Evaluating the potential health risk of toxic trace elements in vegetables: Accounting for variations in soil factors

Cadmium uptake and transport in vegetables near a zinc-lead mine: Novel insights from Cd isotope fractionation

In this study, Cd isotope analysis was conducted on drought-tolerant (cowpea and sesame) and less drought-tolerant vegetables (water spinach, green pepper, and mung bean) to elucidate the mechanisms underlying Cd uptake and transport. Cd isotopes in plants were identical to or lighter than those in the available pool and exhibited negative fractionation from roots to straws (Δ114/110Cd = -0.22 ‰ to -0.17 ‰) in drought-tolerant vegetables, whereas contrasting results were obtained for less drought-tolerant vegetables (Δ114/110Cd = -0.050 ‰ to 0.39 ‰). Positive Cd isotope fractionation from straws to fruits in drought-tolerant vegetables (Δ114/110Cd = 0.33 ‰ ± 0.03 ‰ and 0.10 ‰ ± 0.03 ‰, respectively) was observed, whereas negligible or negative fractionation was found in less drought-tolerant vegetables (Δ114/110Cd = 0.01 ‰ ± 0.04 ‰ and -0.34 ‰ ± 0.02 ‰, respectively). The vast secretion of organic acids might have led to positive available pool-to-roots and negative roots-to-straws isotope fractionation in drought-tolerant vegetables. In contrast, preferential xylem transport resulted in negative straws-to-fruits isotope fractionation in less drought-tolerant vegetables. This study demonstrated that Cd isotope fractionation in the soil-plant system is associated with plant drought tolerance, and drought-tolerant and less-tolerant plants developed a distinct Cd detoxification mechanism, corresponding to a reversed fractionation of Cd isotopes.

Synergistic interaction between brassinosteroid and jasmonate pathways in rice response to cadmium toxicity

Brassinosteroids (BRs) and jasmonic acid (JA) are known to be involved in regulating plant responses to cadmium (Cd) stress. However, their specific roles and interaction in this process remain unclear. In this study, we discovered that exogenous BR alleviated Cd-mediated growth inhibition of rice seedlings. Enhanced Cd tolerance was also observed in m107, a BR-overproduction mutant. Phenotypic analysis of genetic materials involved in BR signaling confirmed the positive role of BR in regulating rice response to Cd toxicity. OsDLT, a key component in the BR signaling pathway, was found to be crucial for BR-mediated Cd tolerance. Further analysis demonstrated that activation of the BR pathway reduced the accumulation of Cd and reactive oxygen species (ROS) by modulating the expression of genes associated with Cd transport and ROS scavenging. Interestingly, transcriptome analysis indicated that the JA pathway was enriched in OsDLT-regulated differently expressed genes (DEGs). Gene expression and hormone assays showed that BR promoted the expression of JA pathway genes and JA levels in plants. Moreover, BR-induced tolerance was compromised in the JA signaling-deficient mutant osmyc2, suggesting that BR-mediated Cd resistance depends on the activation of the JA signaling pathway. Overall, our study revealed the synergistic interaction between BR and JA pathways in rice response to Cd stress, providing insights into the complex hormonal interplay in plant tolerance to heavy metals.

Phytoavailability, translocation, and accompanying isotopic fractionation of cadmium in soil and rice plants in paddy fields

Rice consumption is a major pathway for human cadmium (Cd) exposure. Understanding Cd behavior in the soil-rice system, especially under field conditions, is pivotal for controlling Cd accumulation. This study analyzed Cd concentrations and isotope compositions (δ114/110Cd) in rice plants and surface soil sampled at different times, along with urinary Cd of residents from typical Cd-contaminated paddy fields in Youxian, Hunan, China. Soil water-soluble Cd concentrations varied across sampling times, with δ114/110Cdwater lighter under drained than flooded conditions, suggesting supplementation of water-soluble Cd by isotopically lighter Cd pools, increasing Cd phytoavailability. Both water-soluble Cd and atmospheric deposition contributed to rice Cd accumulation. Water-soluble Cd's contribution increased from 28-52% under flooded to 58-87% under drained conditions due to increased soil Cd phytoavailability. Atmospheric deposition's contribution (12-72%) increased with potential atmospheric deposition flux among sampling areas. The enrichment of heavy Cd isotopes occurred from root-stem-grain to prevent rice Cd accumulation. The different extent of enrichment of heavy isotopes in urine indicated different Cd exposure sources. These findings provide valuable insights into the speciation and phytoavailability changes of Cd in the soil-rice system and highlight the potential application of Cd isotopic fingerprinting in understanding the environmental fate of Cd.

