Bioavailability Of Zn Research Articles

Immobilization of Pb and Zn in Contaminated Soil Using Alumina–Silica Nano-Amendments Synthesized from Coal Fly Ash

To apply coal fly ash to the remediation of heavy-metal-contaminated soil, an alumina-silica nano-amendment (ASNA) was synthesized from coal fly ash and was used for the immobilization of lead and zinc in contaminated soil. The investigation on the synthesis of the ASNA shows that the ASNA can be obtained under a roasting temperature of 700 °C, a ratio of alkali to coal fly ash of 1.2:1, and a molar ratio of silicon to aluminum of 1:1. The ASNA could increase the soil pH and cation exchange capacity (CEC) and decrease the bioavailability of Pb and Zn. When the ASNA addition increased from 0 to 2%, the bioavailability (extracted by CaCl2) of Pb and Zn decreased by 47% and 72%, respectively. Moreover, the addition of the ASNA facilitated the transformation of Pb from a reducible fraction to oxidizable and residual fractions and Zn from an exchangeable fraction to a residual fraction. The correlation analysis and cluster analysis verify that the ASNA modulates the chemical speciation of heavy metals by increasing the soil's CEC and pH, thereby immobilizing heavy metals. It is expected that this study can provide a new method for the remediation of Pb- and Zn-contaminated soil.

Millet bran protein hydrolysates derived peptides-zinc chelate: Structural characterization, security prediction in silico, zinc transport capacity and stability against different food processing conditions.

A novel peptide Ser-Asp-Asp-Val-Leu (SDDVL) of excellent zinc-chelating capacity (13.77mg/g) was identified in millet bran protein hydrolysates. In silico prediction demonstrated that SDDVL had no potential toxicity. The results of structural characterization demonstrated that both amino group and carboxyl group of SDDVL were the primary zinc-chelating sites. Moreover, SDDVL-zinc chelate showed higher stability (p<0.05) than ZnSO4 and zinc gluconate under different processing conditions including most pasteurization conditions, heating at 100°C for 10-50min, various pH values (8.0-10.0), treatment of glucose (4-8g/100g) or NaCl (1-4g/100g), and simulated gastrointestinal digestion. In addition, SDDVL-zinc chelate showed higher zinc transport capacity than ZnSO4 and zinc gluconate in Caco-2 cells (p<0.05). These results suggested that millet bran peptide had a positive effect on the gastrointestinal stability and bioavailability of Zn, and SDDVL-zinc chelate could be used as ingredient of zinc supplements. PRACTICAL APPLICATION: The current study provided a practical method to identify peptides of excellent zinc-chelating capacity from millet bran protein hydrolysates. This study demonstrated that in silico prediction assisted with suitable database was a fast, practical, and economic way to evaluate the security and to analysis the physicochemical properties of novel peptides. Moreover, it provided an efficient method to assess the stability of peptide-zinc chelate under different food processing conditions, which was the theoretical basis for utilization of peptide as ingredient of zinc fortifications.

Pinus halepensis in Contaminated Mining Sites: Study of the Transfer of Metals in the Plant-Soil System Using the BCR Procedure.

The study aimed at evaluating the geochemical fractions of Zn, Pb, Cd and their bioavailability in soil in-depth and around the root of Pinus halepensis grown on heavily contaminated mine tailing in south-western Sardinia, Italy. The contaminated substrates were partly investigated in a previous study and are composed of pyrite, dolomite, calcite, quartz, gypsum, barite, iron-sulfate and iron-oxide. The geochemical fractions and bioavailability of Zn, Pb and Cd were measured through the BCR extractions method. Cadmium in the superficial contaminated substrates was mainly found in the exchangeable BCR fraction. Zinc and lead were often found in the residual BCR fraction. PCA confirmed that the uppermost alkaline-calcareous layers of mine waste were different with respect to the deeper acidic layers. We demonstrated that Pb and Zn were less present in the exchangeable form around the roots of P. halepensis and in soil depth. This can be due to uptake or other beneficial effect of rhizospheres interaction processes. Further studies will shed light to confirm if P. halepensis is a good candidate to apply phytostabilization in mine tailing.

