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This study monitored the concentration and distribution of the oxides of Cr, Ni, Cu, Zn and As in soils overlained by different lithological materials in southeast Nigeria. A 30 × 30 m spatial resolution of digital elevation model guided the selected eight soil profile pits dug for the study. A total of n = 27 soil samples were collected from the eight soil profile pits. Samples were air dried, and milled into 3–4 µm powder and analyzed using X-ray fluorescence. The result revealed that the oxides were irregularly distributed vertically, with the least heavy metal oxides obtained in the Ap horizons. Nevertheless, Cr2O3 was the most dominant and potentially toxic alongside NiO in Ishibori. Also, As2O3 was potentially toxic in most of the studied soils, with those in Ishibori as the most prone. Using multiple linear regression, the prediction was within the acceptable range (R2 > 0.50) except for As. For the prediction function of Cr, fine and coarse sand were negatively correlated with Cr, while CEC was positively correlated with Cu and Zn.

Colluvisols represent an important part of the soil cover, occupying concave slope elements especially in landscapes with undulating relief. Their development reacts to changes in land use or climate, manifested by intense erosion activity or longer resting periods with predominantly in-situ pedogenesis. In climatically, pedologically and historically different regions, diverse colluvial profiles can be encountered. In this study, we investigated deep colluvial profiles in three agricultural plots in Czechia with different soil cover, climatic and geological conditions in order to identify differences in the depositional pattern and erosion history of the areas. In each of the plots, two profiles (depths ranging from 200 to 400 cm) were opened in the toe-slope and side valley areas. Individual layers were investigated by various methods, including optically stimulated luminescence dating, 137Cs activity, concentration of vertically stable geochemical tracers (organochlorine pesticides, nutrients) or micromorphology and clay mineralogy, allowing the layers to be linked to periods of human activity. In all study areas, a significant difference in the colluvial deposition mechanism was found in the toe-slope and side valley areas. While the positions in the side valleys were mainly composed of older material with a minimum concentration of human-bound substances, the profiles in the toe-slopes are characterized by a significant deposition of recently accumulated material. The most pronounced redistribution of material was recorded in the Chernozem area on loess. In the toe-slope area, maxima of 137Cs, DDT (up to 350 µg/kg) and phosphorus were found at 100-140 cm, indicating the very low age of this layer (from the mid-20th century). The mineralogical and chemical composition of this layer and the layer below (140-220 cm) shows considerable similarities to the substrate material, indicating severe truncation of the source soils and accumulation of ploughed parent material. In contrast, in the side valley, this new material was found only in the topsoil, with approximately 3 m of older, humus-rich material beneath. This area is therefore not an area of recent deposition, but rather of material transport. The original buried Chernozem was found in both cases at a depth of about 300-350 cm. In the Cambisol area, the combination of rill and sheet erosion led to the formation of a highly stratified profile with a large variation in texture or humus content. The maximum of human-bound substances (137Cs, HCB, DDT) was found at a depth of 1 m, underlain by older material with signs of post-depositional pedogenesis (weathering and redox processes). The area of side valley was, as in the previous area, almost unaffected by recent sedimentation. In Luvisol area, the concentration on human-bound substances was generally lower and affected only the upper, humus-rich layer (ca 80 cm) of the Colluvisols, both at the toe-slope and the side valley. Below this layer, the profiles are characterised by relatively pronounced pedogenesis in the sedimentary material (clay coatings visible at the thin sections), indicating slower sedimentation and a longer period of sedimentary quiescence.Study was supported by grant nr. 21-11879S of the Czech science foundation and MEYS CR project nr. CZ.02.1.01/0.0/0.0/16_019/0000845.

Soil degradation due to water erosion is one of the greatest problems of agricultural soils worldwide. To be able to map the extent of soil degradation and consequently propose actions for soil improvement, an effective approach is needed. Soil organic carbon (SOC) content and its time fluctuations is one of the key features characterizing the given site and occurring processes. It is widely accepted as the main soil quality indicator and therefore can be used for soil degradation assessment. Traditional laboratory techniques (dry combustion, wet oxidization) of soil organic carbon determination are usually labor intensive and time consuming, which means they are not suitable for large sample collections (e.g., large areas or continual monitoring). Therefore, there is a need for fast, reliable, and cost-effective techniques. Our previous study documented that the VIS-NIR reflectance spectroscopy and magnetic susceptibility can be a very efficient tool for SOC mapping with the Chernozem (a loess region of South Moravia, Czech Republic) areas heavily affected by water erosion. Within this area colluvial soils with up to an about 4 m deep humus enriched horizon were developed. Distribution of soil properties within the colluvial soil profiles at several positions were evaluated using standard and novel methods to distinguishing the different sedimentation phases and understanding colluvial soil formation. The same study was also performed in another two locations (Cambisol and Luvisol areas). Results showed that while both methods could be used for estimation of SOC distribution within the soil profiles in the Chernozem area, in the other two areas the VIS-NIR reflectance spectroscopy method was less accurate and magnetic susceptibility was inaccurate because there was no correlation between SOC and content of ferrimagnetic particles. Acknowledgement: Study was supported by the Czech Science Foundation, project "Pedogenesis of colluvial soils: a multidisciplinary approach in modeling the dynamics of development in the soil-landscape environment" (No. 21-11879S) and also by the European Structural and Investment Funds, projects NutRisk (No. CZ.02.1.01/0.0/0.0/16_019/0000845).

