Anthropogenic enrichment of the chemical composition of bottom sediments of water bodies in the neighborhood of a non-ferrous metal smelter (Silesian Upland, Southern Poland)

An assessment was carried out of the anthropogenic enrichment of the chemical composition of the bottom sediments of water bodies situated in an area with an urban and industrial character (63.7% of the total area). The endorheic catchments of the water bodies studied are lithologically uniform with sandy formations accounting for more than 90% of the surface area. On the basis of geoaccumulation index values, it was found that the bottom sediments of the water bodies studied were contaminated with the following elements: Cd, Zn, S, As, Pb, Sr, Co, Cr, Cu, Ba, Ni, V, Be, in degrees ranging from moderate to extreme, with lower contamination (or absence of contamination) with the same elements being found in the formations present in the vicinity and in the substrate of the basins of water bodies. It was found that one consequence of the fact that these water bodies are located in urban and industrial areas is that there is anthropogenic enrichment of the chemical composition of bottom sediments with certain basic components (organic matter, Mn, Ca and P compounds) and trace elements: Cd, Zn, Pb, Sb, As, Cu and Co, Br, Ni, S, Be, Cs, Sr, V, Cr, Sc, Ba, U, Ce, Eu and Th, with virtually no enrichment of sediments with the other basic and trace components analysed (La, Rb, K2O, Nd, Sm, Na2O, Hf, SiO2, Zr).

Laboratory research. Laboratory tests were carried out at the Laboratory for Soil and Rock Analysis of the Faculty of Earth Sciences of the University of Silesia in Sosnowiec (Poland) and at Activation Laboratories Ltd. at Ancaster (Canada) 21 .
The mechanical composition of sediments was determined using the sieving and areometric methods 22 . During the preparation of samples for geochemical tests, the material was ground in an agate mortar and the <0.063 mm fraction was isolated using chemically inert sieves.
Chemical composition was determined using inductively coupled plasma (ICP) atomic emission spectrometry and instrumental neutron activation analysis (INAA) in accordance with the standards applied at Activation Laboratories Ltd 23,24 .
The ICP method was used to determine the concentrations of the following elements: SiO 2 , Al 2 O 3 , Fe 2 O 3 , MnO, MgO, CaO, Na 2 O, K 2 O, TiO 2 , P 2 O 5 , loss on ignition, Ba, Be, Sr, V, Y, Zr 23 . Samples were prepared and analysed in batches with each batch containing a method reagent blank, certified reference material and 17% replicates. The samples analysed were mixed with lithium metaborate and lithium tetraborate and fused in an induction furnace. Subsequently, the molten material was poured into a solution of 5% nitric acid containing an internal standard and mixed continuously for about 30 minutes until it dissolved completely 23,25 . The samples were then tested for the presence of major oxides and of selected trace elements on a combination simultaneous-sequential Thermo Jarrell-Ash ENVIRO II ICP spectrometer 23,26 . Using the same method, the content of Cd, Cu, Pb, Ni, S and Zn was determined after the complete dissolution of 0.25 g aliquots. The sample aliquot was digested with a mixture of HClO 4 , HNO 3 , HCl, and HF at 200 °C to fuming and was then diluted with aqua regia 23 .
During the ICP analysis, reagent blanks with and without the lithium borate flux were analysed alongside the method reagent blank. Interference correction verification standards were analysed as well 10,23 . Multiple USGS and CANMET certified reference materials were used for calibration (two standards for every group of ten samples) in order to bracket groups of samples. Internal standards were also added to the sample solution, which was then further diluted. USGS and CANMET certified reference materials were used for calibration purposes. A proprietary methodology was used to introduce the sample into the Perkin Elmer SCIEX ELAN 6000 mass spectrometer 23 . The precision and accuracy of the analyses conducted are as follows: a) at the lower detection limit: +/− 100%; b) at 10 times the lower detection limit: +/− 15-25%; c) at 100 times the lower detection limit: better than 10% 23 .
Water body name and number of samples ( Fig. 1) Table 1. Morpho-and hydrometric parameters of the water bodies studied (after Rzetała 20 ; revised and supplemented).

