Toxic effects of cadmium on the physiological and biochemical attributes of plants, and phytoremediation strategies: A review

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.

Modulation of rhizosphere microbial community and metabolites by bio-functionalized nanoscale silicon oxide alleviates cadmium-induced phytotoxicity in bayberry plants

Cadmium (Cd) is an extremely toxic heavy metal that can originate from industrial activities and accumulate in agricultural soils. This study investigates the potential of biologically synthesized silicon oxide nanoparticles (Bio-SiNPs) in alleviating Cd toxicity in bayberry plants. Bio-SiNPs were synthesized using the bacterial strain Chryseobacterium sp. RTN3 and thoroughly characterized using advanced techniques. A pot experiment results demonstrated that Cd stress substantially reduced leaves biomass, photosynthesis efficiency, antioxidant enzyme activity, and induced oxidative damage in bayberry (Myrica rubra) plants. However, Bio-SiNPs application at 200 mg kg-1 significantly enhanced plant biomass, chlorophyll content (26.4 %), net photosynthetic rate (8.6 %), antioxidant enzyme levels, and mitigated reactive oxygen species production under Cd stress. Bio-SiNPs modulated key stress-related phytohormones by increasing salicylic acid (13.2 %) and abscisic acid (13.7 %) contents in plants. Bio-SiNPs augmented Si deposition on root surfaces, preserving normal ultrastructure in leaf cells. Additionally, 16S rRNA gene sequencing demonstrated that Bio-SiNPs treatment favorably reshaped structure and abundance of specific bacterial groups (Proteobacteria, Actinobacteriota, and Acidobacteriota) in the rhizosphere. Notably, Bio-SiNPs application significantly modulated the key metabolites (phenylacetaldehyde, glycitein, maslinic acid and methylmalonic acid) under both normal and Cd stress conditions. Overall, this study highlights that bio-nanoremediation using Bio-SiNPs enhances tolerance to Cd stress in bayberry plants by beneficially modulating biochemical, microbial, and metabolic attributes.

A comparative study on cadmium tolerance and applicability of two Solanum lycopersicum L. cultivars

Solanum lycopersicum L. can be classified into low Cd-accumulating and high Cd-accumulating types based on their accumulation characteristics of cadmium (Cd). There are many common S. lycopersicum varieties available in the market, but their specific Cd tolerance and enrichment abilities are not well understood. This article uses two S. lycopersicum cultivars, Yellow Cherry and Yellow Pearl, as experimental materials. The experimental method of soil pot planting was adopted, and Cd concentrations in the soil were added at 0, 0.6, 1.5, 2.5, 5, and 10 mg/kg. The changes in Cd content, biomass, photosynthetic pigment content, and photosynthetic parameters of the two S. lycopersicum cultivars were analyzed to screen for low-accumulation S. lycopersicum cultivars. The results showed that S. lycopersicum are Cd-sensitive plants. The Cd accumulation, photosynthetic parameters, and other basic indicators of Yellow Cherry basically showed significant differences when the soil Cd concentration was 0.6 mg/kg, and the biomass showed significant differences when the soil Cd concentration was 1.5 mg/kg. Except for the Cd accumulation in the roots and leaves of Yellow Pearl, which showed significant differences at a soil Cd concentration of 0.6 mg/kg, the other indicators basically showed significant differences when the soil Cd concentration was 1.5 mg/kg. When the soil Cd concentration was 0.6 mg/kg, the Cd accumulation in the fruit of Yellow Pearl was 0.04 mg/kg, making it a low-accumulation S. lycopersicum variety suitable for promoting cultivation in Cd-contaminated soil at 0.6 mg/kg. In conclusion, the Cd accumulation in the fruit of Yellow Pearl is significantly lower than that of Yellow Cherry and even below the Cd limit value for fresh vegetables specified in GB2762-2017. Therefore, Yellow Pearl can be grown as edible crops in soils with Cd concentrations ≤0.6 mg/kg. Furthermore, Yellow Cherry demonstrate strong Cd tolerance and can be used for the remediation of Cd-contaminated soils.

Recent trends in the phytoremediation of radionuclide contamination of soil by cesium and strontium: Sources, mechanisms and methods: A comprehensive review

This comprehensive review examines recent trends in phytoremediation strategies to address soil radionuclide contamination by cesium (Cs) and strontium (Sr). Radionuclide contamination, resulting from natural processes and nuclear-related activities such as accidents and the operation of nuclear facilities, poses significant risks to the environment and human health. Cs and Sr, prominent radionuclides involved in nuclear accidents, exhibit chemical properties that contribute to their toxicity, including easy uptake, high solubility, and long half-lives. Phytoremediation is emerging as a promising and environmentally friendly approach to mitigate radionuclide contamination by exploiting the ability of plants to extract toxic elements from soil and water. This review focuses specifically on the removal of 90Sr and 137Cs, addressing their health risks and environmental implications. Understanding the mechanisms governing plant uptake of radionuclides is critical and is influenced by factors such as plant species, soil texture, and physicochemical properties. Phytoremediation not only addresses immediate contamination challenges but also provides long-term benefits for ecosystem restoration and sustainable development. By improving soil health, biodiversity, and ecosystem resilience, phytoremediation is in line with global sustainability goals and environmental protection initiatives. This review aims to provide insights into effective strategies for mitigating environmental hazards associated with radionuclide contamination and to highlight the importance of phytoremediation in environmental remediation efforts.