The purpose of this study was to investigate the key geochemical and mineralogical factors that could affect the fractionation of stable thallium (Tl) isotopes in soil. A set of grassland soil samples enriched in geogenic Tl in combination with selected Tl-containing mineral materials from the Czech Republic (Kluky) were investigated for this purpose. A combination of X-ray diffraction analysis (XRD), chemical extractions and stable isotope analysis were used to understand the behaviour of Tl and its isotope systematics within the soil profile. The results demonstrate significant incorporation of Tl in pedogenic Mn-oxide, which led to a large accumulation of the heavy 205Tl isotope (~+14 ε205Tl units), presumably resulting from continuous redox reactions with Mn-oxides and systematic accumulation of heavy isotope fraction onto the oxide surface(s). Consequently, we concluded that the Mn-oxide-controlled Tl uptake is the primary cause of the observed 205Tl enrichment in the middle profile zone, at the A/B soil horizon interface, with up to +4 of ε205Tl. Furthermore, our results displayed a clear relationship between the Tl isotopic fractionation degree and the Mn-oxide soil concentration (R2 = 0.6), as derived from the oxalate-extractable data. A combination of soil and mineralogical considerations suggests that 205Tl enrichment in the soil samples is also partly due to the Tl present in micaceous clay minerals, mainly illite, which is the predominant pedogenic Tl host phase. Supported by our previous results, this Tl behaviour can be inferred from systematic Mn-oxide degradation and the associated Tl (enriched in 205Tl) cycling in the studied soils and therefore, presumably in the redoximorphic soils in general.

Microbial sulfidogenesis plays a potentially important role in As biogeochemistry within wetland soils, sediments, and aquifers. This study investigated the effects of microbial sulfidogenesis on As mineralogy in the As-enriched wetland soil found at the natural geochemical anomaly of the Smolotely-Lisnice (Czech Republic) historical gold district. The distribution and speciation of As as a function of soil depth, and the metabolic properties of microbial communities in different sulfidogenic domains were examined by bulk soil as well as pore water analyses, selective chemical extractions, S isotopes, and DNA extractions. Total solid-phase analyses and selective extractions of the soil samples below ∼40 cm showed that As (up to 1.16 g kg−1) and Fe(II) are coupled to S and TOC, and had accumulated to a considerable extent in the exterior parts of NOM fragments (up to 19 wt.% As). Microscale imaging and Raman spectroscopy revealed that As speciation in the NOM exteriors is a combination of realgar (α-As4S4), bonazziite (β-As4S4) and arsenian Fe sulfides, primarily greigite (Fe3S4) and framboidal pyrite (FeS2). The sulfide phases were depleted in the 34S isotope by 6.3–29.4‰ relative to pore water SO42−; thus implying their biologically induced formation. Microbial communities associated with sulfidogenic environments in NOM and bulk soil had variable compositions, although the dissimilative SO42− reduction was usually the main metabolic trait. Relatively low isotopic fractionation in sulfide-rich NOM fragments (6.3–11.6‰) compared to bulk soil (down to −26.1‰) revealed a reservoir effect that developed probably at mm-scales. This indicates formation of sulfide phases in highly localized environments depleted in aqueous SO42− due to strong microbial sulfidogenesis when compared to the transfer rate of the solutes. The very high proportion of fermenting microorganisms in sulfide-rich NOM fragments provided further evidence of strongly reducing conditions, which are a prerequisite for sulfide phase precipitation. We have shown that by the development of suitable conditions for sulfidogenesis, NOM fragments play an active role in As immobilization in an As-enriched wetland soil. Regarding the effectiveness of As sulfidogenesis in shallow wetland soils to remediate groundwater, our findings imply that As contamination may either be limited by the low content of labile organic matter or by the fast transfer of solutes (groundwater flow).

The dynamics of Cu and Pb were studied in eight soil profiles (Luvisols, Chernozems), located at various distances from the tailing dams near a closed Cu-Pb-(Zn)-Ag mine at Kombat (Namibia) by a combination of isotope and elemental studies, leaching techniques and speciation modelling. Tailings, soils and bedrocks were analyzed for the bulk Cu and Pb concentrations, for their chemical forms using the sequential extraction procedure and for the isotope compositions of Cu (δ65Cu) and Pb (206Pb/207Pb, 208Pb/206Pb). In spite of the differences in the contamination of the studied profiles by tailing dust, both soil types exhibit characteristic trends in the behaviour of metals and distribution of their isotopes. While most Luvisols exhibit an increase in the metal content towards depth in the profile, Chernozems exhibit the opposite trend (decrease in metal content with depth) or similar contents in the whole profile. Luvisols were mostly characterized by changing δ65Cu values as a function of depth. The value of δ65Cu decreases with depth to the Bt horizon and then the δ65Cu value increases with increasing depth. Chernozems mostly yielded uniform Cu concentrations and isotope compositions in all the soil horizons, clearly contrasting with the isotopically lighter compositions of the carbonate bedrocks. Positive δ65Cu values in the tailing material affect the surface of the soil, especially soil sampled in its vicinity. In most Luvisols and Chernozems, the isotope composition of Pb exhibits similar patterns with a low 206Pb/207Pb ratio on the surface of the profile and with a slight increase to depth. The low 206Pb/207Pb values at the surface of the profiles are caused by dust from the tailings. The elemental and isotopic patterns of both contaminated and uncontaminated soil types reflect not only the distance from the tailing dam but also pedogenetic processes in the profiles and geochemical behaviour of both contaminants. The copper elemental and isotope patterns reflect the formation of more mobile species in the surface environment and movement of solutions and colloids and precipitation onto secondary minerals in Luvisols. Plant uptake of lighter isotopes in Chernozems can influence the Cu isotope patterns in these soil types. The limited movement of colloids and higher sorption capacity of Chernozems is manifested in the isotope compositions of Cu and Pb in their profiles.

