Low-molecular-mass organic acids (LMMOA) are of key importance for mobilisation and fate of metals in soil, by functioning as ligands that increase the amount of dissolved metal in solution or by ...dissociation of metal binding minerals. Column leaching experiments were performed on soil polluted with As and Pb, in order to determine the specificity of LMMOA related release for individual elements, at varying organic acid concentrations. Acetic, citric and oxalic acids were applied in 12h leaching experiments over a concentration range (0.5–25mM) to soil samples that represent organic and mineral horizons. The leaching of As followed the order: oxalic>citric>acetic acid in both soils. Arsenic leaching was attributed primarily to ligand-enhanced dissolution of mineral oxides followed by As released into solution, as shown by significant correlation between oxalic and citric acids and content of Al and Fe in leaching solutions. Results suggest that subsurface mineral soil layers are more vulnerable to As toxicity. Leaching of Pb from both soils followed the order: citric>oxalic>acetic acid. Mineral soil samples were shown to be more susceptible to leaching of Pb than samples characterised by a high content of organic matter. The leaching efficiency of citric acid was attributed to formation of stable complexes with Pb ions, which other acids are not capable of. Results obtained in the study are evidence that the extent of As and Pb leaching in contaminated surface and subsurface soil depends significantly on the types of carboxylic acid involved. The implications of the type of acid and the specific element that can be mobilised become increasingly significant where LMMOA concentrations are highest, such as in rhizosphere soil.
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•Leaching of As followed the order oxalic>citric>acetic acid from organic and mineral soil.•Dissolution of mineral oxides by oxalate led to arsenic release into solution.•Leaching of Pb followed the order citric>oxalic>acetic acid from both soils.•Efficiency of Pb leaching into citric acid was attributed to formation of stable complexes.•Overall, underlying mineral soil is more susceptible to leaching of As and Pb into organic acid solutions.
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 ε205Tl 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 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 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.
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•Manganese-oxide was found to be the key control for Tl isotopic fractionation.•We identified up to +14 ε205Tl units in pedogenic Mn-oxide nodules.•The soil Mn-oxide concentration affected the Tl isotopic fractionation degree.•Heavy 205Tl isotope enrichment was present at the soil A/B horizon interface.•The heavy 205Tl isotope was probably enriched in illite as well.
Manganese (III,IV)-oxides represent the key control for Tl isotopic fractionation in soil.
•Low pH and the presence of citrate complexes enhanced metal mobility.•Formation of oxalate surface complexes decreased metal leachability.•Amorphous Mn oxide accelerated the stabilisation of Pb, Zn, ...Cu, Cd and As in soil.•Nano-maghemite showed to be stable in low-molecular-weight organic acids.•Amorphous Mn oxide was partly dissolved and secondary MnCO3 precipitated.
Various low-molecular-weight organic acids (LMWOAs) play an important role in the mobilisation of contaminants and their subsequent uptake by plants. Nano-maghemite (NM) and an amorphous Mn oxide (AMO) were investigated for their stabilisation potential under simulated rhizosphere conditions in terms of their use during chemical stabilisation and aided phytostabilisation of metal(loid)s in contaminated soils. In order to understand the reactivity of these potential sorbents of contaminants in soils and subsequent mobility of metal(loid)s, a set of time-dependent batch leaching experiments was performed using a mix of acetic, lactic, citric, malic and formic acids simulating root exudates. Despite being relatively unstable under given conditions, the AMO proved to be an efficient amendment for rapid stabilisation of both metals and As compared to NM. Generally, low pH (∼4) and the presence of citrate complexes resulted in higher mobility of metals in the non- and NM-amended soil. In contrast, the presence of AMO in the soil accelerated the neutralisation reactions related to pH increase and (co-) precipitation of secondary Fe/Mn/Al oxyhydroxides. Mineralogical transformations of the AMO showed to be crucial for contaminant immobilisation.
Protection and appropriate management of forests is one of the key instruments for climate change adaptation. Soil amendments with biochar have shown to be promising in achieving this goal; however, ...the evaluation of its long-term effects on forest soils has largely been neglected. To assess the advantages and drawbacks of biochar in forest soils, data from relict charcoal hearths (RCH) can be a potent tool as they show changes in soil properties after up to several hundred years. RCHs can be found in places of former metallurgical hot spots and their presence leaves characteristic formations identifiable on a large scale using laser detection technologies. Forest soils with biochar amendment show an increase in base cations, shift towards more alkaline pH, smaller bulk density and seem to be especially beneficial to hostile environments. Sites with favourable conditions may show little to no improvement or may even be adversely affected. Still, with proper investigation, areas with affordable feedstock materials and poor forest soils—such as spruce monocultures of Central Europe—may benefit from biochar amendments and continue to do so in the long term.
