Investigating arsenic toxicity in tropical soils: A cell cycle and DNA fragmentation approach

Stabilization of arsenic-cadmium co-contaminated soil with the iron-manganese sludge derived amendment: Effects and mechanisms

An iron-manganese sludge-derived amendment was proposed to remediate arsenic (As) and cadmium (Cd) co-contaminated soil, with a strong adsorptive capacity across pH 4 to 10. The Langmuir model defined maximum adsorption at 78.17 mg/g for As(III), 110.48 mg/kg for As(V), and 65.77 mg/g for Cd(II). The X-ray photoelectron spectroscopy (XPS) spectra provided insights into the chemical interactions: As was predominantly complexed or ligand exchanged with iron(hydr)oxides. In contrast, cadmium exhibited a tendency to bond with acylamino and carboxyl groups, in addition to the ferric hydroxyl groups. Notably, 42.15% of the adsorbed As(III) was oxidized into As(V) by Mn(IV) oxides present in the amendment. The soil-verification experiment demonstrated that an amendment dosage of 40 g/kg was efficacious in reducing the leaching concentration of As and Cd to maintained below the safety thresholds of 0.1 mg/L and 0.01 mg/L, respectively, for pH levels 4 to 11, meeting the Chinese Surface Water Quality Standard V (GB3838-2002). After the stabilization, the exchangeable fractions of As and the acid-soluble fractions of Cd were significantly reduced, with these elements being transformed into more stable forms. The amendment maintained the soil's neutral pH and adjusted the soil physicochemical properties. This article presents a holistic approach by examining the organic-inorganic composite of iron-manganese oxides with polyacrylamide, modified as a stabilizing amendment for As and Cd co-contaminated soil. This innovative amendment adeptly navigates the previously conflicting stabilization mechanisms for anionic and cationic metals. Offering dual advantages, the amendment not only remediates soil but also addresses the disposal of waste, presenting a win-win solution for environmental management.

Exogenous curcumin mitigates As stress in spinach plants: A biochemical and metabolomics investigation

The spinach (S. oleracea L.) was used as a model plant to investigate As toxicity on physio-biochemical processes, exploring the potential mitigation effect of curcumin (Cur) applied exogenously at three concentrations (1, 10, and 20 μM Cur). The employment of Cur significantly mitigated As-induced stress in spinach photosynthetic performance (Fv/Fm, Fo/Fm, and Fv/Fo). Moreover, the co-incubation of Cur with As improved physiological processes mainly associated with plant water systems affected by As stress by recovering the leaf's relative water content (RWC) and osmotic potential (ψπ) nearly to the control level and increasing the transpiration rate (E; 39-59%), stomatal conductivity (gs; 86-116%), and carbon assimilation rate (A; 84-121%) compared to As stressed plants. The beneficial effect of Cur in coping with As-induced stress was also assessed at the plant's oxidative level by reducing oxidative stress biomarkers (H2O2 and MDA) and increasing non-enzymatic antioxidant capacity. Untargeted metabolomics analysis was adopted to investigate the main processes affected by As and Cur application. A multifactorial ANOVA discrimination model (AMOPLS-DA) and canonical correlation analysis (rCCA) were employed to identify relevant metabolic changes and biomarkers associated with Cur and As treatments. The results highlighted that Cur significantly determined the accumulation of glucosinolates, phenolic compounds, and an increase in glutathione redox cycle activities, suggesting an overall elicitation of plant secondary metabolisms. Specifically, the correlation analysis reported a strong and positive correlation between (+)-dihydrokaempferol, L-phenylalanine (precursor of phenolic compounds), and serotonin-related metabolites with antioxidant activities (ABTS and DPPH), suggesting the involvement of Cur application in promoting a cross-talk between ROS signaling and phytohormones, especially melatonin and serotonin, working coordinately to alleviate As-induced oxidative stress. The modulation of plant metabolism was also observed at the level of amino acids, fatty acids, and secondary metabolites synthesis, including N-containing compounds, terpenes, and phenylpropanoids to cooperate with As-induced stress response.

Regulatory Mechanisms Underlying Arsenic Uptake, Transport, and Detoxification in Rice

Arsenic (As) is a metalloid environmental pollutant ubiquitous in nature that causes chronic and irreversible poisoning to humans through its bioaccumulation in the trophic chain. Rice, the staple food crop for 350 million people worldwide, accumulates As more easily compared to other cereal crops due to its growth characteristics. Therefore, an in-depth understanding of the molecular regulatory mechanisms underlying As uptake, transport, and detoxification in rice is of great significance to solving the issue of As bioaccumulation in rice, improving its quality and safety and protecting human health. This review summarizes recent studies on the molecular mechanisms of As toxicity, uptake, transport, redistribution, regulation, and detoxification in rice. It aims to provide novel insights and approaches for preventing and controlling As bioaccumulation in rice plants, especially reducing As accumulation in rice grains.