Ore mining and processing in semi-arid areas is responsible for the generation of metal(loid)-containing dust, which is easily transported by wind to the surrounding environment. To assess the human exposure to dust-derived metal(loid)s (As, Cd, Cu, Pb, Sb, Zn), as well as the potential risks related to incidental dust ingestion, we studied mine tailing dust (n = 8), slag dust (n = 5) and smelter dust (n = 4) from old mining and smelting sites in northern Namibia (Kombat, Berg Aukas, Tsumeb). In vitro bioaccessibility testing using extraction in simulated gastric fluid (SGF) was combined with determination of grain-size distributions, chemical and mineralogical characterizations and leaching tests conducted on original dust samples and separated PM10 fractions. The bulk and bioaccessible concentrations of the metal(loid)s were ranked as follows: mine tailing dusts

Kabwe Town and its surroundings (central Zambia) belong to the most contaminated districts in Africa due to mining and smelting of local Pb-Zn ores. To assess the extent and intensity of this anthropogenic contamination, samples of topsoil (from a depth of 0 to 3 cm), together with reference subsurface soil from a depth of 70–90 cm, were collected in the area. In the Kitwe Town and downwind, the Pb and Zn contents in topsoils were found to be significantly higher compared to the permissible ecological limits used in Canada with regard to various land uses. Other elements (Cu, Fe, Mn, Cr, Ni and Ba) in topsoil demarcate only a small area of the former ore processing and smelter grounds. The gastric bioaccessibility of metals in topsoils was tested by a US EPA-adopted in vitro method using a simulated gastric fluid. The results revealed that the intake of Cd, Cu, Zn, Co, and As does not exceed the tolerable daily intake (TDI) values for children but, for Pb, almost 50% of the samples exceeded TDI. Therefore, the concentrations of gastric bioaccessible Pb in highly contaminated topsoils or in resuspended soil-derived dust particles may be considered to be an important health risk in the Kabwe area. The amounts of plant-available metals in topsoils were established by extraction with a diethylentriaminopentanacetic acid (DTPA) and triethanolamine (TEA) solution. These tests showed that the amounts of plant-available metals increase (median values, in mg kg−1) in the sequence: Cd (0.7) → Cu (3.9) → Mn (76) → Fe (79) → Zn (110) → Pb (126). Chemical stabilization of the pollutants in soils using a phosphate amendment caused a significant reduction of the plant-available fraction of Pb and Cd, but did not suppress their gastric bioaccessibility. Based on our results, various measures were suggested to reduce the impact of the pollution on the Kabwe Town population.

Vertical profiles of Tl, Pb and Zn concentrations and Tl and Pb isotopic ratios in a contaminated peatland/fen (Wolbrom, Poland) were studied to address questions regarding (i) potential long-term immobility of Tl in a peat profile, and (ii) a possible link in Tl isotopic signatures between a Tl source and a peat sample. Both prerequisites are required for using peatlands as archives of atmospheric Tl deposition and Tl isotopic ratios as a source proxy. We demonstrate that Tl is an immobile element in peat with a conservative pattern synonymous to that of Pb, and in contrast to Zn. However, the peat Tl record was more affected by geogenic source(s), as inferred from the calculated element enrichments. The finding further implies that Tl was largely absent from the pre-industrial emissions (>~250 years BP). The measured variations in Tl isotopic ratios in respective peat samples suggest a consistency with anthropogenic Tl (e205Tl between ~ -3 and −4), as well as with background Tl isotopic values in the study area (e205Tl between ~0 and −1), in line with detected 206Pb/207Pb ratios (1.16–1.19). Therefore, we propose that peatlands can be used for monitoring trends in Tl deposition and that Tl isotopic ratios can serve to distinguish its origin(s). However, given that the studied fen has a particularly complicated geochemistry (attributed to significant environmental changes in its history), it seems that ombrotrophic peatlands could be better suited for this type of Tl research.

The former Pb-Zn mining town of Kabwe in central Zambia is ranked amongst the worst polluted areas both in Africa and in the world. The fine dust particles from the ISF and Waelz slags deposited in Kabwe represent a health risk for the local population. Here, we combined a detailed multi-method mineralogical investigation with oral bioaccessibility testing in simulated gastric fluid (SGF; 0.4 M glycine, pH 1.5, L/S ratio of 100, 1 h, 37 °C) to evaluate the risk related to the incidental dust ingestion. The slag dust fractions contain up to 2610 mg/kg V, 6.3 wt% Pb and 19 wt% Zn. The metals are mainly bound in a slag glass and secondary phases, which formed during the slag weathering or were windblown from nearby tailing stockpiles (carbonates, Fe and Mn oxides, phosphates, vanadates). The bioaccessible fractions (BAFs) are rather high for all the main contaminants, with the BAF values generally higher for the ISF slags than for the Waelz slags: Pb (24-96%), V (21-100%) and Zn (54-81%). The results clearly indicate the potential risks related to the incidental slag dust ingestion. Even when a conservative value of the dust daily intake (100 mg/day) is considered, the daily contaminant intake significantly exceeds the tolerable daily intake limits, especially for Pb ≫ V Zn. At higher ingestion rates, other minor contaminants (As, Cd) also become a health risk, especially for children. The slag heaps in Kabwe should be fenced to prevent local people entering and should be covered to limit the dust dispersion.

The possibility of an adequate use of data and maps from historical soil surveys depends, to a large measure, on their harmonisation. Legacy data originating from a large-scale national mapping campaign, “Systematic soil survey of agricultural soils in Czechoslovakia (SSS, 1961–1971)”, were harmonised and converted according to the World Reference Base 2014 (WRB). Applying three different methods of taxonomic distance computation and quantitative analysis and reclassification of the selected soil properties, the conversion of so-called Basic soil representatives (BSR) – mapping soil units providing information about soil (type, subtype, variety) and lithology (parent material, texture, soil depth, skeleton content) – to their counterparts in the WRB has been effectuated. The results proved the good potential of the used methods for soil data harmonisation. The values of taxonomic distance correspond to the different concepts and settings of the soil classes in the harmonized soil classifications. Classes with specific and narrowly defined diagnostics, often with one or few strong and distinctive features, show close distances with their counterparts, and, often, have only one relevant counterpart. On the contrary, soils with variable soil properties were approximating several related units. The additional information on the soil skeleton content, texture, depth and parent material showed the potential in the specification of some units, though the harmonisation of the soil texture turned out to be problematic due to the different categorisation of soil particles. The resulting soil classes have been presented for each polygon (so-called soil district) as i) one to one conversion, when each BSR is converted to one, most probable, WRB soil class (Reference soil group, RSG) and ii) soil association corresponding to the three closest RSGs. The validation of the results in the study region showed an average overall accuracy for a one-to-one (59.4 %) conversion and a very good accuracy (83.8 %) for the polygons presented as soil associations. The conversion accuracy differed significantly in the individual soil units, and ranged from 92 % in Fluvizems to 0 % in Technosols and Histosols. The extreme cases of a complete mis-classification can be attributed to inconsistencies originating in the historical database and maps. The study showed the potential of modern quantitative methods in the legacy data harmonisation and also the necessity of a critical approach to historical databases and maps.Supported by the Ministry of Agriculture of the Czech Republic, Project No. QK1820389.