Ecotoxicity of Cadmium along the Soil-Cotton Plant-Cotton Bollworm System: Biotransfer, Trophic Accumulation, Plant Growth, Induction of Insect Detoxification Enzymes, and Immunocompetence

Cadmium (Cd) is a hazardous element that may jeopardize environmental safety and human health through biotransfer and trophic accumulation. Here, we tested Cd toxicity on cotton plants, cotton bollworms, and their responses. Results demonstrated that Cd accumulated in plant roots, aerial parts, insect larvae, pupae, and frass in a dose-dependent pattern. The ∼9.35 mg kg-1 of Cd in plant aerial parts, ∼3.68 in larvae, ∼6.43 in pupae, and high transfer coefficient (∼5.59) indicate significant mobility. The ∼19.61 mg kg-1 of Cd in larvae frass suggests an effective detoxification strategy, while BAFcotton (∼1.14) and BAFworm (∼0.54) indicated low bioaccumulation. Cadmium exposure resulted in compromised plant growth and yield as well as alterations in photosynthetic pigment contents, antioxidant enzyme activities, and certain life history traits of cotton bollworms. Furthermore, carboxylesterase activity and encapsulation rates of insect larvae decreased with increasing Cd concentrations, whereas acetylcholinesterase, phenol oxidase, glutathione S-transferase, and multifunctional oxidase exhibited hormesis responses.

Nitric oxide alleviates programmed cell death induced by cadmium in Solanum lycopersicum seedlings through protein S-nitrosylation

Cadmium (Cd), as a non-essential and toxic heavy metal in plants, has deleterious effects on plant physiological and biochemical processes. Nitric oxide (NO) is one of the most important signaling molecules for plants to response diverse stresses. Here, we found that Cd-induced programmed cell death (PCD) was accompanied by NO bursts, which exacerbated cell death when NO was removed and vice versa. Proteomic analysis of S-nitrosylated proteins showed that the differential proteins in Cd-induced PCD and in NO-alleviated PCD mainly exist together in carbohydrate metabolism and amino acid metabolism, while some of the differential proteins exist alone in metabolism of cofactors and vitamins and lipid metabolism. Meanwhile, S-nitrosylation of proteins in porphyrin and chlorophyll metabolism and starch and sucrose metabolism could explain the leaf chlorosis induced by PCD. Moreover, protein transport protein SEC23, ubiquitinyl hydrolase 1 and pathogenesis-related protein 1 were identified to be S-nitrosylated in vivo, and their expressions were increased in Cd-induced PCD while decreased in NO treatment. Similar results were obtained in tomato seedlings with higher S-nitrosylation. Taken together, our results indicate that NO might be involved in the regulation of Cd-induced PCD through protein S-nitrosylation, especially proteins involved in PCD response.

Effects of Cadmium Stress on Tartary Buckwheat Seedlings

Cadmium (Cd) is a naturally occurring toxic heavy metal that adversely affects plant germination, growth, and development. While the effects of Cd have been described on many crop species including rice, maize, wheat and barley, few studies are available on cadmium's effect on Tartary buckwheat which is a traditional grain in China. We examined nine genotypes and found that 30 µM of Cd reduced the root length in seedlings by between 4 and 44% and decreased the total biomass by 7 to 31%, compared with Cd-free controls. We identified a significant genotypic variation in sensitivity to Cd stress. Cd treatment decreased the total root length and the emergence and growth of lateral roots, and these changes were significantly greater in the Cd-sensitive genotypes than in tolerant genotypes. Cd resulted in greater wilting and discoloration in sensitive genotypes than in tolerant genotypes and caused more damage to the structure of root and leaf cells. Cd accumulated in the roots and shoots, but the concentrations in the sensitive genotypes were significantly greater than in the more tolerant genotypes. Cd treatment affected nutrient uptake, and the changes in the sensitive genotypes were greater than those in the tolerant genotypes, which could maintain their concentrations closer to the control levels. The induction of SOD, POD, and CAT activities in the roots and shoots was significantly greater in the tolerant genotypes than in the sensitive genotypes. We demonstrated that Cd stress reduced root and shoot growth, decreased plant biomass, disrupted nutrient uptake, altered cell structure, and managed Cd-induced oxidative stress differently in the sensitive and tolerant genotypes of Tartary buckwheat.

Multi-walled carbon nanotubes affect yield, antioxidant response, and rhizosphere microbial community of scented rice under combined cadmium-lead (Cd-Pb) stress

