Arsenic in soils and waters around the Kori Kollo gold mine on the Bolivian Altiplano: redox-induced speciation and mobilization

Mining activities in the Bolivian Altiplano have caused considerable negative environmental consequences on the water, soils, vegetation resources, biodiversity, and the atmosphere over the years. In this study, samples of soils, sediments, river water, water from drinking pools, and groundwater were collected from the area around the Kori Kollo gold mine, located near the city of Oruro on the Bolivian Altiplano to investigate the concentrations of arsenic (As) as an important contaminant associated with the mining activities in this area. Moreover, the redox-induced speciation, mobilization, and release dynamics, of As in soil/sediment samples was studied under controlled reducing and oxidizing conditions using an automated biogeochemical microcosm apparatus. The total As concentrations in the soils ranged between 10 and 81 mg kg-1 and exceeded the international trigger action values (10-65 mg kg-1) of As in agricultural soils. Arsenic concentrations (µg L-1) reached values up to 2,688, 952, and 300 in the groundwater, drinking pools, and surface water, respectively and exceeded the current WHO provisional guideline value of 10 µg L-1. The total dissolved concentrations of As varied from 368 to 3,130 µg L-1. The dissolved concentrations of As increased under oxidizing conditions and decreased under reducing conditions. Data of As speciation showed that the As (III) accounted from 0.0 to 79% of the total dissolved As and increased under reducing conditions, while the As (V) accounted from 21-100% of the total dissolved As and increased under oxidizing conditions. The results conclude that i) although the total concentrations of As in the soils around the mine are not very high, the concentrations of As in the waters were very high, 2) the concentrations of total dissolved As were very high which might indicate the high mobilization of As and support the anthropogenic source of As in theses soils, 3) the release and mobilization of As increased under oxidizing conditions as compared to the reducing conditions, and 4) the As (III) accounted values up to 79% of total dissolved As, which might increase the toxicity and risk of As in the soils and waters especially under reducing conditions. These results highlight the environment risk of As which might be a main reason for the gradual death of goats and cows, the biodiversity and the decline of fishing and agricultural sources in this area

Mercury speciation, transformation, and transportation in soils, atmospheric flux, and implications for risk management : a critical review

Mercury (Hg) is a potentially harmful trace element in the environment and one of the World Health Organization's foremost chemicals of concern. The threat posed by Hg contaminated soils to humans is pervasive, with an estimated 86 Gg of anthropogenic Hg pollution accumulated in surface soils worldwide. This review critically examines both recent advances and remaining knowledge gaps with respect to cycling of mercury in the soil environment, to aid the assessment and management of risks caused by Hg contamination. Included in this review are factors affecting Hg release from soil to the atmosphere, including how rainfall events drive gaseous elemental mercury (GEM) flux from soils of low Hg content, and how ambient conditions such as atmospheric O3 concentration play a significant role. Mercury contaminated soils constitute complex systems where many interdependent factors, including the amount and composition of soil organic matter and clays, oxidized minerals (e.g. Fe oxides), reduced elements (e.g. S2−), as well as soil pH and redox conditions affect Hg forms and transformation. Speciation influences the extent and rate of Hg subsurface transportation, which has often been assumed insignificant. Nano-sized Hg particles as well as soluble Hg complexes play important roles in soil Hg mobility, availability, and methylation. Finally, implications for human health and suggested research directions are put forward, where there is significant potential to improve remedial actions by accounting for Hg speciation and transportation factors

Seltene Erden und ihre Mobilisierung unter dynamischen Redoxbedingungen in einem zeitweise überfluteten Boden