We studied arid desert soils from Namibia (Rosh Pinah) that were contaminated with up to 7 mg kg−1 of thallium (Tl) via dust emitted from a local flotation tailing dam. Chemical extractions of waste and soil materials indicated that most of the Tl is strongly bound, in accordance with X-ray diffraction and X-ray absorption spectroscopy data that point to the predominant association of Tl with metal sulfides and phyllosilicates. The isotope fractionation factor e205Tl of the soil samples (from −0.4 to +3.8) shows a positive linear relationship (R2 = 0.62) with 1/Tl, indicative for the mixing of two major Tl pools, presumably anthropogenic Tl and geogenic Tl. The e205Tl value for the topmost soil samples (∼+3) closely matches the e205Tl value for post-flotation waste particles with a diameter of

The Tsumeb mining District (Namibia) is affected by prolonged exposure to multisource contamination related to the mining and smelting of copper ores. This study was performed to assess the extent of contamination of topsoil and grass shoots on the basis of the copper isotopic composition. Compared to an uncontaminated area (δ65Cusoil = −0.01 to +0.14‰; δ65Cugrass = −0.17 to +0.03‰), the soil and grass in the contaminated area are enriched in the heavy isotope (δ65Cusoil = +0.13 to +0.76‰ and δ65Cugrass = +0.15 to +0.64‰). The Δ65Cugrass-soil value exhibits small variations (+0.06 to −0.17) due to the variable degree of grass surface contamination, depending on the grass washing procedure used. The enrichment of soil and grass in the contaminated area in 65Cu reflects the Cu isotopic composition of old flotation tailings (δ65Cu = +0.95 to +1.1‰), slag (+0.11 to +0.55‰) and particles which originate from the smelting and flue gas cleaning processes (+0.15 to +0.49‰). The long history of mining and processing of copper ores in the Tsumeb area and the different isotopic composition of ore concentrates smelted in the local metallurgical plant do not allow assessment of whether the smelting process leads to isotope fractionation of copper. However, the isotopic composition of Cu in the sulfidic feed, slag and dust particles sampled over several hours showed that the dust collected from the dusthouse of the local smelter is isotopically lighter (δ65Cu = +0.15‰) relative to the isotopic composition of the charge (δ65Cu = +0.28 and +0.44‰). The results of this investigation demonstrate that the isotopic composition of Cu in soils and grasses can be used to assess the intensity of contamination in areas where Cu ores are mined and processed provided that the isotopic compositions of the ore processing products are different from the isotopic compositions of the uncontaminated soils and vegetation.

Dust emissions from copper smelters processing arsenic-bearing ores represent a risk to soil environments due to the high levels of As and other inorganic contaminants. Using an in situ experiment in four different forest and grassland soils (pH 3.2–8.0) we studied the transformation of As-rich (>50 wt% As) copper smelter dust over 24 months. Double polyamide bags with 1 g of flue dust were buried at different depths in soil pits and in 6-month intervals; then those bags, surrounding soil columns, and soil pore waters were collected and analysed. Dust dissolution was relatively fast during the first 6 months (5-34%), and mass losses attained 52% after 24 months. The key driving forces affecting dust dissolution were not only pH, but also the water percolation/retention in individual soils. Primary arsenolite (As2O3) dissolution was responsible for high As release from the dust (to 72%) and substantial increase of As in the soil (to a 56 × increase; to 1500 mg kg−1). Despite high arsenolite solubility, this phase persisted in the dust after 2 years of exposure. Mineralogical investigation indicated that mimetite [Pb5(AsO4)3(Cl,OH)], unidentified complex Ca-Pb-Fe-Zn arsenates, and Fe oxyhydroxides partly controlled the mobility of As and other metal(loid)s. Compared to As, other less abundant contaminants (Bi, Cu, Pb, Sb, Zn) were released into the soil to a lesser extent (8-40% of total). The relatively high mobility of As in the soil can be seen from decreases of bulk As concentrations after spring snowmelt, high water-extractable fractions with up to ∼50% of As(III) in extracts, and high As concentrations in soil pore waters. Results indicate that efficient controls of emissions from copper smelters and flue dust disposal sites are needed to prevent extensive contamination of nearby soils by persistent As.

Thallium (Tl) concentration and isotope data have been recorded for contaminated soils and a set of industrial wastes that were produced within different stages of Zn ore mining and metallurgical processing of Zn-rich materials. Despite large differences in Tl levels of the waste materials (1-500mgkg-1), generally small changes in e205Tl values have been observed. However, isotopically lighter Tl was recorded in fly ash (e205Tl∼-4.1) than in slag (e205Tl∼-3.3), implying partial isotope fractionation during material processing. Thallium isotope compositions in the studied soils reflected the Tl contamination (e205Tl∼-3.8), despite the fact that the major pollution period ended more than 30 years ago. Therefore, we assume that former industrial Tl inputs into soils, if significant, can potentially be traced using the isotope tracing method. We also suggest that the isotope redistributions occurred in some soil (subsurface) horizons, with Tl being isotopically heavier than the pollution source, due to specific sorption and/or precipitation processes, which complicates the discrimination of primary Tl. Thallium isotope analysis proved to be a promising tool to aid our understanding of Tl behavior within the smelting process, as well as its post-depositional dynamics in the environmental systems (soils).

