Circulation of Selenium in the Environment

In order to function properly, every living organism must have favourable conditions for its operation, i.e. it must be systematically supplied with the necessary nutrients. On the example of selenium (Se), it can be seen how important is the right balance between providing the right amount of it, without exceeding the level above which it is toxic. The amount of Se in soil is closely correlated with its content in the parent rock; therefore, it differs depending on the soil type and may change even in a small area. Considerable dispersion of the element in the soils of Poland is related to their formation, mainly from dump materials of various glaciations. The problem of maintaining the balance between deficiency and excess of Se in the diet of humans and animals is related primarily to the uneven distribution of this element in nature. In this paper, on the basis of scientific literature, the current issues related to the deficiency and excess of Se in the soil and its possible sources are presented. The relationship between the content in the soil and the supply of Se in plants, animals and humans was also shown. The aim of this study was to summarise the state of knowledge on the complexity of Se occurrence in the environment and its importance in the soil-plant-animals-human system.

Enzymatic Activity and Physicochemical Properties of Soil Profiles of Luvisols

Most studies on soil enzymes are focused on the upper horizons of the soil profile, even though they transform the soil organic matter at every depth of the soil profile. The aim of this work was to investigate the distribution of β-glucosidase (GLU), nitrate reductase (NR), urease (UR), phosphatase (PHA), dehydrogenase (DHA) and catalase (CAT) activity through 14 trunked soil profiles of the Luvisols formed from a glacial till. The content of microbial biomass carbon (MBC) as well as physicochemical properties such as organic carbon (CORG), total nitrogen (NTOT), available P, K and Mg, soil density and porosity, pH in KCl and fractional composition were also studied. In general, enzymatic activity was highest in the top 30 cm layer of the profiles and decreased progressively towards the deeper horizons. The exceptions were the NR activity, which was active only in the Ap horizon and whose activity decreased sharply to nearly zero in the Bt horizon and parent rock, and the PHA activity, which was highly active even in the parent rock depth. The decreased availability of carbon and nutrients was the main driver of decreases in microbial abundance and enzymatic activity with depth. The enzymatic activity, when expressed on a CORG and MBC basis, behaves differently compared to the activity expressed on a soil mass basis. The activity decreased (NR), increased (PHA, UR), showed no clear pattern (GLU) or the changes were not significant (DHA, CAT). The content of CORG, NTOT, K and PAVAIL generally decreased with depth, while for Mg, there was no clear direction in the profile distribution. Future studies to characterize the substrate distribution within the soil profile and enzyme stability will provide further insight into the controls on nutrient cycling and related enzymes throughout the soil profiles.

Isotopic signatures reveal zinc cycling in the natural habitat of hyperaccumulator Dichapetalum gelonioides subspecies from Malaysian Borneo

Background Some subspecies of Dichapetalum gelonioides are the only tropical woody zinc (Zn)-hyperaccumulator plants described so far and the first Zn hyperaccumulators identified to occur exclusively on non-Zn enriched 'normal' soils. The aim of this study was to investigate Zn cycling in the parent rock-soil-plant interface in the native habitats of hyperaccumulating Dichapetalum gelonioides subspecies (subsp. pilosum and subsp. sumatranum). We measured the Zn isotope ratios (δ66Zn) of Dichapetalum plant material, and associated soil and parent rock materials collected from Sabah (Malaysian Borneo). Results We found enrichment in heavy Zn isotopes in the topsoil (δ66Zn 0.13 ‰) relative to deep soil (δ66Zn -0.15 ‰) and bedrock (δ66Zn -0.90 ‰). This finding suggests that both weathering and organic matter influenced the Zn isotope pattern in the soil-plant system, with leaf litter cycling contributing significantly to enriched heavier Zn in topsoil. Within the plant, the roots were enriched in heavy Zn isotopes (δ66Zn ~ 0.60 ‰) compared to mature leaves (δ66Zn ~ 0.30 ‰), which suggests highly expressed membrane transporters in these Dichapetalum subspecies preferentially transporting lighter Zn isotopes during root-to-shoot translocation. The shoots, mature leaves and phloem tissues were enriched in heavy Zn isotopes (δ66Zn 0.34–0.70 ‰) relative to young leaves (δ66Zn 0.25 ‰). Thisindicates that phloem sources are enriched in heavy Zn isotopes relative to phloem sinks, likely because of apoplastic retention and compartmentalization in the Dichapetalum subspecies. Conclusions The findings of this study reveal Zn cycling in the rock-soil-plant continuum within the natural habitat of Zn hyperaccumulating subspecies of Dichapetalum gelonioides from Malaysian Borneo. This study broadens our understanding of the role of a tropical woody Zn hyperaccumulator plant in local Zn cycling, and highlights the important role of leaf litter recycling in the topsoil Zn budget. Within the plant, phloem plays key role in Zn accumulation and redistribution during growth and development. This study provides an improved understanding of the fate and behaviour of Zn in hyperaccumulator soil-plant systems, and these insights may be applied in the biofortification of crops with Zn.

