) – the concentration below which no negative impact is observed. The probable value of PEC (Probable Effect Concentration) – the concentration of the element above which its more harmful effects may occur more frequently in aquatic organisms – was also calculated [MacDonald et al. 2000]. If the concentration of the heavy metal is smaller than the TEC values, it could be considered that the contamination level is weak, whereas when the concentration of specified element is larger than the PEC values, harmful biological effects deserved to be considered [Gao et al. 2019]. To determine potential risk to the benthic fauna, values of analyzed metals were compared to corresponding TEC and PEC values (Tab. 1).

The spatial distributions of some elements in soil are depicted in maps compiled using Inverse Distance Weighted (IDW) method of interpolation and geometric progression to define the distribution classes. The geochemical maps of sediments are constructed in the form of pie-chart maps, assigning the respective pie-chart diameters to individual content classes, usually arranged in a geometric progression.

The soil in the area under study developed on Carboniferous and Triassic bedrock, as well as Quaternary deposits. The predominant soil types are podzols and pseudopodzols that developed on Carboniferous sandstones and Quaternary glaciofluvial sediments. The parent rock for the cambisols is glacial till. In the Kłodnica River valley, muddy-swampy soils were the predominant type present [Lazar 1962; Program, 2013/2014].

Topsoil in the southwestern districts of Katowice shows massive enrichment with almost all analysed elements compared to the geochemical background levels in the Upper Silesia Region. The high values of standard deviation and coefficient of variability for these elements also indicate high results dispersion compared to the average values (Tab. 2).

The topsoil samples under study showed a wide range of pH, from alkaline to acidic (Tab. 2). High CV values (> 200) for As, Hg and Zn suggest that they are not lithogenic in origin and might have been introduced artificially into the environment. The Cd, Pb, S and Sr concentrations appear to have a similar origin.

To assess the tested soil’s degree of contamination with potentially harmful elements, the contamination factor, CF, was used; higher values indicated unnatural concentrations of heavy metals, originating largely from anthropogenic sources [Kobierski et al. 2015; Pasieczna 2018].

A CF index of 6 or higher was recorded for all analysed elements and in many analysed soil samples. Forty-three samples reached this level with their Sr content, 30 did with their Ba content, and 26 did for Cu (Fig. 4).

Figure 4.

A high degree of contamination/enrichment (3 ≤ CF < 6) was recorded for all analysed elements, reaching this range in 61 samples for Ba, 48 for Co, 70 for Cu, 47 for Hg, 63 for Sr, and 40 for Zn. The largest majority of soils tested showed a moderate degree of contamination/enrichment (1 ≤ CF < 3). In the case of Ag, 268 samples were characterized by this indicator; 174 samples in the case of S; 167 samples in the case of Cr; and over 100 samples in the case of As, Ba, Cd, Co, Cu, Fe, Hg, Mn, Ni, Pb, S and Zn. About 30% of the soils were characterized by a low degree of contamination (CF < 1). About 30% of soils are characterized by a low degree of contamination (CF < 1).

The geoaccumulation index (I_geo) values indicate that the tested soils’ degree of pollution with heavy metals varied widely from moderately to heavily contaminated (Fig. 5).

Figure 5.

Only one sample was found to be heavily-to-extremely contaminated with As, Hg and Zn (Igeo > 5). Moderate-to-heavy contamination (2 < Igeo ≤3) was noted in 34 samples in the case of Sr, 25 in the case of Ba, and 20 for Cu. Conversely, almost all 265 soil samples presented Igeo values for Ag < 0.

PCA analysis allowed to distinguish four main factors in soils (Tab. 3).

Obtained four factors are as follows: factor F1 (loading on Ag, As, Cd, Pb, and Zn), explaining 31.07% of the total variance in topsoils; factor F2 (loading on Co, Cr, Fe, and Mn), explaining 20.97%; factor F3 (loading on Ba and Sr), explaining 17.90%; and factor F4 (loading on Hg), explaining 6.82%.

Statistical parameters of element content in stream sediments calculated for 58 samples from the Katowice area are presented in Table 4. High values of standard deviation (Mn, Zn) and coefficient of variation (e.g. Cr, Hg, Cd, S) indicate the scattering of data in relation to average values and their uneven distribution.

Geoaccumulation index values were calculated for stream sediments in the same way as they were with soil (Fig. 6). Only one of all samples was strongly contaminated with Cd and Hg (Igeo > 5). Moderate-to-extremely-heavy contamination levels (2 < Igeo ≤ 5) of As, Cd, Hg, S, and Zn were found in more than five samples.

Figure 6.