Year of creation
The INAA method was used to determine the concentrations of the following elements: As, Br, Ce, Co, Cr, Cs, Eu, Hf, La, Nd, Rb, Sc, Sb, Sm, Th and U 21,23 . A 1 g aliquot was placed in a polyethylene vial and irradiated with flux wires and an internal standard (one for 11 samples) at a thermal neutron flux of 7 × 10 12 n cm −2 s −1 . After a delay of seven days introduced to allow Na-24 to decay, the samples were counted using a high purity Ge detector with a resolution higher than 1.7 KeV for the 1332 KeV Co-60 photopeak 23,27 . The decay-corrected activities were compared to a calibration obtained with the use of multiple certified international reference materials using flux wires. From 10% to 30% of the samples were rechecked by running the measurement again. The standard present served only to check measurement accuracy and was not used for calibration purposes 23 . The precision and accuracy of the analyses conducted are as follows: a) at the lower detection limit: +/− 100%; b) at 10 times the lower detection limit: +/− 10-15%; c) at 100 times the lower detection limit: better than 5% 23 .
The I AP index was used to assess the anthropogenic enrichment of deposits with toxic metals, non-metals and metalloids (Eq. 2). The anthropogenic enrichment factor of bottom sediments indirectly reflects the effectiveness of accumulation of allochthonous and autochthonous matter in the water body; this accumulation is often identified with contamination. For a given element, the I AP value is the ratio of its mean content in bottom sediments and its mean content in the sediments in the vicinity of the basin and its substrate (the mean value can be regarded as the result of tests of so-called mixed samples or as the mean value for multiple samples tested). An I AP value greater than unity (I AP > 1.0) indicates that the bottom sediments have been enriched. This value increases as the ratio of the concentration of the element in question in bottom sediments to its concentration in the vicinity of the basin increases. The index value drops below 1.0 (0.0 < I AP > 1.0) if the concentration of the element in question in the sediments is lower than its concentration in the formations surrounding the basin; this indicates that there has been no enrichment of bottom sediments. This index is calculated as follows 11,31 : where: I AP -the anthropogenic enrichment factor for bottom sediments (dimensionless number); C BS -the average concentration of the substance in question in bottom sediments of the water body; C SR -the average concentration of the element in question in substrate sediments and in the vicinity of the basin.

Results
Lithological properties and land use. The study area has a peculiar geological structure which enabled a unique geochemical comparison to be made between the sediments in the vicinity and the substrates of the basins of the water bodies and of the bottom sediments. A cover of Pleistocene sediments rests on a geological foundation formed by Carboniferous rocks, and the river valleys are filled with Holocene sediments. The most widespread of the surface formations are Pleistocene sediments (79.7% of total area). These are sands and gravels of glacial and fluvio-glacial origin alongside Pleistocene sandy and silty boulder clay eluvia and sands and gravels on accumulation terraces. In lithological terms, these are mainly sandy and gravelly deposits, which attracted economic interest and started to be exploited in the first half of the 20 th century. Holocene fluvial deposits were found in 12.6% of the area. In ca. 7.7% of the area, Carboniferous grey shales with sandstones and coal, sandstones and conglomerates are exposed (Fig. 2). (2019) 9:14445 | https://doi.org/10.1038/s41598-019-51027-w www.nature.com/scientificreports www.nature.com/scientificreports/ The water bodies are surrounded by typical urban and industrial areas. Built-up urban areas are the most prevalent (34.4%) within ca. 14 km 2 (Fig. 3); industrial areas together with industrial wasteland account for 21.2% and 8.1% is occupied by communications infrastructure and associated unused land. Forests, plantations, scrub and cultivated green areas occupy 16.3% of the surface area, and meadows and arable land account for 8.9% and 2.9% respectively. The surface covered with water is more than 1.1 km 2 (8.2%). the chemical composition of the sediments. In geochemical terms, the sediments studied are clearly differentiated. This concerns both their basic composition and their content of trace elements (Tables 2 and 3).
The geochemistry of the sediments present in the vicinity of water bodies is equally varied. As concerns their basic composition, the following substances were identified: SiO 2 (79.90-86.10%), Al 2 O 3 (5.75-9.20%), Discussion the geochemical properties of the sediments. Variations in the chemical composition of sediments between individual endorheic water bodies are conditioned by the geological substrate, the manner in which the catchment is utilised and the type of atmospheric deposition 9 . The chemical composition of bottom sediments is varied and indicates strong human impact (Tables 2 and 3).