Rice production is threatened by heavy metal stress. The use of multi-walled carbon nanotubes (MWCNTs) in agriculture has been reported in previous studies. We aimed to quantify the impact of MWCNTs on the growth and physiological characteristics of scented rice under cadmium (Cd) and lead (Pb) stresses. Therefore, a pot experiment was conducted, two scented rice varieties Yuxiangyouzhan and Xiangyaxiangzhan were used as materials grown under different concentrations of MWCNTs (0, 100, and 300 mg kg-1 recorded as CK, CNPs100, and CNPs300, respectively). The yield, antioxidant response, and rhizosphere microbial community of scented rice were studied. The results showed that compared with the CK treatment, the CNPs100 and CNPs300 treatments increased leaf dry weight by 17.95%-56.22% at the heading stage, and the H2O2 content in leaves decreased significantly by 36.64%-42.27% at the maturity stage. Under CNPs100 treatment, the grain yield of two scented rice varieties increased significantly by 17.54% and 27.40%, respectively. The MWCNTs regulated the distribution of the Cd and Pb in different plant tissues. The content of Cd (0.11-0.20 mg kg-1) and Pb (0.01-0.04 mg kg-1) in grain were at a safety level (<0.2 mg kg-1). Moreover, MWCNTs increased soil microbial community abundance and altered community composition structure under Cd-Pb stress, which in turn improved agronomic traits and quality of scented rice. Overall, this study suggested that the application of MWCNTs regulates the growth, yield, physiological response, and soil microbial community, the genotypes response effect of scented rice to MWCNTs is needed further studied.

Testicular dysfunction and "its recovery effect" after cadmium exposure

In recent years, with the acceleration of industrialization, the decline of male fertility caused by heavy metal pollution has attracted much attention. However, whether the inhibition of testicular function after cadmium exposure is reversible remains to be studied. In this study, we constructed rat models of cadmium exposure and dis-exposure, and collected relative samples to observe the changes of related indicators. The results showed that cadmium exposure could reduce the fertility, inhibit the hypothalamic-pituitary-testis axis and activate hypothalamic-pituitary-adrenal axis function, the testicular GR/PI3K-AKT/AMPK signal was abnormal, cell proliferation was inhibited and apoptosis was enhanced. Four weeks after the exposure was stopped, the fertility was still decreased, testicular testosterone synthesis and spermatogenesis were inhibited, cell proliferation was inhibited and apoptosis was enhanced, but all of them were reversed. After eight weeks of cadmium exposure, the above indicators were observed to return to normal. At the same time, by giving different concentrations of corticosterone to spermatogonium, we confirmed that corticosterone may regulate the proliferation and apoptosis of spermatogonium through GR/PI3K-AKT/AMPK signal. In this study, the reproductive toxicity of cadmium, a metal environmental pollutant, was analyzed in depth to provide a new theoretical and experimental basis for ensuring male reproductive health.

The Uptake, Transfer, and Detoxification of Cadmium in Plants and Its Exogenous Effects

Cadmium (Cd) exerts a toxic influence on numerous crucial growth and development processes in plants, notably affecting seed germination rate, transpiration rate, chlorophyll content, and biomass. While considerable advances in Cd uptake and detoxification of plants have been made, the mechanisms by which plants adapt to and tolerate Cd toxicity remain elusive. This review focuses on the relationship between Cd and plants and the prospects for phytoremediation of Cd pollution. We highlight the following issues: (1) the present state of Cd pollution and its associated hazards, encompassing the sources and distribution of Cd and the risks posed to human health; (2) the mechanisms underlying the uptake and transport of Cd, including the physiological processes associated with the uptake, translocation, and detoxification of Cd, as well as the pertinent gene families implicated in these processes; (3) the detrimental effects of Cd on plants and the mechanisms of detoxification, such as the activation of resistance genes, root chelation, vacuolar compartmentalization, the activation of antioxidant systems and the generation of non-enzymatic antioxidants; (4) the practical application of phytoremediation and the impact of incorporating exogenous substances on the Cd tolerance of plants.

Foliar application protected vegetable against poisonous element cadmium and mitigated human health risks

Foliar application has been reported as an effective method to facilitate plant growth and mitigate cadmium (Cd) accumulation. However, the application of foliar fertilizers on plant production, Cd uptake and health risks of Solanaceae family remains unknown. In this study, four foliar fertilizers were applied to investigate their effects on the production, Cd accumulation and human health risk assessment of two varieties of pepper (Capsicum annuum L.) and eggplant (Solanum melongena L.), respectively. Compared with CK, the foliar application increased vegetable production to 104.16 %-123.70 % in peppers, and 100.83 %-105.17 % in eggplants, accordingly. The application of foliar fertilizers largely decreased Cd TF (transportation factor) by up to 23.32 % in JY, 18.37 % in GJ of pepper varieties, and up to 14.47 % in ZL, 15.24 % in HGR of eggplant varieties. Moreover, Cd BAF (bioaccumulation factor) also declined to different extents after the application of foliar fertilizers. As for human health risk assessments, foliar application diminished the hazard index (HI) and carcinogenic risk (CR) of both pepper and eggplant varieties. The results concluded that the application of composed foliar fertilizers was most effective, and could be a promising alternative for the improvement of vegetable production and mitigation of vegetable Cd accumulation and human health risks as well. The results further highlighted the understanding of foliar fertilizer application on vegetable production and health risks, which benefited better vegetable safe production and further guaranteed human health.

Zinc oxide nanoparticles alleviate cadmium toxicity and promote tolerance by modulating programmed cell death in alfalfa (Medicago sativa L.)

