Soil cadmium enrichment: Allocation and plant physiological manifestations

Strengthen sunflowers resilience to cadmium in saline-alkali soil by PGPR-augmented biochar

In the center of the Nile Delta in Egypt, the Kitchener drain as the primary drainage discharges about 1.9 billion m3 per year of water, which comprises agricultural drainage (75 %), domestic water (23 %), and industrial water (2 %), to the Mediterranean Sea. Cadmium (Cd) stands out as a significant contaminant in this drain; therefore, this study aimed to assess the integration of biochar (0, 5, and 10 ton ha-1) and three PGPRs (PGPR-1, PGPR-2, and PGPR-3) to alleviate the negative impacts of Cd on sunflowers (Helianthus annuus L.) in saline-alkali soil. The treatment of biochar (10 ton ha-1) and PGPR-3 enhanced the soil respiration, dehydrogenase, nitrogenase, and phosphatase activities by 137 %, 129 %, 326 %, and 127 %, while it declined soil electrical conductivity and available Cd content by 31.7 % and 61.3 %. Also, it decreased Cd content in root, shoot, and seed by 55.3 %, 50.7 %, and 92.5 %, and biological concentration and translocation factors by 55 % and 5 %. It also declined the proline, lipid peroxidation, H2O2, and electrolyte leakage contents by 48 %, 94 %, 80 %, and 76 %, whereas increased the catalase, peroxidase, superoxide dismutase, and polyphenol oxidase activities by 80 %, 79 %, 61 %, and 116 %. Same treatment increased seed and oil yields increased by 76.1 % and 76.2 %. The unique aspect of this research is its investigation into the utilization of biochar in saline-alkali soil conditions, coupled with the combined application of biochar and PGPR to mitigate the adverse effects of Cd contamination on sunflower cultivation in saline-alkali soil.

Biogenic silicon nanoparticles mitigate cadmium (Cd) toxicity in rapeseed (Brassica napus L.) by modulating the cellular oxidative stress metabolism and reducing Cd translocation

Nano-enabled strategies have emerged as promising alternatives to resolve heavy metals (HMs) related harms in an eco-friendly manner. Here, we explored the potential of biogenic silicon nanoparticles (SiNPs) in alleviating cadmium (Cd) stress in rapeseed (Brassica napus L.) plants by modulating cellular oxidative repair mechanisms. Biogenic SiNPs of spherical shapes with size ranging between 14 nm and 35 nm were synthesized using rice straw extract and characterized through advanced characterization techniques. A greenhouse experiment results showed that SiNPs treatment at 250 mg kg-1 significantly improved growth parameters, including fresh weight (33.3 %) and dry weight (32.6 %) of rapeseed plants than Cd-treated control group. Photosynthesis and leaf gas exchange parameters were also positively influenced by SiNPs treatment, indicating enhanced photosynthetic efficiency. Additionally, SiNPs treatment at 250 mg kg-1 increased the activities of antioxidant enzymes such as superoxide dismutase (19.1 %), peroxidase (33.4 %), catalase (14.4 %), and ascorbate peroxidase (33.8 %), which may play a crucial role in ROS scavenging and reduction in Cd-induced oxidative stress. TEM analysis revealed that SiNPs treatment effectively mitigated Cd-induced damage to leaf ultrastructure, while qPCR analysis showed that SiNPs treatment changed the expressions of the antioxidant defense and stress related genes. Moreover, SiNPs treatment significantly influenced the Cd accumulation and Si contents in plants. Overall, our findings revealed that biogenic SiNPs have great potential to serve as a sustainable, eco-friendly, and non-toxic alternative for the remediation of Cd toxicity in rapeseed plants.

Hydrogel-potassium humate composite alleviates cadmium toxicity of tobacco by regulating Cd bioavailability

Cadmium (Cd) removal from soil to reduce Cd accumulation in plants is essential for agroecology, food safety, and human health. Cd enters plants from soil and affects plant growth and development. Hydrogels can easily combine with Cd, thereby altering its bioavailability in soil. However, few studies have evaluated the effects of hydrogel on the complex phytotoxicity caused by Cd uptake in plants and the microbial community structure. Herein, a new poly (acrylic acid)-grafted starch and potassium humate composite (S/K/AA) hydrogel was added to soil to evaluate its impact on tobacco growth and the soil microenvironment. The results indicate that the addition of S/K/AA hydrogel can significantly improve the biomass, chlorophyll (Chl) content, and photosynthetic capacity of tobacco plants during Cd stress conditions, and decrease Cd concentration, probably by affecting Cd absorption through the expression of Cd absorption transporters (e.g., NRAMP5, NRAMP3, and IRT1). Moreover, the application of S/K/AA hydrogel not only reduced the accumulation of reactive oxygen species (ROS), but also reduced the antioxidant activities of peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT), suggesting that S/K/AA hydrogel alleviates Cd toxicity via a non-antioxidant pathway. Notably, we further analyzed the effectiveness of the hydrogel on microbial communities in Cd-contaminated soil and found that it increased the Cd-tolerant microbial community (Arthrobacter, Massilia, Streptomyces), enhancing the remediation ability of Cd-contaminated soil and helping tobacco plants to alleviate Cd toxicity. Overall, our study provides primary insights into how S/K/AA hydrogel affects Cd bioavailability and alleviates Cd toxicity in plants.

Metabolomics: a promising tool for deciphering metabolic impairment in heavy metal toxicities

Heavy metals are the metal compounds found in earth's crust and have densities higher than that of water. Common heavy metals include the lead, arsenic, mercury, cadmium, copper, manganese, chromium, nickel, and aluminum. Their environmental levels are consistently rising above the permissible limits and they are highly toxic as enter living systems via inhalation, ingestion, or inoculation. Prolonged exposures cause the disruption of metabolism, altered gene and/or protein expression, and dysregulated metabolite profiles. Metabolomics is a state of the art analytical tool widely used for pathomolecular inv22estigations, biomarkers, drug discovery and validation of biotransformation pathways in the fields of biomedicine, nutrition, agriculture, and industry. Here, we overview studies using metabolomics as a dynamic tool to decipher the mechanisms of metabolic impairment related to heavy metal toxicities caused by the environmental or experimental exposures in different living systems. These investigations highlight the key role of metabolomics in identifying perturbations in pathways of lipid and amino acid metabolism, with a critical role of oxidative stress in metabolic impairment. We present the conclusions with future perspectives on metabolomics applications in meeting emerging needs.

Cadmium-treatment efficiency and membrane fouling during electrodialysis of wastewater discharged from zinc smelting

Zinc smelting wastewater contains high concentrations of Cd. Here, the treatment efficiency of Cd using electrodialysis was evaluated. In addition, scale accumulation of ion-exchange membrane (IEM) was analyzed, and fouling control was studied. The results showed that spacers effectively improved the limiting current density but accelerated foulant accumulation. The Cd-treatment efficiency improved to 85.4% without a spacer. Dissolved organic carbon (DOC) and hydrophobic DOC levels in diluted water decreased by 0.65 mg L^-1 and 2.1 mg L^-1, respectively; in contrast, hydrophilic DOC level increased by 1.45 mg L^-1. Some of the hydrophobic DOC in the diluted water was converted to hydrophilic DOC and subsequently to low-molecular-weight (LMW) DOC. DOC level in the concentrated water did not change substantially, but the LMW fraction of the hydrophilic DOC increased. In the cation-exchange membrane, a material composed of calcium sulfate accumulated in the bottom layer, and hydroxides of divalent and trivalent ions accumulated on top of it. In contrast, the anion-exchange membrane was fouled by humic substances. In terms of fouling control, physical and acid cleaning of IEMs was more effective than the reversal operation.