•Reactive oxygen species (ROS) can stimulate SOM and lignin degradation.•ROS oxidize SOM and increase adsorption of carbohydrate-like molecules to goethite.•Adsorption confers SOM stability and ROS ...can alter the nature of stable SOM pools.
Reactive oxygen species (ROS), formed during redox fluctuations in iron-rich soils, have been known to stimulate lignin degradation, although not much is known about how they alter soil organic matter (SOM) composition and interaction with mineral surfaces. We conducted a laboratory experiment to see how ROS altered SOM composition and adsorptive fractionation onto Fe-mineral surfaces. We reacted water extracts of SOM with ·OH, produced by the Fenton reaction, and then conducted a sorption experiment of the extracts with goethite to analyze the amount and quality of SOM adsorbed. The Fenton reaction preferentially consumed low-O, mostly aromatic molecules, and new high-O molecules were detected post-Fenton, nearly half of which were carbohydrate-like. Although the amount of C adsorbed did not change after oxidation, the post-Fenton adsorbed molecules were more oxidized. Pre-Fenton adsorption was dominated by aromatic molecules (90%), but post-Fenton, the adsorbed molecules were 75% aromatic and 25% carbohydrate-like. We show that the ·OH radical oxidized SOM and shifted patterns of adsorption to a more oxidized pool. Because adsorption to minerals is thought to stabilize SOM, our results suggest that ROS may alter the availability and stabilization patterns of SOM.
In order to monitor Potentially Toxic Elements (PTEs) in anthropogenic soils on brown coal mining dumpsites, a large number of samples and cumbersome, time-consuming laboratory measurements are ...required. Due to its rapidity, convenience and accuracy, reflectance spectroscopy within the Visible-Near Infrared (Vis-NIR) region has been used to predict soil constituents. This study evaluated the suitability of Vis-NIR (350-2500 nm) reflectance spectroscopy for predicting PTEs concentration, using samples collected on large brown coal mining dumpsites in the Czech Republic. Partial Least Square Regression (PLSR) and Support Vector Machine Regression (SVMR) with cross-validation were used to relate PTEs data to the reflectance spectral data by applying different preprocessing strategies. According to the criteria of minimal Root Mean Square Error of Prediction of Cross Validation (RMSEPcv) and maximal coefficient of determination (R2cv) and Residual Prediction Deviation (RPD), the SVMR models with the first derivative pretreatment provided the most accurate prediction for As (R2cv) = 0.89, RMSEPcv = 1.89, RPD = 2.63). Less accurate, but acceptable prediction for screening purposes for Cd and Cu (0.66 ˂ R2cv) ˂ 0.81, RMSEPcv = 0.0.8 and 4.08 respectively, 2.0 ˂ RPD ˂ 2.5) were obtained. The PLSR model for predicting Mn (R2cv) = 0.44, RMSEPcv = 116.43, RPD = 1.45) presented an inadequate model. Overall, SVMR models for the Vis-NIR spectra could be used indirectly for an accurate assessment of PTEs' concentrations.
Forest soils play an important role in the global ecosystem, providing many beneficial services. Protection of forests and their soils from anthropogenic impacts is therefore of utter importance to ...conservation efforts. Lead (Pb) is one of the most widespread anthropogenic pollutants and has been introduced into forests of the Czech Republic since medieval times, mostly from smelting, coal burning, and later also leaded gasoline. Lead can cause serious damage to the environment and forest soils and whose levels in the environment thus need to be closely monitored. In order to best evaluate possible sources of Pb pollution, 120 soils were sampled across forest areas of the Czech Republic. These sites were selected to be in areas largely unaffected by major pollution sources such as highways, large cities, and industrial complexes. Soils were digested using aqua regia and analyzed using ICP-MS for Pb isotopic ratios. Sampled forest soils have displayed isotopic signatures in a range of 1.1635–1.2269 for
206
Pb/
207
Pb and 2.3918–2.5235 for
208
Pb/
207
Pb and have had mostly uniform isotopic signature, with mean values of 1.1779
206
Pb/
207
Pb and 2.4624
208
Pb/
207
Pb, likely stemming from widespread atmospheric pollution. The exception to this uniformity was floodplain forests (average
206
Pb/
207
Pb 1.1939,
208
Pb/
207
Pb 2.4610), potentially due to a greater influx of materials from the river bed or surface runoff. These findings may aid future conservation efforts in determining background values for soil Pb and monitoring the state and health of forests in the Czech Republic.