Historical Pb–Zn mining and smelting in Kabwe in Zambia have made it one of the most polluted cities in the world. Four soil profiles were collected around the smelter and in remote locations, and two pine trees (Pinus montezumae L.) were sampled for tree ring cores. These were analyzed for Pb, Zn and Cu contents and Pb isotopic ratio. Furthermore, the C isotopic composition of tree rings was also assessed. High concentrations of metals are present only in the top layers of soil and are higher in soils closer to the smelter (up to 16000 mg kg−1 Pb; 14000 mg kg−1 Zn; 600 mg kg−1 Cu) compared to remote soils (up to 194 mg kg−1 Pb; 438 mg kg−1 Zn; 46 mg kg−1 Cu). Metals are also present in trees and the one located furthest from the slag dump contains higher metal concentrations (up to 6.48 mg kg−1 Pb; 10.6 mg kg−1 Zn; 10.2 mg kg−1 Cu), possibly due to the deposition of wind-blown particles. Results of a sequential extraction procedure (SEP) showed that metal contaminants are not available for tree root uptake and the above-ground processes must be more important. The Pb isotopic ratios of slags, tree rings, and topsoils average at 206Pb/207Pb = 1.15, corresponding to the signature of local ores and smelting slags, thus confirming that the mine and smelter are the main sources of contamination in the area. The results were compared to the historical records of smelter production. Tree ring Pb and Zn concentrations, δ13C and 206Pb/207Pb reveal linear dependence on production with different statistical significance.

We studied Fe-Mn concentric nodules from Cutanic Luvisol in the northern part of Namibia, where agricultural fields are irrigated with the drainage water from the Kombat Cu-Pb-(Zn) mine (pH 7, metal concentrations in μg l − 1 : Fe 7, Mn 10, Zn 7, Cu 18). Concentric nodules (0.5–2 cm in size) were mostly found towards the bottom of the sampled soil profile (Btcg2 horizon, depth 100–120 cm). Comparisons with the bulk chemical composition of the soil matrix showed that Fe-Mn nodules were enriched in metals, metalloids and other trace elements (with a few exceptions, enrichment factors varied in the range 1.3–6.4). The concentrations of the elements of interest in the Fe-Mn nodules were as follows (mg kg − 1 ): As 23.1, Ba 3840, Cd 6.83, Cu 450, Pb 597, Zn 137. The X-ray diffraction analysis indicated that the nodules were composed of quartz, goethite, hematite, illite/mica, pyrochroite, lithiophorite and birnessite. The scanning electron microscopy (SEM) observations confirmed that the internal structure of the nodules with concentric rings reflected seasonal changes in the redox conditions. Spot analyses and X-ray elemental maps performed using energy/wavelength dispersion spectrometry (EDS/WDS) showed that the concentrations of metalloids were rather low except for the slightly elevated Ba concentrations, which were observed only within the Mn oxide-rich zones. Selective extractions were used to understand the partitioning of trace elements within the individual phases. Whereas Mn oxides sequestered the majority of the Cd (up to 98%), Ba, Pb and rare earth elements (REEs) (up to 78%), other metals such as Cu and Zn exhibited much lower values (47–65%) and, together with oxyanionic species (As, Cr, V), were also significantly bound to Fe oxides. The pH-static leaching test conducted in the pH range 2–12 indicated that the majority of the trace elements were mostly leached under acidic conditions with the exception of As, which was highly solubilized at pH 12 (up to 17%). Whereas Ba, Cd, Cu and Zn were significantly released under acidic conditions (up to 12%), the leaching of Pb was almost negligible over the entire pH range. Our results show that Fe-Mn nodules act as significant traps for trace metals in Luvisols irrigated by mine water. However, an abrupt decrease in the pH and changes in the redox conditions may cause the dissolution of Fe-Mn nodules and subsequent release of contaminants into the soil system.

Legacy soil data currently represents an irreplaceable source of data for many national and international applications. Their full use at the international level largely depends on adequate harmonization. In this study, we adopted different methods of taxonomic distance and reclassification of soil properties to convert a large-scale database originating from an extensive national mapping campaign of agricultural soils in Czechoslovakia (1961–1971), according to the criteria of the World Reference Base for Soil Resources (WRB), version 2014. The harmonization was effectuated at two levels of detail represented by two different types of soil mapping units [soil type and general soil representative (GSR)] and resulted in the conversion of original soil units into their counterparts in the WRB (Reference Soil Groups). The results showed a good potential of the adopted methods for soil data harmonization. The conceptual differences of the two harmonised classifications decreased the applicability of the taxonomic distance in the case of broadly defined and less developed soil classes lacking specific diagnostic features. The replacement of a simple conversion by soil association was a relevant approach, especially at the soil type level, where the simple one-to-one conversion showed only poor accuracy (39.5%). The accuracy at the GSR level was satisfactory (reaching ca 60%) and increased with soil association (72%). The conversion accuracy of different soil classes significantly differed from very high (e.g. 92% in Luvisols) to completely mismatched (Technosols and Histosols). The latter can be attributed to a questionable determination of soil classes in legacy maps. The study showed the potential of taxonomic distance methods in soil data harmonization and the limits of historical databases resulting from the way data were collected and recorded.