Sulfate supplementation affects nutrient and photosynthetic status of Arabidopsis thaliana and Nicotiana tabacum differently under prolonged exposure to cadmium

Hydroponic experiments were performed to examine the effect of prolonged sulfate limitation combined with cadmium (Cd) exposure in Arabidopsis thaliana and a potential Cd hyperaccumulator, Nicotiana tabacum. Low sulfate treatments (20 and 40 µM MgSO₄) and Cd stress (4 µM CdCl₂) showed adverse effects on morphology, photosynthetic and biochemical parameters and the nutritional status of both species. For example, Cd stress decreased NO₃^- root content under 20 µM MgSO₄ to approximately 50% compared with respective controls. Interestingly, changes in many measured parameters, such as chlorophyll and carotenoid contents, the concentrations of anions, nutrients and Cd, induced by low sulfate supply, Cd exposure or a combination of both factors, were species-specific. Our data showed opposing effects of Cd exposure on Ca, Fe, Mn, Cu and Zn levels in roots of the studied plants. In A. thaliana, levels of glutathione, phytochelatins and glucosinolates demonstrated their distinct involvement in response to sub-optimal growth conditions and Cd stress. In shoot, the levels of phytochelatins and glucosinolates in the organic sulfur fraction were not dependent on sulfate supply under Cd stress. Altogether, our data showed both common and species-specific features of the complex plant response to prolonged sulfate deprivation and/or Cd exposure.

Simultaneous screening of zebrafish larvae cardiac and respiratory functions: a microfluidic multi-phenotypic approach

Multi-phenotypic screening of multiple zebrafish larvae plays an important role in enhancing the quality and speed of biological assays. Many microfluidic platforms have been presented for zebrafish phenotypic assays, but multi-organ screening of multiple larvae, from different needed orientations, in a single device that can enable rapid and large-sample testing is yet to be achieved. Here, we propose a multi-phenotypic quadruple-fish microfluidic chip for simultaneous monitoring of heart activity and fin movement of 5-7-day postfertilization zebrafish larvae trapped in the chip. In each experiment, fin movements of four larvae were quantified in the dorsal view in terms of fin beat frequency (FBF). Positioning of four optical prisms next to the traps provided the lateral views of the four larvae and enabled heart rate (HR) monitoring. The device's functionality in chemical testing was validated by assessing the impacts of ethanol on heart and fin activities. Larvae treated with 3% ethanol displayed a significant drop of 13.2 and 35.8% in HR and FBF, respectively. Subsequent tests with cadmium chloride highlighted the novel application of our device for screening the effect of heavy metals on cardiac and respiratory function at the same time. Exposure to 5 $\mu$g/l cadmium chloride revealed a significant increase of 8.2% and 39.2% in HR and FBF, respectively. The device can be employed to monitor multi-phenotypic behavioral responses of zebrafish larvae induced by chemical stimuli in various chemical screening assays, in applications such as ecotoxicology and drug discovery.

Impact of old environmental burden in the Spiš region (Slovakia) on soil and home-grown vegetable contamination, and health effects of heavy metals

Due to several centuries of ongoing mining activities, Middle Spiš (Slovakia) is one of the areas with a damaged environment. The contents of Fe, Mn, Zn, Cu, Ni, Pb, Cd, and Hg were determined in the soils and home-grown vegetables (potatoes, carrots, tomatoes). Except for Pb, the contents of heavy metals in the soils of some plots were higher than the limit values. Based on the values of Contamination factor (C_f), Degree of contamination (C_deg), Geo-accumulation index (I_geo), and Pollution load index (PLI), very high Fe, Cd, and Hg contamination (C_f ≥ 6), very high soil contamination (C_deg ≥ 20), extremely heavy Fe and Hg contamination (I_geo > 5), resp. moderately pollution to non-pollution (1 < PLI ≤ 2) was found in all plots. In vegetable samples, the maximum levels were exceeded for Cu, Pb, Hg (potato), Pb (carrot, tomato), and Hg (carrot, plot E). Bioaccumulation factor values BAF > 1 were for Cu (carrots, potatoes). Estimated daily intake values for all heavy metals were lower than their tolerable daily intake. Chronic daily intake of heavy metals ranged 2.495E−06 (Hg)—0.1416 (Fe) mg/kg/day. Based on Hazard index values, potato consumption poses a risk (0.8068–1.3057). The results showed that the monitoring of soils and cultivated production is necessary for the investigated area.

Spatiotemporal assessment of potentially toxic elements in sediments and roadside soil samples and associated ecological risk in Ropar wetland and its environs

Sediments from banks of the Sutlej River and roadside soils from vicinity of Ropar wetland (collected during pre- and post-monsoon seasons, 2013) were analysed to determine the spatiotemporal distribution of potentially toxic elements (PTEs, viz. arsenic, cadmium, cobalt, chromium, copper, iron, manganese, lead and zinc), which when present in high concentrations may pose health hazards and ecological risk. Contamination factor, degree of contamination, modified degree of contamination, metal pollution index, pollution load index, enrichment factor, geoaccumulation index and ecological risk index were also determined for these PTEs in the study area. Sediment and soil samples were found to be alkaline and non-saline (pH > 7.0; EC < 4500 μS cm^-1) with sodium and potassium as major ions. Iron (mg kg^-1) was found to be most abundant in sediments (1477.59-6512.45) and soils (922.64-12,455.00). Cadmium content in sediments exceeded the threshold value (0.99 mg kg^-1) at 2 (pre-monsoon) and 3 (post-monsoon) sampling sites. In both seasons, cadmium (0.10-2.05) and cobalt (11.40-17.52) contents (mg kg^-1) exceeded the threshold limits (0.06 and 8.00 respectively) in all roadside soils. Significant spatiotemporal variation (p ≤ 0.05) was observed for pH; EC; and calcium, magnesium, copper, iron and zinc contents. Low to moderate potential ecological risk was observed for both roadside soils (31.80-213.82) and sediments (41.47-236.73). Contamination factor, enrichment factor and geoaccumulation index for cadmium were highest in roadside soils (6.84, 46.91 and 2.19, respectively) and sediments (7.64, 167.46 and 2.35, respectively) due to settlement of coal fly ash released from the industrial setups, on sediments/soils of the study area.

Assessment of Potentially Toxic Elements in the Urban Soil and Plants of Kirkuk City in Iraq

Kirkuk city is known for its industrial activities, especially oil and cement production, as well as its road traffic. The aim of this study was to assess potentially toxic elements (PTEs) in the soil and plants from urban areas by measuring pollution indices and estimating the effect that this pollution has on the environment. Leaf and soil samples were taken from 10 different locations in Kirkuk. These samples were pre-treated using the acid digestion method and concentrations of 12 elements were determined using inductively coupled plasma mass spectrometry (ICP-MS). The results indicate a high content of aluminum and magnesium (mg/kg) in the soil samples from all study sites. For leaf samples, the results showed a moderate to low amount of magnesium and aluminum. Based on our results, the PTE concentrations were found in the following order—Mg > Al > Ni > Cu > Cr > Pb > Co > As > Se > Cd > Hg > Ti—in leaf samples from all 10 study sites. However, in the soil samples, PTE concentrations were in the following order—Mg > Al > Cr > Ni > Cu > Pb > Co > As > Se > Ti > Cd > Hg—from all study sites. Pollution indices showed a moderate level of contamination of Pb, Cd, and Ni, and a high level of contamination of As and Hg in plant and soil samples from all study sites in Kirkuk city.