Cadmium (Cd) can induce programmed cell death (PCD) and zinc oxide nanoparticles (ZnO NPs) effectively alleviate Cd stress. However, the mechanisms of ZnO NPs-mediated Cd detoxification in alfalfa (Medicago sativa L.) are limited. The pot experiment was conducted with Cd soil (19.2 mg kg-1) and foliar ZnO NPs (100 mg L-1) on alfalfa. The results showed that Cd reduced shoot height and biomass, and accumulated reactive oxygen species (ROS), resulting in oxidative stress and further PCD (plasmolysis, cytosolic and nuclear condensation, subcellular organelle swelling, and cell death). ZnO NPs positively regulated the antioxidant system, cell membrane stability, ultrastructure, osmotic homeostasis, and reduced PCD, indicating a multi-level coordination for the increased Cd tolerance. ZnO NPs up-regulated the activity and expression of antioxidant enzymes and regulated PCD-related genes to scavenge ROS and mitigate PCD caused by Cd. The genes related to ZnO NPs-mediated Cd detoxification were significantly enriched in cell death and porphyrin and chlorophyll metabolism. Overall, it elucidates the molecular basis of ZnO NPs-mediated Cd-tolerance by promoting redox and osmotic homeostasis, maintaining cellular ultrastructure, reducing Cd content, and attenuating Cd-induced PCD. it provides a promising application of ZnO NPs to mitigate Cd phytotoxicity and the related cellular and biochemical mechanisms. ENVIRONMENTAL IMPLICATION: Cd, one of the most toxic heavy metals, has caused serious environmental pollution. ZnO NPs can effectively alleviate Cd stress on plants and the environment. This study revealed that foliar-applied ZnO NPs alleviate Cd toxicity by mitigating the oxidative damage and regulating Cd-induced PCD via morphological, physiological, and transcriptomic levels. The findings elucidated the molecular basis of ZnO NPs-mediated Cd tolerance by promoting osmotic and redox homeostasis, reducing Cd content and lipid peroxidation, attenuating Cd-induced PCD features, and altering PCD-related genes in alfalfa. The study laid a theoretical foundation for the safe production of alfalfa under Cd pollution.

Potential strategies for phytoremediation of heavy metals from wastewater with circular bioeconomy approach

Water pollution is an inextricable problem that stems from natural and human-related factors. Unfortunately, with rapid industrialization, the problem has escalated to alarming levels. The pollutants that contribute to water pollution include heavy metals (HMs), chemicals, pesticides, pharmaceuticals, and other industrial byproducts. Numerous methods are used for treating HMs in wastewater, like ion exchange, membrane filtration, chemical precipitation, adsorption, and electrochemical treatment. But the remediation through the plant, i.e., phytoremediation is the most sustainable approach to remove the contaminants from wastewater. Aquatic plants illustrate the capacity to absorb excess pollutants including organic and inorganic compounds, HMs, and pharmaceutical residues present in agricultural, residential, and industrial discharges. The extensive exploitation of these hyperaccumulator plants can be attributed to their abundance, invasive mechanisms, potential for bioaccumulation, and biomass production. Post-phytoremediation, plant biomass can be toxic to both water bodies and soil. Therefore, the circular bioeconomy approach can be applied to reuse and repurpose the toxic plant biomass into different circular bioeconomy byproducts such as biochar, biogas, bioethanol, and biodiesel is essential. In this regard, the current review highlights the potential strategies for the phytoremediation of HMs in wastewater and various strategies to efficiently reuse metal-enriched biomass material and produce commercially valuable products. The implementation of circular bioeconomy practices can help overcome significant obstacles and build a new platform for an eco-friendlier lifestyle.

Cadmium exposure and cardiovascular disease risk: A systematic review and dose-response meta-analysis

Exposure to toxic metals is a global public health threat. Among other adverse effects, exposure to the heavy metal cadmium has been associated with greater risk of cardiovascular disease (CVD). Nonetheless, the shape of the association between cadmium exposure and CVD risk is not clear. This systematic review summarizes data on the association between cadmium exposure and risk of CVD using a dose-response approach. We carried out a literature search in PubMed, Web of Science, and Embase from inception to December 30, 2023. Inclusion criteria were: studies on adult populations, assessment of cadmium exposure, risk of overall CVD and main CVD subgroups as endpoints, and observational study design (cohort, cross-sectional, or case-control). We retrieved 26 eligible studies published during 2005-2023, measuring cadmium exposure mainly in urine and whole blood. In a dose-response meta-analysis using the one-stage method within a random-effects model, we observed a positive association between cadmium exposure and risk of overall CVD. When using whole blood cadmium as a biomarker, the association with overall CVD risk was linear, yielding a risk ratio (RR) of 2.58 (95 % confidence interval-CI 1.78-3.74) at 1 μg/L. When using urinary cadmium as a biomarker, the association was linear until 0.5 μg/g creatinine (RR = 2.79, 95 % CI 1.26-6.16), after which risk plateaued. We found similar patterns of association of cadmium exposure with overall CVD mortality and risks of heart failure, coronary heart disease, and overall stroke, whereas for ischemic stroke there was a positive association with mortality only. Overall, our results suggest that cadmium exposure, whether measured in urine or whole blood, is associated with increased CVD risk, further highlighting the importance of reducing environmental pollution from this heavy metal.

