Zn Toxicity Research Articles

Effects of Marginal Zn Excess and Thiamine Deficiency on Microglial N9 Cell Metabolism and Their Interactions with Septal SN56 Cholinergic Cells

Mild thiamine deficiency aggravates Zn accumulation in cholinergic neurons. It leads to the augmentation of Zn toxicity by its interaction with the enzymes of energy metabolism. Within this study, we tested the effect of Zn on microglial cells cultivated in a thiamine-deficient medium, containing 0.003 mmol/L of thiamine vs. 0.009 mmol/L in a control medium. In such conditions, a subtoxic 0.10 mmol/L Zn concentration caused non-significant alterations in the survival and energy metabolism of N9 microglial cells. Both activities of the tricarboxylic acid cycle and the acetyl-CoA level were not decreased in these culture conditions. Amprolium augmented thiamine pyrophosphate deficits in N9 cells. This led to an increase in the intracellular accumulation of free Zn and partially aggravated its toxicity. There was differential sensitivity of neuronal and glial cells to thiamine-deficiency-Zn-evoked toxicity. The co-culture of neuronal SN56 with microglial N9 cells reduced the thiamine-deficiency-Zn-evoked inhibition of acetyl-CoA metabolism and restored the viability of the former. The differential sensitivity of SN56 and N9 cells to borderline thiamine deficiency combined with marginal Zn excess may result from the strong inhibition of pyruvate dehydrogenase in neuronal cells and no inhibition of this enzyme in the glial ones. Therefore, ThDP supplementation can make any brain cell more resistant to Zn excess.

Co-pyrolysis with pine sawdust reduces the environmental risks of copper and zinc in dredged sediment and improves its adsorption capacity for cadmium

Proper treatment of heavy metal-contaminated dredged sediment (DS) is crucial to avoid secondary pollution. Effective and sustainable technologies are desired for the treatment of Zn- and Cu-contaminated DS. Due to the advantages of low energy consumption and time saving, co-pyrolysis technology was innovatively applied to treat Cu- and Zn-polluted DS in this study, and the effects of the co-pyrolysis conditions on Cu and Zn stabilization efficiencies, potential stabilization mechanisms, and the possibility for resource utilization of co-pyrolysis product were also investigated. The results showed that pine sawdust is an appropriate co-pyrolysis biomass for the stabilization of Cu and Zn based on the leaching toxicity analysis. The ecological risks of Cu and Zn in DS were reduced after co-pyrolysis treatment. The total concentrations of Zn and Cu in co-pyrolysis products were decreased by 5.87%–53.45% and 8.61%–57.45% of that in DS before co-pyrolysis. However, the total concentrations of Zn and Cu in DS remained basically unchanged after co-pyrolysis, which indicating the decreases in total concentrations of Zn and Cu in co-pyrolysis products were mainly related to dilution effect. Fraction analysis indicated that co-pyrolysis treatment contributed to transforming weakly bound Cu and Zn into stable fractions. The co-pyrolysis temperature and mass ratio of pine sawdust/DS had a greater influence than co-pyrolysis time on the fraction transformation of Cu and Zn. The leaching toxicity of Zn and Cu from the co-pyrolysis products was eliminated when the co-pyrolysis temperature reached 600 and 800 °C, respectively. Analysis of the X-ray photoelectron spectroscopy and X-ray diffraction results demonstrated that co-pyrolysis treatment could transform mobile Cu and Zn in DS into metal oxides, metal sulfides, phosphate compounds, etc. Batch adsorption procedures suggested that the co-pyrolysis product possessed a high adsorption capacity for Cd (95.70 mg/g at 318 K). The formation of CdCO3 precipitates and the complexation effects of oxygen-containing functional groups were the principal adsorption mechanisms of the co-pyrolysis product. Overall, this study provides new insights into sustainable disposal and resource utilization for heavy metal-contaminated DS.