As concerns overall composition, SiO 2 prevails in almost all samples and the accompanying loss on ignition (measure of organic matter content) is usually inversely proportional to SiO 2 content. SiO 2 content ranges from 21.75% to 80.76% and loss on ignition ranges from 4.20% to 32.19%. Generally, the correlation between higher SiO 2 content and lower loss on ignition results from catchment conditions (substrates consisting of sandy Pleistocene formations) and human impact (former mineral workings without any overburden and deposit). A high loss on ignition indicates a significant organic matter content in the sediments 10 . The coastal zones of lakes, which are often colonised by compact stands of rushes, play a major role in determining the amount of this matter 32 . These stands exhibit high bioproductivity and the plant fall originating there as autochthonous matter has a significant impact on the chemical composition of sediments 8,9 . Apart from organic matter and silica, bottom sediments also include the following minerals or their components as their basic building materials: Al 2 O 3 and Fe 2 O 3 as well as manganese, magnesium, calcium, sodium, potassium, titanium and phosphorus compounds. Their percentage shares in sediments are also dependent on catchment lithology and the nature of the human impact 20 . Against the background of all test results concerning basic components, Al 2 O 3 content (in the range from 6.71% to 11.70%) stands out, which may indicate a relationship between the concentration of this substance in the sediments and the long-standing activity of a nearby non-ferrous metal smelter. Fe 2 O 3 concentration in the bottom sediments examined (from 3.06% to 12.23%) should be considered typical of water bodies in sand workings situated in catchments with a high proportion of post-glacial sandy formations 15 . In some places, Fe 2 O 3 may arise as a consequence of the presence of traces of bog iron ores. In addition the impact of local landfill sites or metallurgical industrial processes on bottom sediments cannot be ruled out. The high content of CaO (in the 0.62%-28.24% range) is related to the waste from non-ferrous smelters present in water body sediments, although the high share of calcium in the sediments 4 -forests, plantations, cultivated green areas, 5 -meadows (including abandoned agricultural land); 6agricultural land; 7 -watercourses and water bodies; 8 -boundaries of endorheic water body catchments; 9non-ferrous metal smelter.  www.nature.com/scientificreports www.nature.com/scientificreports/ in neighbouring areas is due to the presence of carbonate Triassic formations in the geological structure and is related to human agricultural activity. The fairly universal and uniform presence of phosphorus in bottom sediments may be attributed to natural processes (e.g. the leaching of bioelements from the rocks present within the catchment) as well as to anthropogenic sources (e.g. discharges of household, municipal and industrial sewage and run-off from agricultural land) 20 .
In addition to the macroelements, the chemical composition of bottom sediments also includes a number of trace elements. Their presence in the environment is determined both by natural processes (e.g. the weathering of rocks) and by their supply from anthropogenic sources (e.g. industrial processes, traffic) 8 . Of special geoecological significance are the quantitative and qualitative differences in the presence of some metals (especially of so-called heavy metals), non-metals and metalloids. Among the elements identified in bottom sediments, Zn and Pb were present in the highest average amounts (thousands of mg/kg). Ba, Zr, Sr, Cu, Cr, Cd and As are present in average concentrations of hundreds of mg/kg. Average concentrations ranging from around a dozen to several dozen mg/kg are reached by Ce, V, Ni, Rb, La, Co, Sb, Nd, Y, Hf, Th, Sc, and Br; the remaining elements are present in smaller amounts (Cs, Sm, U, Be, Eu); the average sulphur content found was 2.4%. The quantities of individual trace elements found in the bottom sediments of the water bodies studied are extremely high on a global scale 20 . This thesis is confirmed by the results of many years of research conducted in different parts of the world where much lower concentrations of the elements identified were found [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] . Record-high concentrations of the measured elements -indicated in the analysis of the results of calculations of standard deviation for the raw data (Table 3) and the anthropogenic enrichment factor of bed sediments (Table 4) -confirm the references to the geochemical background of the formations occurring in the upper part of the Earth's crust [52][53][54] , as well as water sediments found in Europe 55 . In addition to the extremely high concentrations of individual elements in the bottom sediments studied, they also exhibit a quite large spatial variability ( Table 3).