Passivation mechanism of Cu and Zn with the introduction of composite passivators during anaerobic digestion of pig manure

Heavy metals in livestock manure pose a threat to the environment after biogas fertilizer being utilized, while its bioavailability is reduced substantially by passivator during the anaerobic digestion. In this study, an optimal composite passivator of humic acid, fly ash and biochar with proportion of 7.5%:7.5%:7.5% and 5.0%:7.5%:7.5% is obtained and the passivation mechanism on Cu and Zn during anaerobic digestion of pig manure is explored. The content of humic acid (HA) in biogas residue increased by 15.66–27.82%, which promoted the transformation from FA-Cu/Zn to HA-Cu/Zn and was beneficial to the passivation of Cu and Zn. The bioavailability of Cu and Zn was reduced by the adsorption and complexation at the early and middle stages of anaerobic digestion. Humic substances play a major role in the passivation of heavy metals at the late stage. The composite passivator can improve the humification degree of biogas residue and reduce heavy metal biotoxicity.

Kernel color and fertilization as factors of enhanced maize quality.

Maize is an important staple crop and a significant source of various nutrients. We aimed to determine the macronutrients, antioxidants, and essential elements in maize genotypes (white, yellow, and red kernel) using three different fertilizers, which could be used as a basis to increase the nutrient density of maize. The fertilizer treatments used bio- and organic fertilizers as a sustainable approach, urea, as a commonly used mineral fertilizer, and the control (no fertilization). We evaluated the yield, concentration of macronutrient (protein, oil, and starch), nonenzymatic antioxidants (phenolics, yellow pigment, total glutathione (GSH), and phytic phosphorus), and reduction capacity of the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, as well as essential elements that are commonly deficient in the diet (Mg, Ca, Fe, Mn, Zn, Cu, and S) and their relationships with phytic acid. The genotype expressed the strongest effect on the variability of grain yield and the analyzed grain constituents. The red-kernel hybrid showed the greatest accumulation of protein, oil, phenolics, and essential elements (Ca, Fe, Cu, and S) than a yellow and white hybrid, especially in the biofertilizer treatment. The yellow kernel had the highest concentrations of yellow pigment, GSH, phytic phosphorous, Mg, Mn, and Zn (19.61 µg g-1, 1,134 nmol g-1, 2.63 mg g-1, 1,963 µg g-1, 11.7 µg g-1, and 33.9 µg g-1, respectively). The white kernel had a greater starch concentration (2.5% higher than that in the red hybrid) and the potential bioavailability of essential metals, particularly under no fertilization. This supports the significance of white maize as a staple food in many traditional diets across the world. Urea was important for the enhancement of the antioxidant status (with 88.0% reduction capacity for the DPPH radical) and increased potential Zn bioavailability in the maize kernels (13.3% higher than that in the biofertilizer treatment). This study underlines the differences in the yield potential and chemical composition of red, yellow, and white-kernel maize and their importance as a necessary part of a sustainable human diet. This information can help determine the most appropriate genotype based on the antioxidants and/or essential elements targeted for kernel improvement.

Comparison of zinc bioavailability in zinc-glycine and zinc-methionine chelates for broilers fed with a corn-soybean meal diet.