Psoralen synergies with zinc implants to promote bone repair by regulating ZIP4 in rats with bone defect

BackgroundThe regulation of dose-dependent biological effects induced by biodegradation is a challenge for the production of biodegradable bone-substitute materials, especially biodegradable zinc (Zn) -based materials. Cytotoxicity caused by excess local Zn ions (Zn2+) from degradation is one of the factors limiting the wide application of Zn implants. Given that previous studies have revealed that delayed degradation of Zn materials by surface modification does not reduce cytotoxicity; in the present study, we explore whether preventing the entry of excess Zn2+ into cells may can reduce local Zn toxicity by applying Psoralen (PRL) to Zn implants and assessing its ability to regulate intracellular Zn2+ concentrations.MethodsThe effects of different concentrations of Zn2+ on cellular activity and cytotoxicity were investigated; briefly, we identified natural compounds that regulate Zn transporters, thereby regulating the concentrations of intracellular Zn2+, and applied them to Zn materials. Of these materials, PRL, a natural, tricyclic, coumarin-like aromatic compound that promotes the proliferation and differentiation of osteoblasts and enhances osteogenic activity, was loaded onto the surface of a Zn material using peptides and chitosan (CS), and the surface characteristics, electrochemical properties, and activity of the modified Zn material were evaluated. In addition, the ability of Zn + CS/pPRL implants to promote bone formation and accelerate large-scale bone defect repairs was assessed both in vitro and in vivo.ResultsWe determined that 180 µM Zn2+ significantly induced pre-osteoblast cytotoxicity, and a 23-fold increase in Zrt- and Irt-like protein 4 (ZIP4) expression. We also found that PRL dynamically regulates the expression of ZIP4 in response to Zn2+ concentration. To address the problem of cytotoxicity caused by excessive Zn2+ in local Zn implants, PRL was loaded onto the surface of Zn implants in vivo using peptides and CS, which dynamically regulated ZIP4 levels, maintained the balance of intracellular Zn2+ concentrations, and enhanced the osteogenic activity of Zn implants.ConclusionsThis study reveals the importance of Zn2+ concentration when using Zn materials to promote bone formation and introduces a natural active ingredient, PRL, that can regulate intracellular Zn2+ levels, and thus may be clinically applicable to Zn implants for the treatment of critical bone defects.Graphical

Toxicity of Zinc to Aquatic Life in Tropical Freshwaters of Low Hardness.

Zinc (Zn) is a metal of potential concern for a uranium mine whose receiving waters are in the World-Heritage listed Kakadu National Park in northern Australia. The chronic toxicity of Zn was assessed using seven tropical species in extremely soft freshwater from a creek upstream of the mine. Sensitivity to Zn was as follows (most sensitive to least sensitive based on 10% effect concentrations [EC10s]): mussel Velesunio angasi > gastropod Amerianna cumingi > fish Mogurnda mogurnda > cladoceran Moinodaphnia macleayi > green hydra Hydra viridissima > green alga Chlorella sp. > duckweed Lemna aequinoctialis, with EC10s (<0.45 µm filtered fraction) ranging from 21 to 320 µg/L Zn and EC50s ranging from 52 to 1867 µg/L Zn. These data were used to inform the risk assessment for the rehabilitation of the mine-site and contribute to the global Zn dataset. Environ Toxicol Chem 2023;42:679-683. © 2023 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2023 SETAC.

Comparison of Multiple Linear Regression and Biotic Ligand Models for Predicting Acute and Chronic Zinc Toxicity to Freshwater Organisms.

Multiple linear regression (MLR) models for predicting zinc (Zn) toxicity to freshwater organisms were developed based on three toxicity-modifying factors: dissolved organic carbon (DOC), hardness, and pH. Species-specific, stepwise MLR models were developed to predict acute Zn toxicity to four invertebrates and two fish, and chronic toxicity to three invertebrates, a fish, and a green alga. Stepwise regression analyses found that hardness had the most consistent influence on Zn toxicity among species, whereas DOC and pH had a variable influence. Pooled acute and chronic MLR models were also developed, and a k-fold cross-validation was used to evaluate the fit and predictive ability of the pooled MLR models. The pooled MLR models and an updated Zn biotic ligand model (BLM) performed similarly based on (1) R2 , (2) the percentage of effect concentration (ECx) predictions within a factor of 2.0 of observed ECx, and (3) residuals of observed/predicted ECx versus observed ECx, DOC, hardness, and pH. Although fit of the pooled models to species-specific toxicity data differed among species, species-specific differences were consistent between the BLM and MLR models. Consistency in the performance of the two models across species indicates that additional terms, beyond DOC, hardness, and pH, included in the BLM do not help explain the differences among species. The pooled acute and chronic MLR models and BLM both performed better than the US Environmental Protection Agency's existing hardness-based model. We therefore conclude that both MLR models and the BLM provide an improvement over the existing hardness-only models and that either could be used for deriving ambient water quality criteria. Environ Toxicol Chem 2023;42:393-413. © 2022 SETAC.