Here, for the first time, we report the thallium (Tl) isotope record in moderately contaminated soils with contrasting land management (forest and meadow soils), which have been affected by emissions from coal-fired power plants. Our findings clearly demonstrate that Tl of anthropogenic (high-temperature) origin with light isotope composition was deposited onto the studied soils, where heavier Tl (ε(205)Tl ∼ -1) naturally occurs. The results show a positive linear relationship (R(2) = 0.71) between 1/Tl and the isotope record, as determined for all the soils and bedrocks, also indicative of binary Tl mixing between two dominant reservoirs. We also identified significant Tl isotope variations within the products from coal combustion and thermo-desorption experiments with local Tl-rich coal pyrite. Bottom ash exhibited the heaviest Tl isotope composition (ε(205)Tl ∼ 0), followed by fly ash (ε(205)Tl between -2.5 and -2.8) and volatile Tl fractions (ε(205)Tl between -6.2 and -10.3), suggesting partial Tl isotope fractionations. Despite the evident role of soil processes in the isotope redistributions, we demonstrate that Tl contamination can be traced in soils and propose that the isotope data represent a possible tool to aid our understanding of postdepositional Tl dynamics in surface environments for the future.

Mine tailings rich in Mn and an adjacent creek at Kanye, southeast Botswana, have been investigated by total decomposition of solids, X-ray diffraction, EMPA techniques, sequential extraction, and water leaching to understand binding and mobility of Mn and other trace elements. The investigation revealed weathering of tailings close to the surface of the tailings and higher concentrations of Fe compared to Mn. There also are high concentrations of Ba and Pb in the tailings solids. The principal minerals of Mn and Fe are cryptomelane, K(Mn4+, Mn2+)8O16, and hematite, Fe2O3, respectively. Most Mn is bound to less crystalline phases dissolved in the reducible step of sequential extraction, suggesting high potential for release of Mn and related trace elements. The situation is very different for Fe, which is found mostly in the residual (Aqua Regia) insoluble fraction. This is in a good agreement with high concentrations of mobilized Mn and with low concentrations of mobilized iron in the water leaching test. The order of water-leached trace elements is Ba>Zn > As>V > Cu > Co > Pb where trace elements bound in Mn-oxyhydroxides are preferentially mobilized. In particular, As and V may represent a potential risk for the environment during rainy periods when mine tailings are probably flooded, and tailings material is transported by water in an ephemeral creek. Currently, sediments in the creek are contaminated at least to the boundaries of the Kanye settlement and they can be a source of groundwater contamination during the rainy period. Another possible source of contamination is wind transport and settling of dust particles from mine tailings with resulting ingestion when local farming products are consumed.

We studied the key geochemical and mineralogical factors that could affect the fractionation of stable thallium (Tl) isotopes in soil. A set of grassland soil samples enriched in geogenic Tl in combination with selected Tl-containing mineral materials from the Czech Republic (Kluky) were investigated for this purpose. The results demonstrate significant incorporation of Tl in pedogenic (specific) Mn-oxide, which led to a large accumulation of the heavy 205Tl isotope (∼+14 e205Tl units), presumably resulting from oxidative Tl sorption. Consequently, we concluded that the Mn-oxide-controlled Tl uptake is the primary cause of the observed 205Tl enrichment in the middle profile zone, at the A/B soil horizon interface, with up to +4 of e205Tl. Furthermore, our results displayed a clear relationship between the Tl isotopic fractionation degree and the Mn-oxide soil concentration (R2 = 0.6), as derived from the oxalate-extractable data. A combination of soil and mineralogical considerations suggests that 205Tl enrichment in respective soil samples is also partly due to the Tl present in micaceous clay minerals, mainly illite, which is the predominant pedogenic Tl host phase. In line with our previous results, this Tl behavior can be inferred from systematic Mn-oxide degradation and the associated Tl (enriched in 205Tl) cycling in the studied soils and thus, presumably in the redoximorphic soils in general.

We studied thallium (Tl) isotope fractionation in white mustard grown hydroponically at different Tl doses. Thallium isotope signatures in plants indicated preferential incorporation of the light 203Tl isotope during Tl uptake from the nutrient solution. Negative isotope fractionation was even more pronounced in dependence on how much the available Tl pool decreased. This finding corresponds to the concept of isotope overprinting related to a high contamination level in the growing media (solution or soil). Regarding Tl translocation in plants, we observed a large Tl isotope shift with an enrichment in the heavy 205Tl isotope in the shoots relative to the roots in treatments with low/moderate solution Tl concentrations (0.01/0.05 mg Tl/L), with the corresponding α205/203Tl fractionation factors of ˜1.007 and 1.003, respectively. This finding is probably a consequence of specific (plant) reactions of Tl replacing K in its cycle. The formation of the S-coordinated Tl(I) complexes, potentially affecting both Tl accumulation and Tl isotope fractionation in plants, however, was not proven in our plants, since we did not have indication for that on the basis of X-ray absorption spectroscopy, suggesting that Tl was mainly present as free/hydrated Tl+ ion or chemically bound to O-containing functional groups.

Soils on the Erzmatt (Switzerland) formed on hydrothermally mineralized dolomite rock are naturally Tl-rich. In this study, we investigated if variations in the stable Tl isotope ratios in soil samples from different profiles can be linked to data on the extractability and speciation of soil Tl and whether the isotopic data allow drawing conclusions on the geochemical processes that affected Tl over the course of soil formation. In two soil profiles, we observed a marked accumulation of the heavy 205Tl isotope in the B horizons, with e205Tl values that were up to 7 higher than in the underlying bedrock. This 205Tl enrichment, however, was neither reflected in the speciation of Tl nor its chemical fractionation. Furthermore, exchangeable soil Tl in the B horizons was found to be much isotopically lighter than the bulk soil Tl. These findings suggest that the observed isotopic shift may be linked to cyclic Tl mobilization and immobilization processes over the period of rock weathering and soil formation. Oxidative Tl uptake by Mn-oxides associated with a 205Tl enrichment, continuous weathering of the Tl(III)-containing phases, followed by a Tl(I) remobilization (leading to enrichment in 205Tl) are suggested to be responsible for the binding of the heavy Tl isotope fraction into other phases, mainly illite (a dominant Tl host), which is not normally expected. Hence, our results show that the Tl isotopic fractionation data measured in a dynamic multi-phase (soil) system can potentially serve as a proxy for tracing redox-controlled processes, but their use for phase or the sorption process identification is much more complicated.