The ecotoxicological classifications (TEC and PEC) of the analysed sediments are presented in figures 7 and 8, respectively.

Figure 7.

Figure 8.

The results allow us to conclude that all sediments were found to have concentrations of Ag below which no negative impact is observed (TEC), and this was also the case with Cr in almost all (56) samples. The situation is completely different when considering that almost all samples (57) had levels of Cd that indicated the possibility of negative impact, 54 had concentrations of Pb reaching this level, and 55 had had this level of Zn. Half or more than half of the samples showed concentrations of Cd, Pb and Zn that exceeded the threshold at which harmful effects on aquatic organisms (PEC) is observed.

PCA analysis allowed us to distinguish four main factors in sediments (Tab. 5). They as are follows: F1 (loading on Cr and Mn), explaining 19.22% of the total variance; F2 (loading on Ag, As, Cd, Pb, and Zn), explaining 24.41%; F3 (loading on Co, Ni, and S), explaining 22.24%; and F4 (loading on Fe), explaining 9.20% of the total variance.

When assessing environmental pollution, as when searching for mineral deposits, it is extremely important to know the spatial distribution of chemical elements in its individual elements by estimating geochemical background values in order to find anomalies [Lis, Pasieczna 2001; Reimann, Garret 2005; Reimann et al. 2005; Santos-Francés et al. 2017]. In the present work, the median values were calculated using 27,941 soil samples and 5,769 sediment samples surveyed for the Detailed Geochemical Map of Upper Silesia conducted in 1999–2021 (eliminating outlier data) to set a regional geochemical background for the analysed elements [Palacz et al. 2021].

Comparison of the median values of the studied elements within the analysed area to the regional geochemical background values for the Upper Silesia region (Table 2) and in Polish soils [Pasieczna 2003] show a clearly heightened concentration of some elements.

For Ag, As, Cd, Co, Fe, Hg, median values in the Katowice-area soils were the same as, or close to, regional geochemical background values, indicating that these elements originated from parent rocks. By contrast, the accumulation of Ba, Sr and Cu were more than double the background values, and there was also significant enrichment in Cr, Ni, Pb and Zn, allowing us to infer an anthropogenic origin for some of these elements.

The highest standard of deviation values, which were found for Ba, Zn, Mn and Pb, and coefficients of variation > 200, which were found for As, Hg and Zn, indicating a large dispersion of data in relation to the average values. This points to a non-uniform distribution of these elements entering the environment, probably as a result of anthropogenic factors.

The content of major and trace elements in soils depends primarily on the chemical composition of their parent rocks. The significant impact of anthropogenic factors on the soils of the studied region is evidenced by the CF values of the results obtained (Fig. 4), indicating that over 30% of the analysed soils are characterised by a high or very high accumulations of Ba, Cu and Sr, and over 20% are characterised by similar accumulation levels of Co, Hg and Zn. Such values allow us to believe that this pollution is caused by long-term industrial activity [Baradovski et al. 2015; Rinklebe et al. 2019].

In the topsoil layer, factor F1 (Ag, As, Cd, Pb and Zn loads), as with factor F2 (Co, Cr, Fe and Mn loads), suggests that the levels of these elements could have been increased relative to their nature levels by the impact of industrial activities. The elements grouped by the F1 factor are mainly associated with the processing of Zn-Pb ores and zinc metallurgy. The period of intensified exploitation and processing of Zn-Pb ores began in the 19th century and lasted several dozen years. The factor F2 group, by contrast, consists of elements associated with iron metallurgy. The most contaminated areas by PHEs grouped in factor 1 and factor 2 are located near former zinc smelters and ironworks in Ligota – Kokociniec, Załęska Hałda and Katowicka Hałda (Fig. 1).

Factor F3 (Ba and Sr loads) may be of mixed lithological and anthropogenic origin. They are obtained mainly from parent-soil materials. Both Quaternary glacial clays and Carboniferous mudstones are characterised by naturally higher concentrations of these elements. Their additional sources for these elements are discharges of mine water into watercourses, particles from coal combustion, and leachates from waste heaps after industrial enrichment of coal with barite. The highest enrichment in Ba and Sr is observed near former and contemporary industrial plants and coal mines.

F4 coefficient values indicate an unnatural Hg content, probably related to the impact of waste generated during the operation of the former zinc smelters and emissions from the combustion of hard coal. The highest contents of Hg were determined in the Brynów district towards the north-east from the railway tracks.