An assessment of nanotechnology-based interventions for cleaning up toxic heavy metal/metalloid-contaminated agroecosystems: Potentials and issues

Heavy metals (HMs) are among the most dangerous environmental variables for a variety of life forms, including crops. Accumulation of HMs in consumables and their subsequent transmission to the food web are serious concerns for scientific communities and policy makers. The function of essential plant cellular macromolecules is substantially hampered by HMs, which eventually have a detrimental effect on agricultural yield. Among these HMs, three were considered, i.e., arsenic, cadmium, and chromium, in this review, from agro-ecosystem perspective. Compared with conventional plant growth regulators, the use of nanoparticles (NPs) is a relatively recent, successful, and promising method among the many methods employed to address or alleviate the toxicity of HMs. The ability of NPs to reduce HM mobility in soil, reduce HM availability, enhance the ability of the apoplastic barrier to prevent HM translocation inside the plant, strengthen the plant's antioxidant system by significantly enhancing the activities of many enzymatic and nonenzymatic antioxidants, and increase the generation of specialized metabolites together support the effectiveness of NPs as stress relievers. In this review article, to assess the efficacy of various NP types in ameliorating HM toxicity in plants, we adopted a 'fusion approach', in which a machine learning-based analysis was used to systematically highlight current research trends based on which an extensive literature survey is planned. A holistic assessment of HMs and NMs was subsequently carried out to highlight the future course of action(s).

Response of Carrot (Daucus carota L.) to Multi-Contaminated Soil from Historic Mining and Smelting Activities

A pot experiment was undertaken to investigate the effect of Cd, Pb and Zn multi-contamination on the physiological and metabolic response of carrot (Daucus carota L.) after 98 days of growth under greenhouse conditions. Multi-contamination had a higher negative influence on leaves (the highest Cd and Zn accumulation) compared to the roots, which showed no visible change in terms of anatomy and morphology. The results showed the following: (i) significantly higher accumulation of Cd, Zn, and Pb in the multi-contaminated variant (Multi) compared to the control; (ii) significant metabolic responses-an increase in the malondialdehyde content of the Multi variant compared to the control in the roots (by 20%), as well as in the leaves (by 53%); carotenoid content in roots decreased by 31% in the Multi variant compared with the control; and changes in free amino acids, especially those related to plant stress responses. The determination of hydroxyproline and sarcosine may reflect the higher sensitivity of carrot leaves to multi-contamination in comparison to roots. A similar trend was observed for the content of free methionine (significant increase of 31% only in leaves); (iii) physiological responses (significant decreases in biomass, changes in gas-exchange parameters and chlorophyll a); and (iv) significant changes in enzymatic activities (chitinase, alanine aminopeptidase, acid phosphatase) in the root zone.

Occurrence of 8 trace elements in Rhizoma Cibotii from China and exposure assessment

The contamination of trace elements in Chinese edible herbs has attracted worldwide concern over the world. The objective of the present study was to investigate the occurrence and exposure assessment of eight trace elements in Rhizoma Cibotii from China. For this purpose, the method of inductively coupled plasma mass spectrometry was employed to detect the contamination levels of target trace elements in 58 Rhizoma Cibotii samples. The results demonstrated that the trace elements of Cr, Ni, Cu, Zn, and Pb were detected in all analyzed samples; the occurrence frequencies of As, Se, and Cd were 98.3%, 96.6%, and 98.3%, respectively. The highest mean levels were found in Zn (17.32 mg/kg), followed by Pb (8.50 mg/kg) and Cu (3.51 mg/kg). For a further step, one-way ANOVA was used to compare the difference of eight elements levels among groups, and Pearson's correlation analysis was used to explore the correlation between elements in Rhizoma Cibotii. A strong positive correlation between Zn and Cd was observed by Pearson's correlation analysis, which indicated that the possible presence of Cd contamination in Rhizoma Cibotii. Based on the contamination levels, the mean exposure of individual element and the health risks of eight trace elements in Rhizoma Cibotii were estimated by health risk assessment models. The calculated HQ values were less than 1, indicating that the contamination of trace elements in Rhizoma Cibotii did not pose significant health risks to human. In conclusion, the study provided baseline information on the contamination levels of trace elements in Rhizoma Cibotii. Moreover, it is necessary to monitor the trend of trace elements levels in Rhizoma Cibotii, which will be useful for ingredient control and human health protection.