The objective of this study was to compare the bioavailability of zinc (Zn) from zinc-glycine (Zn-Gly) and zinc-methionine (Zn-Met) as compared with zinc sulfate (ZnSO4) used as a standard in broilers. A total of 1,200 one-day-old male broilers (Cobb 500) were randomly allotted to one of 10 treatments with eight replicate cages of 15 birds each. The broilers were fed a corn-soybean meal basal diet (containing 26.46mg Zn/kg; control) or the basal diet added with 40, 80, and 120mg Zn/kg as Zn-Gly, Zn-Met, or ZnSO4 for 14days. The relative bioavailability value (RBV) was calculated based on multiple linear regression slope ratios of Zn concentrations in tibia and pancreas, pancreas metallothionein (MT) concentration, and pancreas MT mRNA abundance on added Zn intake. When comparing the control with all Zn-supplemented treatments, Zn addition did not significantly affect average feed intake and bodyweight gain during days 1-14 (p > 0.10). However, Zn concentrations in the tibia, pancreas, and liver and pancreas MT concentration and MT mRNA abundance increased in all Zn-supplemented treatments compared with the control (p < 0.05), and these indices increased linearly (p < 0.001) with increasing added Zn levels on days 7 and 14. The RBV of Zn as Zn-Met was similar to that as Zn-Gly or ZnSO4 (p > 0.40) on days 7 and 14, based on tibia and pancreas Zn. In contrast, on days 7 and 14, the RBVs of Zn were in the following order: Zn-Met > Zn-Gly > ZnSO4 (p < 0.05), based on pancreas MT concentration. The bioavailable Zn from Zn-Met was 1.20 or 1.25 times that from Zn-Gly on day 7 or 14, respectively, evaluated by pancreas MT content. The RBV of Zn as Zn-Met was similar to that as Zn-Gly or ZnSO4 on day 7, whereas it was higher than that as Zn-Gly or ZnSO4 on day 14, based on pancreas MT mRNA abundance. In conclusion, Zn-Met had higher bioavailable Zn than Zn-Gly for the starter broilers fed with the corn-soybean meal diet, using pancreas MT concentration as the response criterion.

The diversity of phytic acid content and grain processing play decisive role on minerals bioavailability in rice

Rice is a staple food and important source of micronutrients for more than three billion people globally. However, the bioavailability of iron (Fe) and zinc (Zn) is affected by phytic acid (PA). In this work, we analyzed 67 genotypes for Fe, Zn and PA contents. Contrasting PA genotypes were selected in each category of high protein, scented, pigmented and general rice for bioavailability analysis. Our results explain that though Fe content in genotype PB 140 was high, the bioavailability was low which might be due to its higher PA content (21.03 g/kg). The Fe and PA are majorly located in outer bran layer of endosperm, therefore, its bioavailability was affected by PA. However, Zn bioavailability was not much affected by PA as it is distributed homogenously in the rice grain. Moreover, PA biosynthetic genes (IPK1, MIPS1) and grain specific phosphorus transporter gene (SPDT) expressed higher in the middle stage of grain filling which was correlated with higher PA accumulation. Our study provides an insight into the improvement of mechanism of Fe and Zn bioavailability in rice grain which help breeders involved in biofortification programme to develop high minerals bioavailable genotypes by targeting PA related genes.

Zinc agronomic biofortification of staple crops may be a cost-effective strategy to alleviate zinc deficiency in Ethiopia.

Inadequate dietary zinc (Zn) supplies and Zn deficiency (ZnD) are prevalent in Ethiopia, where cereals are major dietary sources, yet low in bioavailable Zn. Zinc agronomic biofortification (ZAB) of staple crops through application of Zn fertilizers may contribute to alleviating ZnD. However, large-scale promotion and adoption of ZAB requires evidence of the feasibility and public health benefits. This paper aimed to quantify the potential cost-effectiveness of ZAB of staple crops for alleviating ZnD in Ethiopia. Current burden of ZnD among children in Ethiopia was quantified using a disability-adjusted life years (DALYs) framework. Evidence on baseline dietary Zn intake, cereal consumption, and fertilizer response ratio was compiled from existing literature and secondary data sources. Reduction in the burden of ZnD attributable to ZAB of three staple cereals (maize, teff, and wheat) via granular and foliar Zn fertilizer applications was calculated under optimistic and pessimistic scenarios. The associated costs for fertilizer, labor, and equipment were estimated in proportion to the cropping area and compared against DALYs saved and the national Gross Domestic Product capita-1. An estimated 0.55 million DALYs are lost annually due to ZnD, mainly due to ZnD-related mortality (91%). The ZAB of staple cereals via granular Zn fertilizer could reduce the burden of ZnD by 29 and 38% under pessimistic and optimistic scenarios, respectively; the respective values for ZAB via foliar application were 32 and 40%. The ZAB of staple cereals via granular fertilizer costs US$502 and US$505 to avert each DALY lost under optimistic and pessimistic scenarios, respectively; the respective values for ZAB via foliar application were US$226 and US$ 496. Foliar Zn application in combination with existing pesticide use could reduce costs to US$260-353 for each DALY saved. Overall, ZAB of teff and wheat were found to be more cost-effective in addressing ZnD compared to maize, which is less responsive to Zn fertilizer. ZAB of staple crops via granular or foliar applications could be a cost-effective strategy to address ZnD, which can be integrated with the existing fertilizer scheme and pesticide use to minimize the associated costs.

