Distribution and speciation of copper in rice (Oryza sativa L.) from mining-impacted paddy soil: Implications for copper uptake mechanisms

Copper stress in rice: Perception, signaling, bioremediation and future prospects

Copper (Cu) is an indispensable micronutrient for plants, animals, and microorganisms and plays a vital role in different physiological processes. However, excessive Cu accumulation in agricultural soil, often through anthropogenic action, poses a potential risk to plant health and crop productivity. This review article provided a comprehensive overview of the available information regarding Cu dynamics in agricultural soils, major sources of Cu contamination, factors influencing its mobility and bioavailability, and mechanisms of Cu uptake and translocation in rice plants. This review examined the impact of Cu toxicity on the germination, growth, and photosynthesis of rice plants. It also highlighted molecular mechanisms underlying Cu stress signaling and the plant defense strategy, involving chelation, compartmentalization, and antioxidant responses. This review also identified significant areas that need further research, such as Cu uptake mechanism in rice, Cu signaling process, and the assessment of Cu-polluted paddy soil and rice toxicity under diverse environmental conditions. The development of rice varieties with reduced Cu accumulation through comprehensive breeding programs is also necessary. Regulatory measures, fungicide management, plant selection, soil and environmental investigation are recommended to prevent Cu buildup in agricultural lands to achieve sustainable agricultural goals.

Exogenous GABA Enhances Copper Stress Resilience in Rice Plants via Antioxidant Defense Mechanisms, Gene Regulation, Mineral Uptake, and Copper Homeostasis

The importance of gamma-aminobutyric acid (GABA) in plants has been highlighted due to its critical role in mitigating metal toxicity, specifically countering the inhibitory effects of copper stress on rice plants. This study involved pre-treating rice plants with 1 mM GABA for one week, followed by exposure to varying concentrations of copper at 50 μM, 100 μM, and 200 μM. Under copper stress, particularly at 100 μM and 200 μM, plant height, biomass, chlorophyll content, relative water content, mineral content, and antioxidant activity decreased significantly compared to control conditions. However, GABA treatment significantly alleviated the adverse effects of copper stress. It increased plant height by 13%, 18%, and 32%; plant biomass by 28%, 52%, and 60%; chlorophyll content by 12%, 30%, and 24%; and relative water content by 10%, 24%, and 26% in comparison to the C50, C100, and C200 treatments. Furthermore, GABA treatment effectively reduced electrolyte leakage by 11%, 34%, and 39%, and the concentration of reactive oxygen species, such as malondialdehyde (MDA), by 9%, 22%, and 27%, hydrogen peroxide (H2O2) by 12%, 38%, and 30%, and superoxide anion content by 8%, 33, and 39% in comparison to C50, C100, and C200 treatments. Additionally, GABA supplementation led to elevated levels of glutathione by 69% and 80%, superoxide dismutase by 22% and 125%, ascorbate peroxidase by 12% and 125%, and catalase by 75% and 100% in the C100+G and C200+G groups as compared to the C100 and C200 treatments. Similarly, GABA application upregulated the expression of GABA shunt pathway-related genes, including gamma-aminobutyric transaminase (OsGABA-T) by 38% and 80% and succinic semialdehyde dehydrogenase (OsSSADH) by 60% and 94% in the C100+G and C200+G groups, respectively, as compared to the C100 and C200 treatments. Conversely, the expression of gamma-aminobutyric acid dehydrogenase (OsGAD) was downregulated. GABA application reduced the absorption of Cu2+ by 54% and 47% in C100+G and C200+G groups as compared to C100, and C200 treatments. Moreover, GABA treatment enhanced the uptake of Ca2+ by 26% and 82%, Mg2+ by 12% and 67%, and K+ by 28% and 128% in the C100+G and C200+G groups as compared to C100, and C200 treatments. These findings underscore the pivotal role of GABA-induced enhancements in various physiological and molecular processes, such as plant growth, chlorophyll content, water content, antioxidant capacity, gene regulation, mineral uptake, and copper sequestration, in enhancing plant tolerance to copper stress. Such mechanistic insights offer promising implications for the advancement of safe and sustainable food production practices.

Plant Growth-Promoting Rhizobacteria (PGPR) Assisted Bioremediation of Heavy Metal Toxicity

Due to a variety of natural and anthropogenic processes, heavy metal toxicity of soil constitutes a substantial hazard to all living beings in the environment. The heavy metals alter the soil properties, which directly or indirectly influence the agriculture systems. Thus, plant growth-promoting rhizobacteria (PGPR)-assisted bioremediation is a promising, eco-friendly, and sustainable method for eradicating heavy metals. PGPR cleans up the heavy metal-contaminated environment using various approaches including efflux systems, siderophores and chelation, biotransformation, biosorption, bioaccumulation, precipitation, ACC deaminase activity, biodegradation, and biomineralization methods. These PGPRs have been found effective to bioremediate the heavy metal-contaminated soil through increased plant tolerance to metal stress, improved nutrient availability in soil, alteration of heavy metal pathways, and by producing some chemical compounds like siderophores and chelating ions. Many heavy metals are non-degradable; hence, another remediation approach with a broader scope of contamination removal is needed. This article also briefly emphasized the role of genetically modified PGPR strains which improve the soil's degradation rate of heavy metals. In this regard, genetic engineering, a molecular approach, could improve bioremediation efficiency and be helpful. Thus, the ability of PGPRs can aid in heavy metal bioremediation and promote a sustainable agricultural soil system.

Carbonate rocks as natural buffers: Exploring their environmental impact on heavy metals in sulfide deposits

Carbonate rocks are closely related to the genesis and spatial distribution of polymetallic sulfide deposits. The natural buffering of carbonate rocks can reduce the ecological impact of heavy metals produced by mining and smelting. Ignoring the buffering effect of carbonate rocks on the heavy metals in the mine environment leads to inaccurate ecological risk assessment, wasting land resources and funds. This study investigates Cd, Zn, and Pb distribution and speciation in the water and soil-rice system in the polymetallic sulfide deposit at Daxin, Guangxi. The study aims to reveal the effects of the natural buffering of carbonate rocks on the migration and transformation of heavy metals. The results show that the water Zn and Cd concentrations decreased from 1857.0 to 0.9 mg L-1 to 0.16 and 0.001 mg L-1, respectively, from the mining area to 4 km downstream. The natural buffering of carbonate increases the water pH from 2.80 to 7.64, resulting in a tendency for Cd, Zn, and Pb to separate from the aqueous phase and enrich the sediments. Soil Cd content in the mining area reached 110.0 mg kg-1 (mean value 55.88 mg kg-1), and rice Cd seriously exceeded the maximum limit. However, the weathering of carbonate reduces the migration ability and bioavailability of Cd. Soil Cd is mainly in the Fe-Mn bound and carbonate-bound fractions, resulting in lower Cd content in downstream soils (mean value 2.73 mg kg-1). Soil CaO, tFe2O3, and Mn hindered the uptake of soil Cd by rice rendering a lower exceedance of Cd in downstream rice. Therefore, this study recommends a farmland management plan under the premise of rice Cd content and integrated soil Cd content, which ensures food safety and fully utilizes farmland resources. This result provides a scientific basis for ecological risk assessment, mine environmental protection, and management in the carbonatite sulfide mine environment.