Changes in the photosynthetic response of lettuce exposed to toxic element multicontamination under hydroponic conditions

The effect of toxic element multicontamination on photosynthetic responses was observed in a greenhouse hydroponic culture of lettuce plants (Lactuca sativa var. capitata). The experiment focused only on the combined effect of selected toxic elements without the influence of soil, due to the hydroponic conditions. Pre-cultivated (six-true-leaf stage) plants were grown in control and contaminated hydroponic culture for 14 d. The mix of toxic elements (As, Cd, Pb, and Zn) in the contaminated solution corresponded to the water-soluble fraction of soil from the anthropogenically contaminated Litavka River area, Czech Republic. The plant response was measured by determining the toxic element contents, dry biomass, and gas-exchange parameters. Lettuce accumulated toxic elements predominantly in the roots, with low translocation to the leaves. The uptake of toxic elements harmed photosynthesis and caused a decrease in net photosynthetic rate, transpiration rate, and stomatal conductance. Consequently, the whole dry biomass of the plants decreased. The results show that contamination in hydroponic conditions had an irreversible effect on plant fitness due to direct contact between the roots and contaminated solutions.

Empirical and Mechanistic Modeling of Release Kinetics of Heavy Metals and Their Chemical Distribution in the Rhizosphere and Non-rhizosphere Soils Under Vegetable Cultivation

Biochemical processes in the rhizosphere affect the availability and distribution of heavy metals (HMs) in various forms. Rhizosphere soil (RS) and non-rhizosphere soil (NRS) samples were collected from 10 fields under tarragon (Artemisia dracunculus L.) cultivation to investigate the release kinetics and distribution of HMs including cadmium (Cd), cobalt (Co), copper (Cu), iron (Fe), and zinc (Zn) in five fractions. The cumulative amounts of Cu and Fe released after 88 h were in the following ranges, respectively: 1.31-2.76 and 3.24-6.35 mg kg^-1 in RS and 1.41-2.72 and 3.15-5.27 mg kg^-1 in NRS. The parabolic diffusion and pseudo-second-order equations provided the best fit to the release kinetics data of Cu and Fe, respectively. The cation exchange model (CEM) based on Gaines-Thomas selectivity coefficients implemented in the PHREEQC program could well simulate the release of Cu and Fe suggesting that cation exchange was the dominant mechanism in the release of Fe and Cu from soils by 0.01 M CaCl₂. Cadmium was predominantly found in fraction F2, while other HMs were mainly present in fraction F5. According to the risk assessment code, there was a very high risk for Cd, a medium risk for Co and Cu, a very low risk for Fe, and a low risk for Zn. Correlation analysis showed that soil physicochemical properties were effective in the distribution and transformation of HMs. Significant positive correlations between five fractions indicated that different forms of HMs can potentially transform into each other.

The Status and Research Progress of Cadmium Pollution in Rice- (Oryza sativa L.) and Wheat- (Triticum aestivum L.) Cropping Systems in China: A Critical Review