A tale of two metals: Biofortification of rice grains with iron and zinc.

Iron (Fe) and zinc (Zn) are essential micronutrients needed by virtually all living organisms, including plants and humans, for proper growth and development. Due to its capacity to easily exchange electrons, Fe is important for electron transport in mitochondria and chloroplasts. Fe is also necessary for chlorophyll synthesis. Zn is a cofactor for several proteins, including Zn-finger transcription factors and redox metabolism enzymes such as copper/Zn superoxide dismutases. In humans, Fe participates in oxygen transport, electron transport, and cell division whereas Zn is involved in nucleic acid metabolism, apoptosis, immunity, and reproduction. Rice (Oryza sativa L.) is one of the major staple food crops, feeding over half of the world's population. However, Fe and Zn concentrations are low in rice grains, especially in the endosperm, which is consumed as white rice. Populations relying heavily on rice and other cereals are prone to Fe and Zn deficiency. One of the most cost-effective solutions to this problem is biofortification, which increases the nutritional value of crops, mainly in their edible organs, without yield reductions. In recent years, several approaches were applied to enhance the accumulation of Fe and Zn in rice seeds, especially in the endosperm. Here, we summarize these attempts involving transgenics and mutant lines, which resulted in Fe and/or Zn biofortification in rice grains. We review rice plant manipulations using ferritin genes, metal transporters, changes in the nicotianamine/phytosiderophore pathway (including biosynthetic genes and transporters), regulators of Fe deficiency responses, and other mutants/overexpressing lines used in gene characterization that resulted in Fe/Zn concentration changes in seeds. This review also discusses research gaps and proposes possible future directions that could be important to increase the concentration and bioavailability of Fe and Zn in rice seeds without the accumulation of deleterious elements. We also emphasize the need for a better understanding of metal homeostasis in rice, the importance of evaluating yield components of plants containing transgenes/mutations under field conditions, and the potential of identifying genes that can be manipulated by gene editing and other nontransgenic approaches.

Impact of plastic sheet mulching on grain Zn concentration, P/Zn ratio and Zn uptake in dryland grown winter wheat

High yield and grain quality are the targets in wheat production. Plastic sheet mulching has improved wheat grain yield in under dryland agriculture, but its impact on grain quality, particularly grain zinc (Zn) concentration is not well known. Seven-site field experiments were conducted during 2014–2016 on drylands of three provinces in the Loess Plateau of China to examine the effect of plastic sheet mulching on wheat grain Zn concentration under different N applications. A split-plot design was adopted with the two main plots (no mulching and plastic sheet mulching) and the subplots with different N application rate. Measurements of Zn uptake, Zn remobilization, Zn distribution to the grain and bioavailability were made, together with biomass, yield and yield components. Study found plastic sheet mulching reduced the grain Zn concentration, and increased the molar ratio of P/Zn, decreasing the Zn bioavailability. Plastic sheet mulching also increased the aboveground Zn accumulation at anthesis by 14.4 %, the straw Zn accumulation at maturity by 14.8 % and the Zn remobilization to the grain by14.2 % but did not affect the availability of soil Zn. For each 100 kg N ha −1 applied under plastic sheet mulching, the grain Zn concentration, the Zn requirement, the aboveground Zn accumulation and remobilization to the grain increased by 3.6 mg kg −1 , 2.8 g Mg −1 , 6.6 g ha −1 and 3.8 g ha −1 , respectively. Aboveground Zn accumulation at maturity and post-anthesis Zn uptake varied with N rates in a linear-plus-plateau model. The reduction in post-anthesis Zn uptake and Zn harvest index were the factors leading to the decrease in grain Zn concentration under plastic sheet mulching. Consequently, under plastic sheet mulching, a rational N fertilizer strategy should be considered to improve the grain Zn concentration in wheat grown in dryland. • Plastic sheet mulching reduces wheat grain Zn bioavailability. • Post-anthesis Zn uptake and Zn harvest index influence wheat grain Zn content. • Rational N fertilization can improve grain Zn content and bioavailability in wheat. • Grain Zn content increased linearly with glutenin content in wheat grain.