Petrography and Shock Metamorphism of the Lunar Breccia Meteorite NWA 13120

Lunar meteorites are the fragments of rocks that fell on Earth because of the impacts of asteroids on the Moon. Such rocks preserve information about the composition, evolutionary process, and shock history of the lunar surface. NWA 13120 is a recently discovered lunar breccia meteorite having features of strong shock, which is composed of lithic and mineral clasts in a matrix of very fine-grained (<10 μm) and recrystallized olivine-plagioclase with a poikilitic-like texture. As the most abundant lithic clasts, the crystalline impact melt (CIM) clasts can be divided into four types according to their texture and mineral composition: (1) anorthosites or troctolitic anorthosite with a poikilitic-like texture, but the mineral content is different from that of the matrix; (2) anorthosites containing basaltic fragments and rich in vesicles; (3) troctolitic anorthosite containing metamorphic olivine mineral fragments; (4) troctolitic anorthosite containing troctolite fragments. Based on the petrology and mineralogy, NWA 13120 is a lunar meteorite that was derived from the ferrous anorthosite suite (FANs) of the lunar highlands, while its texture suggests it is a crystalline impact melt breccia. In addition, we infer that the parent rock of NWA 13120 is a lunar regolith breccia enriched in glass fragments. During the shock process, at pressures of more than 20 GPa, all plagioclase fragments were transformed into maskelynites, and olivine fragments occurred metamorphism. The post-shock temperature led to the partial melting of the basaltic fragments. Subsequently, all glass with diverse components in the parent rock were devitrified and recrystallized, forming the common olivine-plagioclase poikilitic-like texture and different CIM clasts. Meanwhile, the devitrification of maskelynite formed the accumulation of a large number of plagioclase microcrystals. Therefore, NWA 13120 is a meteorite of great significance for understanding the local shock metamorphism of lunar rocks on the lunar surface.

Monitoring the content of manganese, zinc, and cobalt in Haplic Chernozem

The paper uses the materials of local agroecological monitoring of arable soils of the Belgorod region on the content of manganese, zinc, and cobalt in haplic chernozem of the steppe part of the Belgorod region. The content of manganese, zinc and cobalt in the arable horizon was 1.42, 1.22 and 1.23 times higher than in the parent rock, respectively. A strong correlation was established between the total contents of zinc and cobalt in the soil profile (r=0.77), and the bonds of manganese with zinc and cobalt had the strength of an average value (r=0.59 and r=0.55). The content of mobile forms of the studied trace elements in haplic chernozem is at a low level. The main reason for the shortage of mobile forms of manganese, zinc and cobalt is their low background content in virgin soil. Keywords: HAPLIC CHERNOZEM, GROSS CONTENT, CONTENT OF MOBILE FORMS, MANGANESE, ZINC, COBALT

Ge/Si and Ge Isotope Fractionation During Glacial and Non-glacial Weathering: Field and Experimental Data From West Greenland

Glacial environments offer the opportunity to study the incipient stages of chemical weathering due to the high availability of finely ground sediments, low water temperatures, and typically short rock-water interaction times. In this study we focused on the geochemical behavior of germanium (Ge) in west Greenland, both during subglacial weathering by investigating glacier-fed streams, as well as during a batch reactor experiment by allowing water-sediment interaction for up to 2 years in the laboratory. Sampled in late August 2014, glacial stream Ge and Si concentrations were low, ranging between 12–55 pmol/L and 7–33 µmol/L, respectively (Ge/Si = 0.9–2.2 µmol/mol, similar to parent rock). As reported previously, the dissolved stable Ge isotope ratio (δ74Ge) of the Watson River was 0.86 ± 0.24‰, the lowest among global rivers and streams measured to date. This value was only slightly heavier than the suspended load (0.48 ± 0.23‰), which is likely representative of the bulk parent rock composition. Despite limited Ge/Si and δ74GeGe fractionation, both Ge and Si appear depleted relative to Na during subglacial weathering, which we interpret as the relatively congruent uptake of both phases by amorphous silica (aSi). Continued sediment-water interaction over 470–785 days in the lab produced a large increase in dissolved Si concentrations (up to 130–230 µmol/L), a much smaller increase in dissolved Ge (up to ∼70 pmol/L), resulting in a Ge/Si decrease (to 0.4–0.5 µmol/mol) and a significant increase in δ74Ge (to 1.9–2.2‰). We argue that during the experiment, both Si and Ge are released by the dissolution of previously subglacially formed aSi, and Ge is then incorporated into secondary phases (likely adsorbed to Fe oxyhydroxides), with an associated Δ74Gesecondary−dissolved fractionation factor of −2.15 ± 0.46‰. In summary, we directly demonstrate Ge isotope fractionation during the dissolution-precipitation weathering reactions of natural sediments in the absence of biological Ge and Si uptake, and highlight the significant differences in Ge behavior during subglacial and non-glacial weathering.