Increased ascorbic acid synthesis by overexpression of AcGGP3 ameliorates copper toxicity in kiwifruit

The widespread application of copper (Cu) -based fertilizers and pesticides could increase the accumulation of Cu in kiwifruit. According to a global survey, red- and yellow-fleshed kiwifruit contained more elevated amounts of Cu than green-fleshed kiwifruit due to weaker disease resistance and higher use of Cu pesticides. Intriguingly, our research revealed that external and endogenous ascorbic acid (AsA) reduced the phenotypic and physiological injury of Cu toxicity in kiwifruit. Cu stress assays and transcriptional analysis have shown that Cu treatment for 12 h significantly increased the AsA content in kiwifruit leaves and up-regulated key genes involved in AsA biosynthesis, such as GDP-L-galactose phosphorylase3 (GGP3) and GDP-mannose-3',5'-epimerase (GME). Overexpressing GGP3 in transgenic kiwifruit significantly increased the endogenous AsA content of kiwifruit, which was beneficial in mitigating Cu toxicity by decreasing levels of reactive oxygen species, malondialdehyde, and electrolyte leakage, as well as reducing damage to the chloroplast structure and photosystem II. This study presented a novel strategy to ameliorate plant Cu stress by increasing the endogenous antioxidant (AsA) content through transgenesis.

Combined pollution effects of Cu and benzotriazole in rice (Oryza sativa L.) verified by split-root experiment

Although the combined effect of organic ligands and heavy metals in the environment on plants have been frequently reported, their complexed interaction in plants and the physiological effects remain to be revealed. Metal complexing agent benzotriazole (BTR) has extensive environmental pollution. In this study, root-splitting experiments were designed to identify the in vivo and in vitro effects of BTR on the accumulation and translocation of Cu in rice (Oryza sativa L.), and the concentrations and translocation factor (TF) of Cu and BTR in different parts of rice were measured. In the in vitro interaction treatments, low BTR concentrations enhanced Cu uptake and lateral transport in rice, while higher levels of BTR's exposure (i.e., ≥ 100 μM) resulted in opposite effects. Differently, significant increase in the lateral transport of Cu and vertical translocation of BTR in rice presented in the in vivo interaction treatments. TF of Cu from root A to root B (TFRA-RB) increased from 0.05 to 0.272 with the BTR concentration increasing from 0 to 100 μM, and higher TF of BTR from root to shoot (TFR-S), ranging from 1.00 to 1.75, compared with single BTR exposure treatments was observed. The phytotoxicity of BTR expressed by the catalase activity was significantly alleviated by the in vivo accumulated Cu in rice.

A novel application of thallium isotopes in tracing metal(loid)s migration and related sources in contaminated paddy soils

Thallium (Tl) is a highly toxic heavy metal, which is harmful to plants and animals even in trace amounts. Migration behaviors of Tl in paddy soils system remain largely unknown. Herein, Tl isotopic compositions have been employed for the first time to explore Tl transfer and pathway in paddy soil system. The results showed considerably large Tl isotopic variations (ε²⁰⁵Tl = -0.99 ± 0.45 ~ 24.57 ± 0.27), which may result from interconversion between Tl(I) and Tl(III) under alternative redox conditions in the paddy system. Overall higher ε²⁰⁵Tl values of paddy soils in the deeper layers were probably attributed to abundant presence of Fe/Mn (hydr)oxides and occasionally extreme redox conditions during alternative dry-wet process which oxidized Tl(I) to Tl(III). A ternary mixing model using Tl isotopic compositions further disclosed that industrial waste contributed predominantly to Tl contamination in the studied soil, with an average contribution rate of 73.23%. All these findings indicate that Tl isotopes can be used as an efficient tracer for fingerprinting Tl pathway in complicated scenarios even under varied redox conditions, providing significant prospect in diverse environmental applications.

Heavy metals and arsenic stress in food crops: Elucidating antioxidative defense mechanisms in hyperaccumulators for food security, agricultural sustainability, and human health

The spread of heavy metal(loid)s at soil-food crop interfaces has become a threat to sustainable agricultural productivity, food security, and human health. The eco-toxic effects of heavy metals on food crops can be manifested through reactive oxygen species that have the potential to disturb seed germination, normal growth, photosynthesis, cellular metabolism, and homeostasis. This review provides a critical overview of stress tolerance mechanisms in food crops/hyperaccumulator plants against heavy metals and arsenic (HM-As). The HM-As antioxidative stress tolerance in food crops is associated with changes in metabolomics (physico-biochemical/lipidomics) and genomics (molecular level). Furthermore, HM-As stress tolerance can occur through plant-microbe, phytohormone, antioxidant, and signal molecule interactions. Information regarding the avoidance, tolerance, and stress resilience of HM-As should help pave the way to minimize food chain contamination, eco-toxicity, and health risks. Advanced biotechnological approaches (e.g., genome modification with CRISPR-Cas9 gene editing) in concert with traditional sustainable biological methods are useful options to develop 'pollution safe designer cultivars' with increased climate change resilience and public health risks mitigation. Further, the usage of HM-As tolerant hyperaccumulator biomass in biorefineries (e.g., environmental remediation, value added chemicals, and bioenergy) is advocated to realize the synergy between biotechnological research and socio-economic policy frameworks, which are inextricably linked with environmental sustainability. The biotechnological innovations, if directed toward 'cleaner climate smart phytotechnologies' and 'HM-As stress resilient food crops', should help open the new path to achieve sustainable development goals (SDGs) and a circular bioeconomy.

Combined forage grass-microbial for remediation of strontium-contaminated soil

Enrichment plants were screened from six forage grasses in this study to establish a complete combined forage grass-microbial remediation system of strontium-contaminated soil, and microbial groups were added to the screened dominant forage grasses. The occurrence states of strontium in forage grasses were explored by the BCR sequential extraction method. The results showed that the annual removal rate of Sudan grass (Sorghum sudanense (Piper) Stapf.) reached 23.05% in soil with a strontium concentration of 500 mg·kg^-1. Three dominant microbial groups: E, G and H, have shown good facilitation effects in co-remediation with Sudan grass and Gaodan grass (Sorghum bicolor × sudanense), respectively. When compared to the control, the strontium accumulation of forage grasses in kg of soil with microbial groups was increased by 0.5-4 fold. The optimal forage grass-microbial combination can theoretically repair contaminated soil in three years. The microbial group E was found to promote the transfer of the exchangeable state and the reducible state of strontium to the overground part of the forage grass. Metagenomic sequencing results showed that the addition of microbial groups increased Bacillus spp. in rhizosphere soil, enhanced the disease resistance and tolerance of forage grasses, and improved the remediation ability of forage grass-microbial combinations.