Bioavailability of Different Zinc Sources in Pigs 0-3 Weeks Post-Weaning.

The bioavailability of dietary zinc (Zn) in pigs may differ according to the Zn source and is affected by other components in the diet. The aim was to determine the biomarkers of Zn bioavailability (apparent total tract digestibility of Zn and serum Zn status) following six different sources of added Zn and their effect on the performance and faecal consistency score in piglets 0-3 weeks after weaning on day 28. The sources of Zn were Zn oxide (ZnO), Zn sulfate (ZnSO4), porous ZnO, Zn-glycinate, amino acid-bound Zn and hydroxy covalent-bound Zn added at 100 mg/kg (ZnO and ZnSO4 also added at 1000 mg/kg), in a total of eight treatments (n = 12/treatment). Pigs were individually housed, and titanium dioxide was included as an indigestible marker in the feed. The digestibility of Zn on day 14 post-weaning was negative for all six Zn sources at 100 mg Zn/kg, indicating insufficient Zn supply. The digestibility of Zn differed according to the Zn source, but the digestibility of Zn from ZnO and ZnSO4 did not differ between processed inorganic or chelated organic sources of Zn. However, the differences in Zn digestibility between Zn sources were not reflected as differences in the serum Zn status, feed intake, gain or probability of diarrhoea.

Improved Zn bioavailability by its enhanced colocalization and speciation with S in wheat grain tissues after N addition

Zinc bioavailability with the presence of other elements in wheat grains might be affected by fertilizers. A long-term field experiment was conducted to examine effects of N fertilizer on Zn bioavailability in wheat grain tissues, with changes in the concentrations, distribution, and speciation of Zn as well as P and sulfur S via synchrotron-based technology. Results showed that addition of N fertilizer was associated with changes in Zn concentrations and distributions in grain tissues, especially in the crease region and endosperm. Simultaneously, N addition enhanced Zn-S colocalization in the crease region and endosperm and lowered the P/Zn ratio and Zn-P colocalization. Addition of N fertilizer with P increased Zn-cysteine (9.2%) and decreased Zn-phytate (47.3%) in the crease region, leading to potentially higher grain Zn bioavailability. Thus, addition of N fertilizer improved concentrations and bioavailability of Zn, by coordinating the relationships among Zn, P and S within wheat grains.

Does a decade of soil organic fertilization promote copper and zinc bioavailability to an epi-endogeic earthworm?