Development of an in Vitro Digestion System to Study the Bioavailability and Bioreactivity of Zinc Sulfate and Zn-Bioplex in Fish Using the RTgutGC Cell Line

Here, we report the development of a novel in vitro digestion system that mimics the digestive process in fish and uses the RTgutGC cell line, a model of the rainbow trout (Oncorhynchus mykiss) intestine, to study the bioavailability, bioreactivity, and toxicity of Zn added as an inorganic (ZnSO4) and organic zinc compound (Zn-Bioplex). Our results showed that, before digestion, Zn-Bioplex was more bioavailable than ZnSO4. However, after in vitro digestion, ZnSO4 and Zn-Bioplex accumulated and were transported equally across the RTgutGC cell epithelium. However, Zn-Bioplex was shown to be less bioreactive than ZnSO4, suggesting that peptide complexation might reduce the intracellular release of zinc as shown by a reduced induction of metallothionein and ZnT1 mRNA levels. This novel method shows promise as a standardized in vitro fish digestion model to study the interactions occurring at the lumen of the intestine and the bioavailability and toxicity of digested compounds in the fish gut.

Soil properties influence the toxicity and availability of Zn from ZnO nanoparticles to earthworms

To develop models that support site-specific risk assessment for nanoparticles (NPs), a better understanding of how NP transformation processes, bioavailability and toxicity are influenced by soil properties is needed. In this study, the influence of differing soil properties on the bioavailability and toxicity of zinc oxide (ZnO) NPs and ionic Zn to the earthworm Eisenia fetida was investigated. Earthworms were exposed to ZnO_NPs and ionic Zn, between 100 and 4400 mg Zn/kg, in four different natural soils (organic matter content: 1.8–16.7%, soil pH: 5.4–8.3, representing sandy loam to calcareous soils). Survival and reproduction were assessed after 28 and 56 days, respectively. Zn concentrations in soil pore waters were measured while labile concentrations of Zn were measured using an in-situ dynamic speciation technique (diffusive gradient in thin films, DGT). Earthworm Zn tissue concentrations were also measured. Soil properties influenced earthworm reproduction between soil controls, with highest reproductive output in soils with pH values of 6–7. Toxicity was also influenced by soil properties, with EC50s based on total Zn in soil ranging from 694 to >2200 mg Zn/kg for ZnO_NP and 277–734 mg Zn/kg for ionic Zn. Soil pore water and DGT measurements showed good agreement in the relative amount of Zn extracted across the four soils. Earthworms exposed to ZnO_NPs survived higher Zn concentrations in the soils and had higher tissue concentrations compared with ionic Zn exposures, particularly in the high organic content calcareous soil. These higher tissue concentrations in ZnO_NP exposed earthworm could have consequences for the persistence and trophic mobility of Zn in terrestrial systems and need to be further investigated to elucidate if there any longer-term risks associated with sustained input of ZnO_NP to soil.

Zinc solubilizing Bacillus sp (SS9) and Enterobacter sp (SS7) promote mung bean (Vigna radiata L.) growth, nutrient uptake and physiological profiles.

