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Abstract

Germanium (Ge) is widespread in the earth crust. As a cognate element to silicon (Si), Ge shows very similar chemical characteristics. Recent use of Ge/Si to trace Si cycles and changes in weathering over time, growing demand for Ge as raw material and consequently an increasing interest in Ge phytomining have contributed to a growing interest in this previously rather scarcely considered element in geochemical studies. This review deals with the distribution of Ge in primary minerals and surface soils as well as the factors influencing the mobility of Ge in soils including the sequestration of Ge in secondary mineral phases and soil organic matter. Furthermore, the uptake and accumulation of Ge in plants and effects of plant-–soil relationships on the availability of Ge in soils and the biogeochemical cycling of Ge are discussed. The formation of secondary soil minerals and soil organic matter are of particular importance for the concentration of Ge in plant-available forms. The transfer from soil to plant is usually low and shows clear differences between species belonging to the functional groups of grasses and forbs. Possible uptake mechanisms in the rhizosphere are discussed. However, the processes that are involved in the formation of plant-available Ge pools in soils and consequently its biogeochemical cycling are not yet well understood. There is, therefore, a need for future studies on the uptake mechanisms and stoichiometry of Ge uptake under field conditions, plant-soil-microbe interactions in the rhizosphere as well as the chemical speciation in different plant parts.
REVIEW ARTICLE
Germanium in the soil-plant systemareview
Oliver Wiche
1,2
&Balázs Székely
2,3,4
&Christin Moschner
1
&Hermann Heilmeier
1,2
Received: 20 April 2018 /Accepted: 6 September 2018 /Published online: 14 September 2018
#Springer-Verlag GmbH Germany, part of Springer Nature 2018
Abstract
Germanium (Ge) is widespread in the Earths crust. As a cognate element to silicon (Si), Ge shows very similar chemical
characteristics. Recent use of Ge/Si to trace Si cycles and changes in weathering over time, growing demand for Ge as raw
material, and consequently an increasing interest in Ge phytomining have contributed to a growing interest in this previously
rather scarcely considered element in geochemical studies. This review deals with the distribution of Ge in primary minerals and
surface soils as well as the factors influencing the mobility of Ge in soils including the sequestration of Ge in secondary mineral
phases and soil organic matter. Furthermore, the uptake and accumulation of Ge in plants and effects of plant-soil relationships on
the availability of Ge in soils and the biogeochemical cycling of Ge are discussed. The formation of secondary soil minerals and
soil organic matter are of particular importance for the concentration of Ge in plant-available forms. The transfer from soil to plant
is usually low and shows clear differences between species belonging to the functional groups of grasses and forbs. Possible
uptake mechanisms in the rhizosphere are discussed. However, the processes that are involved in the formation of plant-available
Ge pools in soils and consequently its biogeochemical cycling are not yet well understood. There is, therefore, a need for future
studies on the uptake mechanisms and stoichiometry of Ge uptake under field conditions and plant-soil-microbe interactions in
the rhizosphere as well as the chemical speciation in different plant parts.
Keywords Availability .Trace element analysis .Soil fractions .Rhizosphere .Biogeochemistry
Introduction
Germanium (Ge) closely follows the properties and behavior
of silicon (Si) in biogeochemical cycles and has often been
considered as Bpseudoisotope^of Si (Goldschmidt 1958;
Pokrovsky et al. 2006a). In the upper continental crust of the
Earth, Ge is the 54th most abundant element (Reimann et al.
2014) with an estimated abundance of 1.31.6 μgg
1
(Taylor
1964;Hölletal.2007;Rosenberg2007; Hu and Gao 2008;
Négrel et al. 2016). Ge shows remarkable geochemical simi-
larities to Si, largely due to their identical outer electron struc-
tures and very similar ionic radii (Si
4+
:40pm,Ge
4+
:53pm)
(Höll et al. 2007). The similarity between tetrahedral GeO
(175 pm) and SiO (164 pm) bond lengths (Martin et al. 1996;
Kurtz et al. 2002) allows Ge to readily substitute for Si in the
tetrahedral site of silicate minerals (DeArgollo and Schilling
1978;Martinetal.1996) according to the principles of cam-
ouflage (Goldschmidt 1958). Germanates and silicates are
known to form isostructural compounds (Höll et al. 2007).