Effects of citric acid on antioxidant system and carbon-nitrogen metabolism of Elymus dahuricus under Cd stress

Exogenous citric acid (CA), which acts as an important intermediate product of the tricarboxylic acid (TCA) cycle, can enhance the TCA cycle activity and activate the branched operation of the TCA cycle, thus providing energy required for resistance to adverse conditions. However, the effects of CA application on TCA cycle-related metabolism under cadmium (Cd) were less reported. To investigate the effects of CA on the Cd tolerance of Dahurian wildrye grass (Elymus dahuricus), the growth, Cd accumulation, antioxidant systems and metabolic pathways of leaves and roots were investigated by a potted soil experiment with Cd (50 mg/kg) and CA (4 mmol/L) treatments. The results showed that Cd stress seriously affected growth and induced the production of reactive oxygen in clover leaves and roots, leading to membrane peroxidation and activation of the antioxidant defense system. Exogenous CA could not only effectively relieve the inhibition of Cd stress on growth and reduce the amount of reactive oxygen by increasing the antioxidant capacities but could also promote an increase in root Cd content. Metabolomic results showed that the application of CA increased the contents of sugars, sugar alcohols, and resistant substances, and promoted the metabolism of amino acids including γ-aminobutyric acid (GABA). These alterations contributed the significant enhancement of the Cd resistance, which may be related to the changes in the TCA cycle activity and the metabolism of the shikimic acid pathway in leaves and roots as well as GABA shunt in roots.

Toxicity of Cadmium and nickel in the context of applied activated carbon biochar for improvement in soil fertility

Toxicity induced by heavy metals deteriorates soil fertility status. It also adversely affects the growth and yield of crops. These heavy metals become part of the food chain when crops are cultivated in areas where heavy metals are beyond threshold limits. Cadmium (Cd) and nickel (Ni) are considered the most notorious ones among different heavy metals. The high water solubility of Cd made it a potential toxin for plants and their consumers. Accumulation of Ni in plants, leaves, and fruits also deteriorates their quality and causes cancer in humans when such a Ni-contaminated diet is used regularly. Both Cd and Ni also compete with essential nutrients of plants, making the fertility status of soil poor. To overcome this problem, the use of activated carbon biochar can play a milestone role. In the recent past application of activated carbon biochar is gaining more and more attention. Biochar sorb the Cd and Ni and releases essential micronutrients that are part of its structure. Many micropores and high cation exchange capacity make it the most acceptable organic amendment to improve soil fertility and immobilize Cd and Ni. In addition to improving water and nutrients, soil better microbial proliferation enhances the soil rhizosphere ecosystem and nutrient cycling. This review has covered Cd and Ni harmful effects on crop yield and their immobilization by activated carbon biochar. The focus was made to elaborate on the positive effects of biochar on crop yield and soil health.

Assessment of the Heavy Metal Contamination of Roadside Soils Alongside Buddha Nullah, Ludhiana, (Punjab) India

The present study was carried out to determine the physico-chemical characteristics and heavy metal contents in roadside soil samples collected during 2 sampling periods (September 2018 and April 2019) from 8 different roadside sites lying parallel to the Buddha Nullah, an old rivulet, flowing through Ludhiana, (Punjab) India. The contents (mg/kg) of seven metals (cadmium, chromium, cobalt, copper, lead, nickel and zinc) were estimated using a flame atomic absorption spectrophotometer. Among the metals analyzed, the contents of Cd, Co, Cu, Pb and Zn were found above the permissible limits. The results of the index of geoaccumulation (Igeo), contamination factor (CF), contamination degree (Cdeg), modified contamination degree (mCdeg), the Nemerow pollution index (PI) and pollution load index (PLI) indicate a moderate to high heavy metal contamination of the analyzed soil samples. The results of the potential ecological risk factor (ERi) and potential ecological risk index (RI) indicate a low to moderate risk of heavy metals in the studied soil samples. The Pearson correlation analysis revealed that most of the variables exhibited a statistically significant correlation with one or more variables during the two samplings. Multivariate analysis demonstrates that contents of heavy metals in the study area are influenced by anthropogenic and geogenic factors.

Phytoremediation of Cadmium Polluted Soils: Current Status and Approaches for Enhancing

Cadmium (Cd) is a heavy metal present in atmosphere, rocks, sediments, and soils without a known role in plants. It is relatively mobile and can easily enter from soil into groundwater and contaminate the food chain. Its presence in food in excess amounts may cause severe conditions in humans, therefore prevention of cadmium entering the food chain and its removal from contaminated soils are important steps in preserving public health. In the last several years, several approaches for Cd remediation have been proposed, such as the use of soil amendments or biological systems for reduction of Cd contamination. One of the approaches is phytoremediation, which involves the use of plants for soil clean-up. In this review we summarized current data on the use of different plants in phytoremediation of Cd as well as information about different approaches which have been used to enhance phytoremediation. This includes data on the increasing metal bioavailability in the soil, plant biomass, and plant accumulation capacity as well as seed priming as a promising novel approach for phytoremediation enhancing.

Phycoremediation of contaminated water by cadmium (Cd) using two cyanobacterial strains (Trichormus variabilis and Nostoc muscorum)

Background

Water pollution with heavy metals is a severe dilemma that concerns the whole world related to its risk to natural ecosystems and human health. The main objective was to evaluate the removal efficiency of Cd of various concentrations from contaminated aqueous solution by use of two cyanobacterial strains (Nostoc muscorum and Trichormus variabilis). For this purpose, a specially designed laboratory pilot-scale experiment was conducted using these two cyanobacterial strains on four different initial concentrations of Cd (0, 0.5, 1.0 and 2.0 mg L−1) for 21 days.

Results

N. muscorum was more efficient than T. variabilis for removing Cd (II), with the optimum value of residual Cd of 0.033 mg L−1 achieved by N. muscorum after 21 days with initial concentration of 0.5 mg L−1, translating to removal efficiency of 93.4%, while the residual Cd (II) achieved by T. variabilis under the same conditions was 0.054 mg L−1 (89.13% removal efficiency). Algal growth parameters and photosynthetic pigments were estimated for both cyanobacterial strains throughout the incubation period.

Conclusions

High Cd concentration had a more toxic impact on algal growth. The outcomes of this study will help to produce treated water that could be reused in agrarian activities.

Alleviation of Cadmium Phytotoxicity Using Silicon Fertilization in Wheat by Altering Antioxidant Metabolism and Osmotic Adjustment

Humans are facing very serious health threats from food contamination with cadmium (Cd), and Cd uptake by wheat is amongst the main causes of Cd entrance into the food chain. The current study examined the effect of foliar application (0, 1.50, 3.00 and 4.00 mM) of various silicate chemicals (calcium silicate and potassium silicate) on wheat growth and Cd addition by wheat under Cd stress 20 mg kg−1 of soil using CdCl2. The results revealed that under control conditions, the application of Si improved all the growth, physiological, biochemical and quality attributes by reducing malondialdehyde contents and electrolyte leakage. Under Cd stress, the supplementation of Si conferred a better growth rate, gaseous exchange for metabolic activity and maintained the tissues’ turgor and membranes’ stabilities compared to those obtained under control (without Si). The enzymatic activities (superoxide dismutase, peroxidase and catalase) also show rapid action by the application of Si supplement, which were associated with elevated osmoprotectant contents and antioxidants, having role in antioxidant defense against Cd stress. These results suggested that a 4.50 mM concentration of Si supplement (potassium silicate) works effectively against Cd stress. The given results showed that Si supplement is beneficial for the enhancement of many metabolic activities that takes places in plants during the growth period that proved a feasible approach in controlling the Cd concentration within wheat plants and, ultimately, in humans.