Zinc (Zn) is a crucial micronutrient required for optimum plant growth. Zn-solubilizing bacteria (ZSB) are potential alternatives for Zn supplementation and convert applied inorganic Zn to available forms. In this study, ZSB were isolated from the root nodules of wild legumes. From a set of 17 bacteria, the isolates SS9 and SS7 were found to be efficient in tolerating 1 g (w/v) Zn. The isolates were identified as Bacillus sp (SS9, MW642183) and Enterobacter sp (SS7, MW624528) based on morphology and 16S rRNA gene sequencing. The screening of PGP bacterial properties revealed that both isolates possessed production of indole acetic acid (50.9 and 70.8 µgmL-1), siderophore (40.2% and 28.0%), and solubilization of phosphate and potassium. The pot study experiment in the presence and absence of Zn revealed that the Bacillus sp and Enterobacter sp inoculated plants showed enhanced mung bean plant growth (45.0% to 61.0% increment in shoot length and 26.9 to 30.9% in root length) and biomass compared to the control. The isolates also enhanced photosynthetic pigments such as total chlorophyll (1.5 to 6.0-fold) and carotenoids (0.5 to 3.0-fold) and 1-2-fold increase in Zn, phosphorous (P), and nitrogen (N) uptake compared to the Zn-stressed control. The present results indicated that the inoculation of Bacillus sp (SS9) and Enterobacter sp(SS7) reduced the toxicity of Zn and, in turn, enhanced the plant growth and mobilization of Zn, N, and P to the plant parts.

Ecological toxicity of Cd, Pb, Zn, Hg and regulation mechanism in Solanum nigrum L.

This study aimed to investigate the combined ecotoxicological effects of Cd, Pb, Zn, Hg and regulation mechanisms in Solanum nigrum L. In this work, the co-exposure of these four heavy metals hindered the transformation of Cd, Zn, and Hg (except Pb) from available to non-available chemical forms. Individual Cd, Pb, Zn and Hg induced the oxidative damages to S. nigrum L., while their combination further enhanced this ecological toxicity. By internal regulation, the ecological toxicity of metals to S. nigrum L. could be alleviated to a certain extent. Specifically, S. nigrum L. was a hyperaccumulator of Cd with BCF ＞1. Moreover, since BCFroot of Pb, Zn and Hg were all greater than BCFshoot, S. nigrum L. could accumulate Pb, Hg and Zn mainly in plant roots, which was beneficial for the detoxification of plants. Meanwhile, the immobilization by cell wall (the proportions of Cd, Pb, Zn and Hg in the cell wall were 54.46–84.92%, 38.33–49.25%, 48.38–56.19% and 45.97–63.47% in low metal concentration treatments) and the sequestration in vacuole (the proportions of Cd, Pb, Zn, and Hg in the soluble fractions are 50.99–59.00%, 41.05–45.46%, 37.54–61.04% and 33.47–61.35% in high metal concentration treatments) also act as important detoxification pathways. The external regulation was mainly the changes of soil microbial communities influenced by plants. Specifically, the richness and diversity of bacteria in rhizosphere soil were increased, and roots of S. nigrum L. recruited some potentially beneficial microbials. This study provided a theoretical basis and guidance for S. nigrum L. as a phytoremediation plant under combined heavy metal pollution.

Single and combined effects of Zn and Al on photosystem II of the green microalgae Raphidocelis subcapitata assessed by pulse-amplitude modulated (PAM) fluorometry

Increasing metal concentrations in aquatic environments are mainly due to anthropogenic actions, which is a matter of concern for the biodiversity of aquatic biota. It is known that metals coexist in environments, however environmental risk assessments do not usually take into account the effects of these mixtures. We aimed to test Zn and Al mixtures on the photosynthetic apparatus of a green microalga, for the first time, using PAM fluorometry. After 72 h exposure, single concentrations from 0.08 to 0.46 µM Zn and 22.24 to 37.06 µM Al affected the photosynthetic parameters of Raphidocelis subcapitata. Metals affected the efficiency of the oxygen-evolving complex - OEC (F0/Fv), increasing it by 25% at 0.46 µM Zn and by 82% at 37.06 µM Al – concentrations where, 57% and 78% of growth inhibition occurred, respectively. We observed that the algal growth was more sensitive to infer Zn toxicity, while F0/Fv was more affected by Al. Regarding quenching, there was an increase in passive energy dissipation ((Y(NO)) at 0.46 µM Zn, and we observed an increase in both regulated ((NPQ and Y(NPQ)) and non-regulated energy dissipation ((qN and (Y(NO)) at 37.06 µM Al. Our results showed synergism and antagonism at different concentrations in mixtures, the antagonism prevailing at higher metal concentrations and, in some cases, synergism at lower concentrations of Zn and Al. Since we observe more than additive and less than additive effects, it is of the utmost importance to take mixture toxicity tests into account when performing risk assessments on green algae.