Efficient remediation of heavily As(III)-contaminated soil using a pre-oxidation and stabilization/solidification technique

The high mobility of As(III) makes it difficult to remediate heavily As(III)-contaminated soil. A novel remediation technique that combines pre-oxidation and stabilization/solidification (PO + S/S) is proposed in this study to remediate heavily As(III)-contaminated soil. After oxidizing As(III) in the contaminated soil using Fenton's reagent, FeCl₃·6H₂O was used as a chemical stabilizing agent to reduce the toxicity and mobility of As. Finally, Portland cement (PC) was used for solidification. The effects and mechanisms of the proposed technique were studied using unconfined compressive strength tests, leaching tests, sequential extraction procedure (SEP), and a series of spectroscopic/microscopic investigations. The experimental results showed that the addition of FeCl₃·6H₂O increased the strength of the curing body because the hydration degree of PC and pore structure were improved. Portland cement can increase the pH of the curing body. At a 1:1 Fe to As molar ratio and a 15 wt% PC dosage, the leached As concentration decreased to 3.25 mg L^-1, and the remediation efficiency reached 99.54%. The SEP results showed that the PO + S/S treatment converted As into more stable phases and effectively reduced the potential mobile phase risk. The majority of As was bound to hydrated iron oxides; however, the increased pH affected the Fe-As interactions and prompted the release of As from the surface of the hydrated iron oxides. Spectroscopic/microscopic investigations indicated that the PO + S/S treatment converted As(III) to less toxic and less mobile As(V) and then immobilized by the encapsulation of calcium silicate hydrate and ion exchange of ettringite. This study provides a scientific basis and theoretical support for the effective remediation of heavily As(III)-contaminated soil.

Arsenic as hazardous pollutant: Perspectives on engineering remediation tools

Arsenic (As) is highly toxic metal (loid) that impairs plant growth and proves fatal towards human population. It disrupts physiological, biochemical and molecular attributes of plants associated with water/nutrient uptake, redox homeostasis, photosynthetic machineries, cell/membrane damage, and ATP synthesis. Numerous transcription factors are responsive towards As through regulating stress signaling, toxicity and resistance. Additionally, characterization of specific genes encoding uptake, translocation, detoxification and sequestration has also explained their underlying mechanisms. Arsenic within soil enters the food chain and cause As-poisoning. Plethora of conventional methods has been used since decades to plummet As-toxicity, but the success rate is quite low due to environmental hazards. Henceforth, exploration of effective and eco-friendly methods is aimed for As-remediation. With the technological advancements, we have enumerated novel strategies to address this concern for practicing such techniques on global scale. Novel strategies such as bioremediation, phytoremediation, mycorrhizae-mediated remediation, biochar, algal-remediation etc. possess extraordinary results. Moreover, nitric oxide (NO), a signaling molecule has also been explored in relieving As-stress through reducing oxidative damages and triggering antioxidative responses. Other strategies such as role of plant hormones (salicylic acid, indole-3-acetic acid, jasmonic acid) and micro-nutrients such as selenium have also been elucidated in As-remediation from soil. This has been observed through stimulated antioxidant activities, gene expression of transporters, defense genes, cell-wall modifications along with the synthesis of chelating agents such as phytochelatins and metallothioneins. This review encompasses the updated information about As toxicity and its remediation through novel techniques that serve to be the hallmarks for stress revival. We have summarised the genetic engineering protocols, biotechnological as well as nanotechnological applications in plants to combat As-toxicity.

Nanoparticles as a potential protective agent for arsenic toxicity alleviation in plants

Aggrandized technological and industrial progression in past decades have occasioned immense depreciation in the quality of environment and ecosystem, majorly due to augmentation in the number of obnoxious pollutants incessantly being released in soil, water or air. Arsenic (As) is one such hazardous metalloid contaminating the environment which has the potential to detrimentally affect the life on earth. Even in minute quantity, As is known to cause various critical diseases in humans and toxicity in plants. Recent studies on nanoparticles (NPs) approve of their ability to qualify the criterion of becoming a potent tool for mitigating As-induced phytotoxicity. Nanoparticles are reported to promote plant growth under As-stress by stimulating various alterations at physiological, biochemical, and molecular levels. In this review, we provide an up-to-date compilation of research that has been carried out in comprehending the mechanisms utilized by nanoparticles including controlled As uptake and distribution in plants, maintenance of ROS homeostasis during stress and chelation and vacuolar sequestration of As so as to reduce the severity of toxicity induced by As, and potential areas of research in this field will also be indicated for future perspectives.