Toxicological Analysis of Gonad Development in Green Mussels (Perna viridis) in Jakarta Bay, Indonesia

&lt;b&gt;Background and Objective:&lt;/b&gt; The accumulation of heavy metals such as cadmium and lead in mussels is very high compared to that in another marine biota. The mussels are sessile, widely distributed filter-feeding organisms, with the ability to sequester many lipophilic organic compounds, absorb anything in their surroundings. The very low mobility allows heavy metal bioaccumulation to occur and cannot avoid pollutants, which increase over time. This bioaccumulation can be toxic to mussels. This study aimed to evaluate the effect of different toxic chemicals and histological changes in green mussels. &lt;b&gt;Materials and Methods:&lt;/b&gt; All archive gonad sample of green mussels in 2015 was fixed in paraformaldehyde 4% solution and were sliced by a rotary microtome at 8 μm thickness and finally, the slides were stained with a solution of hematoxylin-eosin. &lt;b&gt;Results:&lt;/b&gt; The obtained results demonstrated that developmental disorders in the testes are characterized by the arrangement of follicle cells in a relatively less dense state and some follicles are not fully filled with spermatozoa. It means that the male gonad samples of green mussels in the port of Muara Angke undergoing toxicity and the process of gonad developmental was disrupted. &lt;b&gt;Conclusion:&lt;/b&gt; The effects of toxicity of the male gonad of green mussels were more sensitive and were more susceptible than the female gonad of the green mussels.

Iron oxide nanoparticles ameliorated the cadmium and salinity stresses in wheat plants, facilitating photosynthetic pigments and restricting cadmium uptake

Cadmium and salinity are the major threats to environmental resources and agricultural practice worldwide. The present work aims green synthesis, characterization, and application of iron oxide nanoparticles for co-alleviation of Cd and salt stresses in wheat plants. The iron oxide NPs were synthesized from a native bacterial strain, Pantoea ananatis strain RNT4, yielding a spherical FeO-NPs with a size ranging from 19 to 40 nm evidenced by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images. Results showed that application of 100 mg kg^-1 of the bioengineered FeO-NPs in an original saline soil stimulated wheat plant growth, gaining 36.7% of additional length as compared with the control scenarios, via alleviating the detrimental effects of abiotic stresses and thereby reprogramming the morpho-physiological state of wheat plants. In addition, the presence of FeO-NPs in soil significantly increased the nutrient concentrations of N, P and K⁺, while reducing the Na⁺ and Cl^- components in the wheat grain. Interestingly, application of the FeO-NPs in Cd-polluted soils eventually reduced wheat plant uptake of Cd by 72.5%, probably due to the adsorption of Cd onto the large surface of NPs and thereby, constraining Cd bioavailability to the plants. It provides the first evidence that a FeO-NPs-based treatment could be a candidate agricultural strategy for mitigating the Cd and salt stresses in Cd-polluted saline soils for safe agriculture practice.

Transcriptome sequencing reveals genes involved in cadmium-triggered oxidative stress in the chicken heart

As a ubiquitous heavy metal, cadmium (Cd) is highly toxic to various organs. However, the effects and molecular mechanism of Cd toxicity in the chicken heart remain largely unknown. The goal of our study was to investigate the cardiac injury in chickens' exposure to Cd. We detected the levels of oxidative stress-related molecules in the Cd-induced chicken heart, and assessed the histopathological changes by hematoxylin and eosin staining. RNA sequencing was performed to identify differentially expressed mRNAs between the Cd-induced group and control group. The expression of candidate genes involved in oxidative stress was certified by quantitative reverse transcription PCR. Our results showed that the expression of glutathione, peroxidase, and superoxide dismutase was significantly decreased and malondialdehyde was increased in the heart of chickens by Cd induction. The disorderly arranged cardiomyocytes, swelled and enlarged cells, partial cardiomyocyte necrosis, blurred morphological structure, and notable inflammatory cell infiltration were observed in the Cd-induced chicken heart. RNA sequencing identified 23 upregulated and 11 downregulated mRNAs in the heart tissues of the chicken in the Cd-induced group, and functional pathways indicated that they were associated with oxidative stress. Moreover, CREM, DUSP8, and ITGA11 expressions were significantly reduced, whereas LAMA1 expression was induced in heart tissue of chickens by Cd treatment. Overall, our findings revealed that oxidative stress and pathological changes in the chicken heart could be triggered by Cd. The mRNA transcriptional profiles identified differentially expressed genes in the chicken heart by Cd induction, revealing oxidative stress-related key genes and enhancing our understanding of Cd toxicity in the chicken heart.

Contamination of rice crop with potentially toxic elements and associated human health risks-a review

Production of rice, a major staple food crop, should be maintained both quantitatively and qualitatively to assure global food security. In recent decades, various natural (biogeochemical weathering of rocks) and anthropogenic (increased application of agrochemicals, solid and liquid waste discharges from domestic and industrial areas, vehicular pollution, etc.) activities have deteriorated soil and water resources by contributing potentially toxic elements (PTEs) to the environment. Shortage of land resources and requirements of the ever-increasing human population has led to increasing global trend of rice cultivation in contaminated soils, causing accumulation of various PTEs such as arsenic (As), mercury (Hg), cobalt (Co), cadmium (Cd), copper (Cu), lead (Pb), and nickel (Ni) in rice crop, especially in the grains. Rice plants uptake and accumulate PTEs leading to their entry into the food chain. Consumption of rice contaminated with PTEs disturbs the human metabolism as PTEs interfere with different physiological/molecular mechanisms causing various health problems such as weak bones; skin problems; respiratory, cardiovascular, endocrine, nervous, reproductive, and hepatic disorders; and cancer. Possible non-carcinogenic and carcinogenic health risks have been determined in some studies by following the guidelines provided by various governmental or non-governmental agencies. Considering these facts, the present study was conducted to give a broader perspective on rice contamination with various potentially toxic elements, their bioconcentration in rice, associated health risks in human beings, and strategies for bioremediation of soil and water resources to eliminate PTEs.

Nanoparticle-based amelioration of drought stress and cadmium toxicity in rice via triggering the stress responsive genetic mechanisms and nutrient acquisition

Cadmium and drought are the most destructive of the abiotic stresses with negative consequences in terms of impaired metabolism, restricted nutrient use efficiency and disruptive photosynthesis of plants. The present study investigated the mitigation strategy of both aforementioned stresses by the application of iron oxide (IONPs) and hydrogel nanoparticles (HGNPs) simultaneously probably for the first time. IONPs were biofabricated by using a locally identified Bacillus strain RNT1, while HGNPs were produced chemically followed by the confirmation and characterization of both NPs through nanomaterials characterization techniques. Results of FTIR and XRD showed the capping of NPs by different functional groups together with their crystalline structure, respectively. SEM and TEM analysis showed the spherical shape along with the particle size ranging from 18 to 94 nm of both NPs, while EDS analysis confirmed the elemental purity of NPs. The results revealed that IONPs-treated rice plants increased biomass, antioxidant enzyme contents, photosynthesis efficiency, nutrient acquisition together with the decrease in reactive oxygen species and acropetal Cd translocation under normal and drought stress conditions as compared with control plants. Furthermore, the expression of the Cd transporter genes, OsHMA2, OsHMA3 and OsLCT1 were curtailed in NPs-treated rice plants under normal and drought stress conditions. The overall significance of the study lies in devising the NPs-based solutions of increasing heavy metal pollution and water availability challenges being faced the farmers around the world.