As a result, Ge has often been used to trace continental and
oceanic Si cycles (e.g., Froelich et al. 1985,1992;Mortlock
and Froelich 1987; Murnane and Stallard 1990; Derry et al.
2005; Baronas et al. 2016) and to determine changes in
weathering over time (Kurtz et al. 2002;Scribneretal.
2006;Lugolobietal.2010). In aqueous solutions, the domi-
nant inorganic species of Ge is the monomeric germanic acid
(Ge(OH)
4
) which has similar dissociation constants to the mo-
nomeric silicic acid (Si(OH)
4
).
However, Ge has a larger atomic radius than Si. This allows
it to form longer bonds with oxygen and sulfur (Bernstein
Responsible editor: Roberto Terzano
*Oliver Wiche
oliver.wiche@ioez.tu-freiberg.de
1
Institute for Biosciences, Biology/EcologyGroup, TU Bergakademie
Freiberg, Freiberg, Germany
2
Interdisciplinary Environmental Centre, TU Bergakademie Freiberg,
Freiberg, Germany
3
Department of Geophysics and Space Science, Eötvös University,
Budapest, Hungary
4
Department of Geodesy and Geoinformation, Vienna University of
Technology, Vienna, Austria
Environmental Science and Pollution Research (2018) 25:3193831956
https://doi.org/10.1007/s11356-018-3172-y
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... However, unlike germanium, which is deemed to be scarce, silicon is considered one of the most abundant elements on earth as a result it has been subjected to numerous extensive studies that would be truly valuable in understanding the potential chemical behavior of germanium (Petrucci et al. 2017). Notably, there is a trend to investigate germanium biogeochemistry cycling by comparing it to silicon in soil (Wiche et al. 2018). Germanium, much like silicon, can form tetrahedral structures with oxygen, resulting in germanates, which can serve as potential substitutes for silicate. ...
... Germanium can be present in various forms within soil minerals, including silicates, hydroxy-sulphates, hydroxides, oxides, and sulphides (Höll et al. 2007). The source of the germanium in soil is closely linked to the soil parent material and the extent of physical, chemical, and biological weathering of the bedrock (Wiche et al. 2018). During the weathering process, germanium and silicon are released from primary minerals at different rates, initiating competition among Fe(III)-oxyhydroxide, aluminosilicate, and organic matter in the soil to incorporate these elements into their chemical structures . ...
... This process is influenced by the soil's physicochemical properties, as well as climatological and biological factors. Thus, Ge is more likely to be found as part of secondary mineral components, particularly clay minerals, rather than as highly reactive free quaternary cations of germanium (Bernstein and Waychunas 1987, Kurtz et al. 2002, Lugolobi et al. 2010, Pokrovski and Schott 1998a, Pokrovski and Schott 1998b, Pokrovsky et al. 2006, Scribner et al. 2006, Wiche et al. 2018. ...
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... We analyze topsoils and cassava leaves in 40 cultivated plots. We determine germanium (Ge) concentrations in topsoils, leaves and phytoliths using the Ge/Si ratio as a proxy to decipher the soil-to-plant transfer of Si (Wiche et al. 2018). Our objective is threefold: (i) to evaluate the range of leaf Si concentrations in cassava grown on soils differing in desilication stage, detect the source of plant available Si in soil, and quantify Si uptake by cassava, (ii) to infer the impact of plant Si status on root yield and viral disease incidence in smallholders' plots farmed with very low to no inputs, (iii) to isolate and analyze cassava phytoliths. ...
... However, though Al concentrations in plant phytoliths cover a substantial range (0.6-9 g kg −1 ) (Bartoli 1985;Buján 2013;Fraysse et al. 2009;Hodson 2016), the Al/ Si is little used to characterize phytoliths, unlike the Ge/Si ratio. Being analog to Si, the variation in Ge concentration follows that of Si in ecosystems (Wiche et al. 2018). Germanium concentrations measured in cassava leaves were within the range of values available for other field-grown plants, most being below 85 µg kg −1 ( Table 7). ...