Genome-Wide Association Study of Zinc Toxicity Tolerance within a Rice Core Collection (Oryza sativa L.).

Zinc (Zn) is an essential micronutrient for rice, but it is toxic at a high concentration, especially in acid soils. It is yet unknown which genes regulate Zn tolerance in rice. In the present study, a genome-wide association study (GWAS) was performed for Zn tolerance in rice at the seedling stage within a rice core collection, named Ting's core collection, which showed extensive phenotypic variations in Zn toxicity with high-density single-nucleotide polymorphisms (SNPs). A total of 7 and 19 quantitative trait loci (QTL) were detected using root elongation (RE) and relative root elongation (RRE) under high Zn toxicity, respectively. Among them, 24 QTL were novel, and qRRE15 was located in the same region where 3 QTL were reported previously. In addition, qRE4 and qRRE9 were identical. Furthermore, we found eight candidate genes that are involved in abiotic and biotic stress, immunity, cell expansion, and phosphate transport in the loci of qRRE8, qRRE9, and qRRE15. Moreover, four candidate genes, i.e., Os01g0200700, Os06g0621900, Os06g0493600, and Os06g0622700, were verified correlating to Zn tolerance in rice by quantitative real time-PCR (qRT-PCR). Taken together, these results provide significant insight into the genetic basis for Zn toxicity tolerance and tolerant germplasm for developing rice tolerance to Zn toxicity and improving rice production in Zn-contaminated soils.

Heavy metal distribution, fractionation, and biotoxicity in sediments around villages in Baiyangdian Lake in North China

The effects of human activities on heavy metal distributions and fractionation in sediments from villages around Baiyangdian Lake (BYDL), North China, were assessed. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in sediments from five villages were determined, and the potential ecological risk index, risk assessment code, and Chironomus sp. larvae toxicity assay were used to assess the bioavailabilities and toxicities of the metals. The contribution of Cd to the potential ecological risk was 45.13-89.53%, the highest among the heavy metals investigated. The contributions of Cd, Pb, and Zn in the non-residual fractions to the total concentrations were 66.23-90.57%, 18.31-96.28%, and 8.89-76.84%, respectively, which indicated that these metals had important anthropogenic sources and were very bioavailable. The mean risk assessment codes decreased in the order of Cd (49.82%) > Zn (20.95%) > Cu (9.35%) > Pb (6.88%) > Ni (4.85%) > Cr (0.30%), and the toxicity of Cd and Zn to biota around BYDL is of concern. The mean survival rate of Chironomus sp. larvae in sediments from Dizhuang village was 44.02%, which indicated that there was a high degree of heavy metal toxicity, particularly in waterways around the village. Carboxylesterase and superoxide dismutase analysis results indicated that heavy metals could markedly increase or decrease enzyme activities in Chironomus sp. larvae. Overall, the results indicated that heavy metal pollution in villages around BYDL should be taken into consideration for its ecological management.

Arbuscular mycorrhiza mitigates zinc stress on Eucalyptus grandis through regulating metal tolerance protein gene expression and ionome uptake.

Arbuscular mycorrhizal (AM) fungi are symbionts of most terrestrial plants and enhance their adaptability in metal-contaminated soils. In this study, mycorrhized and non-mycorrhized Eucalyptus grandis were grown under different Zn treatments. After 6 weeks of treatment, the growing status and ionome content of plants as well as the expression patterns of metal tolerance proteins and auxin biosynthesis-related genes were measured. In this study, mycorrhized E. grandis showed higher biomass and height at a high level of Zn compared with non-mycorrhized plants. In addition, AM plants accumulated P, Mg, and Mn in roots and P, Fe, and Cu in shoots, which indicate that AM fungi facilitate the uptake of ionome nutrients to promote plant growth. In addition, mycorrhiza upregulated the expression of EgMTP1 and EgMTP7, whose encoding proteins were predicted to be located at the vacuolar membrane. Meanwhile, Golgi membrane transporter EgMTP5 was also induced in AM shoot. Our results suggest that AM likely mitigates Zn toxicity through sequestrating excess Zn into vacuolar and Golgi. Furthermore, the expression of auxin biosynthesis-related genes was facilitated by AM, and this is probably another approach for Zn tolerance.

