A comprehensive assessment of heavy metal(loid) contamination in leafy vegetables grown in two mining areas in Yunnan, China-a focus on bioaccumulation of cadmium in Malabar spinach

Silicon and selenium alleviate cadmium toxicity in Artemisia selengensis Turcz by regulating the plant-rhizosphere

Soil cadmium (Cd) pollution has emerged as a pressing concern due to its deleterious impacts on both plant physiology and human well-being. Silicon (Si) is renowned for its ability to mitigate excessive Cd accumulation within plant cells and reduce the mobility of Cd in soil, whereas Selenium (Se) augments plant antioxidant capabilities and promotes rhizosphere microbial activity. However, research focusing on the simultaneous utilization of Si and Se to ameliorate plant Cd toxicity through multiple mechanisms within the plant-rhizosphere remains comparatively limited. This study combined hydroponic and pot experiments to investigate the effects of the combined application of Si and Se on Cd absorption and accumulation, as well as the growth and rhizosphere of A. selengensis Turcz under Cd stress. The results revealed that a strong synergistic effect was observed between both Si and Se. The combination of Si and Se significantly increased the activity and content of enzymes and non-enzyme antioxidants within A. selengensis Turcz, reduced Cd accumulation and inhibiting its translocation from roots to shoots. Moreover, Si and Se application improved the levels of reducing sugar, soluble protein, and vitamin C, while reducing nitrite content and Cd bioavailability. Furthermore, the experimental results showed that the combination of Si and Se not only increased the abundance of core rhizosphere microorganisms, but also stimulated the activity of soil enzymes, which effectively limited the migration of Cd in the soil. These findings provided valuable insights into the effective mitigation of soil Cd toxicity to plants and also the potential applications in improving plant quality and safety.

Multicontamination Toxicity Evaluation in the Model Plant Lactuca sativa L

Many contaminated soils contain several toxic elements (TEs) in elevated contents, and plant-TE interactions can differ from single TE contamination. Therefore, this study investigated the impact of combined contamination (As, Cd, Pb, Zn) on the physiological and metabolic processes of lettuce. After 45 days of exposure, TE excess in soil resulted in the inhibition of root and leaf biomass by 40 and 48%, respectively. Oxidative stress by TE accumulation was indicated by markers-malondialdehyde and 5-methylcytosine-and visible symptoms of toxicity (leaf chlorosis, root browning) and morpho-anatomical changes, which were related to the change in water regime (water potential decrease). An analysis of free amino acids (AAs) indicated that TEs disturbed N and C metabolism, especially in leaves, increasing the total content of free AAs and their families. Stress-induced senescence by TEs suggested changes in gas exchange parameters (increase in transpiration rate, stomatal conductance, and intercellular CO2 concentration), photosynthetic pigments (decrease in chlorophylls and carotenoids), a decrease in water use efficiency, and the maximum quantum yield of photosystem II. These results confirmed that the toxicity of combined contamination significantly affected the processes of lettuce by damaging the antioxidant system and expressing higher leaf sensitivity to TE multicontamination.

Effects of wollastonite and phosphate treatments on cadmium bioaccessibility in pak choi (Brassica rapa L. ssp. chinensis) grown in contaminated soils

Cadmium (Cd) contamination of soil can strongly impact human health through the food chain due to uptake by crop plants. Inorganic immobilizing agents such as silicates and phosphates have been shown to effectively reduce Cd transfer from the soil to cereal crops. However, the effects of such agents on total Cd and its bioaccessibility in leafy vegetables are not yet known. Pak choi (Brassica rapa L. ssp. chinensis) was here selected as a representative leafy vegetable to be tested in pots to reveal the effects of silicate-phosphate amendments on soil Cd chemical fractions, total plant Cd levels, and plant bioaccessibility. The collected Cd contaminated soil was mixed with control soil at 1:0, 1:1, 1:4, 0:1 with a view to Cd high/moderate/mild/control soil samples. Three heavy metal-immobilizing agents: wollastonite (W), potassium tripolyphosphate (KTPP), and sodium hexametaphosphate (SHMP) were added to the soil in order to get four different treatment groups, i.e., control (CK), application of wollastonite alone (W), wollastonite co-applied with KTPP (WKTPP), application of wollastonite co-applied with SHMP (WSHMP) for remediation of soils with different levels of Cd contamination. All three treatments increased the effective bio-Cd concentration in the soils with varying levels of contamination, except for W under moderate and heavy Cd contamination. The total Cd concentration in pak choi plants grown in mildly Cd-contaminated soil was elevated by 86.2% after WKTPP treatment compared to the control treatment could function as a phytoremediation aid for mildly Cd-contaminated soil. Using an in vitro digestion method (physiologically based extraction test) combined with transmission electron microscopy, silicate and phosphorus agents were found to reduce the bioaccessibility of Cd in pak choi by up to 66.13% with WSHMP treatment. Application of silicate alone reduced soil bio-Cd concentration through the formation of insoluble complexes and silanol groups with Cd, but the addition of phosphate may have facilitated Cd translocation into pak choi by first co-precipitating with Ca in wollastonite while simultaneously altering soil pH. Meanwhile, wollastonite and phosphate treatments may cause Cd to be firmly enclosed in the cell wall in an insoluble form, reducing its translocation to edible parts and decreasing the bioaccessibility of Cd in pak choi. This study contributes to the mitigation of Cd bioaccessibility in pak choi by reducing soil Cd concentration through in situ remediation and will help us to extend the effects of wollastonite and phosphate on Cd bioaccessibility to other common vegetables. Therefore, this study thus reveals effective strategies for the remediation of soil Cd and the reduction of Cd bioaccessibility in crops based on two indicators: total Cd and Cd bioaccessibility. Our findings contribute to the development of methods for safer cultivation of commonly consumed leafy vegetables and for soil remediation.