Biochar co-pyrolyzed from peanut shells and maize straw improved soil biochemical properties, rice yield, and reduced cadmium mobilization and accumulation by rice: Biogeochemical investigations

Biochar is an eco-friendly amendment for the remediation of soils contaminated with cadmium (Cd). However, little attention has been paid to the influence and underlying mechanisms of the co-pyrolyzed biochar on the bioavailability and uptake of Cd in paddy soils. The current study explored the effects of biochar co-pyrolyzed from peanut shells (P) and maize straw (M) at different mixing ratios (1:0, 1:1, 1:2, 1:3, 0:1, 2:1 and 3:1, w/w), on the bacterial community and Cd fractionation in paddy soil, and its uptake by rice plant. Biochar addition, particularly P1M3 (P/M 1:3), significantly elevated soil pH and cation exchange capacity, transferred the mobile Cd to the residual fraction, and reduced Cd availability in the rhizosphere soil. P1M3 application decreased the concentration of Cd in different rice tissues (root, stem, leaf, and grain) by 30.0%- 49.4%, compared to the control. Also, P1M3 enhanced the microbial diversity indices and relative abundance of iron-oxidizing bacteria in the rhizosphere soil. Moreover, P1M3 was more effective in promoting the formation of iron plaque, increasing the Cd sequestration by iron plaque than other treatments. Consequently, the highest yield and lowest Cd accumulation in rice were observed following P1M3 application. This study revealed the feasibility of applying P1M3 for facilitating paddy soils contaminated with Cd.

Contributions of selenium-oxidizing bacteria to selenium biofortification and cadmium bioremediation in a native seleniferous Cd-polluted sandy loam soil

Selenium (Se) is a trace element that is essential for human health. Daily dietary Se intake is governed by the food chain through soil-plant systems. However, the cadmium (Cd) content tends to be excessive in seleniferous soil, in which Se and Cd have complex interactions. Therefore, it is a great challenge to grow crops containing appreciable amounts of Se but low amounts of Cd. We compared the effects of five Se-transforming bacteria on Se and Cd uptake by Brassica rapa L. in a native seleniferous Cd-polluted soil. The results showed that three Se-oxidizing bacteria (LX-1, LX-100, and T3F4) increased the Se content of the aboveground part of the plant by 330.8%, 309.5%, and 724.3%, respectively, compared to the control (p < 0.05). The three bacteria also reduced the aboveground Cd content by 15.1%, 40.4%, and 16.4%, respectively (p < 0.05). In contrast, the Se(IV)-reducing bacterium ES2-45 and weakly Se-transforming bacterium LX-4 had no effect on plant Se uptake, although they did decrease the aboveground Cd content. In addition, the three Se-oxidizing bacteria increased the Se available in the soil by 38.4%, 20.4%, and 24.0%, respectively, compared to the control (p < 0.05). The study results confirm the feasibility of using Se-oxidizing bacteria to simultaneously enhance plant Se content and reduce plant Cd content in seleniferous Cd-polluted soil.

Biotic Ligand Modeling for the Effect of Major Cations on the Uptake of Cadmium in Folsomia candida Exposed in a Sand-Solution Medium

Biotic ligand modeling (BLM) approaches are already applied to predict the bioavailability and possible risk of metals in surface water, but need further development for soils. The present study investigated the effect of major cations (Ca2+ , Mg2+ , Na+ , K+ , and H+ ) on cadmium bioaccumulation in the springtail Folsomia candida. To avoid the complexity of real soils and enable control of elemental speciation in the exposure medium, the animals were exposed to different cadmium concentrations in an inert quartz sand-solution medium. Accumulation of cadmium in the animals was measured after 7 days exposure at different cation concentrations. Among the cations, only Ca2+ significantly affected the uptake of cadmium in the springtails. Mg2+ also had higher effects compared with other selected cations. Using a BLM approach, the uptake of cadmium in the animals predicted by taking into account both Ca2+ and Mg2+ activities correlated well with the measured values (R2  = 0.68). The final estimated conditional binding constants for cadmium (log KCd-BL ), Ca (log KCa-BL ), and Mg (log KMg-BL ) of 1.06, 2.14, and 1.23 L/mol, respectively, were in agreement with previously reported values. The match between predicted and measured uptake data confirms the applicability and usefulness of the BLM for predicting the bioavailability of cadmium to springtails and opens the way for its application in soil. Environ Toxicol Chem 2024;00:1-7. © 2024 SETAC.

Safe utilization evaluation of two typical traditional Chinese medicinal materials in Cd-contaminated soil based on the analysis of Cd transfer and AHP model

Due to the increasing scarcity of wild resources, most traditional Chinese medicinal materials (TCMMs) in the market are produced via artificial cultivation. The widespread pollution of cadmium (Cd) in soil limits the safe cultivation and use of TCMMs. This study investigated Cd accumulation, distribution, and the medicinal component content under simulated field conditions to clarify the differences in the Cd absorption, transfer and detoxification mechanisms of Polygonatum cyrtonema Hua and Bletilla striata, and provide the preliminary safe utilization conditions of TCMMs based on the analytic hierarchy process (AHP). The results showed that the Cd content of P. cyrtonema Hua was lower than the safety threshold under a high soil Cd concentration of 0.91 mg/kg (Cd-L), while B. striata was safe only at a low Cd concentration of 0.25 mg/kg (CK). Cd at 0.91 mg/kg induced hormesis affecting the net increase in biomass and medicinal component content for both TCMMs, while P. cyrtonema Hua showed better potential for safe utilization. Additionally, P. cyrtonema Hua had stronger resistance to Cd stress, exhibiting superior characteristics for synergistic absorption of Cd with mineral elements, transfer to nonmedical part and safer fixation forms in subcellular components. In contrast, B. striata showed insufficient Cd tolerance, and Cd was easily accumulated in organelles to inhibit plant growth. Our findings may attract more attention to the safe cultivation of TCMMs and provide insight into guidance for the safe utilization of slightly Cd-contaminated soil.