Plant Cytogenetics in the Micronuclei Investigation-The Past, Current Status, and Perspectives

Cytogenetic approaches play an essential role as a quick evaluation of the first genetic effects after mutagenic treatment. Although labor-intensive and time-consuming, they are essential for the analyses of cytotoxic and genotoxic effects in mutagenesis and environmental monitoring. Over the years, conventional cytogenetic analyses were a part of routine laboratory testing in plant genotoxicity. Among the methods that are used to study genotoxicity in plants, the micronucleus test particularly represents a significant force. Currently, cytogenetic techniques go beyond the simple detection of chromosome aberrations. The intensive development of molecular biology and the significantly improved microscopic visualization and evaluation methods constituted significant support to traditional cytogenetics. Over the past years, distinct approaches have allowed an understanding the mechanisms of formation, structure, and genetic activity of the micronuclei. Although there are many studies on this topic in humans and animals, knowledge in plants is significantly limited. This article provides a comprehensive overview of the current knowledge on micronuclei characteristics in plants. We pay particular attention to how the recent contemporary achievements have influenced the understanding of micronuclei in plant cells. Together with the current progress, we present the latest applications of the micronucleus test in mutagenesis and assess the state of the environment.

Bioaugmentation with As-transforming bacteria improves arsenic availability and uptake by the hyperaccumulator plant Pteris vittata (L)

Inorganic arsenic (As) is a toxic and carcinogenic pollutant that has long-term impacts on environmental quality and human health. Pteris vittata plants hyperaccumulate As from soils. Soil bacteria are critical for As-uptake by P. vittata. We examined the use of taxonomically diverse soil bacteria to modulate As speciation in soil and their effect on As-uptake by P. vittata. Aqueous media inoculated with Pseudomonas putida MK800041, P. monteilii MK344656, P. plecoglossicida MK345459, Ochrobactrum intermedium MK346993 or Agrobacterium tumefaciens MK346997 resulted in the oxidation of 5-30% As(III) and a 49-79% reduction of As(V). Soil inoculated with P. monteilii increased extractable As(III) and As(V) from 0.5 and 0.09 in controls to 0.9 and 0.39 mg As kg^-1 soil dry weight, respectively. Moreover, and P. vittata plants inoculated with P. monteilii, P. plecoglossicida, O. intermedium strains, and A. tumefaciens strains MK344655, MK346994, MK346997, significantly increased As-uptake by 43, 32, 12, 18, 16, and 14%, respectively, compared to controls. The greatest As-accumulation (1.9 ± 0.04 g kg^-1 frond Dwt) and bioconcentration factor (16.3 ± 0.35) was achieved in plants inoculated with P. monteilii. Our findings indicate that the tested bacterial strains can increase As-availability in soils, thus enhancing As-accumulation by P. vittata. Novelty statement Pteris vittata, a well-known As-hyperaccumulator, has the remarkable ability to accumulate higher levels of As in their above-ground biomass. The As-tolerant bacteria-plant interactions play a significant role in bioremediation by mediating As-redox and controlling As-availability and uptake by P. vittata. Our studies indicated that most of the tested bacterial strains isolated from As-impacted soil significantly enhanced As-uptake by P. vittata. P. monteilii oxidized 20% of As(III) and reduced 50% of As(V), increased As-extraction from soils, and increased As-uptake by 43% greater compared with control. Therefore, these strains associated with P. vittata can be used in large-scale field applications to remediate As-contaminated soil.

Metallothionein Attenuated Arsenic-Induced Cytotoxicity: The Underlying Mechanism Reflected by Metabolomics and Lipidomics

Arsenic ions (As³⁺) have been recognized as a hazard that threatens the health of humans. Metallothionein (MT) rich in cysteine may provide favorable binding sites for chelation of As³⁺. However, the influence of MT on As³⁺-induced toxicity and the underlying mechanism are poorly understood, especially at the metabolic level. Herein, the effects of MT on As³⁺-induced toxicity were evaluated. Cell viability analysis suggested that MT alleviated As³⁺-induced cytotoxicity. The metabolic response of PC12 cells to As³⁺ investigated by lipidomics and metabolomics indicated that the presence of As³⁺ disrupted phospholipids metabolism and induced cell membrane damage. Moreover, energy and amino acid metabolism were perturbed by As³⁺. The perturbation of As³⁺ on metabolism was further illustrated by the decrease of the mitochondrial membrane potential and the rise of cellular reactive oxygen species (ROS). On the contrary, MT rescued As³⁺-induced metabolic disorder and suppressed ROS accumulation. In addition, the binding process between As³⁺ and MT was characterized. The results proved that the As³⁺-MT complex was formed and chelated As³⁺-scavenged ROS, thus alleviating the toxic effects of As³⁺. These results revealed that MT would be a potential agent to reduce As³⁺-induced cytotoxicity.