The historical mining and processing of Zn–Pb–V ores at Berg Aukas in northern Namibia left large amounts of various wastes. This study focuses on the mineralogical and geochemical investigation of the V-rich slags issued from the processing of the local ores in the Waelz kiln, which was operational between 1968 and 1980 and left ca. 500 kt of slag deposited on the adjacent dump. A combination of mineralogical methods, bulk chemistry, leaching tests and speciation-solubility modeling was used to understand the binding of the major contaminants (Zn, Pb, V) in the solid phase and their potential release under the changing environmental conditions. The average concentrations of the metal(loid) contaminants in the slags are 3.78 wt% Zn, 3370 mg/kg Pb, 5880 mg/kg V, 767 mg/kg Cu, 578 mg/kg As and 92 mg/kg Sb. The mineralogy is dominated by high-temperature silicates (clinopyroxene, melilite, olivine-family phases) and Zn-bearing phases (willemite, zincite). All the primary silicates and oxides are Zn-rich, but vanadium is mainly concentrated in clinopyroxene (up to 5 wt% V2O3). Metallic Fe inclusions, formed under highly reducing conditions in the kiln, are highly weathered. Secondary Fe(III) (hydr)oxides, corresponding to the main weathering products in the slag, efficiently sequester the metal(loid)s (mainly As and Sb). The EU regulatory leaching tests indicated that the release of the metal(loid) contaminants is quite low at the natural pH (deionized water extract: 8.5–10.4) obtained by extraction in the deionized water and only Sb in all the slag samples exceeds the EU limits for the landfilling of inert waste. The pH-static leaching tests revealed up to 5 orders of magnitude higher release of Pb and Zn under acidic conditions (up to 38% and 63% of their total concentration, respectively), compared to the natural pH. In contrast, V exhibits relatively flat pH-dependent leaching patterns with only

Composition of soil vegetation cover and land management directly influences the cycling of chemical elements and is a key factor for soil biogeochemistry and also Al behaviour. Moreover, Al is an important factor limiting the growth of cultural plants. Our results are based on long-term observations of soils translocated from selected small areas of eight 1 ha plots of different land-use gradient, with identical geological, climatic and geographical conditions, located in the North of Congo Basin (near Mbalmayo, Cameroon). The plots are established in primary and secondary forests, cocoa agroforestry systems and a maize field (two plots per habitat). All soil plots were exchanged between each other in two layers; A. 0–5 cm, and B. 5–20 cm of depths. The soil was sampled at the times 0, +3, +6 months, and soil chemical parameters were determined. The most important differences between the particular habitats comprise of vegetation cover as a consequence of the land management. Particular plots differed mainly in their pH, organic C, exchangeable Al and contents of base cations. The most marked trends comprise of significant decrease of pH, increase of Al and decrease of the Ca/Al ratio in A layer after translocation to the agricultural plots. All translocations resulted into rapid loss of organic C and release of Al, which was more obvious when the forest-to-agriculture translocation took place.

The impact of a natural wetland ("dambo" in Zambia) on neutral mine drainage at Luanshya in the Zambian Copperbelt has been investigated during an intermediate discharge period (July) using a multi-method characterization of solid phase samples, sequential extraction analysis, X-ray diffraction, Mossbauer spectroscopy, and scanning electron microscopy combined with water analyses, isotopic analyses, and geochemical modeling. In the wetland, the principal identified solid phases in sediments were carbonates, gypsum, and ferric oxyhydroxides. A significant portion of the ochres was present as insoluble hematite. Mine drainage pH values decrease, and log [Formula: see text] values increase after inflow of water into the wetland; dissolved and suspended concentrations of Fe, Mn, Cu, and Co also decrease. Based on speciation calculations, there is no precipitation of secondary Cu and Co minerals in the period of sampling, but it can occur later in dry period when the flow rate is reduced. Concentrations of sulfate decrease, and values of δ34S(SO4) in the wetland increase in parallel, suggesting sulfate reduction is occurring. In more advanced dry period, the discharge in mine drainage stream is probably much lower and water can reach supersaturation with respect to minerals such as gypsum, which has been found in sediments. Wetlands have a positive impact on mine drainage water quality due to the removal of metals by adsorption, co-precipitation, and filtration of colloids. However, there can also be a rebound of contamination by seepage inflow downstream from the wetland. Ongoing climate change with extreme hydrologic events may enhance differences between dry and rainy seasons with resulting faster mobilization of contaminants.

Acid mine drainage from mine tailings at Selebi Phikwe, eastern Botswana, has been investigated using a combination of total decomposition, sequential extraction, X-ray diffraction, Mossbauer spectroscopy, and SEM analyses of solid phase samples, water analyses, isotopic analyses, and geochemical modeling. The principal ferric phases in the seepage stream sediments are jarosite and goethite, which incorporate Ni and Cu. The Mossbauer spectroscopy (MS) indicated exclusively 3+ oxidation state of iron with typical features of ferric hydroxides/sulfates. A fraction of dissolved sulfate is also sequestered in gypsum which precipitates further downstream. Significant portions of Fe, Ni, and Cu are transported in suspension. Values of pH decreased downstream due to H+ generated by the precipitation of jarosite. Values of δ2H and δ18O indicate evaporation of pore water in the mine tailings before seepage. Values of δ34S(SO4) are consistent with the oxidation of sulfides, but sample from the seepage face is affected by dissolution of gypsum. No minerals of Ni and Cu were detected and the principal attenuation processes seem to be adsorption and co-precipitation with jarosite. Higher contents of Cu are sequestered in solid phases compared to Ni, in spite of much higher dissolved Ni concentrations. Based on the speciation calculations, seepage water is undersaturated with respect to all Ni and Cu phases and adsorption and co-precipitation with jarosite seems to be the principal attenuation processes. Direct geochemical modeling was able to reproduce downstream pH trends, thus confirming the precipitation of jarosite as the principal pH-controlling process.