Foliar spraying of lanthanum activates endocytosis in lettuce (Lactuca sativa L.) root cells, increasing Cd and Pb accumulation and their bioaccessibility

Cadmium (Cd) and lead (Pb) accumulate easily in leafy vegetables and can harm human health. Lanthanum (La) have been used to improve agricultural yield and quality, but the effect of La application on Cd/Pb enrichment in leafy vegetables remains incomplete currently. A previous study reported that the endocytosis in lettuce leaf cells can be activated by La, leading to an increase in Pb accumulation in lettuce leaves. However, it has not been investigated whether foliar application of La enhances root cellular endocytosis and promotes its uptake of Cd and Pb. In this study, the influence of La on the uptake of Cd and Pb, Cd bioaccessibility, and the safety risks of cultivating lettuce under Cd and Pb stress were explored. It was found that La increased Cd (16-30 % in shoot, 16-34 % in root) and Pb (25-29 % in shoot, 17-23 % in root) accumulation in lettuce. The increased accumulation of Cd and Pb could be attributed to La-enhanced endocytosis. Meanwhile, La enhanced the toxicity of both Cd and Pb, inhibited lettuce growth, and aggravated the damage to the photosynthetic and antioxidant systems. Finally, gastrointestinal simulation experiments showed that La increased the Cd bioaccessibility in both gastric and intestinal phase by 7-108 % and 9-87 %, respectively. These results offer valuable insights into the safety of REEs for agricultural applications.

Heavy metal-tolerant bacteria Bacillus cereus BCS1 degrades pyrethroid in a soil-plant system

The heightened concern about the environmental impacts of pollutants drives interest in reducing their threats to humans and the environment. Bioremediating polluted sites under environmental stresses like biotic and abiotic poses significant challenges. This study aimed to isolate a bacterium that effectively degrades pyrethroids even under abiotic stresses involving heavy metals and biotic stresses with autochthonous factors. Here, a bacterial strain, Bacillus cereus BCS1 was isolated. The response surface methodology was established to quantify the environmental impacts on pyrethroid degradation. BCS1 effectively degraded pyrethroids across conditions at 21-36 °C, pH 6.5-8.0 and inoculum sizes 1.9-4.1 mg·L-1, exceeding 90% degradation. Notably, over 84% of β-cypermethrin (β-CP) was degraded even when exposed to various concentrations of lead (10-1000 mg·L-1), chromium (10-1000 mg·L-1), or cadmium (0.5-50 mg·L-1). Moreover, BCS1 significantly accelerated β-CP degradation in soil-plant systems, displaying biotic stress tolerance, with lower half-life values (10.1 and 9.5 d) in soil and higher removal (92.1% and 60.9%) in plants compared to controls (27.7 and 25.7 d), and (18.2% and 24.3%). This study presents a novel strain capable of efficiently degrading pyrethroids and displaying remarkable environmental stress resistance. Findings shed light on bioremediating organic pollutants in complex soil ecosystems.

Toxic effects of lead (Pb), cadmium (Cd) and tetracycline (TC) on the growth and development of Triticum aestivum: A meta-analysis

The environmental issue of lead (Pb), cadmium (Cd), and tetracycline (TC) contamination in cereal crops has become a growing concern worldwide. An in-depth understanding of this issue would be of importance to promote effective management strategies for heavy metals and antibiotics worldwide. The present study was conducted to assess the toxic effects of heavy metals (Cd, Pb) and antibiotics (TC) on Triticum aestivum (T. aestivum, common wheat) based on studies conducted in the past 22 years. Data pertaining to the growth and development of T. aestivum were extracted and analyzed from 89 publications spanning from 2000 to 2022. Our results showed that Pb, Cd and TC significantly reduced growth and development by 11 %, 9 %, and 5 %, respectively. Additionally, significant accumulation of Cd (42 %) and Pb (17 %) was observed in T. aestivum samples, although there was little change in TC accumulation, which showed limited absorption, accumulation, and translocation of TC in wheat plants. Pb had the greatest impact on the yield of T. aestivum, followed by Cd, while TC had no apparent effect. Furthermore, exposure to Cd, Pb and TC reduced the photosynthetic rate due to chlorophyll reduction, with Cd having the most pronounced effect (58 %), followed by Pb (37 %) and TC (8 %). Cd exposure also significantly enhanced gaseous exchange (37 %) compared to TC and Pb, which reduced gaseous exchange by 4 % and 10 %, respectively. However, the treatments with TC (>50-100 mgL-1), Pb (>1000-2000 mg L-1) and Cd (>500-1000 mg L-1) increased the defense system of T. aestivum samples by 38 %, 15 %, and 11 %, respectively. The obtained findings have significant implications for risk assessment, pollution prevention, and remediation strategies to address soil contamination from Pb, Cd and TC in farmland.