The accumulation of cadmium in rice (Oryza sativa L.) and wheat (Triticum aestivum L.) is a serious threat to the safe use of farmland and to the health of the human diet that has attracted extensive attention from researchers. In this review, a bibliometric analysis was performed using a VOS viewer (1.6.18, Netherlands) to investigate the status of cadmium contamination in rice and wheat growing systems, human health risks, mechanisms of Cd uptake and transport, and the corresponding research hotspots. It has a certain reference value for the prevention and control of cadmium pollution in rice and wheat planting systems in China and abroad. The results showed that the Cd content in rice and wheat planting systems in the Yangtze River Basin was significantly higher than that in other areas of China, and the Cd content in rice and wheat grains and the hazard quotient (HQ) in Hunan Province was the highest. The average Cd concentration exceeded the recommended limit by about 62% for rice and 81% for wheat. The main reasons for the high Cd pollution in rice and wheat growing areas in Hunan are mining activities, phosphate fertilizer application, sewage irrigation, and electronic equipment manufacturing. In this review, we demonstrate that cadmium toxicity reduces the uptake and transport of essential elements in rice and wheat. Cadmium stress seriously affected the growth and morphology of plant roots. In the shoots, Cd toxicity was manifested by a series of physiological injuries, such as decreased photosynthesis, soluble protein, sugar, and antioxidant enzyme activity. Cadmium that accumulates in the shoots is transferred to grains and then passes up the food chain to people and animals. Therefore, methods for reducing cadmium content in grains of rice and wheat are urgently needed, especially in Cd-contaminated soil. Current research on Cd pollution in rice and wheat planting systems focuses on the bioavailability of Cd, soil rhizosphere changes in wheat and rice, and the role of antioxidant enzyme systems in alleviating heavy metal stress in rice and wheat.

Factors Influencing Consumption Behaviour towards Aquatic Food among Asian Consumers: A Systematic Scoping Review

Asia accounts for over 70% of total global aquatic food consumption, but aquatic food consumption behaviours and attitudes among Asian consumers are poorly documented and understood. This paper synthesises literature on factors influencing aquatic food consumption behaviour in Asia and the potential to support transitions toward more sustainable food consumption patterns. We identified 113 studies for inclusion in a scoping review, and identified five clusters of publications: (1) product attributes, availability, and accessibility (24% of publications); (2) willingness to pay for aquatic foods (25%); (3) psychosocial factors (e.g., attitudes and subjective norms) (17%); (4) sociodemographic and lifestyle factors (21%); and (5) miscellaneous factors, including food safety and social status (13%). This study indicates that multiple interacting factors influence aquatic food consumption behaviours among Asian consumers, among which price is central. Knowledge of, and attitudes toward, the perceived quality and safety of aquatic foods were identified as important but were mediated by household characteristics. Sustainable production practices, country of origin, and ecolabels were found to be less influential on consumption behaviour. We found that improving consumers' knowledge and attitudes about the quality and safety of aquatic foods might positively influence aquatic food consumption behaviour. Future multidisciplinary research is required to better understand interactions among the multiple factors that influence Asian consumers' aquatic food consumption behaviour.

Anthropogenic activities affecting metal transfer and health risk in plastic-shed soil-vegetable-human system via changing soil pH and metal contents

Accumulation and concomitant risk of metals in plastic-shed soil (PSS)-vegetable system around industrial areas have attracted growing public concern recently, while limited studies have focused on human bioaccessible metals in various plastic-shed vegetables and health risk calculated using bioaccessible metals. Previous studies showed that intensive farming and industrial activities could prominently affect metal migration from PSS to vegetables via altering PSS pH, total and bioavailable metal contents. In contrast, whether changes in PSS pH and metal contents control bioaccessible metals in vegetables and health risk is still unknown. For PSS management and sustainable plastic-shed vegetable production in the areas with rapid industrialization, 41 PSS and 32 plastic-shed vegetable samples were sampled from the industrial areas of Yangtze River Delta, China to systematically clarify the specific connections among anthropogenic activities, soil pH and metal contents, and metal transfer and health risk in PSS-vegetable-human system. The results indicated that Cr and Cd contents in 15.6% and 9.38% of vegetable samples exceeded the allowable limits in China. Tolerable cancer risk existed and was mainly induced by bioaccessible Cr in vegetables. Decreased PSS pH mainly caused by heavy use of nitrogen fertilizers increased bioavailable Ni, Cd, Zn, Pb, and Cu in PSS and subsequently enhanced their total and bioaccessible contents in vegetables. Prominent Cr accumulation in PSS induced by industrial wastewater irrigation exacerbated Cr uptake by vegetables, which increased bioaccessible Cr in vegetables and contributed greatly to cancer risk. To reduce transfer and health risk especially of Cd and Cr in the food chain, some appropriate measures related to source control and remediation should be proposed for preventing and mitigating PSS acidification and Cr accumulation.