Detailed geochemical maps developed for the southwestern districts of Katowice allowed for the identification of areas with increased PHEs content, which may be useful in spatial development planning, assessment of local plans, and decision-making regarding environmental restrictions. The spatial distribution of selected PHEs (As, Cd, Zn) is presented in Figures 9–11. The As content in most soils of the analysed area does not vary significantly and rarely exceeds 20 mg/kg (Fig. 2, 9). Soils formed on sandy Quaternary sediments have the lowest As content (< 10 mg/kg). Slightly larger amounts (20–40 mg/kg) were recorded in the soils of river valleys rich in organic components. In the valley of the stream draining the Ligota region and feeding the Kłodnica River, there is a local arsenic anomaly with levels as high as 304 mg/kg. Its probable source is pollution from chemical plants that are no longer in operation. Chemical plants began operating in this area before World War I, and closed in the 1960s. Over the course of those years, they produced paints, impregnations, Glauber’s salt and hydrochloric acid. Paints and wood impregnation, in particular, commonly used arsenic compounds. Among other plants operating in the area were an oil refinery, a brickyard, and an acetylene plant [Studium… 2012].

Figure 9.

Figure 10.

Figure 11.

Arsenic is also easily absorbed by river-bottom sediments, especially organic matter and iron and aluminium hydroxides [Herath et al. 2016]. An anomalous content of this element may cause its migration to the soil profile during soil acidification, which in turn poses a threat to the groundwater. [Shaw 2006; Patel et al. 2023; Wang et al. 2023].

In the area where arsenic anomalies were found, much larger anomalies of Cd (Fig. 10), Cu, Pb and Zn (Fig. 11) were also recorded. The presence of these elements can be associated with the activities of chemical and metallurgy plants located between Kokociniec and Ligota [Szaraniec 1984].

Soils in the vicinity of Załęska Hałda and Katowicka Hałda were also polluted, though to a lesser extent, with these elements; historically, these were areas of hard coal mining, and following exploitation, landfills.

Possible sources of these heavy metals could have been dust precipitation emitted from the ironworks “Ida” and zinc smelters “Victor” and “Frieden”, and the dispersal of metals during the transport and storage of ores, flux, and slag. Emissions from the “Baildon” steelworks, operating in nearby Dąb district in the 19th century [Rzewiczok 2009], also generated metal-bearing dust. In the area of the described anomalies, soils were found to have contents as high as 78 mg/kg of Cd; 172 mg/kg of Cu; 2,458 mg/kg of Pb; and 11,026 mg/kg of Zn.

The north-eastern part of the analysed area (parts of the Załęska Hałda and Katowicka Hałda districts) were where the zinc smelters “Victor”, “Henrietta” and “Johanna” operated [Degenhardt, 1870]. Here, the Cd content ranges from 20.1–26.5 mg/kg; Cu, 58–69 mg/kg; Pb, 743–1,324 mg/kg; and Zn, 4,132–4,796 mg/kg.

Comparison of the metal content in the analysed soils with literature data indicates their similar or higher contents in ore mining and metallurgy areas. Soils in areas contaminated by metallurgical activities often contain high amounts of heavy metals. Many authors showed that soils in the vicinity of lead smelters contain more than 30 000 mg Pb/kg, 20 000 mg Zn/kg, and 90 mg Cd/kg (Rieuwerts et al. 1999, Basta, Gradwohl 2000, Basta, McGowen 2004; Ettler et al. 2005; Vaněk et al. 2005). The average metal content in soils from the region of the old Pb-Zn mine in south-eastern Spain was similar to those obtained for the Katowice region: 59–2,632 mg/kg Pb, 1.5– 65 mg/kg Cd and 9.9–279.9 mg/kg As [Navarro et al. 2006]. In mine tailings, the average concentrations were 28,453 mg/kg Pb, 7,000 mg/kg Zn, 20.57 mg/kg Cd and 308 mg/kg Cu [Rodríguez et al. 2009].

The content of Ba and Sr in the tested soils can be attributed to both lithological and anthropogenic origins. Barium sources include Carboniferous clay rocks and Quaternary clays, and the sources of Sr are primarily Ca-rich sediments [Kabata-Pendias, Mukherjee 2007; Migaszewski, Gałuszka 2016], the outcrops of which occur in the Ochojec area. The median Ba content of the soil in the Upper Silesia Region is 59 mg/kg, and the median Sr content is 9 mg/kg (Tab. 2). Much higher contents of these elements – > 400 mg/kg of Ba and > 80 mg/kg of Sr – were also recorded, primarily in the soils in the area of the Wujek hard coal mine and east of the Kokociniec estate. The Ba originates with dust from coal combustion [Różkowska, Ptak 1995a, b; Jabłońska et al. 2016] and leachate from heaps, onto which heavy liquids (containing Ca, Fe and Ba compounds) have been dumped following enrichment [Sanak-Rydlewska et al. 2011]. Coal-waste leaching is a primary pathway for trace elements entering the environment [Nádudvari et al. 2021].