Evaluating Zinc Nutrition In Perennial Ryegrass Grown In An Andisol

Zinc is an essential nutrient for humans, animals, and plants. Zinc uptake by crops is dictated by zinc availability in the soil, which in turn may be dictated, at least in part, by soil mineralogy. Little is known about the phytoavailability of Zn in Andisols, which are important agricultural soils in volcanic regions, such as Japan, New Zealand, and southern Chile. In this study, we assessed the vegetative growth response of perennial ryegrass (Lolium perenne, L.) to Zn fertilization in an Andisol from southern Chile. Ryegrass was grown in a greenhouse pot experiment with twelve rates of Zn application from 0 to 6075 mg Zn/kg soil. After 63 days, shoot length, specific leaf area, and biomass were measured. Foliar Zn concentrations were measured and correlated with plant-available Zn as measured by a diethylenetriaminepentaacetic acid (DTPA)-soil extraction (DTPA-Zn hereafter). Zinc toxicity to ryegrass was assessed using the Toxicity Relationship Analysis Program. This study demonstrated that a DTPA-Zn level of 1 mg Zn/kg soil was not limiting for ryegrass growth. Although Zn fertilization did not improve ryegrass growth in the studied Andisol, this study still has practical implications. Zinc deficiency in humans is a global problem and increasing Zn in staple food and forage crops may require Zn fertilization. This study suggests that Andisols can be fertilized with high doses of Zn without a risk of causing Zn toxicity to crops. However, a DTPA-Zn level of &gt;489 mg Zn/kg soil decreased shoot length, indicating a toxicity response.

Effects of fungal seed endophyte FXZ2 on Dysphania ambrosioides Zn/Cd tolerance and accumulation

Metal-induced oxidative stress in contaminated soils affects plant growth. In the present study, we evaluated the role of seed endophyte FXZ2 on Dysphania ambrosioides Zn/Cd tolerance and accumulation. A series of pot experiments were conducted under variable Zn (500, 1,000, and 1,500 mg kg–1) and Cd (5, 15, 30, and 60 mg kg–1). The results demonstrated that FXZ2-inoculation significantly enhanced the growth of D. ambrosioides and improved its chlorophyll and GSH content. In the rhizosphere, FXZ2 inoculation changed the chemical speciation of Zn/Cd and thus affected their uptake and accumulation in host plants. The exchangeable and carbonate-bound fractions (F1 + F2) of Zn decreased in the rhizosphere of FXZ2-inoculated plants (E+) as compared to non-inoculated plants (E-) under Zn stress (500 and 1,000 mg kg–1), correspondingly, Zn in the shoots of E+ decreased (p < 0.05). However, at Cd stress (30 and 60 mg kg–1), the F1 + F2 fractions of Cd in E+ rhizospheric soils increased; subsequently, Cd in the shoots of E+ increased (p < 0.05). FXZ2 could exogenously secrete phytohormones IAA, GA, and JA. The study suggests that seed endophyte FXZ2 can increase Zn/Cd tolerance of host plant by altering Zn/Cd speciation in rhizospheric soils, as well as exogenous production of phytohormones to promote growth, lowering oxidative damage while enhancing antioxidant properties. For Zn/Cd accumulation, it has opposite effects: Zn uptake in E+ plants was significantly (p < 0.05) decreased, while Cd accumulation in E+ plants was significantly (p < 0.05) increased. Thus, FXZ2 has excellent application prospects in Cd phytoextraction and decreasing Zn toxicity in agriculturally important crops.