Metal(loid) concentrations, bioaccessibility and stable lead isotopes in soils and vegetables from urban community gardens

Community gardens are "green oases" of recent cities with many benefits for human society. From a human health perspective, these benefits can be damaged by chemical contamination of soil and cultivated vegetables. Using geochemical approaches, this study characterised (i) total metal(loid) concentrations in soils and two commonly grown vegetables in urban community gardens (Bratislava, Slovakia), (ii) gastrointestinal bioaccessibility using a modified physiologically based extraction test (PBET), and (iii) stable lead (Pb) isotopes in order to identify sources of metal(loid)s, solubilisation in the human body and migration of Pb from soil to vegetables. While some soils could be considered contaminated when compared to the Slovak legislation for agricultural soil, the bioaccessibility of metal(loid)s did not exceed 20% in the intestinal phase, with the exception of cadmium (Cd). Tomatoes and lettuce contained low total and bioaccessible concentrations of metal(loid)s, being safe for people who consume their own grown vegetables. There were differences in Pb isotope composition among bulk soils, vegetables and bioaccessible Pb, with less radiogenic Pb being preferentially mobilised. Statistical methods considering the compositional nature of the geochemical data and the enrichment factor (EF) distinguished well metal(loid)s of natural origin (As, Co, Cr, Fe, Mn, Ni, V) from those with anthropogenic contributions. This research has shown the usefulness of integrating different methodologies to better understand the geochemistry of metal(loid)s in urban soils with their highly diversified sources.

A risk-based approach for the safety analysis of eight trace elements in Chinese flowering cabbage (Brassica parachinensis L.) in China

BACKGROUND

Most countries set regulatory values for the total trace element (TE) concentrations in soil, although there is growing interest in using a risk-based approach to evaluate the bioavailable TE using dilute salt extractants or other soil parameters, including pH and organic carbon_. The present study compares the current regulatory system (based on total TEs and pH) and a risk-based approach using 0.01 mol L^-1 CaCl₂ to estimate the bioavailable fraction.

RESULTS

In total, 150 paired samples of Chinese flowering cabbages (Brassica parachinensis) and their growth soils were collected, and the total and extractable concentrations of chromium (Cr), cadmium (Cd), lead (Pb), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As) and mercury (Hg), as well as soil pH and organic matter content, were measured. No more than 3.33% of the edible parts exceeded Chinese food safety standards, even when growing in soils exceeding the current regulatory thresholds by over 50%. The total soil Cd (1.5 mg kg^-1 ), as well as the extractable concentrations of Cd (0.1 mg kg^-1 ), Ni (0.03 mg kg^-1 ) and Zn (0.1 mg kg^-1 ), are the key factors affecting the TE concentrations in B. parachinensis.

CONCLUSION

Our findings suggest that the current soil regulatory guidelines for safe production of B. parachinensis are overly strict and conservative. A risk-based approach based on the extractable TE concentrations would provide a better indication for plant uptake of soil TEs and avoid the waste of farmlands that can still produce safe vegetables. Future research should focus on providing crop-specific available TE concentration guidelines to promote effective utilization of farmlands. © 2021 Society of Chemical Industry.

Foliar application of seed water extract of Nigella sativa improved maize growth in cadmium-contaminated soil

Cadmium (Cd) is a widespread heavy metal, which commonly exert negative impacts on agricultural soils and living organisms. Foliar application of seed water extract of black cumin (Nigella sativa L.) can mitigate the adverse impacts of Cd-toxicity in plants through its rich antioxidants. This study examined the role of seed water extracts of N. sativa (NSE) in mitigating the adverse impacts of Cd-toxicity on maize growth. Two maize genotypes (synthetic ‘Neelum’ and hybrid ‘P1543’) were grown under 0, 4, 8 and 12 mg Cd kg^-1 soil. The NSE was applied at three different concentrations (i.e., 0, 10 and 20%) as foliar spray at 25 and 45 days after sowing. All Cd concentrations had no effect on germination percentage of both genotypes. Increasing Cd concentration linearly decreased root and allometric attributes, gas exchange traits and relative water contents of hybrid genotype. However, gas exchange traits of synthetic genotype remained unaffected by Cd-toxicity. Overall, hybrid genotype showed better tolerance to Cd-toxicity than synthetic genotype with better germination and allometric attributes and less Cd accumulation. Foliar application of NSE lowered negative effects of Cd-toxicity on all studied traits, except relative water contents. In conclusion, foliar application of NSE seemed a viable option to improve maize growth in Cd-contaminated soil.