Human health risks associated with metals in paddy plant (Oryza sativa) based on target hazard quotient and target cancer risk

Paddy plants (Oryza sativa) contaminated with metals could be detrimental to human health if the concentrations of metals exceed the permissible limit. Thus, this study aims to assess the risk of the concentrations of As, Se, Cu, Cr, Co, and Ni and their distributions in various parts (roots, stems, leaves, and grains) of paddy plants collected from Sekinchan, Malaysia. Both soil and plant samples were digested according to the United States Environmental Protection Agency (USEPA) Method 3050B and the metal concentrations were determined by the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The highest mean translocation factor (TF) was from soil to roots (TF roots/soil ranged from 0.12 to 6.15) and the lowest was from leaves to grain (TF grain/leaves ranged from 0.06 to 0.87). Meanwhile, the bioaccumulation factor (BAF) for all metals was less than 1.0 indicating that paddy plants only absorb metals from the soil but do not accumulate in the grains. The average daily intake for As (1.15 ± 0.25 µg/kg/day) has exceeded the limit proposed by ATSDR and IRIS USEPA (0.30 µg/kg/day). Target cancer risk (TR) of 1.10 × 10^-3 for As through rice consumption indicates that the potential cancer risk exists in one out of 1000 exposed individuals. The results from this study could serve as a reference for researchers and policymakers to monitor and formulate strategies in managing As and other metals in paddy plants, especially in Southeast Asian countries.

Incorporation of Cu into Goethite Stimulates Oxygen Activation by Surface-Bound Fe(II) for Enhanced As(III) Oxidative Transformation

The dark production of reactive oxygen species (ROS) coupled to biogeochemical cycling of iron (Fe) plays a pivotal role in controlling arsenic transformation and detoxification. However, the effect of secondary atom incorporation into Fe(III) oxyhydroxides on this process is poorly understood. Here, we show that the presence of oxygen vacancy (OV) as a result of Cu incorporation in goethite substantially enhances the As(III) oxidation by Fe(II) under oxic conditions. Electrochemical and density functional theory (DFT) evidence reveals that the electron transfer (ET) rate constant is enhanced from 0.023 to 0.197 s^-1, improving the electron efficiency of the surface-bound Fe(II) on OV defective surfaces. The cascade charge transfer from the surface-bound Fe(II) to O₂ mediated by Fe(III) oxyhydroxides leads to the O-O bond of O₂ stretching to 1.46-1.48 Å equivalent to that of superoxide (^•O₂^-), and ^•O₂^- is the predominant ROS responsible for As(III) oxidation. Our findings highlight the significant role of atom incorporation in changing the ET process on Fe(III) oxyhydroxides for ROS production. Thus, such an effect must be considered when evaluating Fe mineral reactivity toward changing their surface chemistry, such as those noted here for Cu incorporation, which likely determines the fates of arsenic and other redox sensitive pollutants in the environments with oscillating redox conditions.

Unraveling the genetics underlying micronutrient signatures of diversity panel present in brown rice through genome-ionome linkages

Rice (Oryza sativa) is an important staple crop to address the Hidden Hunger problem not only in Asia but also in Africa where rice is fast becoming an important source of calories. The brown rice (whole grain with bran) is known to be more nutritious due to elevated mineral composition. The genetics underlying brown rice ionome (sum total of such mineral composition) remains largely unexplored. Hence, we conducted a comprehensive study to dissect the genetic architecture of the brown rice ionome. We used genome-wide association studies, gene set analysis, and targeted association analysis for 12 micronutrients in the brown rice grains. A diverse panel of 300 resequenced indica accessions, with more than 1.02 million single nucleotide polymorphisms, was used. We identified 109 candidate genes with 5-20% phenotypic variation explained for the 12 micronutrients and identified epistatic interactions with multiple micronutrients. Pooling all candidate genes per micronutrient exhibited phenotypic variation explained values ranging from 11% to almost 40%. The key donor lines with larger concentrations for most of the micronutrients possessed superior alleles, which were absent in the breeding lines. Through gene regulatory networks we identified enriched functional pathways for central regulators that were detected as key candidate genes through genome-wide association studies. This study provided important insights on the ionome variations in rice, on the genetic basis of the genome-ionome relationships and on the molecular mechanisms underlying micronutrient signatures.

Trace Metal(loid) Migration from Road Dust to Local Vegetables and Tree Tissues and the Bioaccessibility-Based Health Risk: Impacts of Vehicle Operation-Associated Emissions

Traffic activities release large amounts of trace metal(loid)s in urban environments. However, the impact of vehicle operation-associated emissions on trace metal(loid) enrichment in road dust and the potential migration of these trace metal(loid)s to the surrounding environment remain unclear. We evaluated the contamination, sequential fraction, and bioaccessibility of trace metal(loid)s in urban environments by assessing their presence in road dust, garden vegetables, and tree tissues, including bark and aerial roots, at a traffic-training venue impacted by vehicle operation emissions and, finally, calculated the bioaccessibility-based health risk. The results indicated a significant accumulation of trace metal(loid)s in road dust, with the highest lead (Pb), cadmium (Cd), and antimony (Sb) concentrations in the garage entrance area due to higher vehicle volumes, frequent vehicle starts and stops, and lower speeds. Aerial roots exposed to hill start conditions exhibited the highest Pb, Zn, and Sb levels, potentially caused by high road dust resuspension, confirming that this tree tissue is an appropriate bioindicator. Sequential extraction revealed high percentages of carbonate-, Fe/Mn oxide-, and organic/sulphide-associated fractions of Pb, copper (Cu), and zinc (Zn) in road dust, while most Cd, Cr, Ni, and Sb occurred as residual fractions. According to the potential mobilizable fractions in sequential extraction, the in vitro gastrointestinal method could be more suitable than the physiologically based extraction test to evaluate the bioaccessibility-related risk of traffic-impacted road dust. The bioaccessibility-based health risk assessment of the road dust or soil confirmed no concern about noncarcinogenic risk, while the major risk originated from Pb although leaded gasoline was prohibited before the venue establishment. Furthermore, the cancer risks (CRs) analysis showed the probable occurrence of carcinogenic health effects from Cd and Ni to adults and from Cd, Cr, and Ni to children. Furthermore, the Cd and Pb concentrations in the edible leaves of cabbage and radish growing in gardens were higher than the recommended maximum value. This study focused on the health risks of road dust directly impacted by vehicle emissions and provides accurate predictions of trace metal(loid) contamination sources in the urban environment.