Differential Physiological Response and Potential Toxicological Risk of White Cabbage Grown in Zinc-Spiked Soil

Physiological, agricultural and toxicological impact of an excess of Zn in the soil is an important issue, as Zn is a heavy metal and impairs many processes of plants and animals. The novelty of this work is that it is a comprehensive approach to facilitate visualization not only of the condition of cabbage plants under Zn stress, but also prediction of the toxicity associated with consumption of such cabbages. We treated plants of two cabbage cultivars, differing in their earliness, with 50 and 200 mg Zn kg−1 soil (Zn50 and Zn200, respectively) above the natural Zn levels of 118.13 mg kg−1 soil (Zn0). Leaf cell membrane integrity, condition of the photosynthetic apparatus (reflected by relative chlorophyll content (SPAD) and Fv/Fm parameter of chlorophyll a fluorescence), head biomass, and Zn bioaccumulation in the heads were analyzed. Toxicological risk was also assessed by Daily Intake of Metal (DIM) and Health Risk Index (HRI) indicators. The data revealed that plants of the late cultivar were more sensitive to soil Zn than those of the early one. Detrimental effects of Zn (especially at the higher dose, Zn200) were manifested in the seedlings just after three weeks of treatment, and then reflected in the yield. We assume that, due to their fast and prolonged response to Zn, the seedlings of the late cultivar can be used as biomarkers of Zn toxicity. Although Zn plants did not indicate toxicological risk, based on DIM and HRI, Zn concentration in the soil should be taken into account prior to cabbage planting, because plants which do not reveal symptoms of injury can accumulate Zn above the permissible level.

Chemical status of zinc in plant phytoliths: Impact of burning and (paleo)environmental implications

Phytoliths are microscopic structures made of amorphous opal (opal-A), an amorphous hydrated silica, dispersed within plant tissues and persisting after the decay of the plant. Silicon is known to alleviate metal toxicity in plants, but the role of phytoliths in metal sequestration and detoxification is unclear. Dry ashing, the most common protocol for phytolith extraction, was previously shown to lead to sequestration of metals by the phytoliths; however, the mechanisms of this process remained elusive. The purpose of this study was to evaluate whether the association between metals and phytoliths results from dry ashing or pre-exists in plant tissues. Thus, we compared phytoliths extracted by dry ashing at 700 °C and plant leaves before and after dry ashing. A combination of ICP-MS, XRD, SEM-EDX and Zn-K-edge EXAFS spectroscopy was used to assess elemental concentrations, morphology and crystallography of silica, and chemical status of Zn. Results demonstrated a phase transition from amorphous opal (opal-A) to opal-CT and α-cristobalite, and the sequestration of metal in phytoliths during dry ashing. For Zn, Mn and Pb, a linear relationship was found between the concentration in phytoliths and in leaves. In the phytoliths, Zn was sequestered in silica in tetrahedral configuration. We hypothesize that this association results form a solid-state reaction during ashing, involving a redistribution of Zn from the organic material to the silica, possibly promoted by the release of structural water from amorphous opal throughout the heating procedure. This study improves our understanding of the impact of high temperature treatments on plant biomass and phytoliths. It suggests that Zn toxicity alleviation in plants by silicon does not rely on its sequestration by phytoliths. In natural settings, wild fire events and biomass burning may lead to metal sequestration in low-soluble form, which should be considered in modeling of biogeochemical cycles and in paleoenvironmental studies.

Chronic toxicity, bioavailability and bioaccumulation of Zn, Cu and Pb in Lactuca sativa exposed to waste from an abandoned gold mine