Biogenic copper nanoparticles synthesized by using a copper-resistant strain Shigella flexneri SNT22 reduced the translocation of cadmium from soil to wheat plants

The mechanistic role of green copper nanoparticles (CuNPs) in cadmium (Cd) toxicity alleviation in plants is poorly understood. Here, the CuNPs, synthesized by using a bacterium Shigella flexneri SNT22, were confirmed through UV-vis spectroscopy with a characteristic peak at 334.50 nm. Moreover, FT-IR, XRD, SEM, and TEM techniques revealed that the spherical shaped crystals of CuNPs with a size range of 17.24 nm to 38.03 nm were stabilized by coating proteins. Diff ;erent levels of CuNPs (e.g., 25, 50, and 100 mg kg^-1 of soil) were examined in pots having Cd-mixed soil to evaluate their effect on wheat plants in a growth chamber under optimal environmental conditions. Treatment of soil with 100 mg kg^-1 of CuNPs increased plant length by 44.4 %, shoot dry weight by 28.26 %, nitrogen contents by 41.60 %, and phosphorus contents by 58.79 %, whereas decreased the acropetal Cd translocation by 49.62 %. An increase in the N, P, K⁺, Ca²⁺, K⁺/Na⁺, and Ca²⁺/Na⁺ contents and decrease in the Na⁺ concentration in wheat plants treated with CuNPs was also recorded. Overall, the results are valuable to establish a green CuNPs-based approach for sustainable wheat growth in metal-contaminated soils.

Ecotoxicological assessment after the world's largest tailing dam collapse (Fundão dam, Mariana, Brazil): effects on oribatid mites

Worldwide, environmental tragedies involving mining dam ruptures have become more frequent. As occurred a few years ago in Brazil (on 5 November 2015, in Minas Gerais state) the Fundão Dam rupture released 60 million m³ of tailings into terrestrial and aquatic ecosystems. Since then, little information on the ecotoxicity of these tailings has been disclosed. In the laboratory, the acute, chronic and bioaccumulation effects of increased Fundão tailing concentrations on oribatid mites (Scheloribates praeincisus) were assessed. Additionally, the bioaccumulation of 11 trace metals (Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn) and the total density of oribatid mites found in the areas contaminated by the Fundão tailings were determined. The percentages of mite survival and reproductive inhibition were higher than 60% and 80%, respectively, in all contaminated areas with the highest concentration (100% mine tailings). Field studies showed an expressive reduction in the total density of oribatids per m^-2 (up to 54 times) in the contaminated areas compared with the reference area. Metal accumulations in the field were 5.4 and 3.2 higher (for Ni and Hg, respectively) and up to two times higher (for most metals) than those in the laboratory for 42 days. The mite responses to the Fundão tailings found in this study suggest long-term interference in their biological development. In this sense, we can conclude that the introduction of mine tailings onto soils tended to compromise the functionality of the mites in the ecosystem, which causes imbalances to cascade other organisms of the trophic web.

Heavy Metals in Wastewater and Sewage Sludge from Selected Municipal Treatment Plants in Eastern Cape Province, South Africa

This study assessed the distribution of five heavy metals (Cd, Pb, Cu, Zn, and Fe) across the various stages of treatment in three selected sewage treatment facilities and their receiving waterbodies in the Eastern Cape Province, South Africa. Aqueous and solid (sludge) samples were collected monthly from September 2015 to February 2016. Quantitation was achieved by atomic absorption spectrometry after necessary sample preparations. Concentrations of heavy metal cations in the sludge generally varied from <DL (below detection limit) to 1.17 mg kg−1, <DL to 0.14 mg kg−1, 27.588 to 69.789 mg kg−1, and <DL to 0.099 mg kg−1 for Cu, Cd, Fe and Pb; while Zn was below detection all through. Similarly, the levels of Cu, Cd, and Fe in the influents, effluents, upstream and downstream across the three plants ranged from <DL–6.588 mg L−1, <DL–0.636 mg L−1, <DL–0.878 mg L−1 and <DL–0.711 mg L−1, respectively; Zn and Pb were less than DL in all the matrices and study locations. All the contaminants were below hazardous levels in all the sludge and aqueous samples except Cd which was higher in effluents and surface waters across the board. Wastewater Treatment Plant (WWTP)-A exhibited better removal capacity for Fe (86.6%), compared to WWTP-B (34.7%) and WWTP-C (56.9%). However, the removal of Cu and Zn was very poor in all the treatment facilities studied. Carcinogenic and non-carcinogenic risks evaluated were sufficiently low. This suggests that the levels of contamination, even with respect to Cd, was minimal. Nevertheless, efforts should be made to keep the concentrations of these contaminants at levels safe for humans and aquatic organisms. Furthermore, the use of the effluents from these facilities for irrigation should be discouraged to prevent unnecessary build-up of metals in the soil and plants grown with such, as well as subsequent bioaccumulation and biomagnification in the food chain.

Biological Responses to Cadmium Stress in Liverwort Conocephalum conicum (Marchantiales)

Oxidative damage (production and localization of reactive oxygen species) and related response mechanisms (activity of antioxidant enzymes), and induction of Heat Shock Protein 70 expression, have been studied in the toxi-tolerant liverwort Conocephalum conicum (Marchantiales) in response to cadmium stress using two concentrations (36 and 360 µM CdCl₂). Cadmium dose-dependent production of reactive oxygen species (ROS) and related activity of antioxidant enzymes was observed. The expression level of heat shock protein (Hsp)70, instead, was higher at 36 µM CdCl₂ in comparison with the value obtained after exposure to 360 µM CdCl₂, suggesting a possible inhibition of the expression of this stress gene at higher cadmium exposure doses. Biological responses were related to cadmium bioaccumulation. Since C. conicum was able to respond to cadmium stress by modifying biological parameters, we discuss the data considering the possibility of using these biological changes as biomarkers of cadmium pollution.