Partitioning and (im)mobilization of arsenic associated with iron in arsenic-bearing deep subsoil profiles from Hong Kong

Understanding the arsenic (As) enrichment mechanisms in the subsurface environment relies on a systematic investigation of As valence species and their partitioning with the Fe (oxyhydr)oxide phases in the subsoil profile. The present study explored the distribution, speciation, partitioning, and (im)mobilization of As associated with Fe in four subsoil cores (∼30 m depth) from Hong Kong using sequential chemical extraction and X-ray absorption near edge spectroscopy. The subsoil profiles exhibited relatively high concentrations of As at 26.1-982 mg/kg (median of 112 mg/kg), and the As was dominated by As(V) (85-96%) and primarily associated with the residual fraction (50.7-94.7%). A small amount of As (0.002-13.2 mg/kg) was easily mobilized from the four subsoil profiles, and a concentration of water-soluble As higher than 100 μg/L was observed for only some subsoil layers. The molar ratios of As:Fe in the oxalate-extractable Fe fraction ranged from 1.2 to 76.5 mmol/mol (median of 11.1 mmol/mol), revealing the participation of poorly crystalline Fe (oxyhydr)oxides in immobilizing most of the high geogenic As. The primary phases of ferric (oxyhydr)oxides were characterized as ferrihydrite (16-53%), lepidocrocite (0-32%), and goethite (0-62%), and these phases contributed to the sufficient ability of the subsoil to sequester 45.3-100% (median of 98.8%) of the exogenous As(V) (1.0 mg/L) in adsorption experiments. In contrast to As(V), exogenous As(III) showed a lower removal percentage (3.9-79.1%, median of 45.1%). The study revealed that the chemical speciation of As and Fe in the subsoil profiles is useful for predicting the immobilization of high geogenic As in the region, which is also helpful for the safe utilization of As-containing soil during land development worldwide.

Copper migration and isotope fractionation in a typical paddy soil profile of the Yangtze Delta

To decipher Cu migration in paddy soils, which is important for understanding Cu supply in rice cultivation, Cu concentrations and isotope compositions were measured in a paddy soil profile in Suzhou, Eastern China, in the central Yangtze Delta. The results show that the variations in δ⁶⁵Cu values and Cu concentrations are not coupled along the profile. From top to bottom, the δ⁶⁵Cu values show small variations (0.07 ± 0.03‰ to 0.25 ± 0.01‰) in the upper layers (Ap-Br1), with a decrease in the subsurface Br2 layer (from 0.16 ± 0.04‰ to -0.19 ± 0.02‰), are almost homogeneous in the transitional Br3-BCrg layers (-0.01 ± 0.01‰ to -0.10 ± 0.02‰), and further decrease to -0.33 ± 0.01‰ in the permanently submerged G1 and G2 layers. Copper concentrations in the Ap layer show some fluctuations (25.8 to 29.0 μg/g), increase in the Br2 and Br3 layers (23.9 μg/g to 31.9 μg/g), and then decrease to 15.1 μg/g in the lower layers. The lack of coupling between δ⁶⁵Cu values and Cu concentrations may be ascribed to various physicochemical conditions in different layers. In the upper layers, Cu(I) enriched in light isotopes migrates downward with soil solutions under flooded conditions, leaving the soils of the Ap and Br1 layers enriched in heavy Cu isotopes. In the Br2 layer, the readsorption of light Cu isotopes on clay minerals results in decreased δ⁶⁵Cu values and increased Cu concentrations. In the Br3-BCrg layers, Cu(I) can be oxidized to Cu(II). The homogeneous Cu isotopes in these layers may mainly result from equilibrium adsorption of Cu on clay minerals. The decreased δ⁶⁵Cu values and Cu concentrations in the G layer are mainly attributed to groundwater transport in this layer. This study represents the Cu isotope variations in a paddy soil profile and the possible mechanism of Cu isotope fractionation.

Exogenous Copper Application for the Elemental Defense of Rice Plants against Rice Leaffolder (Cnaphalocrocis medinalis)

Metals that accumulate in plants may confer protection against herbivorous insects, a phenomenon known as elemental defense. However, this strategy has not been widely explored in important crops such as rice (Oryza sativa L.), where it could help to reduce the use of chemical pesticides. Here, we investigated the potential of copper (Cu) and iron (Fe) micronutrient supplements for the protection of rice against a major insect pest, the rice leaffolder (Cnaphalocrocis medinalis). We found that intermediate levels of Cu (20 μM CuSO₄) and high concentrations of Fe (742 μM Fe) did not inhibit the growth of C. medinalis larvae but did inhibit rice root growth and reduce grain yield at the reproductive stage. In contrast, high levels of Cu (80 μM CuSO₄) inhibited C. medinalis larval growth and pupal development but also adversely affected rice growth at the vegetative stage. Interestingly, treatment with 10 μM CuSO₄ had no adverse effects on rice growth or yield components at the reproductive stage. These data suggest that pest management based on the application of Cu may be possible, which would be achieved by a higher effective pesticide dose to prevent or minimize its phytotoxicity effects in plants.

Speciation of metals in indigenous plants growing in post-mining areas: Dihydroxynicotianamine identified as the most abundant Cu and Zn ligand in Hypericum laricifolium

Ag, As, Cu, Pb and Zn were found to be the principal metallic contaminants of a post-mining area of Peru (Hualgayoc, Cajamarca). Study of metal distribution amongst roots, stems, and leaves of four indigenous hypertolerant plant species, Arenaria digyna, Puya sp., Hypericum laricifolium, Nicotiana thyrsiflora indicated significant translocation of Zn (0.6 < TF ≤ 10.0) and Cu (0.4 < TF ≤ 6.5) into aerial plant organs and substantial water-extractable fraction (20-60%) of these metals, except for A. digyna (root and stems). A study of the metal speciation by ultrahigh-performance size-exclusion (fast-SEC) and hydrophilic ion interaction (HILIC) liquid chromatography with dual ICP (inductively coupled plasma) and electrospray (ESI) Orbitrap MS detection revealed the presence of nicotianamine and deoxymugineic acid copper and zinc complexes in roots, stem and leaves of N. thyrsiflora and Puya sp., and nicotianamine alone in A. digyna. A previously unreported compound, dihydroxy-nicotianamine was identified as the most abundant Cu and Zn ligand in H. laricifolium. The presence of arsenobetaine and an arsenosugar was confirmed by ESI MS. Ag and Pb were hardly translocated to leaves and were found as high molecular species; one of the Pb-containing species co-eluted in fast-SEC-ICP MS with rhamnogalacturonan-II-Pb complex commonly found in in the walls of plants.