Contamination and health risks brought by arsenic, lead and cadmium in a water-soil-plant system nearby a non-ferrous metal mining area

Heavy metal(loid)s contamination prevails in the water-soil-plant system around non-ferrous metal mining areas. The present study aimed to evaluate the heavy metal(loid)s contamination in Nandan Pb-Zn mining area (Guangxi, China). A total of 36 river water samples, 75 paired paddy soil and rice samples, and 128 paired upland soil and plant samples were collected from this area. The concentrations of arsenic (As), lead (Pb), and cadmium (Cd) in these samples were measured. Results showed that the average water quality indexes (WQIs) at the 12 sampling sites along the main river ranged from 41 to 5008, indicating the water qualities decreasing from "Excellent" to "Undrinkable". The WQIs nearby tailings or industrial park were significantly higher than those at the other sites. 34.0% and 64.5% of soil samples exceeded the risk screening values for As and Cd. The Pb and Cd concentrations in all rice samples exceeded the Chinese food safety limits by 18.7% and 82.7%, respectively. Leafy vegetables had a higher concentration of As, Pb, and Cd than other vegetables, exceeding the maximum permissible limits by 14.1%, 61.2%, and 40.0%, respectively. The biological accumulation coefficient (BAC) of Cd was the highest in rice and lettuce leaves. The hazard quotients (HQs) of As and Cd, indicating non-carcinogenic risks, were 4.15 and 1.76 in adult males, and 3.40 and 1.45 in adult females, all higher than the permitted level (1.0). The carcinogenic probabilities of As and Cd from rice and leafy vegetables consumption were all higher than 1 × 10-4. We conclude that metal(loid)s contamination of the water-soil-plant system has posed great non-carcinogenic and carcinogenic risks to the local population.

Ecological Risk and Pollution Assessment of Heavy Metals in Farmland Soil Profile with Consideration of Atmosphere Deposition in Central China

Heavy metals (HMs) in agricultural land have caused serious environmental problems, resulting in severe contamination of the food chain and posing potential health threats. This study aims to investigate the pollution levels and potential ecological risks of HMs in farmland soils in central China, taking into account atmospheric deposition. Several indices were used to assess the status of HMs and compare surface soil with deeper soil. Descriptive statistics, Pearson correlation, and UMAP clustering methods were utilized to identify the characteristics of HMs. Additionally, stepwise linear regression models were employed to quantify the contributions of different variables to the potential ecological risks of HMs. The results showed that the average content of Zn in surface soil (289.41 ± 87.72 mg/kg) was higher than in the deeper soil (207.62 ± 37.81 mg/kg), and similar differences were observed in the mean values of related Igeo (1.622 ± 0.453 in surface soil and 1.183 ± 0.259 in deeper soil) and PEI (0.965 ± 0.292 in surface soil and 0.692 ± 0.126 in deeper soil) indices. This indicates that surface soil is more heavily polluted. The UMAP results confirmed the high variability of HMs in the surface soil, while PCA results suggested the importance of pollution and ecological risk indices. The stepwise linear model revealed that different variable structures contribute differently to the risk. In conclusion, Cr and Zn were found to be the major contaminants in the local farmland soil, with higher concentrations in the surface soil. The geoaccumulation and total potential ecological risk were classified as low risk. High variability of HMs was observed in the surface soil. Therefore, HM-related pollution indices and ecological risk indices are important for assessing the contamination status of local HMs. The local potential ecological risk can be attributed to specific heavy metals, each of which can have different effects on the local ecological risk.