While long-term organic fertilizer (OF) applications tend to decrease copper (Cu) and zinc (Zn) availability in agricultural soils, earthworm bioturbation has been reported to have the opposite effect. Thus, the consequences of OF amendments in earthworm-inhabited soils on Cu and Zn bioavailability to earthworms are still under debate. Here, we assessed the effect of a decade of agronomically realistic OF applications on Cu and Zn availability in earthworm-inhabited soils and the consequences on Cu and Zn bioavailability to earthworms. An epi-endogeic species (Dichogaster saliens) was exposed in microcosms to three field-collected soils that had received either no, mineral, or organic fertilization for a decade. Dissolved organic matter (DOM) properties (i.e., concentration, aromaticity, and binding properties toward Cu), pH, and Cu and Zn availability (i.e., total concentration and free ionic activity) were determined in the solution of the soil containing earthworms. Cu and Zn bioavailability was assessed by measuring the net accumulation (ng) and concentration of Cu and Zn in earthworms (mgkg-1). Despite soil Cu and Zn contamination induced by a decade of OF applications, organic fertilization induced an increase in soil pH and DOM properties that drove the reduction of Cu and Zn availability in earthworm-inhabited soils, while bioturbation had little effect on soil pH, DOM properties, and Cu and Zn availability. Consistently, Cu and Zn bioavailability to earthworms did not increase with OF applications. From an ecotoxicological perspective, our results suggest that agronomically realistic applications of OF for a decade should not pose a risk to earthworms in terms of Cu and Zn net accumulation, but further studies have to be undertaken to understand consequent long-term toxicity after exposure.

Assessment of selenium and zinc enriched sludge and duckweed as slow-release micronutrient biofertilizers for Phaseolus vulgaris growth

Selenium (Se) and zinc (Zn) are essential micronutrients that are often lacking in the diet of humans and animals. Application of mineral Se and Zn fertilizers into soils may lead to a waste of Se and Zn due to the fast leaching and low utilization by plants. Slow-release Se and Zn biofertilizer may therefore be beneficial. This study aims to assess the potential of SeZn-enriched duckweed and sludge produced from wastewater as slow-release Se and Zn biofertilizers. Pot experiments with green beans (Phaseolus vulgaris) and sampling of Rhizon soil pore water were conducted to evaluate the bioavailability of Se and Zn in sandy and loamy soils mixed with SeZn-enriched duckweed and sludge. Both the Se and Zn concentrations in the soil pore water increased upon amending the two biomaterials. The concentration of Se released from SeZn-enriched duckweed rapidly decreased in the first 21 days and slowly declined afterwards, while it remained stable during the entire experiment upon application of SeZn-enriched sludge. The Zn content in the soil pore water gradually increased over time. The application of SeZn-enriched duckweed and sludge significantly increased the Se concentrations in plant tissues, in particular in the form of organic Se-methionine in seeds, without a negative impact on plant growth when an appropriate dose was applied (1 mg Se/kg soil). While, it did not increase Zn concentrations in plant seeds. The results indicate that the SeZn-enriched duckweed and sludge could be only used as organic Se biofertilizers for Se-deficient soils. Particularly, the SeZn-enriched sludge dominated with elemental nano-Se was an effective Se source and slow-release Se biofertilizer. These results could offer a theoretical reference to choose an alternative to chemical Se fertilizers for biofortification, avoiding the problem of Se losses by leaching from mineral Se fertilizers while recovering resources from wastewater. This could contribute to the driver for a future circular economy.

Zinc Concentrations in Different Parts of the Gastropod, Faunus ater, Collected from Intertidal Areas of Peninsular Malaysia

Intertidal gastropods, Faunus ater (F. ater), were collected from four sampling sites in Peninsular Malaysia. It was found that the concentrations of Zinc (Zn) (mg/kg dry weight) ranged from 347.23 to 356.21 for Digestive Caecum (DC), 95.00 to 100.91 for foot, 102.73 to 109.00 for muscle, 42.73 to 177.72 for operculum, 87.57 to 161.76 for remainder, and 24.42 to 53.96 for shell of F. ater. Current results indicate that the intertidal waters of Pantai Sri Tujoh has a higher bioavailability of Zn and require further research. According to the current findings, F. ater may be employed as a biomonitor of Zn pollution and bioavailability.