Cu phytoextraction and biomass utilization as essential trace element feed supplements for livestock

Copper (Cu), as an essential element, is added to animal feed to stimulate growth and prevent disease. The forage crop alfalfa (Medicago sativa L.) produced during Cu phytoextraction may be considered a biofortified crop to substitute the Cu feed additives for livestock production, beneficially alleviating Cu contamination in soils and reducing its input into agriculture systems. To assess this, alfalfa was grown in three similar soils with different Cu levels, i.e., 11, 439 and 779 mg kg^-1 for uncontaminated soil (A), moderately Cu-contaminated soil (B) and highly Cu-contaminated soil (C), respectively. EDDS (Ethylenediamine-N,N'-disuccinic acid) was applied to the soils seven days before the first cutting at four rates (0, 0.5, 2 and 5 mmol kg^-1) to enhance bioavailable Cu uptake. Alfalfa grew well in soils A and B but not in the highly Cu-contaminated soil. After applying EDDS, a significant biomass reduction of the first cutting shoot was only observed with 5 mmol kg^-1 EDDS in the highly Cu-contaminated soil, with a 45% (P < 0.05) decrease when compared to the control. Alfalfa grown in the three soils gradually wilted after the first cutting with 5 mmol kg^-1 EDDS, and Cu concentrations in the first cutting shoot were augmented strongly, by 250% (P < 0.05), 3500% (P < 0.05) and 6700% (P < 0.05) compared to the controls, respectively. Cu concentrations in alfalfa shoots were found to be higher in this study than in some fodder plants and further augmented in soils with higher Cu levels and with EDDS application. These findings suggest that alfalfa grown on clean soils or soils with up to 450 mg Cu kg^-1 (with appropriate EDDS dosages) has the potential to be considered as a partial Cu supplementation for livestock. This research laid the foundation for the integration between Cu-phytoextraction and Cu-biofortification for livestock.

The ethylene-responsive transcription factor of durum wheat, TdSHN1, confers cadmium, copper, and zinc tolerance to yeast and transgenic tobacco plants

Cadmium (Cd), copper (Cu), and zinc (Zn) are among the most common heavy metals (HMs) present in polluted soils. While some HMs are required for key biological processes, they are toxic when present in excess. This toxicity damages plant health, decreases crop yields, and can impact human health via the food chain. For example, durum wheat is a staple food that is known to accumulate Cd when grown on polluted soils. Plant response to HM stress is complex and involves several transcription factors (TFs) among which members of the ERF family. Although roles of SHINE-type ERF transcription factors in abiotic stress tolerance have been thoroughly investigated, there is little information concerning their role in HM stress tolerance. In the present study, we investigated the role of durum wheat TdSHN1 TF in HM response and tolerance. Results showed that TdSHN1 expression was strongly induced by Cd, Cu, and Zn in durum wheat seedlings. In addition, TdSHN1 gene promoter directed HM-inducible GUS gene expression in transgenic tobacco. Overexpression of TdSHN1 encoding cDNA in transgenic yeast and tobacco conferred Cd, Cu, and Zn tolerances. Interestingly, transgenic tobacco lines exhibited longer roots and greater biomass accumulation, retained more chlorophyll, and produced less ROS than WT plants, when subjected to excess HMs. In addition, transgenic tobacco lines had higher activities of ROS-scavenging enzymes (SOD and CAT) which might have contributed to their HM tolerance. This study suggested that TdSHN1 is a potential candidate for improving HM tolerance in plants and phytoremediation of HM-contaminated soils.

Copper stress alleviation in corn (Zea mays L.): Comparative efficiency of carbon nanotubes and carbon nanoparticles

Copper (Cu) stress is one of the predominant crop yield-reducing factors in agriculture. Application of carbon nanomaterials (CNMs) could have promotive effects on crop growth; however, their effects on alleviation of Cu stress for plants have rarely been documented. In this study, we investigated the comparative role of carbon nanotubes (CNTs) and carbon nanoparticles (CNPs) in corn (Zea mays) seed germination, seedling growth as well as Cu stress alleviation. The results showed that CNTs and CNPs stimulated corn seed germination by significantly increasing germination rate (GR), shortening the mean germination time (MGT), and increasing overall germination index (GI). They also significantly elongated seedling length and increased fresh biomass with optimal application rates ranging from 50 to 100 mg L^-1. Principle component analysis (PCA) confirmed that seed germination indexes and seedling growth were positively affected by CNTs or CNPs, but inversely influenced by high levels of Cu stress (> 20 mg L^-1). Furthermore, higher Cu accumulation and anti-oxidative enzyme activity (SOD, POD, CAT) were observed in plants co-exposed to Cu²⁺ and either CNTs or CNPs compared to plants exposed to Cu²⁺ alone. CNPs had stronger improvement on plant growth and Cu stress alleviation than CNTs, which suggest they may be cost-effective agriculture amendments to improve plant growth under heavy metal stress.

A Combined Remediation Strategy of Arsenic and Cadmium in the Paddy Soil of Polymetallic Mining Areas

The combined pollution of arsenic (As) and cadmium (Cd) are quite common in the polymetallic mining areas located in southern China. In the present study, field experiments were established for the purpose of exploring a simultaneous remediation strategy of rice variety-water management-contaminant immobilization on the As and Cd contamination in paddy soil. The obtained results revealed that the Maba Yinzhan was the best low-accumulation rice variety, with As and Cd concentrations of 0.54 and 0.16 mg kg^-1, respectively, in the rice grains. On the basis of water management during heading stage, the treatment using 0.15 wt% lime plus 0.5 wt% ferro-ferric oxide (FO) decreased the As and Cd concentrations by 64.02% and 34.78%, respectively, in the grains. The results of this study potentially provide an effective remediation solution for the As/Cd contaminated soils in polymetallic mining areas.

Copper bioavailability, uptake, toxicity and tolerance in plants: A comprehensive review

Copper (Cu) is an essential element for humans and plants when present in lesser amount, while in excessive amounts it exerts detrimental effects. There subsists a narrow difference amid the indispensable, positive and detrimental concentration of Cu in living system, which substantially alters with Cu speciation, and form of living organisms. Consequently, it is vital to monitor its bioavailability, speciation, exposure levels and routes in the living organisms. The ingestion of Cu-laced food crops is the key source of this heavy metal toxicity in humans. Hence, it is necessary to appraise the biogeochemical behaviour of Cu in soil-plant system with esteem to their quantity and speciation. On the basis of existing research, this appraisal traces a probable connexion midst: Cu levels, sources, chemistry, speciation and bioavailability in the soil. Besides, the functions of protein transporters in soil-plant Cu transport, and the detrimental effect of Cu on morphological, physiological and nutrient uptake in plants has also been discussed in the current manuscript. Mechanisms related to detoxification strategies like antioxidative response and generation of glutathione and phytochelatins to combat Cu-induced toxicity in plants is discussed as well. We also delimits the Cu accretion in food crops and allied health perils from soils encompassing less or high Cu quantity. Finally, an overview of various techniques involved in the reclamation and restoration of Cu-contaminated soils has been provided.