The Hg content in most soils does not exceed 0.20 mg/kg. A not-very-extensive anomaly (with a maximum of 4.49 mg/kg) occurs in the area of Brynów, near the railway tracks. The area of the anomaly demands more detailed research due to the chemical and biological activity of Hg, which is considered one of the most toxic metals, even at very low concentrations [Kabata-Pendias, Mukherjee 2007].

This presence of Hg may have resulted from dust dispersion during coal combustion [Bojakowska, Sokołowska 2001; Hławiczka 2008]. It may also be related to Hg compounds in wood-protection products used on railway sleepers [Wiłkomirski et al. 2011; Stojič. et al. 2017] or the presence of this element in Zn and Pb sulfides processed in zinc smelting plants [Pasieczna et al. 2020].

The reaction of the soil in the eastern part of the area is generally neutral and sometimes alkaline (pH > 7.4), similarly to other urbanized regions of Poland [Pasieczna 2016; Tomassi-Morawiec 2016]. The Ca content of many of these soils exceeds 0.50% [Pasieczna 2016], and its anthropogenic source is probably alkaline dust precipitation from coal combustion, as well as the presence of construction debris rich in Ca compounds.

In the soils of the western forested part, Ca content rarely exceeds 0.25% and pH ranges from 5 to 7. The acidic reaction of these soils, together with their high concentrations of sulphur and heavy metals (HM), can be very dangerous for the environment. Moreover, the massive oxidation of sulphides in Ca2+ ion-deficient conditions may cause a decrease in pH and the occurrence of acidic waste drainage. These conditions encourage further leaching of other HM from the mineral phases present in these soil/waste. Acidic drainage and strong environmental pollution can thus develop in wastes rich in metal sulphides (Fe, Zn, Cu) under even moderate climatic conditions [López-Pamo et al. 1999; Nieva et al. 2018].

Sediments from inland streams and still-water reservoirs are formed as a result of sedimentation of mineral and organic suspensions from erosion, as well as precipitation of components from water. Their chemical composition depends on local lithology, climate, and development, as well as the use of catchment areas [Zgłobicki 2008; Rzętała et al. 2013; Tytła, Kostecki 2019; Jabłońska-Czapla, Grygoych 2020]. In industrialized and urbanized regions, potentially harmful trace elements (As, Cd, Cr, Cu, Hg, Pb, Zn) and organic compounds are found in leachate from waste dumps; in industrial and municipal sewage discharged to surface waters; and surface runoff that may accumulate in sediments [Ciszewski 2002; 2005; Bojakowska et al. 2006; Kozieł, Zgłobicki 2010; Korban 2011; Sojka et al. 2013; Cempiel et al. 2014]. High concentrations of pollutants may cause them to accumulate in the food chains of aquatic organisms [Friese 2002; Harnischmacher 2007; Siebielec et al. 2015]. Polluted sediments transferred to flood terraces may cause an increased concentration of many substances in the soil of river valleys.

The chemical state of the sediments draining from streams in the considered region of Katowice under study was influenced by pollution from old industrial waste heaps, surface runoff from polluted soils, as well as the composition of the subsurface rock.

The sediments in the Kłodnica and Ślepotka catchment areas have different chemistries. In general, the sediments of the Kłodnica and its tributaries, which drain from Carboniferous mudstones and Quaternary clays, are characterized by a higher content of elements of lithogenic origin (Ba, Co, Cr, Fe, Mn, Ni and Sr) compared to the sediments of the Ślepotka, which flows through areas covered by Pleistocene glacial sands.

Comparison of the median values of the analysed elements in the sediments of the studied area with the value of the regional geochemical background (Table 4) allows us to notice an almost twofold enrichment of the sediments in Cu and Zn, and as well as increased concentrations of Cd, Pb and S. This constitutes the basis for the conclusion that anthropogenic pollutants originating from industrial and domestic sewage discharges have a greater impact on the chemical composition of sediments than do natural factors. As in the case of soils, for some elements there are high values of standard deviation (Mn, Zn) and coefficients of variation (Cd, Cr, Hg, Fe, S), indicating the dispersion of data in relation to average values and an uneven distribution. This allows us to assume that some elements were artificially introduced into the environment.