Identifying cadmium and lead co-accumulation from living rice blade spectrum

Neither cadmium (Cd) nor lead (Pb) is necessary for crop growth, but they both can accumulate in soil and crop tissues, resulting in land degradation and crop reduction. Few researchers have explored how to detect Cd-Pb co-accumulation in leaves using proximal sensing techniques, especially by low-cost, easy-to-use leaf clips that capture hyperspectral reflections at suitable foliar positions. In this study, a hyperspectral imager was employed to collect images of the rice canopy from a designed greenhouse experiment that included 16 pretreatments of Cd-Pb co-accumulation, followed by spectral extractions from 3 foliar positions: the blade root, the middle of the leaf, and the leaf apex. A support vector machine with leave-one-out cross-validation was performed to diagnose the contaminative levels based on the feature wavelengths selected by an improved successive projection algorithm. Partial least squares regression was used to predict Cd-Pb concentrations in rice blades. The results indicated that diagnostic accuracies were varied using spectra of different foliar positions. The blade root and leaf apex of rice blades were the optimal foliar position for detecting Cd and Pb contamination, respectively. At the optimal foliar positions, diagnostic accuracies exceeded 0.80 for distinguishing whether the rice is subject to Cd-Pb contamination. The Cd prediction performed 'very good' with a residual prediction deviation (RPD) of 2.21, a R2 of 0.79, and a root mean square error (RMSE)of 6.14, while that of Pb was 1.62, 0.61, and 186.54. Important wavelengths were identified at 659-694 nm and 667-694 nm to detect Cd and Pb contamination. In summary, our results verified the feasibility and clarified the optimal foliar positions of rice blades to detect Cd-Pb contamination. The wavelengths selecting have the great potential in the design of future leaf clips, and the optimal foliar position can provide suggestions to improve diagnostic performances in field applications.

Natural enrichment of Cd and Tl in the bark of trees from a rural watershed devoid of point sources of metal contamination

To help understand the bioaccumulation of Cd and Tl in beaver tissue, we examined the enrichment of these metals in vegetation available to the animals. Bark was collected from 40 species of trees and shrubs, along with a complete soil weathering profile, within a small watershed devoid of trace metal contamination. Weathering resulted in a 5x enrichment of Cd in the soils relative to the underlying sediments, and a 6x Tl depletion: while Cd was lost from calcite and accumulates in the organic matter and oxyhydroxide fractions, Tl occurred only in the residual fraction. Soil processes alone, however, cannot explain the anomalous concentrations and enrichments of Cd in willow and poplar which contain up to 8.5 mg/kg Cd. The concentrations of Cd and Tl in the dissolved fraction (<0.45 μm) of the Wye River are similar (1.2 ± 0.4 and 1.6 ± 0.1 ng/L, respectively), and are taken to estimate their bioavailability in soil solutions. Normalizing the Cd/metal ratios in bark to the corresponding ratios in water yields the Stream Enrichment Factor: this novel approach shows that all plant species are enriched in Cd relative to Ni; 33 relative to Cu, 13 relative to Zn, and 7 relative to Mn. Thus, many plants preferentially accumulate Cd, especially willow and poplar, over these essential micronutrients. Clearly, the enrichment of Cd over Tl in bark is not a reflection of differences in bioavailability, but rather on the preferential uptake of Cd by the plants. The profound natural bioaccumulation of Cd in the bark of willow and poplar, the two favourite foods of the beaver, has ramifications for the use of these aquatic mammals as biomonitors of environmental contamination, as well as for the direct and indirect consumption of bark for traditional food and medicine.

A review on heavy metal biosorption utilizing modified chitosan

Heavy metal pollution in water bodies is a global concern. The prominent source of metal contamination in aqueous streams and groundwater is wastewater containing heavy metal ions. Elevated concentrations of heavy metals in water bodies can have a negative impact on water quality and public health. The most effective way to remove metal contaminants from drinking water is thought to be adsorption. A deacetylated derivative of chitin, chitosan, has a wide range of commercial uses since it is biocompatible, nontoxic, and biodegradable. Due to its exceptional adsorption behavior toward numerous hazardous heavy metals from aqueous solutions, chitosan and its modifications have drawn a lot of interest in recent years. Due to its remarkable adsorption behavior toward a range of dangerous heavy metals, chitosan is a possible agent for eliminating metals from aqueous solutions. The review has focused on the ideas of biosorption, its kinds, architectures, and characteristics, as well as using modified (physically and chemically modified) chitosan, blends, and composites to remove heavy metals from water. The main objective of the review is to describe the most important aspects of chitosan-based adsorbents that might be beneficial for enhancing the adsorption capabilities of modified chitosan and promoting the usage of this material in the removal of heavy metal pollutants.