Potential mobilization of cadmium and zinc in soils spiked with smithsonite and sphalerite under different water management regimes

Particulate cadmium (Cd) and zinc (Zn) are ubiquitous in agricultural soils of Pb–Zn mining regions. Water management serves as an important agronomic measure altering the bioavailability of Zn and Cd in soils, but how this affects particulate Cd and Zn and the underlying mechanisms remain largely unknown. Microcosm soil incubation combined with spectroscopic and microscopic characterization was conducted. During a two-year-long incubation period we observed that the concentrations of soil CaCl2-extractable Zn and Cd increased 3–10 times in sphalerite-spiked soils and 1–2 times in smithsonite-spiked soils under periodic flooding conditions due to the long-term dissolution of sphalerite (SP) and smithsonite (SM). However, the increase in the concentration of CaCl2-extractable metals (Zn: from 0.607 mg kg−1 to 1.051 mg kg−1 and Cd: from 0.047 mg kg−1 to 0.119 mg kg−1) was found only in SP-treatment under continuous flooding conditions, indicating the mobilization of metals. Ultrafiltration analysis shows that the nanoparticulate fraction of Zn and Cd in soil pore water increased 5 and 7 times in SP-treatments under continuous flooding conditions, suggesting the increment of metal pools in soil pore water. HRTEM-EDX-SAED further reveals that these nanoparticles were mainly crystalline ZnS and Zn-bearing sulfate nanoparticles in the SP-treatment and amorphous ZnCO3 and ZnS nanoparticles in the SM-treatment. Therefore, the formation of the stable crystalline Zn-bearing nanoparticles in the SP-treatment may explain the elevation of the concentration of soil CaCl2-extractable Zn and Cd under continuous flooding. The potential mobility of particulate metals should therefore be expected in scenarios of continuous flooding such as paddy soils and wetland systems.

Coupling Molecular-Scale Spectroscopy with Stable Isotope Analyses to Investigate the Effect of Si on the Mechanisms of Zn-Al LDH Formation on Al Oxide.

While silicate has been known to affect metal sorption on mineral surfaces, the mechanisms remain poorly understood. We investigated the effects of silicate on Zn sorption onto Al oxide at pH 7.5 and elucidated the mechanisms using a combination of X-ray absorption fine structure (XAFS) spectroscopy, Zn stable isotope analysis, and scanning transmission electron microscopy (STEM). XAFS analysis revealed that Zn-Al layered double hydroxide (LDH) precipitates were formed in the absence of silicate or at low Si concentrations (≤0.4 mM), whereas the formation of Zn-Al LDH was inhibited at high silicate concentrations (≥0.64 mM) due to surface-induced Si oligomerization. Significant Zn isotope fractionation (Δ66Znsorbed-aqueous = 0.63 ± 0.03‰) was determined at silicate concentrations ≥0.64 mM, larger than that induced by sorption of Zn on Al oxide (0.47 ± 0.03‰) but closer to that caused by Zn bonding to the surface of Si oxides (0.60-0.94‰), suggesting a presence of Zn-Si bonding environment. STEM showed that the sorbed silicates had a close spatial coupling with γ-Al2O3, indicating that >Si-Zn inner-sphere complexes (">" denotes surface) likely bond to the γ-Al2O3 surface to form >Al-Si-Zn ternary inner-sphere complexes. This study not only demonstrates that dissolved silicate in the natural environment plays an important role in the fate and bioavailability of Zn but also highlights the potential of coupled spectroscopic and isotopic methods in probing complex environmental processes.

Zero-valent iron drives the passivation of Zn and Cu during composting: Fate of heavy metal resistant bacteria and genes

Livestock and poultry manures usually contain substantial heavy metals, especially Cu and Zn, which may induce the enrichment of heavy metal resistant genes (HMRGs) and heavy metal resistant bacteria (HMRB). This study aims to clarify the relationship among heavy metal bioavailability, HMRB and HMRGs during composting, so as to assess and alleviate potential ecological risks of manure application to land. In this study, zero-valent iron (ZVI) was used as passivator, and HMRGs and their host microorganisms were investigated by metagenomic analysis. The results showed that ZVI effectively promoted the passivation of Zn and Cu, and the bioavailability of Zn and Cu decreased by 8.25% and 19.84%, respectively. Proteobacteria was the main HMRB in composting, among which Escherichia, Pseudomonas and Salmonella contained abundant HMRGs, and the succession of these bacteria was closely related to the fate of HMRGs. Spearman correlation analysis showed that metal exchangeable and reducible fractions were positively correlated with the abundance of most HMRGs. Furthermore, structural equation model showed that heavy metal passivation can also indirectly reduce the abundance of HMRGs by regulating the succession of HMRB. These results suggested that the fate of HMRGs is closely related to the chemical speciation of heavy metals in composting habitats.