Rare earth elements (REE) are an emerging field of environmental research. Although they occur naturally in minerals; however, they are used in many key technologies such as mobile phones, solid state lasers, catalysers in cars, in storage media for data handling, lodestones, photovoltaic cells etc. currently. In consequence, REE attain to the Environment. However, considerable knowledge gaps exist about the fate of REE in flooded soils up to date. To our best knowledge, the impact of systematic and pre-definite redox conditions on the release dynamics of REEs in floodplain soils has not been mechanistically studied up to date. Thus, we quantified the impact of pre-definite EH-conditions on the release dynamics of dissolved REEs, and to elucidate underlying redox-driven processes including the the determining factors pH, iron (Fe), manganese (Mn), aluminum (Al), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and sulfate (SO42-) in a floodplain soil. For this purpose, we were able to use an advanced, highly sophisticated automatic biogeochemical microcosm system allowing controlled adjustment of redox conditions. The novelty of our study is very high: this is the first time, where this particular topic is addressed. The redox potential (EH) ranged between +82 and +498 mV during the experiment. The systematic increase of EH caused a decreasing pH from 4.6 to 6.6 which resulted in an enhanced mobilization and release of REEs along with Fe, Al, and Mn under oxic and acidic conditions. Also, a gradual oxidation of REE-bearing sulfides seems to contribute to the mobilization of REE from reducing to oxidizing conditions. A factor analysis identified that the REEs form one group with EH, Fe, Al, and Mn what indicates that they have a similar geochemical behavior which substantially differs from those of pH, DOC, and DIC which are together in another cluster. The geochemical distribution of the REEs revealed that the majority of the REEs was in the residual fraction, followed by the reducible, the oxidisable and the water soluble / exchangeable / carbonate bound fraction. Future studies should further elucidate the specific release kinetics of REEs, their determining factors and the underlying mobilization processes in highly dynamic wetland soils around the globe

Silicon fractionation in Mollic Fluvisols along the Central Elbe River, Germany

Quantification of Si in its different forms in soil is a prerequisite to understand the geochemical distribution and fate of Si along with their driving biogeochemical processes. However, different Si fractions in floodplain soils have not been quantified yet, and little is known about the processes driving Si fractionation in these soils. The aim of this study was to clarify the processes that drive formation and distribution of Si among fractions in floodplain soils. We obtained and quantified these fractions using a sequential Si extraction method (Georgiadis et al., 2013) in three Mollic Fluvisols along the Central Elbe River. The highest Si proportion apart from the residual fraction was found in minerogenic amorphous silica (up to 5.6% of total Si), followed by Si occluded in pedogenic oxides and hydroxides (up to 0.7% of total Si). Silicon from biogenic amorphous silica amounted to 0.02-0.6% of total Si. The smallest proportion of Si was found in the mobile Si fraction and made up about 0.01% of the total Si. The results of this study demonstrate the importance of the soil water budget on the accumulation of easy-to-mobilise Si, Si occluded in pedogenic oxides and hydroxides and amorphous silica. Reductive dissolution of Fe and Mn oxides may induce Si release into the soil solution, subsequent oxidizing conditions may induce Si accumulation by adsorption, co-precipitation and occlusion of Si on/with newly formed Fe and Mn oxides. Accumulation of bio-opal after flooding may induce larger amounts of biogenic amorphous silica in floodplain soils than in terrestrial soils. Finally, floodplain soils may accumulate larger amounts of Si bound to occluded particulate SOM than terrestrial soils, which experience less input of particulate SOM than floodplain soils

Überblick über Spurenelemente in Böden der Aue der Mittleren Elbe

Floodplain soils across the Central Elbe River, Germany, have unique features. These soils vary considerably in their properties due to rapid fluvial processes and in metal contents due to frequent industrial discharge into the river. Although there have been works studying such soils, there has never been a comprehensive study that would monitor a large number of entire soil profiles along the Elbe River. Our aim was to describe the main properties of 94 profiles representing different soils along the Elbe River, their content from 15 potentially toxic elements (PTEs) in various depths, and assess various soil contamination and health risk indices. We measured soil properties auch as pH, organic carbon (OC), particle size distribution, as well as total concentrations of aluminium (Al), arsenic (As), barium (Ba), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), lead (Pb), nickel (Ni), rubidium (Rb), strontium (Sr), tin (Sn), vanadium (V), zirconium (Zr), and zinc (Zn) in all soil profiles. We presented the data for all soil horizons and in top- (0-30 cm depth) and subsoil (>30 cm depth). We found that pH, OC, and clay differed significantly between top- and subsoil horizons reflecting different water regimes and other factors. On the other hand, Al, Fe, and Mn were not affected significantly by depth. Among the studied PTEs, Sn was found to be generating the highest values in Contamination Factor, Geoaccumulation Index, and Enrichment Factor; it was followed by As, Zn, and Pb. Other PTEs such as Ba, Rb, Sr, V, and Zr, and exhibited much lower soil contamination index values. The Pollution Load Index was very high. Health risk assessment indicated rather unexpectedly that Zr was the primary contributor to total risk. We conclude that in multi-element contamination cases, even PTEs with low soil concentrations (such as Zr here) may have predominant role in the risk related to soil contamination