... The sharp and systematic decrease in Ge/Si (µmol mol −1 ) from leaf (0.65-5.94) to phytolith (0.11-1.83) ( Table 4) indicated that Ge accumulation in cassava leaves was not solely driven by its incorporation in phytoliths as reported in other plant species (Kaiser et al. 2020). Actually, Ge and Si follow different pathways in plant tissues (Delvigne et al. 2009;Kaiser et al. 2020;Sparks et al. 2011) due to the higher reactivity of Ge with many organic functional groups (Wiche et al. 2018). ...
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... Germanium is primarily introduced into the body through the consumption of vegetable-based foods with an average daily human dose of only 0.4-1.5 mg [14,15]. Research on the determination of this element in plant raw materials unexpectedly revealed an elevated content in plants and mushrooms that are traditionally used in ethnoscience, particularly in China [7,[16][17][18]. Germanium compounds in natural sources have long been considered a therapeutic agent with anticancer, antitumor, antiviral and anti-inflammatory effects [19]. ...
... This phenomenon was called aerobic glycolysis A number of Ge (IV) complexes with natural polyphenols were synthesized and shown to be promising pharmacologically active substances for cancer treatment. The quercetingermanium complex (17) (Figure 18) showed high cytotoxicity against four tumor cell lines (PC-3, Hela, EC9706 and SPC-A-1) [150,151]. A number of Ge (IV) complexes with natural polyphenols were synthesized and shown to be promising pharmacologically active substances for cancer treatment. ...
... A number of Ge (IV) complexes with natural polyphenols were synthesized and shown to be promising pharmacologically active substances for cancer treatment. The quercetin-germanium complex (17) (Figure 18) showed high cytotoxicity against four tumor cell lines (PC-3, Hela, EC9706 and SPC-A-1) [150,151]. Among the other polyphenolic compounds that were used in the synthesis of complexes with Ge (IV), we noted a natural coumarin daphnetin (18) and glucosylxanthone mangiferin (19) (Figure 19) [152]. ...
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... Group V: For Ge, chemically related to Si, the less attention has been paid on its availability in soils since germanium is identified as neither an essential element for life nor a strongly toxic element in environment. The global mean Ge concentration in topsoils is about 2 mg kg −1 and varies in a narrow range of < 0.1 to 15 mg kg −1 (Wiche et al. 2018). The data of T_Ge concentrations in the present region was well within this range (Table 2). ...
... They found that the Ge concentration is related to parent materials, OM, Fe/Al oxides, and pH, while the predominant factor is parent materials and OM, and being a weak relationship with soil pH (Dong et al. 2022;Tyler and Olsson 2002;Duan et al. 2020). Consequently, under high soil pH conditions, both enhanced dissolved humic compounds and breakdown of OM released associated-Ge into soil solution (Tyler and Olsson 2001a;Wiche et al. 2018), thus decreasing the Ge storage by leaching or runoff of these soluble species. ...
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... Вважається, що концентрація його в ґрунтах коливається від 0,5 до 2,5 мг/кг (Kabata-Pendias & Mukherjee, 2007). Водночас вивчення закономірностей розподілення і геохімічної поведінки Германію в різних типах ґрунтів деяких регіонів виявило досить широкий діапазон його концентрацій від <0,1 до 15 мг/кг (Wiche et al., 2018). Так, середні значення вмісту Германію у ґрунтовому покриві сільськогосподарських (Ap-horizon, 0-20 см) і пасовищних угідь (Gr-horizon, 0-10 см) деяких європейських регіонів (в Скандинавії, Німеччині, Франції, Іспанії та на Балканах) майже однакові -0,037 та 0,034 мг/кг відповідно (Negrel et al., 2016). ...
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... mg . kg −1 , when considering the variety of soils forming under strongly different pedogenic conditions (Wiche et al. 2018). The global concentration of germanium in soil depends on geogenic and anthropogenic factors. ...
... In ICP-MS techniques, the application of a dynamic reaction cell (DRC) allows for the elimination of mass spectral interference (Zhang et al. 2017). Little is known about the geochemical behaviour and speciation of Ge in soils (Wiche et al. 2018). Ge speciation in soil solutions and its mobility in soils may strongly depend on the pH. ...