The very high concentrations of zinc and lead in water body sediments are typical of areas situated in close proximity to ore smelting centres and waste dumps from non-ferrous smelters. Owing to the proximity of a non-ferrous smelting plant (1.0-2.0 km) to the water bodies studied, the area is contaminated with these elements.  54 . The concentrations of these elements are also much higher than the regional geochemical background for water sediments determined by Lis and Pasieczna 28 at 259.0 mg/kg for zinc and 59.0 mg/kg for lead.  www.nature.com/scientificreports www.nature.com/scientificreports/ In a similar manner to zinc and lead, the concentrations of other heavy metals (Cu, Cr, Cd, Ni) found in the bottom sediments of water bodies situated within the zones affected by non-ferrous smelting plants are very high 16 . The regional geochemical background for copper in water body sediments corresponds to the average amount of this element present in the Earth's crust at 15 mg/kg 28,56 , while in the sediments studied its concentration ranges from 20.0 to 298.0 mg/kg. The concentrations of chromium (69.0-203.0 mg/kg), cadmium (8.5-444.0 mg/kg) and nickel (20.0-148.0 mg/kg) found in sediments are significantly higher than the natural concentrations of these elements in the region determined by Lis and Pasieczna 28 , which amount to 9.0 mg/kg (Cr), 2.5 mg/kg (Cd) and 11.0 mg/kg (Ni). The geochemical background for chromium in various sedimentary rocks ranges from 5 to 120 mg/kg 56 . The average cadmium content in the Earth's crust is 0.1 mg/kg and nickel content in the Earth's crust averages 20-135 mg/kg 54 .
The presence of cobalt in aquatic ecosystems may be caused to a large extent by the denudation of the natural rock and soil environment 51 . Cobalt, which is present in the lithosphere at ca. 40 mg/kg 56 , was detected in the bottom sediments of the water bodies examined in amounts ranging from 10.0 to 90.0 mg/kg. In each case the concentrations of Co are higher than the regional geochemical background determined by Lis and Pasieczna 28 at 4.0 mg/kg. Some of the trace elements found in the sediments are alkaline Earth metals (e.g. beryllium, barium, strontium) and their content in the Earth's crust is lower than that of calcium and magnesium, which are the most  www.nature.com/scientificreports www.nature.com/scientificreports/ common among this group of elements 56 . Strontium, which is widely used in industry, is present in the bottom sediments of the water bodies studied in amounts ranging from 89.0 mg/kg to 1,107.0 mg/kg. Barium concentrations range from 430.0 mg/kg to 1,940.0 mg/kg. The natural strontium content in crustal rocks is estimated at 350 mg/kg and that of barium at 570 mg/kg 57 . Beryllium was found in bottom sediments of water bodies in amounts ranging from 1.0 to 7.0 mg/kg, which in most cases corresponds to its natural content (1.0-3.0 mg/kg) in the Earth's crust 54 , and is greater than or equal to the value (2 mg/kg) typical of sedimentary rocks as determined by Kabata-Pendias and Pendias 56 . The main anthropogenic source of this metal in the environment is the process of fuel combustion and therefore its migration to groundwater is highly influenced by the contact of water bodies with piles of waste rock, dust from power plants and municipal and industrial sewage.
Several of the elements identified belong to so-called lanthanides (cerium, europium, neodymium, samarium) that are present in the Earth's crust in trace amounts 56 . Although some of them are radiotoxic in higher concentrations, the amounts found in the bottom sediments studied do not pose any environmental threat.
Hafnium and zirconium, which occur together, are so-called transition metals, similar to lanthanum. In the Earth's outer crust, zirconium is present at concentrations of 167.0 mg/kg on average 56 , and in the sediments studied its concentration ranges from 72.0-1,195.0 mg/kg. Lanthanum, which occurs in the Earth's crust at 11-30 mg/ kg 54 , reaches concentrations from 25.0 mg/kg to 52.2 mg/kg in the sediments studied. Vanadium is a metal used in industry whose natural concentration in the Earth's crust is estimated at 140 mg/kg; its concentration in the bottom sediments studied is lower (44.0-140.0 mg/kg). Another metal is scandium with a natural concentration in the Earth's crust of 11 mg/kg 56 ; in the sediments studied the level is similar (6.9-16.3 mg/kg). Yttrium is another metal that occurs in the Earth's crust at a level of 20 mg/kg 54 ; in the sediments studied, it was found in similar amounts (14.0-38.0 mg/kg).