The Influence of the Magmatic to Postmagmatic Evolution of the Parent Rock on the Co Deportment in Lateritic Systems: The Example of the Santa Fé Ni-Co Deposit (Brazil)

The Santa Fé Ni-Co deposit is a major undeveloped lateritic deposit located in the Goiás State of Central Brazil. The deposit comprises two properties that together have indicated resources of 35.7 million tonnes (Mt), grading 1.14% Ni and 0.083% Co, and inferred resources of 104.3 Mt at 1.03% Ni and 0.054% Co. The laterite was derived from Late Cretaceous alkaline ultramafic lithologies that experienced an initial silicification from Eocene to Oligocene, followed by lateritization and partial reworking in Miocene-Pliocene. The deposit is characterized both by oxide- and phyllosilicate-dominated ore zones. In the former, Ni- and Co-bearing hematite and goethite dominate the supergene mineralogical assemblage, while ore-bearing Mn oxyhydroxides occur as minor components. In the phyllosilicate-dominated horizons the major Ni-carrying phase is chlorite. Multivariate statistical analyses (factor analysis and principal components analysis) conducted on the drill core assay database (bulk-rock chemical analyses) showed that significant differences exist between Ni and Co distributions. The Ni distribution is not controlled by any clear geochemical correlation. This is because the highest Ni concentrations have been measured in the ferruginous and in the ochre saprolite zones, where Ni-bearing minerals (chlorite and goethite) are mostly associated with reworked material and only in a limited way, with zones affected by in situ ferrugination. Cobalt has an atypical statistical distribution at Santa Fé if compared with other laterites, correlated not only with Mn but also with Cr in the majority of the laterite facies. From microchemical analyses on several potential Co-bearing minerals, it was found that the Co-Cr association is related to elevated Co contents in residual spinels, representing unweathered phases of the original parent rock now included in the laterite. This element distribution is atypical for Ni-Co laterite deposits, where Co is normally associated with Mn in supergene oxyhydroxides. In the case of the Santa Fé laterite, the Co concentration in spinels is likely related to magmatic and postmagmatic processes that affected the original parent rock before lateritization, specifically (1) orthomagmatic enrichment of Co in chromite, due to its high affinity to spinels in alkaline melts, and (2) trace elements (i.e., Co, Mn, Ni, and Zn) redistribution during the hydrothermal alteration of chromite into ferritchromite. The Santa Fé deposit represents a good example of how the prelateritic evolution of a parent rock strongly affects the efficiency of Co mobilization and enrichment during supergene alteration. Based on the interpretation of metallurgical test work, a fraction of total Co between 20 and 50% is locked in spinels.

EVALUATION OF THE GROWING CONDITIONS OF SEA-BUCKTHORN PLANTATIONS UNDER INUNDATIVE IRRIGATION

Sea-buckthorn grows well on slope lands that are high-ly drained and lack stagnant water. The optimum soil mois-ture content for sea-buckthorn corresponds to 70% of the lowest moisture capacity. Under continuous soil moisture deficit, the leaf surface area decreased, the fruits were poorly set as a result of ovary drop during the first half of the growing season, and berry size decreased. In this re-gard, the study of the water regime of the soil under sea-buckthorn plantations the possibility of its regulation re-mained quite topical. The available moisture in the humus horizons of chernozem in May 2004 corresponded to a satisfactory level. At the end of summer, the moisture con-tent of the chernozem decreased to unsatisfactory state. As a result, the plants experienced water deprivation throughout the growing season. Naturally, the need arose for irrigation, especially in June and August with irrigation rates of 490 and 280 t per m3, respectively. In the underly-ing horizons, the soil moisture deficit was weaker. In the humus horizons, the available moisture in the chernozem in the middle of the slope did not differ much from the mois-ture content at its top. At the same time, in the transitional BC layer in the second half of summer, the available mois-ture content was significantly higher. This difference was also found in the parent rock. In the lower part of theslope, the one-meter soil layer contained a greater amount of moisture which contributed to the decrease of its deficit during the entire growing season. This was especially no-ticeable in the illuvial horizon and parent rock. In the sec-ond half of summer,the available moisture content here remained higher than in the upper slope sites. In conclu-sion, it should be noted that only humus-accumulative hori-zons A (arable) + AB needed irrigation with different irriga-tion rates depending on the location of the sea-buckthorn plantations on the slope and their growth features.