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Chapter
Wastewaters often contain an array of economically valuable elements, including elements considered critical raw materials and elements for fertilizer production. Plant-based treatment approaches in constructed wetlands, open ponds, or hydroponic systems represent an eco-friendly and economical way to remove potentially toxic metal(loid)s from wastewater (phytoextraction). Concomitantly, the element-enriched biomass represents an important secondary raw material for bioenergy generation and the recovery of raw materials from the harvested plant biomass (phytomining). At present, phytoextraction in constructed wetlands is still considered a nascent technology that still requires more fundamental and applied research before it can be commercially applied. This chapter discusses the different roles of plants in constructed wetlands during the phytoextraction of economically valuable elements. It sheds light on the utilization of plant biomass in the recovery of raw materials from wastewater streams. Here, we consider phytoextraction of the commonly studied water pollutants (N, P, Zn, Cd, Pb, Cr) and expand this concept to a group of rather exotic metal(loid)s (Ge, REE, PGM) highlighting the role of phytoextraction in the face of climate change and finite resources of high-tech metals.
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We present measurements of Ge isotope composition and ancillary data for samples of river water, low- and high-temperature hydrothermal fluids, and seawater. The dissolved δ⁷⁴Ge composition of analyzed rivers ranges from 2.0 to 5.6 ‰, which is significantly heavier than previously determined values for silicate rocks (δ⁷⁴Ge = 0.4 - 0.7 ‰, Escoube et al., GGR, 36(2), 2011) from which dissolved Ge is primarily derived. An observed negative correlation between riverine Ge/Si and δ⁷⁴Ge signatures suggests that the primary δ⁷⁴Ge fractionation mechanism during rock weathering is the preferential incorporation of light isotopes into secondary weathering products. High temperature (>150 °C) hydrothermal fluids analyzed in this study have δ⁷⁴Ge of 0.7 - 1.6 ‰, most likely fractionated during fluid equilibration with quartz in the reaction zone. Low temperature (25 - 63 °C) hydrothermal fluids are heavier (δ⁷⁴Ge between 2.9 and 4.1 ‰) and most likely fractionated during Ge precipitation with hydrothermal clays. Seawater from the open ocean has a value of 3.2 0.4 ‰, and is indistinguishable among the different ocean basins at the current level of precision. This value should be regulated over time by the isotopic balance of Ge sources and sinks, and a new compilation of these fluxes is presented, along with their estimated isotopic compositions. Assuming steady-state, non-opal Ge sequestration during sediment authigenesis likely involves isotopic fractionation that is -0.6 1.8 ‰.
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The rice plant (Oryza sativa L. cv Oochikara) is known to be a Si accumulator, but the mechanism responsible for the high uptake of Si by the roots is not well understood. We investigated the role of root hairs and lateral roots in the Si uptake using two mutants of rice, one defective in the formation of root hairs (RH2) and another in that of lateral roots (RM109). Uptake experiments with nutrient solution during both a short term (up to 12 h) and relatively long term (26 d) showed that there was no significant difference in Si uptake between RH2 and the wild type (WT), whereas the Si uptake of RM109 was much less than that of WT. The number of silica bodies formed on the third leaf in RH2 was similar to that in WT, but the number of silica bodies in RM109 was only 40% of that in WT, when grown in soil amended with Si under flooded conditions. There was also no difference in the shoot Si concentration between WT and RH2 when grown in soil under upland conditions. Using a multi-compartment transport box, the Si uptake at the root tip (0-1 cm, without lateral roots and root hairs) was found to be similar in WT, RH2, and RM109. However, the Si uptake in the mature zone (1-4 cm from root tip) was significantly lower in RM109 than in WT, whereas no difference was found in Si uptake between WT and RH2. All these results clearly indicate that lateral roots contribute to the Si uptake in rice plant, whereas root hairs do not. Analysis of F2 populations between RM109 and WT showed that Si uptake was correlated with the presence of lateral roots and that the gene controlling formation of lateral roots and Si uptake is a dominant gene.
Book
Mankind is using a greater variety of metals in greater quantities than ever before. As a result there is increasing global concern over the long-term availability of secure and adequate supplies of the metals needed by society. Critical metals, which are those of growing economic importance that might be susceptible to future scarcity, are a particular worry. For many of these we have little information on how they are concentrated in the Earth's crust, how to extract them from their ores, and how to use, recycle and dispose of them effectively and safely. Published with the British Geological Survey, the Critical Metals Handbook brings together a wealth of knowledge on critical metals and provides a foundation for improving the future security and sustainability of critical metal supplies. Written by international experts, it provides a unique source of authoritative information on diverse aspects of the critical metals, including geology, deposits, processing, applications, recycling, environmental issues and markets. It is aimed at a broad non-specialist audience, including professionals and academics working in the exploration and mining sectors, in mining finance and investment, and in mineral processing and manufacturing. It will also be a valuable reference for policy makers concerned with resource management, land-use planning, eco-efficiency, recycling and related fields.