Two actinides -thorium and uranium -are present in the samples of bottom sediments examined in amounts (6.0-24.0 mg/kg -Th, 1.3-7.9 mg/kg -U) equivalent to or slightly higher than their natural concentrations in the Earth's crust, which are assessed by Kabata-Pendias and Pendias 56 at ca. 12.0 mg/kg and ca. 2.5 mg/kg respectively.
As alkali metals, caesium and rubidium are considered -in spite of being easily soluble -not highly mobile and rapidly adsorbed by clay minerals 56 . In the samples of bottom sediments tested, caesium was found in amounts of 3.8-14.9 mg/kg. Rubidium is present in bottom sediments in amounts ranging from 20.0 mg/kg to 90.0 mg/kg. Some of the elements identified (arsenic and antimony) are metalloids with properties that are intermediate between metals and non-metals 58 . Their presence in the bottom sediments of the water bodies studied is probably the result of non-ferrous ore mining and metallurgy as well as combustion processes and their fairly widespread use. Arsenic and antimony, whose natural contents in the lithosphere are up to 18 mg/kg and 0.2 mg/ kg respectively 56 , were found in amounts ranging from 14.0 to 330.0 mg/kg (arsenic) and from 3.5 to 80.6 mg/kg (antimony).
Bromine is a non-metal which is present in the Earth's crust at a natural level of ca. 1 mg/kg 56 while the samples analysed contained 2.0-34.0 mg/kg. Sulphur content ranges from 0.3% to 4.7%; it is among the common ingredients of bottom sediments in the water bodies analysed which are subject to the impact of human industrial activity.
The values of the anthropogenic enrichment index of bottom sediments in water bodies indicate that basins in which water is retained fulfil the function of local sedimentary basins in which autochthonous as well as transit (allochthonous) pollutants accumulate 11 . The considerable increase in the concentration of some main components and trace elements in bottom sediments against the background of their concentrations in the vicinity of the basin indicates the presence of an important issue with both environmental and social implications. Basins of such water bodies which, like their endorheic catchments, have been transformed by human activity, are in contact with the waste left after processing zinc and lead ores. The long-standing impact of non-ferrous metallurgy amplifies human-induced environmental changes, which are typical of urban and industrial areas.
The anthropogenic enrichment of bottom sediments in the water bodies analysed has the characteristics of contamination. Its equivalent is the presence of the so-called zinc desert in the vicinity of the water bodies 59 . Contamination with heavy metals (and particularly toxic metals) probably explains the high mortality of tench in the Hubertus water body and the disappearance of eels from the Morawa Lake 8,59 . Kostecki 59,60 states that the heavy metal concentrations recorded in aquatic ecosystems already pose a threat to human health and the concentrations recorded in phyto-and zooplankton, vascular plants and ichthyofauna point to contamination 9 .

conclusions
The study area is an urban and industrial one (63.7% of the area in total). The endorheic catchments of the water bodies studied are lithologically uniform with sandy formations accounting for more than 90% of the surface area. www.nature.com/scientificreports www.nature.com/scientificreports/ On the basis of geoaccumulation index values it was found that the bottom sediments of the water bodies studied were contaminated with the following elements: Cd, Zn, S, As, Pb, Sr, Co, Cr, Cu, Ba, Ni, V, Be, in degrees ranging from moderate to extreme, with lower contamination (or absence of contamination) with the same elements being found in the formations present in the vicinity and in the substrate of the basins of water bodies.
The magnitude of anthropogenic enrichment of bottom sediments against the background of surface formations in the vicinity can be used as a complementary or alternative indicator of the extent of contamination of bottom sediments and the geoecological status of aquatic ecosystems. The values of the anthropogenic enrichment index for sediments should be taken into account when planning the economic use of such water bodies and carrying out remediation work.