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 ε205Tl 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 ε205Tl value for the topmost soil samples (∼+3) closely matches the ε205Tl value for post-flotation waste particles with a diameter of <0.05 mm, whereas the bulk flotation waste exhibits a significantly larger ε205Tl value (∼+6). These variations are in accordance with predominant atmospheric transfer of Tl from the tailings to the adjacent soils via fine (dust) particles. The identified minimal Tl alteration in soils indicates that only a small part of the Tl could be potentially released and passively enter the vegetation, local population and/or food chain in the long term. From this viewpoint, Tl does not represent such an important environmental concern as other (abundant) contaminants at the locality. Furthermore, there could be a relevance for other alkaline desert soils, including those where Tl pollution plays a major role.
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•Thallium contamination may be traced using Tl isotopes.•Thallium is very stable in mining wastes/soils compared to other metals.•Thallium migrates in the form of (micro)particles.•A large isotope variation among different-sized waste materials.•First study dealing with Tl and Tl isotopes in a desert area.
Thallium isotopes may be used for tracing Tl pollution and particulate Tl migration in desert areas.
Abstract
Mining and smelting activities can contaminate soils and affect farming due to high emissions and input of potentially toxic elements (PTE) into the environment. Soils (sampled from two ...depths) and market vegetables from vegetable gardens located within the vicinity of unconfined slag deposits from decades of mining and smelting activities in Kutná Hora, Czechia were assessed to determine to what extent they pose a health hazard to communities that use these gardens. Pseudo-total As concentrations in the soils exceeded background levels (4.5 mg kg
−1
) 1.9–93 times, with higher concentrations in the deeper layer. The pseudo-total concentrations of PTE in soils ranked in the order As > Zn > Cd > Pb. Phyto-available concentrations of PTE in soils were relatively low, compared to pseudo-total concentrations. Concentration of As, Cd, Pb and Zn in the vegetables exceeded guideline values, with the highest concentrations found in the fruits of cucumber, peppers, and zucchini. Despite low phyto-available PTE concentrations in soils, all the PTE concentrations in the vegetables surpassed the guidelines set by the Czech Ministry of Health and EU directive, indicating a health hazard to consumers.
Strains of Limosilactobacillus reuteri are used as starter and bioprotective cultures and contribute to the preservation of food through the production of fermentation metabolites lactic and acetic ...acid, and of the antimicrobial reuterin. Reuterin consists of acrolein and 3-hydroxypropionaldehyde (3-HPA), which can be further metabolized to 1,3-propanediol and 3-hydroxypropionic acid (3-HP). While reuterin has been the focus of many investigations, the contribution of 3-HP to the antimicrobial activity of food related reuterin-producers is unknown. We show that the antibacterial activity of 3-HP was stronger at pH 4.8 compared to pH 5.5 and 6.6. Gram-positive bacteria were in general more resistant against 3-HP and propionic acid than Gram-negative indicator strains including common food pathogens, while spoilage yeast and molds were not inhibited by ≤ 640 mM 3-HP. The presence of acrolein decreased the minimal inhibitory activity of 3-HP against E. coli indicating synergistic antibacterial activity. 3-HP was formed during the growth of the reuterin-producers, and by resting cells of L. reuteri DSM 20016. Taken together, this study shows that food-related reuterin producers strains synthesize a second antibacterial compound, which might be of relevance when strains are added as starter or bioprotective cultures to food products.
•The food microbe Limosilactobacillus reuteri has the potential to produce the antibacterial 3-hydroxypropionic acid.•The antibacterial activity against food pathogens of 3-hydroxypropionic acid was pH dependent.•The antibacterial activity of acrolein and 3-hydroxypropionic acid both produced by L. reuteri was synergistic.•Growth of spoilage yeast and mycelial fungi was only inhibited by propionic acid at low pH.
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