Mechanistic insight into the interactions of EDDS with copper in the rhizosphere of polluted soils

The biodegradable S,S-ethylenediaminedisuccinic acid (EDDS) is a promising chelant for chelant-assisted phytoextraction of trace metals in polluted soil. The interactions between EDDS and trace metals/major elements in the soil affect the metal bioavailability and their subsequent phytoextraction efficiency. This study aimed to investigate the macroscopic and molecular-level interactions of EDDS with Cu in the rhizosphere and non-rhizosphere of a Cu-polluted agricultural soil. A multi-interlayer rhizobox planted with ryegrass was used to simulate the transport of EDDS and Cu from the non-rhizosphere to rhizosphere soils. The results showed that EDDS (5 mM kg^-1) significantly dissociated Cu (285-690 fold), Fe (by 3.47-60.2 fold), and Al (2.43-5.31 fold) from the soil in comparison with a control group. A combination of micro-X-ray fluorescence, X-ray absorption near-edge structure spectroscopy, and sequential extraction analysis revealed that EDDS primarily chelated the adsorbed fraction of Cu by facilitating the dissolution of goethite. Moreover, as facilitated by ryegrass transpiration, CuEDDS was moved from the non-rhizosphere to rhizosphere and accumulated in ryegrass. In situ processes of Cu extraction and transport by EDDS in the rhizosphere were further elucidated with chemical speciation analysis and geochemical modeling methods.

Use of polymeric nanoparticles to improve seed germination and plant growth under copper stress

Plant seedlings are susceptible to copper (Cu) toxicity. As copper levels in soil continue to rise with the use of Cu-based agrochemicals, alleviation of Cu stress is of paramount importance. Traditional approaches to allay Cu stress are well documented but are typically found to be either costly or inefficient. Given their small size, ionic character, and high biocompatibility, specific polymeric nanoparticles (NPs) may have the potential for mitigating metal toxicity to crops. In this pioneering study, we investigated the effects of newly synthesized polysuccinimide NPs (PSI-NPs) on corn (Zea mays L.) seed germination and seedling growth under different levels of Cu stress. The results showed that PSI-NPs influenced seed germination in a dose-dependent manner with an optimal rate of 200 mg L^-1. In addition, the positive effects of PSI-NPs on seed germination indexes were found to be positively correlated with enhanced seed imbibition (r = 0.82). The addition of PSI-NPs significantly mitigated Cu stress as indicated by improved growth of shoots and roots, and higher antioxidant enzyme activity observed with co-exposure to PSI-NPs as compared to Cu stress treatment only. Cu concentrations in seedling root and shoot significantly increased with increasing Cu treatment rate. Higher uptake of Cu by plant was observed in the Cu-PSI-NPs co-treatment than single Cu treatment. The alleviation effect of PSI-NPs could be explained by the enhanced antioxidant enzyme activities and storage of Cu as Cu-PSI complexes in plants with reduced phytotoxicity. These findings will open the opportunity of using PSI-NPs as a regulator to enhance seed germination and improve seedling growth under stress of heavy metals like Cu.

Selenium enhances iron plaque formation by elevating the radial oxygen loss of roots to reduce cadmium accumulation in rice (Oryza sativa L.)

The inhibition of cadmium (Cd) absorption by selenium (Se) in rice may be associated with iron plaque (IP) formation, but the driving mechanisms are still unclear. This study investigated the effects of Se on the growth, oxidative toxicity, radial oxygen loss (ROL), IP formation, and Cd absorption of rice exposed to Cd. The results of this study showed that Cd stress elevated the levels of O₂- and H₂O₂ and depressed superoxide dismutase (SOD) and catalase (CAT) activities. The maximum ROL and IP were reduced by 43.3 % and 74.5 %, respectively. However, Se alleviated Cd toxicity by stimulating SOD and CAT activities by scavenging O₂- and H₂O₂ and enhancing the ROL profiles. Under culture conditions without Fe²⁺, Se had no impact on the total Cd levels in rice (T_Cd). However, with the addition of Fe²⁺, T_Cd was significantly reduced by 23.3 % due to the enhancement of IP formation by Se. These results indicated that Se can reduce Cd accumulation in rice in the presence of Fe²⁺ treatments. However, Se just alleviated Cd toxicity in the absence of Fe²⁺ treatments. The enhancement of ROL was a potential reason for the elevated IP formation induced by Se.

Differential impact of some metal(loid)s on oxidative stress, antioxidant system, sulfur compounds, and protein profile of Indian mustard (Brassica juncea L.)

Levels of arsenic (As), chromium (Cr), and copper (Cu) are increasing in the soils worldwide. Such contaminants cause toxicity in the plant systems which adversely affects growth and productivity. The objective of the present investigation was to elucidate individual and combined effects of As, Cr, and Cu (100 μM each) stress in metal hyper-accumulator plant Indian mustard (Brassica juncea L.), exposed for a week. The highest accumulation was in the roots and in decreasing order viz. Cu > As > Cr. The magnitude of oxidative stress was maximal in combined stress, followed by As, Cr, and then Cu stress. Glutathione in conjunction with glutathione reductase, glutathione peroxidase, and glutathione S-transferase increased in all set of stress treatments, notably when exposed to Cr alone. In addition, the level of sulfur-rich compounds like cysteine, phytochelatins, and non-protein thiols increased under each stress indicating efficient coupling of the enzyme system and sulfur-containing compounds during stress conditions. The highest tolerance or growth index of plants was recorded for Cu. Protein profiling of leaf tissues showed modulation of protein patterns in each stress. Mediator of RNA polymerase II transcription subunit 1 isoform X1, RuBisCO (large subunit), and ribosomal protein S3 proteins were more abundant under Cr and Cu stress. Zinc finger A20/AN1 domain-containing stress-associated protein 5-like protein was more abundant under Cu stress. HSP (15.7 kDa) and autophagy protein 5-like were in higher abundance under As and combined stress. Our results suggest that Indian mustard has a differential mode of defense against a particular stressor at the level of protein expression profile.