Effects of EDTA, citric acid, and tartaric acid application on growth, phytoremediation potential, and antioxidant response of Calendula officinalis L. in a cadmium-spiked calcareous soil

The improved efficiency of cadmium (Cd) phytoextraction potential of Calendula officinalis L. was evaluated in Cd-spiked calcareous soil, using various chelating agents. In a greenhouse study, three chelating agents, including EDTA, citric acid (CA), and tartaric acid (TA), were applied to Cd-spiked soils (50 and 100 mg kg^-1) under C. officinalis L. cultivation. According to the results, C. officinalis grew normally without any toxicity signs at various Cd levels of the soil; however, with increasing the Cd levels, the plant dry weight biomass decreased, and activities of antioxidant enzymes (AOEs) increased. The application of CA and TA in Cd-spiked soils improved the physiologic traits of plants and mitigated the Cd stress since the activities of AOEs decreased. Oppositely, due to increasing the Cd excessive permeability to the root of the plant, EDTA application diminished the physiologic traits and increased the activities of AOEs. The results also showed that all the chelators, especially EDTA, markedly increased the Cd mobility factor (from 58.80% to 65.20-89.60%) in Cd-spiked soils. The bioconcentration factor (BCF = 1.3-2.90) and translocation factor (TF = 1.28-1.58) of Cd, which were >1 in all treated and untreated plant samples, as well as the accumulated Cd >100 mg kg^-1, demonstrated that C. officinalis is a Cd-hyperaccumulator plant which could remediate Cd by the phytoextraction process. Regarding the biodegradation of CA, as well as the increased TF efficiency of Cd and plant biomass of CA treatments (by decreasing oxidative stress), compared to EDTA and TA treatments, it is recommended that CA be used as a superior chelating agent to enhance the efficiency of Cd phytoremediation in C. officinalis.

Effects of Exogenous Organic Acids on Cd Tolerance Mechanism of Salix variegata Franch. Under Cd Stress

Chelate induction of organic acids has been recognized to enhance metal uptake and translocation in plants, but the underlying mechanism remains unclear. In this study, seedlings of Salix variegata were hydroponically exposed to the combinations of Cd (0 and 50 μM) and three exogenous organic acids (100 μM of citric, tartaric, or malic acid). Plant biomass, antioxidant enzymes, non-protein thiol compounds (NPT) content, and the expression of candidate genes associated with Cd accumulation and tolerance were determined. Results showed that Cd significantly inhibited plant biomass but stimulated the activity of antioxidant enzymes in the roots and leaves, while the lipid peroxidation increased as well. Respective addition of three organic acids greatly enhanced plant resistance to oxidative stress and reduced the lipid peroxidation induced by Cd, with the effect of malic acid showing greatest. The addition of organic acids also significantly increased the content of glutathione in the root, further improving the antioxidant capacity and potential of phytochelatin biosynthesis. Moreover, Cd induced the expression level of candidate genes in roots of S. variegata. The addition of three organic acids not only promoted the expression of candidate genes but also drastically increased Cd accumulation in S. variegata. In summary, application of citric, tartaric, or malic acid alleviated Cd-imposed toxicity through the boost of enzymatic and non-enzymatic antioxidants and candidate gene expression, while their effects on Cd tolerance and accumulation of S. variegata differed.

Effects of aluminium and cadmium on hatching and swimming ability in developing zebrafish

Aluminium and cadmium are biologically non-essential metals with a role in neurodegenerative and neuromuscular diseases. As an attractive model for neurobehavioural studies, zebrafish at 6 h post fertilization were exposed to 9, 18, 36 and 72 μM CdCl₂ and 50, 100 and 200 μM AlCl₃, respectively, for 72 h, and motility such as distance moved, mean velocity, cumulative movement, meander and heading were measured by DanioVision equipment. The hatching time was also analysed. A delay in the exit from the chorion was observed in all treated larvae with respect to the controls. CdCl₂ acted on the exit from the chorion of larvae with a dose-dependent delay. By contrast, the delay caused by AlCl₃ was greater at low concentrations. A dose-dependent reduction in swimming performance was observed in the larvae exposed to CdCl₂. Instead, for those exposed to AlCl₃, swimming performance improved at higher concentrations although values were in general lower than those of control. All the parameters had a similar trend except the meander parameter which showed a dose-dependent reduction. These data show that cadmium and aluminium can delay hatching and alter swimming ability in the early developmental stages of zebrafish, albeit with different effects, suggesting that exposure to sublethal concentrations of both metals can change behavioural parameters.

Cd induced generation of free radical species in Brassica juncea is regulated by supplementation of earthworms in the drilosphere

The antioxidant defense system of Brassica juncea under Cd stress was examined on supplementation of earthworms in the rhizosphere at different concentrations of Cd (0.50, 0.75, 1.00 and 1.25 mM i.e. 56, 84, 112 and 140 mg kg^-1 respectively). Seedlings were raised in small pots containing soil spiked with Cd and earthworms under controlled conditions for 15 days. Improved Cd accumulation, as well as enhanced plant dry weight and metal tolerance were observed following the addition of earthworms. Earthworm supplementation reduced reactive oxygen species (ROS) generation by 7.3% for hydrogen peroxide (H₂O₂), 7.1% for superoxide anion (O₂^-), and 8.4% for malondialdehyde (MDA) in plants treated with 1.25 mM (140 mg kg^-1) Cd. Confocal microscopy revealed improved cell viability and reduced H₂O₂ content due to enhanced antioxidative activity. Activity and expression levels of genes coding for antioxidative enzymes (superoxide dismutase; SOD, catalase; CAT, guaicol peroxidase; POD, glutathione reductase; GR, and glutathione-S-transferase; GST) were higher in plants raised in soils inoculated with earthworms, with expression of SOD increasing by 58.8%, CAT by 75%, POD by 183%, GR by 106.6%, and GST by 11.8%. Moreover, plant pigment (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids) concentrations increased by 8%, 9.1%, 9.1%, and 7.7% respectively, in plants grown in soils supplemented with earthworms. The results of our study suggest that the addition of earthworms to soil increases antioxidative enzyme activities, gene expression in plants, and ROS inhibition, which enhances tolerance to Cd during the phytoextraction process.

Breeding Low-Cadmium Wheat: Progress and Perspectives

Farmland cadmium (Cd) contamination has adverse impacts on both wheat grain yield and people’s well-being through food consumption. Safe farming using low-Cd cultivars has been proposed as a promising approach to address the farmland Cd pollution problem. To date, several dozen low-Cd wheat cultivars have been screened worldwide based on a Cd inhibition test, representing candidates for wheat Cd minimization. Unfortunately, the breeding of low-Cd wheat cultivars with desired traits or enhanced Cd exclusion has not been extensively explored. Moreover, the wheat Cd inhibition test for variety screening and conventional breeding is expensive and time-consuming. As an alternative, low-Cd wheat cultivars that were developed with molecular genetics and breeding approaches can be promising, typically by the association of marker-assisted selection (MAS) with conventional breeding practices. In this review, we provide a synthetics view of the background and knowledge basis for the breeding of low-Cd wheat cultivars.

Comparative analysis of cadmium-induced stress responses by the aromatic and non-aromatic rice genotypes of West Bengal

Constant exposure of the living ecosystems to heavy metals, like cadmium (Cd), induces a detectable change at the biochemical and genetic level. Repeated application of phosphate fertilizers in paddy fields, leads to increase in Cd content of soil. Cd being highly mobile is transported to shoot and grain, thereby entering into the food chain of animal system. In the present study, treatment of 7-day old rice seedlings with 10 μM cadmium chloride resulted in Cd toxicity across the seven non-aromatic and six aromatic rice cultivars and landraces used for the study. Free proline and malondialdehyde content of treated samples were higher in comparison to the untreated samples, which indicated Cd induced tissue damage in plants. Photosynthetic pigment content of treated samples was also found to be much lower in comparison to the untreated samples, which is probably due to peroxidation of membrane, leading to compromised and lower photosynthetic efficiency of treated plants. At the genetic level, Randomly Amplified Polymorphic DNA assay was found to efficiently detect the genetic polymorphisms (caused by alterations in DNA bases) induced by Cd. Production of unique polymorphic bands in Cd-treated plants helps in assessment of the degree of damage Cd imparts on the plant system. Cluster analysis was performed and the rice genotypes were grouped into five distinct clusters, with IR64 and Tulsibhog in two distinct groups. Based on the variability in responses, the 13 rice genotypes were grouped into sensitive and tolerant ones.