Are high-risk heavy metal(loid)s contaminated vegetables detrimental to human health? A study of incorporating bioaccessibility and toxicity into accurate health risk assessment

Heavy metal(loid)s in the environment threaten food safety and human health. Health risk assessment of vegetables based on total or bioaccessible heavy metal(loid)s was widely used but can overestimate their risks, so exploring accurate methods is urgent for food safety evaluation and management. In this study, a total of 224 frequently consumed vegetables and their corresponding grown soils were collected from Yunnan, Southwest China. The total contents and bioaccessibilities of heavy metal(loid)s in vegetables were measured, their health risks were evaluated using the non-carcinogenic and carcinogenic risk models provided by USEPA. Besides, the gastrotoxicity of high-risk vegetables was also evaluated using a human cell model. Results showed that 6.25-43.8 % of Cr, Cd, and Pb contents in Zea mays L., Coriandrum sativum L., or Allium sativum L. exceeded the maximum permissible level of China, which were not consistent with those in corresponding soils. The bioaccessibility of Cr, Cd, As, Pb, Cu, Zn, Ni, and Mn in vegetables in the gastric phase was 0.41-93.8 %. Health risks based on bioaccessibility were remarkably decreased compared with total heavy metal(loid)s, but the unacceptable carcinogenic risk (CR > 10-4) was found even considering the bioaccessibility. Interestingly, gastric digesta of high-risk vegetables did not trigger adverse effects on human gastric mucosa epithelial cells, indicating existing health risk assessment model should be adjusted by toxic data to accurately reflect its hazards. Taken together, both bioaccessibility and toxicity of heavy metal(loid)s in vegetables should be considered in accurate health risk assessment and food safety-related policy-making and management.

Biochar performance for preventing cadmium and arsenic accumulation, and the health risks associated with mustard (Brassica juncea) grown in co-contaminated soils

Cadmium (Cd) and arsenic (As) in co-contaminated soil can enter the human body harming health via the food chain, such as vegetables. Biochar derived from waste has been used to reduce heavy metal uptake by plant, but long-term effects of biochar under Cd and As co-contaminated soil needs to be investigated. A following mustard (Brassica juncea) was grown on co-contaminated soil amended with different raw materials of biochar including biochars pyrolyzed by lignite coal (LCB), rice straw (RSB), silkworm excrement (SEB), and sugar refinery sludge (SSB). The results showed that compared to the control, Cd and As contents of mustard shoot in SSB treatment decreased by 45-49% and 19-37% in two growing seasons, respectively, which was the most effective among 4 biochars. This probably due to SSB owns more abundant Fe-O functional groups. Biochar also altered the microbial community composition, specifically SSB increased proteobacteria abundance by 50% and 80% in the first and second growing seasons, thereby promoted the simultaneous immobilization of Cd and As in soils which may reduce the potential risks to humans. In summary, considering the long-term effects and security of SSB application on mustard, not only is it an effective waste recycle option, but it should also be promoted as a promising approach for safe vegetable production in Cd and As co-contaminated soils.

Effect of Arsenic Soil Contamination on Stress Response Metabolites, 5-Methylcytosine Level and CDC25 Expression in Spinach

Experimental spinach plants grown in soil with (5, 10 and 20 ppm) arsenic (As) contamination were sampled in 21 days after As(V) contamination. Levels of As in spinach samples (from 0.31 ± 0.06 µg g^-1 to 302.69 ± 11.83 µg g^-1) were higher in roots and lower in leaves, which indicates a low ability of spinach to translocate As into leaves. Species of arsenic, As(III) and As(V), were represented in favor of the As (III) specie in contaminated variants, suggesting enzymatic arsenate reduction. In relation to predominant As accumulation in roots, changes in malondialdehyde levels were observed mainly in roots, where they decreased significantly with growing As contamination (from 11.97 ± 0.54 µg g^-1 in control to 2.35 ± 0.43 µg g^-1 in 20 ppm As). Higher values in roots than in leaves were observed in the case of 5-methylcytosine (5-mC). Despite that, a change in 5-mC by As contamination was further deepened in leaves (from 0.20 to 14.10%). In roots of spinach, expression of the CDC25 gene increased by the highest As contamination compared to the control. In the case of total phenolic content, total flavonoid content, total phenolic acids content and total antioxidant capacity were higher levels in leaves in all values, unlike the roots.