Health risk assessment of trace elements exposure through the soil-plant (maize)-human contamination pathway near a petrochemical industry complex, Northeast China

The trace elements contamination of agricultural soils near petrochemical industry complexes is a concern due to the risk of accumulating in food systems and subsequently affecting human health. We measured representative trace elements (Cu, Ni, Cr, Pb, Zn, Pb, Hg and As) through the soil-plant (maize)-human contamination pathway near a petrochemical industry complexes in an agricultural region from September 20 to 28, 2016. We found that the soil was mildly to moderately polluted by multiple trace elements, which was also confirmed by the contamination factor and enrichment factor values. Cd (enrichment factor = 2.28), Cu (2.75), Zn (1.85) and Pb (1.70) should be given more attention and prioritized over the other trace elements due to their higher potential risks. Furthermore, the trace elements contamination in maize grains was lower than the corresponding limits. The sequence of the transfer coefficient values was Zn > Cd > Cu > Hg > Ni > As > Cr > Pb. Maize grain safety was threatened mainly by Zn, Cd and Cu. There was no risk to humans through soil ingestion, while a potential health risk from maize grain consumption existed. Children were more sensitive than adults to the non-carcinogenic risks of maize grain consumption. Trace element As was found to be the priority metal for risk control. For carcinogenic risk, adults were more sensitive than children; As, Cr and Cd were the priority metals for risk control, with CR_maize values exceeding the risk threshold (1 × 10^-4). Overall, strict, intensive monitoring, especially of Cr and Cd, and soil protection measures are needed to prevent any furthertrace elements contamination and to ensure food safety. This study also provides a reference for similar studies worldwide.

The role of rice (Oryza sativa L.) in sequestering phosphorus compounds and trace elements: Speciation and dynamics

In southern Florida, the sequestering of nutrients through the cultivation of rice (Oryza sativa L.) in alternation with sugarcane (Saccharum spp.) crops is an essential step in minimizing downstream eutrophication of the Florida Everglades. Phosphorus (P) is known to be the leading cause of this eutrophication; however, the cultivation/harvesting of rice effectively reduces P and additional macro and micro-nutrients from agrarian soil and runoff through plant uptake. In this study, soil, water, sugarcane, and rice plants at two different stages (flooded and vegetative) were analyzed for twelve different elements (Al, As, Co, Cr, Cu, Fe, Ni, Zn, Ca, Mn, Mg, and P) by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). ³¹P Nuclear Magnetic Resonance (NMR) spectra of the rice plants confirmed ten different P compounds being transported and/or transformed throughout the entirety of the sugarcane and rice plants. On average, dried rice plants contained 1677 ± 14 mg-P, of which 1277 ± 3.0 mg-P was in the panicle at the vegetative stage. Harvesting of the rice panicle has the potential to remove about 14.7 kg-P/ha for the top 10 cm of the soil. This present study demonstrates that in rotations with sugarcane crops and with no added P fertilizer, rice cultivation can reduce considerable amounts of P that would otherwise leach into the Greater Everglades from the Everglades Agricultural Area.

Cation-π Interactions with Coexisting Heavy Metals Enhanced the Uptake and Accumulation of Polycyclic Aromatic Hydrocarbons in Spinach

Few studies have considered the effect of co-occurring heavy metals on plant accumulation of hydrophobic organic compounds (HOCs), and less is known about the role of intermolecular interactions. This study investigated the molecular mechanisms of Cu/Zn effects on hydroponic uptake of four deuterated polycyclic aromatic hydrocarbons (PAHs-d₁₀) by spinach (Spinacia oleracea L.). Both solubility enhancement experiment and quantum mechanical calculations demonstrated the existence of [PAH-Cu(H₂O)_0-4]²⁺ and [2·PAH-Cu(H₂O)_0-2]²⁺ via cation-π interactions when Cu²⁺ concentration was ≤100 μmol/L. Notably, PAH-d₁₀ concentrations in both roots and shoots increased significantly with Cu²⁺ concentration. This was because the formation of phytoavailable PAH-Cu²⁺ complexes decreased PAH-d₁₀ hydrophobicity and consequently decreased their sorption onto dissolved organic carbon (DOC, i.e., root exudates), thereby increasing phytoavailable concentrations and uptake of PAHs-d₁₀. X-ray absorption near-edge structure analysis showed that PAH-Cu²⁺ complexes could enter defective spinach roots via apoplastic pathway. However, Zn²⁺ and PAHs-d₁₀ cannot form the cation-π interactions because of the high desolvation penalty of Zn²⁺. Actually, Zn²⁺ decreased the spinach uptake of PAHs-d₁₀ due to the increase of DOC induced by Zn. This work provides molecular insights into how metals could selectively affect the plant uptake of HOCs and highlights the importance of considering the HOC phytoavailability with coexisting metals.

Xylem-based long-distance transport and phloem remobilization of copper in Salix integra Thunb

Due to high biomass and an ability to accumulate metals, fast-growing tree species are good candidates for phytoremediation. However, little is known about the long-distance transport of heavy metals in woody plants. The present work focused on the xylem transport and phloem remobilization of copper (Cu) in Salix integra Thunb. Seedlings with 45 d preculture were grown in nutrient solutions added with 0.32 and 10 μM CuSO₄ for 5 d. Micro X-ray fluorescence imaging showed the high Cu intensity in xylem tissues of both stem and root cross sections, confirming that the xylem played a vital role in Cu transport from roots to shoots. Cu was presented in both xylem sap and phloem exudate, which demonstrates the long-distance transport of Cu via both vascular tissues. Additionally, the ⁶⁵Cu spiked mature leaf exported approximately 78 % ⁶⁵Cu to newly emerged shoots, and approximately 22 % downward to the new roots, confirming the bidirectional transport of Cu via phloem. To our knowledge, this is the first report to characterize Cu vascular transport and remobilization in fast-growing woody plants, and the findings provide valuable mechanistic understanding for the phytoremediation of Cu-contaminated soils.

Improvement of water quality in the Pearl River Estuary, China: a long-term (2008-2017) case study of temporal-spatial variation, source identification and ecological risk of heavy metals in surface water of Guangzhou

A series of environmental protective policies have been taken recently in the Pearl River Estuary (PRE) to alleviate water pollution; however, their influence on the reduction of heavy metals in estuarine water has not been known. This study selected Guangzhou as a representative city in the PRE and collected estuarine water monthly from 2008 to 2017 to track the variation of As, Hg, Pb, Cd, Cu, Zn, and Se. During the last decade, the high time-resolved record showed that the concentration of Hg, Pb, Cd, Cu, and Zn in estuarine water reduced by 39.5%, 91.0%, 86.2%, 74.6%, and 97.3%, respectively. However, the concentration of As kept in a stable range (1.89-2.69 μg L^-1) and Se (0.17-0.65 μg L^-1) increased slightly. The principal component analysis (PCA) and absolute principal component scores-multiple linear regression (APCS-MLR) results suggested that the upstream industrial effluents were major sources for Hg (45.5-92.7%), Pb (47.3-100%), Cd (42.0-90.6%), Cu (85.5-100%), and Zn (100%) and the geogenic source was major origin for As (84.6-98.3%) and Se (0-67.5%). The risk quotient of Hg, Pb, Cd, Cu, and Zn to aquatic organisms largely decreased from 0.03, 0.59, 0.03, 2.06, and 0.26 in 2008 to 0.02, 0.05, 0.006, 0.52, and 0.007 in 2017, respectively. The effective control of heavy metal pollution in the study area can be primarily due to the relocation of hundreds of polluting factories during the last decade.