Cadmium-induced conformational changes in type 2 metallothionein of medicinal plant Coptis japonica: insights from molecular dynamics studies of apo, partially and fully metalated forms

Plants play an important role in the removal of excess heavy metals from soil and water. Medicinal plants can also have non-traditional use in phytoremediation technologies. Among the heavy metals, Cadmium (Cd) is the most abundant and readily taken up by the crop plants. Plant metallothioneins (MTs) are small proteins having cysteine-rich residues and appear to play key roles in metal homoeostasis. Plant metallothionein 2 (MT 2) from Coptis japonica (Gold-thread; CjMT 2) is a typical member of this subfamily and features two cysteine-rich regions containing eight and six cysteine residues, respectively, separated by 42 amino acids long linker region. In-silico analysis of MT 2 protein sequences of C. japonica was performed. In this study, ab initio methods were utilised for the prediction of three-dimensional structure of CjMT 2. After structure validation, heavy metal-binding sites were predicted for the selected modelled structures of CjMT 2. To obtain Cd_i-CjMT 2 (i = 1-7), metalated complex individual docking experiments were performed. The stability of the metalated docked structures was assessed by molecular dynamics (MD) simulation studies. Our study showed that CjMT 2 binds up to 4 Cd²⁺ ions in two distinct domains: a N-terminal β-domain that binds to 2 Cd²⁺ ions and a C-terminal α-domain that binds with 2 Cd²⁺ ions. Our analysis revealed that Cys residues of alpha and beta domain and some residues of spacer region of CjMT 2 protein might be important for the cadmium interaction. MD simulation studies provided insight into metal-induced conformational changes and mechanism of metalation of CjMT 2, an intrinsically disordered protein. This study provides useful insights into mechanism of cadmium-type 2 metallothionein interaction.

Silicon deposition in roots minimizes the cadmium accumulation and oxidative stress in leaves of cowpea plants

Silicon (Si) frequently accumulates in plants tissues, mainly in roots of dicotyledons, such as cowpea. By contrast, Cadmium (Cd) is a metal that is extremely toxic to plant metabolism. This research aims to investigate if the deposition of Si in root can reduce Cd contents and minimize its negative effects on leaves, measuring gas exchange, chlorophyll fluorescence, antioxidant metabolism, photosynthetic pigments and growth, which may explain the possible role of Si in the attenuation of Cd toxicity in cowpea. This study had a factorial design, with all factors completely randomized and two Cd concentrations (0 and 500 µM Cd, termed as - Cd and + Cd, respectively) and three Si concentrations (0, 1.25 and 2.50 mM Si). Si reduced Cd contents in the roots and in other plant organs, such as stems and leaves. The Si contents were highest in roots, followed by stems and leaves, which was explained by the passive absorption of Si. The application of Si promoted increase in both the macro- and micronutrient contents in all tissues, suggesting that Si mitigates the effect of Cd on nutrient uptake. Si attenuated Cd-mediated effects on light absorption of photosystem II (PSII), increasing the effective quantum yield of PSII photochemistry and the electron transport rate. Additionally, toxic effects induced by Cd on gas exchange were mitigated by the action of Si. Plants treated with Cd + Si showed increase in the activities of antioxidant enzymes and reductions in oxidant compounds; these modifications were promoted by Si via detoxification mechanisms. Increases in the photosynthetic pigments and growth of plants treated with Si and exposed to Cd stress were detected and were due to the reduced deterioration of cell membranes and maintenance of chloroplasts, which had positive repercussions on growth and development. This study validated the hypothesis that the accumulation of Si in roots induces benefits on metabolism and alleviates the toxic effects caused by Cd in leaves of cowpea.

Genetic, Reproductive and Hematological Toxicity Induced in Mice Exposed to Leachates from Petrol, Diesel and Kerosene Dispensing Sites

BACKGROUND

With a population of over 165,000,000, growing at an average rate of 2.7% per annum and an economic growth rate of about 5.7% in the past five years, the market for refined petroleum products in Nigeria is growing. As a result, the number of filling stations is increasing.

OBJECTIVES

The present study evaluated the reproductive and genetic toxicity of simulated leachate of soil from petrol, diesel and kerosene dispensing sites in a filling station using the murine sperm abnormality test, sperm count and bone marrow micronucleus assay.

METHODS

Simulated leachate of soil collected from petrol, diesel and kerosene dispensing sites in a filling station was intraperitoneally administered to mice at different concentrations. Bone marrow micronucleus assay was carried out after 5-days exposure, while sperm morphology assay was carried out 35 days from the first day of exposure. Alterations to hematological parameters were evaluated and physico-chemical analysis of the leachate samples was also carried out.

RESULTS

The results showed a significant (p<0.05) concentration-dependent increase in abnormal sperm cells and decrease in mean sperm count in all the samples tested. Increased induction of micronucleated polychromatic erythrocytes was observed in the exposed mice. Hematological analysis showed a significant (p<0.05) increase in the values of white blood cell count (WBC), lymphocytes, neutrophils, monocytes, eosinophils and mean corpuscular volume (MCV), while a significant (p<0.05) reduction in basophils, hemoglobin, mean corpuscular hemoglobin (MCH), packed cell volume and mean corpuscular hemoglobin concentration (MCHC) values were observed.

DISCUSSION

In the present study, simulated leachates from soil obtained from petrol, diesel and kerosene dispensing sites were shown to cause genomic disruptions in germ and somatic cells, and hematotoxicity in an animal model. These observed reproductive, genetic and hemato-toxicities are believed to be caused by the presence of lead, copper, mercury, polycyclic aromatic hydrocarbons, and benzene in the samples.

CONCLUSIONS

This study showed the negative impact of petroleum products in the contamination of soil, with a capability of inducing genetic damage in somatic and germ cells of exposed plants and animals.

ETHICS APPROVAL

The study was approved by the ethical committee of the Federal University of Technology, Akure, Ondo State, Nigeria.

Cadmium phytoextraction from loam soil in tropical southern China by Sorghum bicolor

The cadmium (Cd) uptake characteristics by Sorghum bicolor cv. Nengsi 2# and Cowley from the acidic sandy loam soil (pH = 6.1) during the entire growth period (100 days) were investigated in pot outdoors in a tropical district of southern China, Hainan Island. The Cd-spiked levels in soil were set as 3 and 15 mg/kg. Correspondingly, the available Cd levels in soil extracted by Mehlich III solution were 2.71 and 9.41 mg/kg, respectively. Basically, two varieties in a full growth period (100 days) did not show a significant difference in their growth and Cd uptake. Under high Cd stress, the plant growth was inhibited and its biomass weight and height decreased by 38.7-51.5% and 27.6-28.5%, respectively. However, S. bicolor showed higher bioaccumulation capability of Cd from soil to plant [bioconcentration factor (BCF)>4], and higher transfer capability of Cd from roots to shoots [translocation factor (TF)>1] under high Cd stress; Cd contents in the roots, stems, and leaves of S. bicolor reached 43.79-46.07, 63.28-70.60, and 63.10-66.06 mg/kg, respectively. S. bicolor exhibited the potential phytoextraction capability for low or moderate Cd-contamination in acidic sandy loam soil.