Phosphorus supplementation modulates nitric oxide biosynthesis and stabilizes the defence system to improve arsenic stress tolerance in mustard

The interaction of mineral nutrients with metals/metalloids and signalling molecules is well known. In the present study, we investigated the effect of phosphorus (P) in mitigation of arsenic (As) stress in mustard (Brassica juncea L.). The study was conducted to investigate potential of 30 mg P·kg^-1 soil P supplement (diammonium phosphate) to cope up with the adverse effects of As stress (24 mg As·kg^-1 soil) in mustard plants Supplementation of P influenced nitric oxide (NO) generation, which up-regulated proline metabolism, ascorbate-glutathione system and glyoxalase system and alleviated the effects of on photosynthesis and growth. Arsenic stress generated ROS and methylglyoxal content was scavenged through P-mediated NO, and reduced As translocation from roots to leaves. The involvement of NO under P-mediated alleviation of As stress was substantiated with the use of cPTIO (NO biosynthesis inhibitor) and SNP (NO inducer). The reversal of P effects on photosynthesis under As stress with the use of cPTIO emphasized the role of P-mediated NO in mitigation of As stress and protection of photosynthesis The results suggested that P reversed As-induced oxidative stress by modulation of NO formation, which regulated antioxidant machinery. Thus, P-induced regulatory interaction between NO and reversal of As-induced oxidative stress for the protection of photosynthesis may be suggested for sustainable crops.

Cytogenetic toxicity from pesticide and trace element mixtures in soils used for conventional and organic crops of Allium cepa L

Pesticides and trace elements occur in complex mixtures in agroecosystems, affecting soil health and food security. Hence, it is necessary to determine their toxicity in field conditions and to develop monitoring approaches to assess conventional and organic agriculture. The aim of this research was to evaluate the associations between Allium cepa L. cytogenetic biomarkers and the realistic mixture of pesticides and trace elements found in soils of conventional, conversion, and organic crops in an intensive agricultural region in Colombia. Pesticide screening was conducted using GC-MS/MS and LC-MS/MS methods. Arsenic, cadmium, lead, and zinc were analyzed by ICP-MS; chromium, copper, nickel, and selenium by ICP-OES; and mercury by a direct analyzer. The meristematic cells in roots of Allium cepa L. were analyzed through microscopic observations to quantify cytogenetic effects. In conventional crops, 26 pesticides were detected in the soil samples, and those were below the limit of quantification in organic crops. The mean levels of As, Cd, Cr, Ni, Pb, and Se were also greater in soils of conventional crops compared to the organics. In addition, the biomarkers of cytotoxicity and genotoxicity appeared augmented in conventional samples, and those were correlated with pesticide and trace element concentrations, pollution indices, and hazard quotients. Subsequently, a discriminant function based on the mitotic index, chromosomal aberrations, and nuclear abnormalities was suitable to classify the samples by crop type. These results demonstrate the sensitivity of Allium cepa L. to the toxicity of complex mixtures in field crops and its potential as an in-situ approach for soil health monitoring in organic and conventional crop systems.

Main nitric oxide (NO) hallmarks to relieve arsenic stress in higher plants

Arsenic (As) is a toxic metalloid that adversely affects plant growth, and poses severe risks to human health. It induces disturbance to many physiological and metabolic pathways such as nutrient, water and redox imbalance, abnormal photosynthesis and ATP synthesis and loss of membrane integrity. Nitric oxide (NO) is a free radical molecule endogenously generated in plant cells which has signalling properties. Under As-stress, the endogenous NO metabolism is significantly affected in a clear connection with the metabolism of reactive oxygen species (ROS) triggering nitro-oxidative stress. However, the exogenous NO application provides beneficial effects under As-stress conditions which can relieve oxidative damages by stimulating the antioxidant systems, regulation of the expression of the transporter and other defence-related genes, modification of root cell wall composition or the biosynthesis of enriched sulfur compounds such phytochelatins (PCs). This review aims to provide up-to-date information on the key NO hallmarks to relieve As-stress in higher plants. Furthermore, it will be analyzed the diverse genetic engineering techniques to increase the endogenous NO content which could open new biotechnological applications, especially in crops under arsenic stress.