Abandoned mines with untreated waste cause environmental pollution. The complex mixture of mining waste includes high metal content, anthropogenic chemicals and sterile rocks. Adverse effects of contaminated soils have been widely assessed by the use of plants. The aim of this study was to assess the chronic toxicity of a contaminated soil by waste from an abandoned gold mine on Lactuca sativa and its relationship with the bioavailability and bioaccumulation of Zn, Cu and Pb. Soil samples were taken from the site of mining waste stacking and a reference site in La Planta (Argentina). Contamination indices were calculated and acute and chronic exposures on L. sativa were carried out. Phytotoxicity indices, morphological and biochemical parameters, and concentrations of Zn, Cu and Pb in pseudo total and bioavailable soil fractions and in plant tissue were determined. Concentration- and time-dependent toxicity effects were observed, especially on plant width, fresh aerial biomass, leaf area and percentage of plants with completely necrotic aerial biomass. High levels of Zn (1453.3 ± 220.3 μg g−1) were found in plant tissue compared to Pb (277.2 ± 18.0 μg g−1) and Cu (255.3 ± 25.6 μg g−1). Toxicological endpoints correlated with metal uptake and mining waste concentration. In addition, bioaccumulation factors correlated with mobilisable and water soluble fractions. The concentration of Pb in aerial biomass surpassed the permissible concentrations in leaf vegetables, even at the reference site, indicating that lettuce crop consumption could be risky for the local population's health. This study demonstrated a strong relationship between metal bioavailability, toxicity endpoints and bioaccumulation, contributing with novel information to future ecotoxicological risk assessments and remediation plans.

The roles of calcium and salinity in protecting against physiological symptoms of waterborne zinc toxicity in the euryhaline killifish (Fundulus heteroclitus)

In fresh water, environmental Ca ameliorates Zn toxicity because Ca2+ and Zn2+ compete for uptake at the gills. Zn toxicity is also lower in sea water, but it is unclear whether this is due to increased Ca2+ concentration, and/or to the other ions present at higher salinity. Using the euryhaline killifish, we evaluated the relative roles of Ca2+ (as CaNO3) versus the other ions contributing to salinity in protecting against physiological symptoms of Zn2+ toxicity. Killifish were exposed to a sublethal level of Zn (500 μg/L, as ZnSO4) for 96 h in either fresh water (0 % salinity) at low (1 mmol/L) and High Ca (10 mmol/L) or 35 ppt sea water (100 % salinity) at low (1 mmol/L) and High Ca (10 mmol/L). At 0 % salinity, High Ca partly or completely protected against the following effects of Zn seen at Low Ca: elevated plasma Zn, hypocalcaemia, inhibited unidirectional Ca2+ influx, inhibited branchial Na+/K+ATPase and Ca2+ATPase activities, and oxidative stress in gills, liver, intestine, and muscle. At 100 % salinity, in the presence of 1 mmol/L (Low Ca), Zn caused no disturbances in most of these same parameters, showing that the “non-Ca” components of sea water alone provided complete protection. However, for a few endpoints (inhibited intestinal Ca2+ATPase activity, oxidative stress in gill and liver), High Ca (10 mmol/L) was needed to provide full protection against Zn in 100 % salinity. There was no instance where the combination of 100 % salinity and High Ca failed to provide complete protection against Zn-induced disturbances in sea water.

Exploring the influence mechanism of dissolved organic matter on the bioavailability and thyroid hormone disrupting effect of zinc: A case study of effluents from galvanizing plants

The effect of dissolved organic matter (DOM) on metal bioavailability and toxicity is a complex process. Effluents from galvanizing plants containing large amounts of DOM and Zn were selected to investigate the potential influence and mechanism of DOM on Zn bioavailability and its role in inducing thyroid hormone disrupting effects. Thyroid hormone disrupting effects were evaluated using a recombinant thyroid hormone receptor β gene yeast assay. The results suggest that Zn could be the main metal contributor to the toxic effects. Then, Zn-binding characteristics with different fluorescent components of DOM were analyzed using three-dimensional excitation emission matrix fluorescence spectroscopy (3DEEM) and revealed that Zn was more susceptible to interactions with fulvic-like materials. Furthermore, DOM altered the cellular biouptake and compartmentalization processes of Zn by downregulating Zn transmembrane transport-related genes (ZRT1, ZRT2 and ZAP1) and upregulating detoxification-related genes (COT1 and ZRC1), thus altering thyroid toxicity. These results provide comprehensive insights into the influence and mechanism of DOM on bioavailability and thyroid toxicity of Zn and suggest that the influence is associated with complex physical, chemical and biological processes, indicating that more refined medium constraints along with subtle biological reactions should be considered when predicting the bioavailability and toxicity of Zn in environmental water samples.