Heavy metals in drinking water: Occurrences, implications, and future needs in developing countries

Heavy metals in drinking water pose a threat to human health. Populations are exposed to heavy metals primarily through water consumption, but few heavy metals can bioaccumulate in the human body (e.g., in lipids and the gastrointestinal system) and may induce cancer and other risks. To date, few thousand publications have reported various aspects of heavy metals in drinking water, including the types and quantities of metals in drinking water, their sources, factors affecting their concentrations at exposure points, human exposure, potential risks, and their removal from drinking water. Many developing countries are faced with the challenge of reducing human exposure to heavy metals, mainly due to their limited economic capacities to use advanced technologies for heavy metal removal. This paper aims to review the state of research on heavy metals in drinking water in developing countries; understand their types and variability, sources, exposure, possible health effects, and removal; and analyze the factors contributing to heavy metals in drinking water. This study identifies the current challenges in developing countries, and future research needs to reduce the levels of heavy metals in drinking water.

Early interconnectivity between metabolic and defense events against oxidative stress induced by cadmium in roots of four citrus rootstocks

The effect of cadmium on roots of four citrus rootstocks was studied to assess the relationships between oxidative stress, carbohydrates, phenolics and antioxidant responses. Swingle citrumelo (SC), Rangpur lime (RL), Troyer citrange (TC) and Volkamer lemon (VL) genotypes were exposed to 0, 5 and 10µM Cd over 7 days, after which Cd accumulation was markedly higher in roots compared with stems and leaves. Malondialdehyde (MDA) and lipoxygenase (LOX) activity increased in Cd-treated SC and RL roots, suggesting that a lipid peroxidation is the main driver of plasma membrane damage. In contrast, in TC and VL genotypes, LOX-mediated lipid peroxidation does not appear to play a key role in Cd-induced lipid peroxidation, but H2O2 accumulation seems to be responsible of less plasma membrane damage. Catalase (CAT), superoxide dismutase (SOD) and guaiacol and syringaldazine peroxidases (G-POD and S-POD respectively) were differentially affected by Cd. Lipid profile and ATPase-dependant proton extrusion indicated higher disfunctionalities of root plasma membrane in SC and RL genotypes than in TC and VL genotypes. Differences in carbohydrates and phenolic compounds were also observed. Histochemical analysis of G-POD activity and lignin and suberin deposition revealed differences among genotypes. A model to explain the relationships among carbohydrates, soluble phenolics, lipid peroxidation and H2O2 accumulation in Cd-exposed roots was proposed.

Phytoextraction of Cd and Zn as single or mixed pollutants from soil by rape (Brassica napus)

This paper analyses the capacity of the rape (Brassica napus) to extract Cd and Zn from the soil and the effect of these metals on the morphometric parameters of the plant (length, weight, surface area, fractal dimension of leaves). Rape plants were mostly affected by the combined toxicity of the Cd and Zn mixture that caused a significant reduction in the rate of seed germination, the plant biomass quantity and the fractal dimension. In the case of Cd soil pollution, the bioaccumulation factor (BAF), bioaccumulation coefficient (BAC) as well as the heavy metal root-to-stalk translocation factor (TF) were determined. The results showed that B. napus had a great potential as a cadmium hyperaccumulator but not as an accumulator of Zn or Cd + Zn mixture. The efficiency of phytoextraction rape was 0.8-1.22 % for a soil heavily polluted with cadmium.

Combined effect of Cd and Pb spiked field soils on bioaccumulation, DNA damage, and peroxidase activities in Trifolium repens

The present study was designed to investigate the combined effects of Cd and Pb on accumulation and genotoxic potential in white clover (Trifolium repens). For this purpose, T. repens was exposed to contaminated soils (2.5-20 mg kg(-1) cadmium (Cd), 250-2000 mg kg(-1) lead (Pb) and a mixture of these two heavy metals) for 3, 10 and 56 days. The resulting bioaccumulation of Cd and Pb, DNA damage (comet assay) and peroxidase activities (APOX and GPOX) were determined. The exposure time is a determinant factor in experiments designed to measure the influence of heavy metal contamination. The accumulation of Cd or Pb resulting from exposure to the two-metal mixture does not appear to depend significantly on whether the white clover is exposed to soil containing one heavy metal or both. However, when T. repens is exposed to a Cd/Pb mixture, the percentage of DNA damage is lower than when the plant is exposed to monometallic Cd. DNA damage is close to that observed in the case of monometallic Pb exposure. Peroxidase activity cannot be associated with DNA damage under these experimental conditions.

Toxicity, mechanism and health effects of some heavy metals

Heavy metal toxicity has proven to be a major threat and there are several health risks associated with it. The toxic effects of these metals, even though they do not have any biological role, remain present in some or the other form harmful for the human body and its proper functioning. They sometimes act as a pseudo element of the body while at certain times they may even interfere with metabolic processes. Few metals, such as aluminium, can be removed through elimination activities, while some metals get accumulated in the body and food chain, exhibiting a chronic nature. Various public health measures have been undertaken to control, prevent and treat metal toxicity occurring at various levels, such as occupational exposure, accidents and environmental factors. Metal toxicity depends upon the absorbed dose, the route of exposure and duration of exposure, i.e. acute or chronic. This can lead to various disorders and can also result in excessive damage due to oxidative stress induced by free radical formation. This review gives details about some heavy metals and their toxicity mechanisms, along with their health effects.

Assessment of cadmium accumulation, toxicity, and tolerance in Brassicaceae and Fabaceae plants--implications for phytoremediation

This study, based on a greenhouse pot culture experiment conducted with 15-day-old rapeseed (Brassica campestris L. cv. Pusa Gold; family Brassicaceae) and moong bean (Vigna radiata L. Wilczek cv. Pusa Ratna; family Fabaceae) plants treated with cadmium (Cd) concentrations (0, 50, and 100 mg kg(-1) soil), investigates their potential for Cd accumulation and tolerance, and dissects the underlying basic physiological/biochemical mechanisms. In both species, plant dry mass decreased, while Cd concentration of both root and shoot increased with increase in soil Cd. Roots harbored a higher amount of Cd (vs. shoot) in B. campestris, while the reverse applied to V. radiata. By comparison, root Cd concentration was higher in B. campestris than in V. radiata. The high Cd concentrations in B. campestris roots and V. radiata shoots led to significant elevation in oxidative indices, as measured in terms of electrolyte leakage, H2O2 content, and lipid peroxidation. Both plants displayed differential adaptation strategies to counteract the Cd burden-caused anomalies in their roots and shoots. In B. campestris, increasing Cd burden led to a significantly decreased reduced glutathione (GSH) content but a significant increase in activities of GSH reductase (GR), GSH peroxidase (GPX), and GSH sulfotransferase (GST). However, in V. radiata, increasing Cd burden caused significant increase in GSH content and GR activity, but a significant decline in activities of GPX and GST. Cross talks on Cd burden of tissues and the adapted Cd tolerance strategies against Cd burden-accrued toxicity indicated that B. campestris and V. radiata are good Cd stabilizer and Cd extractor, respectively, wherein a fine tuning among the major components (GR, GPX, GST, GSH) of the GSH redox system helped the plants to counteract differentially the Cd load-induced anomalies in tissues. On the whole, the physiological/biochemical characterization of the B. campestris and V. radiata responses to varying Cd concentrations can be of great help in elaborating the innovative plant-based remediation technologies for metal/metalloid-contaminated sites.