The area of the city of Tsumeb in northern Namibia is strongly affected by gaseous emissions and by dust fallout from the local smelter. This is also reflected in increased concentrations of lead and arsenic in blood and urine of the residents. Consequently, modeling of the dispersion of dust and SO2 emissions from the smelter was used in this study to delineate the contaminated area and to assess the health risks. The modeling results were verified by ground-based geochemical survey of soil and grass in the area. The results of modeling revealed that the concentrations of SO2 in the Tsumeb town were relatively low, whereas the highest dust fallout concentrations were found around the Tsumeb smelter. The Tsumeb town residential area was less affected due to favorable landscape morphology between the smelter and the city (the Tsumeb Hills). The results of modeling of dust fallout and geochemical survey coincided very well. Since the anthropogenic contamination was bound only to the surface layer of soil, the local soils were sampled at two depth horizons: topsoil and the deeper soil horizon. This enabled us to distinguish between the anthropogenic contamination of soil surface from natural (geogenic) concentrations of studied metals in the deeper part of the soil profile. Concentrations of metals in grass correlated with the concentration of metals in topsoil. In contrast to a good conformity with the modeling of dust fallout from the smelter and geochemical survey, the results of modeling of SO2 contents in the air, and total sulfur content in soils were different. Differences can be explained by additional sources of contamination, as for example a sulfate-rich dust fallout from local tailings ponds and slag dumps that were not considered in the SO2 dispersion model. The results of the present investigation can be used by the mining companies in the management of air quality, assessment of the efficacy of applied remediation measures, and in reducing the impact of dust fallout on the local ecosystem. The Municipal Administration may use these results to plan further development of the city of Tsumeb, especially in terms of further expansion of housing construction.

The work focused on the biogeochemical behavior of synthetic Tl-modified phases, namely birnessite, ferrihydrite, and calcite, in a neutral soil Leptosol. The data presented here clearly demonstrate a strong relationship between the mineralogical position of Tl in the soil and its uptake by the studied plant ( Sinapis alba L.). All tested Tl phases behaved as potential Tl sources in the rhizosphere, with a maximum for ferrihydrite and minimum for birnessite. Therefore, it can be concluded that Mn(III,IV) oxides, if present in the soil system, may reduce biological uptake of Tl to a substantial degree, including the case of Tl-accumulating species (i.e., Brassicaceae ). It was proven that even Tl-enriched calcite present in the carbonate-rich soil is an important precursor for further contaminant mobilization, despite its relative resistance to degradation. Our data indicate that the fate of secondary Tl phases in the rhizosphere might be significantly influenced by the pH of the soil matrix, i.e., soils with lower pHs reduce their stability, making them more susceptible to further degradation by root exudates. Bulk soil mineralogy and the content and quality of soil organic matter are thus suggested to be critical parameters controlling the bioaccumulation potential for Tl.

Subsoil has been recognized as large reservoir of soil organic carbon in recent years. In our study, we investigated deep colluvial soils as a potentially important source of SOC due to high mass redistribution driven by soil erosion. Three agriculture plots from the Chernozem, Luvisol, and Cambisol regions were studied to assess the SOC storage in topsoil (0–25 cm), at 2 m depth (0–200 cm), and over the total soil depth (0–450 cm) as a function of relief. The study is based on 558 borings, and soil profile description and classification to facilitate the colluvial soil delineation. Among these locations, SOC content was measured at 230 sampling points. Prediction of the SOC stock for the plots was based on support vector machine algorithms using digital elevation model derivatives as predictors. Total SOC stock varied among the study plots. The highest relative SOC stock was measured in the Chernozem (CH) plot (144.7 t·ha− 1), while at the Luvisol (LU) plot, it reached 68.4 t·ha− 1 and was 73.4 t·ha− 1 at the Cambisol (CM) plot. The role of colluvial soils regarding their spatial extent and SOC stock differs among the studied plots. Colluvial soils at the CH plot represent an important soil cover both spatially (13%) and by the volume of SOC stock (37%). A moderate importance of colluvial soils is determined for the LU plot (12% of SOC stock), and a low importance for the CM plot (5% of SOC stock). SOC stock contained in topsoil and subsoil differs in each plot. In the Luvisol and Cambisol plots, more than one half of SOC is retained in topsoil (53.4%, 60.3%). In contrast, more than two thirds of the SOC stock (73.1%) occurs in subsoil in the Chernozem plot. Moreover, 19.0% of the total SOC stock occurs at depths below 2 m. This finding indicates the importance of the incorporation of deep colluvial soil horizons in SOC stock estimations.

Mine tailings at Rosh Pinah located in semiarid southern Namibia were investigated by the combination of mineralogical methods and leaching using water and simulated gastric solution. They are well-neutralized with leachate pH > 7 and neutralization potential ratios (NPR) up to 4. Neutralization is mainly due to abundant Mn-rich dolomite in the matrix. Concentrations of released contaminants in water leachate follow the order Zn > Pb > Cu > As. Relatively high leached concentrations of Zn and partly also of Pb are caused by their link to relatively soluble carbonates and Mn-oxyhydroxides. In contrast, As is almost immobile by binding into Fe-oxyhydroxides, which are resistant to dissolution. Barium is released by the dissolution of Ba-carbonate (norsethite) and precipitates in sulfate-rich pore water as barite. Dissolved concentrations in neutral mine drainage water collected in the southern pond are low, but when total concentrations including colloidal fraction are taken into account, more than 70% of Zn is in colloidal form. Groundwater upgradient of the mine tailings is of poor quality and there seems to be no negative impact on groundwater downgradient from mine tailings. Contaminant concentrations in simulated gastric leachates are in the order Ba > Pb > Zn > Cu > As with a maximum gastric bioaccessibility of 86.6% for Ba and a minimum of 3.3% for As. These results demonstrate that total contaminant content and toxicity in the solid phase are poor predictors of risk, and therefore mineralogical and bioavailability/bioaccessibility studies are necessary for evaluation of contaminant environmental impact.