Book
An understanding of the mineral nutrition of plants is of fundamental importance in both basic and applied plant sciences. The Second Edition of this book retains the aim of the first in presenting the principles of mineral nutrition in the light of current advances. This volume retains the structure of the first edition, being divided into two parts: Nutritional Physiology and Soil-Plant Relationships. In Part I, more emphasis has been placed on root-shoot interactions, stress physiology, water relations, and functions of micronutrients. In view of the worldwide increasing interest in plant-soil interactions, Part II has been considerably altered and extended, particularly on the effects of external and interal factors on root growth and chapter 15 on the root-soil interface. The second edition will be invaluable to both advanced students and researchers.
Article
Effects of citric acid and desferrioxamine B (DFO-B) on the availability of Ge and selected REEs (La, Nd, Gd, Er) to P. arundinacea were investigated. A soil dissolution experiment was conducted to elucidate the effect of citric acid and DFO-B at different concentrations (1 and 10 mmol l−1 citric acid) on the release of Ge and REEs from soil. In a greenhouse plants of P. arundinacea were cultivated on soil and on sand cultures to investigate the effects of citric acid and DFO-B on the uptake of Ge and REEs by the plants. Addition of 10 mmol l−1 citric acid significantly enhanced desorption of Ge and REEs from soil and uptake into soil–grown plants. Applying DFO-B enhanced the dissolution and the uptake of REEs, while no effect on Ge was observed. In sand cultures, presence of citric acid and DFO-B significantly decreased the uptake of Ge and REEs, indicating a discrimination of the formed complexes during uptake. This study clearly indicates that citric acid and the microbial siderophore DFO-B may enhance phytoextraction of Ge and REEs due to the formation of soluble complexes that increase the migration of elements in the rhizosphere.
Article
The total concentrations and chemical fractionation of Germanium (Ge) and selected rare earth elements (REEs) in top soils and soil-grown plants of different land use types (moist grassland, mesic grassland, arable land) were investigated in the post-mining area of Freiberg (Saxony, Germany). The study area covers approximately 1000 km2 in the south of Central Saxony, and 138 samples from 46 sampling sites were examined. Ge and REEs in soils were partitioned by a sequential extraction procedure into mobile/exchangeable (Fraction 1), acid soluble (Fraction 2), bound to organic matter (Fraction 3), amorphous Fe/Mn-oxyhydroxides (Fraction 4), crystalline Fe/Mn-oxides (Fraction 5) and residual fractions (Fraction 6). Total concentrations of Ge and REEs in soil varied considerably ranging from 1.0 μg g− 1 to 4.3 μg g− 1 for Ge (mean 1.9 μg g− 1) and 97 μg g− 1 to 402 μg g− 1 (mean 168 μg g− 1) for total REE contents, accounting for 17% and 14% to the investigated light REEs La and Nd, respectively and 2.8% and 1.5% to the investigated heavy REEs Gd and Er, respectively. Elements in potentially plant available fractions represented 8% of total Ge and 30% of total REEs, respectively. Soils on moist grasslands characterized as acidic fluvisols and gleysols with high organic matter content contained significantly higher total concentrations of Ge and REEs and higher concentrations of Ge and REEs in the potentially plant available Fractions 1–3 compared to soils of mesic grassland and arable land. Grass species accumulated significantly higher concentrations of Ge than herb species. Highest concentrations of Ge were measured in plant species growing on moist grassland (Phalaris arundinacea: 449 ng g− 1), while there were no significant differences with regard to the concentrations of REEs in plants among the different land use types. The results of this study indicate that moist grasslands may act as sinks for Ge and REEs. In these soils high amounts of soil organic matter and low pH may foster the retention of labile forms, increasing the pool of Ge and REEs accessible for phytoextraction. However, the species-specific processes involved during the uptake of REEs need to be understood in order to optimize phytomining techniques.