Effect of fermentation stages on the nutritional and mineral bioavailability of cacao beans (Theobroma cacao L.)

Analysis of the complex composition of cacao beans during the fermentation stages provided critical information for evaluating its quality and nutritional attributes. In this work, the effect of fermentation on cacaos’ nutritional, mineral, and bioavailability was established from day 0 (d0) to day 8 (d8). Standard AOAC method was used to determine the proximate composition. Total mineral content was determined using the cost-effective MP-AES. Simulation of the human digestive process from the mouth to the small intestine was used to establish the mineral bioavailability. As a result, increasing fermentation days reduces the amount of nutritional content and increases its fat content. Fermentation causes an outward migration, which reduces total mineral content while having a positive effect on reducing potential heavy metals such as Pb and Ni at about 60 % and 50 %, respectively, in d6 at pH 4.84. Mobility of the minerals increases as the pH level decreases due to the penetration of organic acid in the beans. The high bioavailability of Mn, Ca, Fe, and Zn was noted in d5 and d6. Aside from flavor precursor development, results suggest that fermenting cacao beans to its optimum day reduces the risk of heavy metals and positively enhances the bioavailability of minerals necessary for human nutrition.

Effect of organic and mineral fertilizers applications in pasture and no-tillage system on crop yield, fractions and contaminant potential of Cu and Zn

Organic wastes, fertilizers, organominerals, and minerals contain nutrients essential to crops and contribute to increase productivity. However their use can also lead to the accumulation of copper and zinc, which changes the distribution of their fractions and enhances the risk of toxicity to plants and the environment, thereby working against the sustainable development goals. However, the effect of manure applications on clayey soils and the effects of increasing Cu and Zn contents over the years on crop productivity remain unknown. This study aimed to evaluate the distribution and the potential for contamination of heavy metals in clayey soil with a history of the application of different types and amounts of fertilizers under Cynodon spp. grazing and no-tillage system for soybeans. In Experiment 1, Cynodon spp. were cultivated for hay production and submitted to applications of the following treatments: 0, 200, and 400 kg ha−1 of total-N in the form of pig slurry and urea. In experiment 2, the soybean was grown and subjected to the following treatments: control, pig slurry, commercial granulated solid organic fertilizer, organomineral fertilizer blended with granules, and mineral fertilizer blended with granules. The dose of each nutrient source was determined based on the soil analysis and the recommendations of the liming and fertilization manual. The experiments were conducted for four agricultural crops where soil samples were collected in the layer of 0.00–0.10 m layer and submitted to chemical fractionation of Cu and Zn. The use of pig manure increased the availability of Cu and Zn in the soil, causing an increase in the distribution of copper organic (40.73% and 57.64% for PS200 and PS400 treatments, respectively, in Experiment 1; 67.33% for PS treatment, in Experiment 2) and residual fractions (10.01% and 7.60% for PS200 and PS400 treatments, respectively, in Experiment 1; 9.80% for PS treatment, in Experiment 2), while zinc was predominant in clay-mineral (61.04% and 92.01% for PS200 and PS400 treatments, respectively, in experiment 1; 278.90% for PS treatment, in Experiment 2) and residual fractions (2.36% for PS200 treatment in experiment 1; 9.90% for PS treatment, in Experiment 2). Additionally, the use of swine manure increased the Cu and Zn contents in the exchangeable fraction, which may potentiate the toxicity to plants and increase the potential for contamination of subsoil water. However, the increased bioavailability of Cu and Zn did not caused a loss of crop productivity but instead increased dry mass production and crop yield.