Biogeochemical factors affecting mercury methylation rate in two contaminated floodplain soils

An automated biogeochemical microcosm system allowing controlled variation of redox potential (EH) in soil suspensions was used to assess the effect of various factors on the mobility of mercury (Hg) as well as on the methylation of Hg in two contaminated floodplain soils with different Hg concentrations (approximately 5 mg Hg kg(-1) and > 30 mg Hg kg(-1)). The experiment was conducted under stepwise variation from reducing (approximately -350 mV at pH 5) to oxidizing conditions (approximately 600 mV at pH 5). Results of phospholipid fatty acids (PLFA) analysis indicate the occurrence of sulfate reducing bacteria (SRB) such as Desulfobacter species (10Me16:0, cy17:0, 10Me18:0, cy19:0) or Desulfovibrio species (18:2 omega 6,9), which are considered to promote Hg methylation. The products of the methylation process are lipophilic, highly toxic methyl mercury species such as the monomethyl mercury ion [MeHg+], which is named as MeHg here. The ln(MeHg/Hg-t) ratio is assumed to reflect the net production of monomethyl mercury normalized to total dissolved Hg (Hg-t) concentration. This ratio increases with rising dissolved organic carbon (DOC) to Hg-t ratio (ln(DOC/Hg-t) ratio) (R-2 = 0.39, p < 0.0001, n = 63) whereas the relation between ln(MeHg/Hg-t) ratio and lnDOC is weaker (R-2 = 0.09; p < 0.05; n = 63). In conclusion, the DOC/Hg-t ratio might be a more important factor for the Hg net methylation than DOC alone in the current study. Redox variations seem to affect the biogeochemical behavior of dissolved inorganic Hg species and MeHg indirectly through related changes in DOC, sulfur cycle, and microbial community structure whereas EH and pH values, as well as concentration of dissolved Fe3+/Fe2+ and Cl-seem to play subordinate roles in Hg mobilization and methylation under our experimental condition

Hanf als Winterzwischenfrucht

Hanf gehört weltweit zu den ältesten Nutzpflanzen und ist eine interessante, alternative Faserpflanze für die Landwirtschaft. Nach der Aufhebung des nationalen Anbauverbotes 1995 in Deutschland, gab es zwar etliche Bemühungen den Anbau von Faserhanf (Cannabis sativa L.) in der traditionellen Sommerkultur und dessen Weiterverarbeitung zu etablieren, doch ist die Anzahl der Hanfanbauflächen als Hauptfrucht seit 1999 kontinuierlich rückläufig. Gründe dafür sind zum einen die Reglementierung des Anbaus durch die Bundesanstalt für Landwirtschaft und Ernährung (BLE), die die Genehmigung des Anbaus, sowie THC-Kontrollen durchführt. Des Weiteren zählen dazu die fehlende Wettbewerbskraft zu landwirtschaftlichen Standardkulturen, insbesondere zu Weizen, sowie die lange Vegetationszeit und die damit zunehmende Witterungsabhängigkeit für die notwendige Röste und der damit einhergehenden Faserqualität. Ein Novum stellt der Anbau des Nutzhanfes über den Winter, mit einer Aussaat im Juli und Ernte im nächsten Frühjahr, dar. Dadurch können die Landwirte ihre Fruchtfolge erweitern und eine zusätzliche Wertschöpfung erzielen. Zusätzlich profitieren sie durch die vielen ökologischen Vorteile des Hanfes, wie z.B. die starke Beikrautunterdrückung, Verbesserung der Bodenstruktur, Erosionsschutz und geringer Nährstoff- und Wasserbedarf, wodurch diese Anbauform sowohl für den konventionellen als auch für den ökologischen Landbau interessant ist. Ziel des Projektes „Hanf als Winterzwischenfrucht“ ist es, die Klima- und Nährstoffansprüche des Hanfes im Winteranbau herauszuarbeiten. Dieses wurde im Praxisversuch auf zwei landwirtschaftlichen Betrieben getestet. Neben der Bodenanalytik, wurden Pflanzenproben während der Wachstumsphase entnommen, bonitiert und auf die Nährstoffverteilung innerhalb der Pflanze analysiert. Die Ergebnisse wurden mit einem Sommeranbau verglichen, um Aussagen über mögliche Unterschiede in Bezug auf Wachstumsverlauf, Ertrag und Faserqualität treffen zu können. Letztendlich soll den Landwirten eine Anbauempfehlung für den Hanf als Winterzwischenfrucht gegeben werden, wobei deutlich die Vorteile dieser Anbauweise aufgezeigt werden. Eine wichtige Rolle spielt hierbei die Aufnahme des Hanfes im Winteranbau in das Greening-Programm der EU