The highest contamination of sediments in the Kłodnica catchment is related to the material supplied by its right-hand tributary flowing from the Ligota and Kokociniec settlements that drains an area of the former chemical plants with highly contaminated soils. The sediments of the Kłodnica River and its tributaries are marked by large amounts of coal sludge particles, which have sorptive properties that facilitate the precipitation and binding of metals [Nocoń, Kostecki 2005]. Sediments of the Kłodnica catchment in the upper reach contain about 30–400 mg/kg of Ba, and in Kokociniec up to 200 mg/kg. Cd concentrations are 4–5 mg/kg and 100–200 mg/kg, respectively. The sediments also contain considerable amounts of Cr (up to 58 mg/kg), Cu (up to 205 mg/kg), Hg (up to 1.77 mg/kg), lead (up to 847mg/kg), Sr (up to 332 mg/kg) and Zn (up to 9,614 mg/kg). As in the case of soils, the cause of sediment contamination is most likely the activities of the Upper Silesian Paint Factory in Ligota (Ligota.info...) and the activities of historical industrial plants in the settlement of Kokociniec, which was founded based on a forge built in 1650. In the 19th century the settlement developed around a steelworks and a metallurgical plant that processed iron ore into steel. In the years 1845–1846, two large coal furnaces and an iron foundry (Kokociniec...) were built here. The most contaminated sediments with As (Fig. 9), Ba and Sr were found in a small stream draining the area of the former chemical plant in the Ligota housing estate. This area showed concentrations of 51–68 mg/kg of As, 315–419 mg/kg of Ba and 42–89 mg/kg of Sr. For comparison, sediments in Kłodnica and Ślepotka usually do not have concentrations exceeding 25 mg/kg of As, 200 mg/kg of Ba or 30 mg/kg of Sr.

The Ślepotka River was engineered in the 1960s and 1980s, and its channel was lined with concrete slabs. In the past the stream was significantly contaminated by sewage illegally discharged by residents of the nearby city quarters. Currently, the sources of contamination are rain and melt water, primarily from urban areas, workshops and industrial plants. Sediments of the watercourse are characterized by lower or close contents of Fe, and Mn in relation to the geochemical background values in the Silesian-Cracow region. Along its entire length, sediments of the stream are contaminated by Cd (1.4–14.1 mg/kg), and in its upper reach by Cr (11–25 mg/kg) and Cu (18–45 mg/kg). The maximum concentrations of PHEs detected in sediments of the streams in analyzed area are as follows: Ag – 3 mg/kg, Cd – 202 mg/kg, Hg – 6.04 mg/kg, Pb – 847 mg/kg, and Zn – 9,614 mg/kg. The concentration of Hg in the watercourse draining the premises of a former hospital (between Śląska Street and the Ślepotka valley) is 6 mg/kg. The likely source of mercury is hospital waste that migrates into the sediments.

In areas of historical exploitation and processing of Zn-Pb ores, stream sediments in many countries are similarly polluted as in Katowice City. Content of PHEs in stream sediments in Slovenia in area of the largest Pb–Zn mine was higher in comparison with investigated sediments in case of Ba (up to 2,407 mg/kg), Cu (up to 271.1 mg/kg), Hg (up to 80 mg/kg), Pb (up to 46,200mg/kg), and Zn (up to 18,200 mg/kg), although even such obtained values are unnatural and dangerous for the environment [Miler et al. 2022]. In comparison, the average Zn and Pb content along the Geul River in eastern Belgium was much lower than those measured in Ligota stream sediments. In the post-flotation sediments of mine ponds and embankment sediments in the catchment area of this river, the average PHEs content was, respectively: Zn – 37,513 and 3,858 mg/kg, Pb – 19,206 and 1,302 mg/kg, Cd – 146 and 7 mg/kg, and As – 679 and 23 mg/kg [Cappuyns et al. 2006].

The use of PCA led us to infer that the elevated concentrations of PHEs and other elements in sediment may be the result of the inflow of contaminated water and sewage from various sources. The data set presented in Table 5 groups elements by their various sources. Factor F1 (Cr and Mn loads) suggests a main source of modern iron and steel metallurgy source. F2 (Ag, As, Cd, Pb, and Zn loads), as in topsoils, combines elements from mining and processing of Zn-Pb ores, as well as zinc metallurgy. F3 (Co, Ni, and S loads) can be associated with lithologicalanthropogenic origin. Iron in F4 comes from source rocks, elevations in its content is mainly associated with the presence of ironworks.

In order to determine the potential ecological risk for benthic organisms, the test results for the analyzed chemical elements in sediments were compared with the appropriate TEC and PEC values. The TEC values for Cd, Pb and Zn were exceeded in almost all samples, and the threshold for Cu was exceeded in more than half of them. PEC values were exceeded for Cd, Pb and Zn in over 50% of the sediment samples; this may pose a serious threat to the health and life of many aquatic organisms.