Molecular mechanisms in phytoremediation of environmental contaminants and prospects of engineered transgenic plants/microbes

Concerns about emerging environmental contaminants have been growing along with industrialization and urbanization around the globe. Among various options for remediating these contaminants, phytotechnology is suggested as a feasible option to maintain the environmental sustainability. The recent advances in phytoremediation, genetic/molecular/omics/metabolic engineering, and nanotechnology are opening new paths for efficient treatment of emerging organic/inorganic contaminants. In this respect, elucidation of molecular mechanisms and genetic engineering of hyperaccumulator plants is expected to enhance remediation of environmental contaminants. This review was organized to offer valuable insights into the molecular mechanisms of phytoremediation and the prospects of transgenic hyperaccumulators with enhanced stress tolerance to diverse contaminants such as heavy metals and metalloids, xenobiotics, explosives, poly aromatic hydrocarbons (PAHs), petroleum hydrocarbons, pesticides, and nanoparticles. The roles of genoremediation and nanoparticles in augmenting the phytoremediation technology are also described in an interrelated framework with biotechnological prospects (e.g., plant molecular nano-farming). Finally, political debate on the preferential use of crops versus non-crop hyperaccumulators in genoremediation, limitations of transgenics in phytotechnologies, and their public acceptance issues are discussed in the policy framework.

Copper stress in flooded soil: Impact on enzyme activities, microbial community composition and diversity in the rhizosphere of Salix integra

Climate change has increased flooding frequency, making the heavy metal polluted areas more vulnerable, and led to increased global land degradation. Information about the alteration of soil microbiota under heavy metal pollution and flooding is still rather limited. Fast-growing trees are candidates for phytoremediation of heavy metal polluted soils. Therefore, the impact of Cu pollution on microbiota in soil used for cultivating Salix integra Thunb. was investigated with and without flooding for 60 d. Bacterial and fungal communities were accessed via partial 16S rRNA (V₃-V₄) and internal transcribed spacer (ITS) genes. The activity of invertase, urease and cellulase were markedly decreased by 28.5-59%, 55.0-76.7% and 17.3-34.1%, respectively, with increasing Cu levels. Flooding significantly increased the activity of polyphenol oxidase and peroxidase by 56.3% and 41.4% at the highest Cu level compared to its respective non-flooded condition. High Cu concentration significantly decreased the richness and diversity of the bacterial community, and fungi were more sensitive than bacteria under flooding conditions. Redundancy analysis suggests that Cu, Fe and soil organic matter are the key determinants affecting the composition of microbial communities. Our findings provide new insight into the responses of soil microbes to Cu-contamination and contribute to our understanding of metal toxicity in soil-woody plant systems under flooded conditions.

Spatial distribution and molecular speciation of copper in indigenous plants from contaminated mine sites: Implication for phytostabilization

Contaminated mining sites require ecological restoration work, of which phytoremediation using appropriate plant species is an attractive option. Our present study is focused on one typical contaminated mine site with indigenous plant cover. The X-ray absorption near edge structure (XANES) analysis indicated that Cu (the major contaminant) was primarily associated with goethite (adsorbed fraction), with a small amount of Cu oxalate-like species (organic fraction) in mine affected soil. With growth of plant species like Miscanthus floridulus and Stenoloma chusanum, the Cu-oxalate like organic species in rhizosphere soil significantly increased, with corresponding decrease in Cu-goethite. In the root cross-section of Miscanthus floridulus, synchrotron-based micro-X-ray fluorescence (μ-XRF) microscopy and micro-XANES results indicated that most Cu was sequestered around the root surface/epidermis, primarily forming Cu alginate-like species as a Cu-tolerance mechanism. From the root epidermis to the cortex and vascular bundle, more Cu(I)-glutathione was observed, suggesting reductive detoxification ability of Cu(II) to Cu(I) during the transport of Cu in the root. The observation of Cu-histidine in root internal cell layers showed another Cu detoxification pathway based on coordinating amino ligands. Miscanthus floridulus showed ability to accumulate phosphorous and nitrogen nutrients in rhizosphere and may be an option for in situ phytostabilization of metals in contaminated mining area.

Accurate quantification of metal-glycinates-sulphate complexes and free metals in feed by capillary electrophoresis inductively coupled plasma mass spectrometry

Traceability of metal-glycinate-sulphate complexes (Metal-GLY) in feed requires specific analysis to differentiate complexes from inorganic forms. A previously described method focused on the quantification of Metal-GLY at one single concentration but not on the quantification of free metal ion forms. The objective of this work was to extend the method to quantify both Metal-GLY and free metal ion forms of various metals at low inclusion levels. A 50/50 w/w mix of corn flour and soybean meal was used as feed. Copper-glycinate(Cu-GLY), Manganese-glycinate (Mn-GLY) and Zinc-glycinate (Zn-GLY) complexes (provided by Pancosma SA) were used for in-feed inclusions. The feed metal background concentrations and species repartitions were assessed. Cu-GLY was spiked on feed at levels matching 5, 15 and 45 mg/kg, corresponding to metal concentrations of 1.2, 3.6 and 10.8 mg/kg. Mn-GLY and Zn-GLY were spiked at 15, 45 and 100 mg/kg, corresponding to 3.3, 9.9, 22 mg/kg Mn and 3.9, 11.7, 26mg/kg Zn, respectively. The water soluble fraction of un-supplemented feed contained 0.06 mg/kg Cu, 0.05 mg/kg Mn and 0.12 mg/kg Zn, with 69.5% of Cu, 33.2% of Mn and 24.3% of Zn being present under free metal ions but 30.4% of Cu being present under Cu-GLY, 66.82% of Mn and 75.7% of Zn being present under Mn-GLY and Zn-GLY, respectively. The supplemented feeds at the 3 tested doses, from the lowest to the highest inclusion levels, contained in total respectively: 1.1, 3.05 and 9.06 mg/kg Cu; 2.99, 8.9 and 18.2 mg/kg Mn; 3.72, 10.9 and 23.4 mg/kg Zn. The M-GLY species recovered by analysis within the different supplemented feeds ranged from 76.26 to 89.32% for Cu-GLY, form 94.5 to 98.51% for Mn-GLY and from 76.05 to 98.96% for Zn-GLY. These results showed that CE-ICP-MS technique can be used to quantify low doses and to measure metal-species repartition between Metal-GLY and free metal ions, when included in feeds. For the first time, this study highlighted that the raw materials used contain Metal-GLY compounds. This raises the question of the occurrence of these compounds within the different raw materials used in feed production that could dramatically affect the way to supplement minerals in animal feed.