Speciation of vanadium in the dissolved, colloidal, and sediment phase under dynamic redox-conditions in a V contaminated soil treated and untreated with biochar

Vanadium is a redox-sensitive toxic element and can exist in a variety of oxidation states: −1, 0, +2, +3, +4, and +5. Vanadium (+5) is considered as a potentially dangerous pollutant. Biochar (BC) can be used to remediate soils contaminated with potential toxic elements (PTEs) including V. However, the efficiency of BC to immobilize V and its on speciation of V in the dissolved and colloidal phase and its mobilization and phytoavailability in the sediment phase under dynamic redox-conditions in highly contaminated soils under dynamic redox conditions has not been studied up to date. Thus, we have i) quantified the impact of pre-definite redox conditions on the speciation and release dynamics of V in the dissolved and colloidal phase as well as on the mobilization and phytoavailability of V in the soil sediments phase in a highly contaminated alkaline soil (CS) (non-treated) (pH = 7.44 and total V = 1,040 mg kg-1) collected from China and in the same soil treated with BC (CS+BC), and ii) assessed the impact of rice husk biochar as soil amendment on the same parameters. The impact of redox potential (EH), pH, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), iron (Fe), manganese (Mn), and sulfate (SO42-) on speciation and release dynamics of V was also determined under dynamic redox conditions. In addition, the used biochar was characterized using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) and nuclear magnetic resonance spectroscopy (NMR). The experiment was conducted in stepwise from moderate reducing (-30 mV in CS and -12 mV in CS+BC) to oxidizing (+218 mV in CS and +333 mV in CS+BC) soil conditions in different cycles using a highly sophisticated automated biogeochemical microcosm apparatus. Flooding of the CS and CS+BC caused significant changes of pH values which varied from 6.15 to 8.33 in the CS and from 5.14 to 7.91 in the CS+BC and the EH correlated negatively with pH. The dissolved concentrations of V varied from 15.2-46.4 mg L-1 in the CS to 14.9-50.2 mg L-1 in the CS+BC, while the colloidal concentrations of V varied from 39.5-49.9 mg L-1 in the CS to 31.8-50.2 mg L-1 in the CS+BC. Different redox cycles affected significantly the speciation and release dynamics of V in the dissolved and colloidal phase and its mobilization and phytoavailability in the sediment phase

Accumulation of chromium in plants and its repercussion in animals and humans

The untreated effluents released from industrial operations have adverse impacts on human health, environment and socio-economic aspects. Environmental pollution due to chromium is adversely affecting our natural resources and ecosystem. Chromium is hazardous carcinogenic element released from spontaneous activities and industrial procedures. Chromium toxicity, mobility and bioavailability depend mainly on its speciation. Chromium mainly exists in two forms, first as an immobile, less soluble trivalent chromium [Cr(III)] species under reducing conditions whereas hexavalent chromium [Cr(VI)] as a mobile, toxic and bioavailable species under oxidizing conditions. Hexavalent chromium is more pernicious in comparison to trivalent form. Chromium negatively affects crop growth, total yield and grain quality. Exposure of chromium even at low concentration enhances its accretion in cells of human-beings and animals which may show detrimental health effects. Many techniques have been utilized for the elimination of chromium. The selection of the green and cost-efficient technology for treatment of industrial effluent is an arduous task. The present review highlights the problems associated with chromium pollution and need of its immediate elimination by suitable remediation strategies. Further, investigations are required to fill the gaps to overcome the problem of chromium contamination and implementation of sustainable remediation strategies with their real-time applicability on the contaminated sites