Transcriptomics and metabolomics association analysis revealed the responses of Gynostemma pentaphyllum to cadmium

Gynostemma pentaphyllum an important medicinal herb, can absorb high amounts of cadmium (Cd) which can lead to excessive Cd contamination during the production of medicines and tea. Hence, it is crucial to investigate the response mechanism of G. pentaphyllum under Cd stress to develop varieties with low Cd accumulation and high tolerance. Physiological response analysis, transcriptomics and metabolomics were performed on G. pentaphyllum seedlings exposed to Cd stress. Herein, G. pentaphyllum seedlings could significantly enhance antioxidant enzyme activities (POD, CAT and APX), proline and polysaccharide content subject to Cd stress. Transcriptomics analysis identified the secondary metabolites, carbohydrate metabolism, amino acid metabolism, lipid metabolism, and signal transduction pathways associated with Cd stress, which mainly involved the XTH, EXP and GST genes. Metabolomics analysis identified 126 differentially expressed metabolites, including citric acid, flavonoid and amino acids metabolites, which were accumulated under Cd stress. Multi-omics integrative analysis unraveled that the phenylpropanoid biosynthesis, starch, and sucrose metabolism, alpha-linolenic acid metabolism, and ABC transporter were significantly enriched at the gene and metabolic levels in response to Cd stress in G. pentaphyllum. In conclusion, the genetic regulatory network sheds light on Cd response mechanisms in G. pentaphyllum.

Involvement of NO in V-ATPase Regulation in Cucumber Roots under Control and Cadmium Stress Conditions

Nitric oxide (NO) is a signaling molecule that participates in plant adaptation to adverse environmental factors. This study aimed to clarify the role of NO in the regulation of vacuolar H+-ATPase (V-ATPase) in the roots of cucumber seedlings grown under control and Cd stress conditions. In addition, the relationship between NO and salicylic acid (SA), as well as their interrelations with hydrogen sulfide (H2S) and hydrogen peroxide (H2O2), have been verified. The effect of NO on V-ATPase was studied by analyzing two enzyme activities, the expression level of selected VHA genes and the protein level of selected VHA subunits in plants treated with a NO donor (sodium nitroprusside, SNP) and NO biosynthesis inhibitors (tungstate, WO42- and N-nitro-L-arginine methyl ester, L-NAME). Our results indicate that NO functions as a positive regulator of V-ATPase and that this regulation depends on NO generated by nitrate reductase and NOS-like activity. It was found that the mechanism of NO action is not related to changes in the gene expression or protein level of the V-ATPase subunits. The results suggest that in cucumber roots, NO signaling interacts with the SA pathway and, to a lesser extent, with two other known V-ATPase regulators, H2O2 and H2S.

Environmental cadmium exposure alters the internal microbiota and metabolome of Sprague-Dawley rats

Cadmium (Cd) is a toxic element that can negatively affect both humans and animals. It enters the human and animal bodies through the respiratory and digestive tracts, following which it tends to accumulate in different organs, thereby seriously affecting human and animal health, as well as hampering social and economic development. Cd exposure can alter the composition of intestinal microbiota. In addition, it can damage the peripheral organs by causing the translocation of intestinal microbiota. However, the relationship between translocation-induced changes in the composition of microbiome in the blood and metabolic changes remains unclear. In the present study, we investigated the effects of Cd exposure on microbiota and serum metabolism in rats by omics analysis. The results demonstrated that Cd exposure disrupted the balance between the blood and intestinal flora in Sprague-Dawley (SD) rats, with a significant increase in gut microbiota (Clostridia_UCG_014, NK4A214_group) and blood microbiome (Corynebacterium, Muribaculaceae). However, Cd exposure caused the translocation of Corynebacterium and Muribaculaceae from the gut into the blood. In addition, Cd exposure was associated with the up-regulation of serum indoxyl sulfate, phenyl sulfate, and p-cresol sulfate; down-regulation of δ-tocopherol and L-glutamine; and changes in blood microbiome and metabolites. In conclusion, we identified novel metabolic biomarkers for Cd toxicity, which will also expand our understanding of the role of blood microbiome in Cd-induced injury.

Endophytic Plant Growth-Promoting Bacterium Bacillus subtilis Reduces the Toxic Effect of Cadmium on Wheat Plants

Heavy metal ions, in particular cadmium (Cd), have a negative impact on the growth and productivity of major crops, including wheat. The use of environmentally friendly approaches, in particular, bacteria that have a growth-stimulating and protective effect, can increase the resistance of plants. The effects of the pre-sowing seed treatment with the plant growth-promoting endophyte Bacillus subtilis 10-4 (BS) on cadmium acetate (Cd)-stressed Triticum aestivum L. (wheat) growth, photosynthetic pigments, oxidative stress parameters, roots' lignin content, and Cd ions accumulation in plants were analyzed. The results showed that the tested Cd-tolerant BS improved the ability of wheat seeds to germinate in the presence of different Cd concentrations (0, 0.1, 0.5, and 1 mM). In addition, the bacterial treatment significantly decreased the damaging effects of Cd stress (1 mM) on seedlings' linear dimensions (lengths of roots and shoots), biomass, as well as on the integrity and permeability of the cell walls (i.e., lipid peroxidation and electrolyte leakage) and resulted in reduced H₂O₂ generation. The pretreatment with BS prevented the Cd-induced degradation of the leaf photosynthetic pigments chlorophyll (Chl) a, Chl b, and carotenoids. Moreover, the bacterial treatment intensified the lignin deposition in the roots under normal and, especially, Cd stress conditions, thereby enhancing the barrier properties of the cell wall. This manifested in a reduced Cd ions accumulation in the roots and in the restriction of its translocation to the aboveground parts (shoots) of the bacterized plants under Cd stress in comparison with non-bacterized controls. Thus, the pre-sowing seed treatment with the endophyte BS may serve as an eco-friendly approach to improve wheat production in Cd-contaminated areas.