The Expression of the StNRAMP2 Gene Determined the Accumulation of Cadmium in Different Tissues of Potato

Cadmium (Cd) is a toxic metal that threatens human health when enriched in crops. NRAMPs are a family of natural macrophage proteins reported to play a key role in Cd transport in plants. In order to explore the gene regulation mechanism of potato under Cd stress and the role of NRAMPs family in it, this study analyzed the gene expression differences of two different Cd accumulation levels in potato after 7 days of 50 mg/kg Cd stress and screened out the key genes that may play a major role in the differential accumulation of Cd in different varieties. Additionally, StNRAMP2 was selected for verification. Further verification showed that the StNRAMP2 gene plays an important role in the accumulation of Cd in potato. Interestingly, silencing StNRAMP2 increased Cd accumulation in tubers but significantly decreased Cd accumulation in other sites, suggesting a critical role of StNRAMP2 in Cd uptake and transport in potatoes. To further confirm this conclusion, we performed heterologous expression experiments in which overexpression of StNRAMP2 gene in tomato resulted in a threefold increase in Cd content, which further confirmed the important role of StNRAMP2 in the process of Cd accumulation compared with wild-type plants. In addition, we found that the addition of Cd to the soil increased the activity of the plant antioxidant enzyme system, and silencing StNRAMP2 partially reversed this effect. This suggests that the StNRAMP2 gene plays an important role in plant stress tolerance, and future studies could further explore the role of this gene in other environmental stresses. In conclusion, the results of this study improve the understanding of the mechanism of Cd accumulation in potato and provide experimental basis for remediation of Cd pollution.

Threonine Facilitates Cd Excretion by Increasing the Abundance of Gut Escherichia coli in Cd-Exposed Mice

Cadmium (Cd) can easily enter the body through the food chain and threaten health since Cd pollution is prevalent in the environment. Gut microbiota is necessary for the reduction of metal ions. To reduce Cd-induced harmful impacts and Cd accumulation in the body, we investigated the effect of amino acids on gut microbiota and Cd excretion in (fecal Cd) Cd-exposed mice. The screening of 20 amino acids showed that threonine (Thr) effectively increased fecal Cd, and reduced Cd-induced intestinal structural damage. The abundance of Escherichia-Shigella genus and KF843036_g significantly increased after the oral administration of Thr. As the type species of the Escherichia-Shigella genus, Escherichia coli exhibited high similarity to KF843036_g species and significantly decreased Cd-induced gut damage. Cd contents in the liver, kidney, and gut of Cd-exposed mice were also significantly (p < 0.05) decreased after E. coli treatment, while the contents in the feces were increased. The results demonstrated the potential roles that gut E. coli might play in Thr-mediated Cd excretion in Cd-exposed mice. The findings may provide important data for better understanding the molecular biological mechanism of Thr in reducing Cd accumulation in the body.

Driving effects and transfer prediction of heavy metal(loid)s in contaminated courtyard gardens using redundancy analysis and multilayer perceptron

The distribution and migration of heavy metal(loid)s in the soil-vegetable systems of courtyard gardens near mining areas have rarely been investigated, leading to potential food safety risks for residents. Moreover, the existing research is mainly focused on the total content of heavy metal(loid)s (tMetals) rather than the bioavailable contents (aMetals). In this study, 26 and 28 pairs of soil and vegetable samples were collected from the courtyard gardens near the Realgar mine in Baiyun Town and the lead-zinc (Pb-Zn) mine in Shuikoushan Town, respectively. The tMetal and aMetal of cadmium (Cd), mercury (Hg), arsenic (As), Pb, chromium (Cr), nickel (Ni), copper (Cu), Zn, manganese (Mn), iron (Fe), and calcium (Ca) in the samples were analyzed in this study. The results showed that courtyard gardens were polluted by various heavy metal(loid)s at varying degrees. The bioavailabilities of different metals varied significantly, among which Cd has the highest bioavailability (> 30%). In the transfer process of heavy metal(loid)s, the transfer rate (Tf) was ranked as soil-roots (1.50) > stems-leaves (1.07) > roots-stems (0.46) > stems-fruits (0.33). Redundancy analysis was used to evaluate the driving effects, and the results revealed that aCa, aZn, and aFe in soil could inhibit the absorption of aCd by plant roots. Soil organic matter was the inhibiting factor regarding the transfer of aAs and aCu, whereas it was also the promoting factor for transferring aPb, aNi, and aCr. Furthermore, the multilayer perceptron (MLP) could effectively predict the Tf of heavy metal(loid)s based on the aMetal. The R² values of the MLP were ranked as follows: 0.91 for As, 0.88 for Zn, 0.85 for Hg, 0.83 for Cu, 0.79 for Cr, 0.66 for Cd, 0.65 for Pb, and 0.52 for Ni. This study emphasizes the aMetal-based ecological characteristics and prediction ability. The study results are significant for guiding residents to strategize appropriate crop planting and ensure the safe production and consumption of vegetables.