Speciation and fate of toxic cadmium in contaminated paddy soils and rice using XANES/EXAFS spectroscopy

The present study was conducted to determine the Cd distribution and speciation in contaminated paddy soils and rice kernels using XANES/EXAFS spectroscopy. The morphology and crystallization of rice and soils were investigated using FE-SEM and XRD techniques. The EXAFS spectra of Cd in soil and rice kernels showed that cadmium oxides (CdO) in soil and rice kernels formed Cd clusters with Cd-O bond distances of 2.35 Å and 2.25 Å (coordination numbers of 2.3 and 3.8), respectively. The XRD patterns show that silica oxide (SiO₂, 2θ = 24.2) and aluminum oxide (Al₂O₃, 2θ = 35.7) were the main components detected. The FE-SEM analysis revealed that the surface characteristics and sizes of the rice kernels are smooth and uneven with particle sizes of 0.5-4 µm, while the soil particles are not uniform and aggregated. Furthermore, the distribution of toxic metals/metalloid (Cd, Pb, Cr, Ni, As, Cu, and Zn) accumulated in the contaminated paddy soils and rice crops were also examined. Interestingly, these results offered an insight into the accumulation mechanism and distribution of heavy metals in contaminated rice farming soils and rice crops.

Interactive effect of potassium and cadmium on growth, root morphology and chlorophyll a fluorescence in tomato plant

A hydroponic experiment was conducted to evaluate the role of potassium (K) in tomato plant growth exposed to cadmium (Cd) stress. In this work, the effects of three potassium nutrition regimes (155, 232 and 310 ppm of K) combined with Cd at different levels (0, 12 and 25 µM of CdCl2) on chlorophyll content index, root and shoot dry weights, root morphology, chlorophyll a fluorescence and translocation factor were analyzed. The results showed a negative effect of cadmium, at different concentrations, on all these parameters. However, optimization of K nutrition has shown promising results by limiting the negative effect of Cd. A positive effect of the high concentration of K (310 ppm) was observed on leaf chlorophyll content and chlorophyll a fluorescence compared to 232 and 155 ppm under Cd stress. K supply improved the electron transport at PSI side indicated by the increase in the amplitude of the I-P phase of OJIP transient. Also, K at a concentration of 310 ppm significantly reduced Cd translocation from root to shoot and improved root and shoot growth parameters in the presence of Cd. K supplementation can reduce the negative effect of Cd by improving photosynthesis and promoting chlorophyll synthesis. The optimization of nutrients composition and concentration might be a good strategy to reduce the impact of Cd on plant growth and physiology.

Enriched isotope tracing to reveal the fractionation and lability of legacy and newly introduced cadmium under different amendments

The newly introduced Cd (Cd_N) has different environmental fates than legacy Cd (Cd_L) and how to distinguish them in soil under different amendments is crucial for understanding natural aging and engineered remediation of Cd pollution in soil. In this study, enriched stable isotope tracer (¹¹²Cd) was introduced to distinguish the fate of Cd_N and Cd_L in paddy soil under pH adjustment and quicklime, slaked lime, and biochar amendments. The behaviors of Cd_N and Cd_L were studied during 56 days of flooding incubation through overlying water analysis, sequential extraction fractionation and lability (exchangeable pool probed by ¹¹⁰Cd isotopic spike) assessment. The results showed that soil pH is the main driving factor controlling the partition of both Cd_N and Cd_L in overlying water. During the incubation, Cd_N transformed quickly from soluble fraction to residual fraction under all treatments. In addition, at the end of the incubation, Cd_N concentrations in residual fraction were much higher than that of Cd_L, suggesting a more thorough aging of Cd_N than Cd_L. The labile Cd_N (ECd_N) under pH adjustment and biochar amendment decreased during incubation and ECd_N% was essentially the same with that of ECd_L% after 28 days, indicating the aging equilibrium of exchangeable pool of Cd_N.

Dynamic interactions between soil cadmium and zinc affect cadmium phytoavailability to rice and wheat: Regional investigation and risk modeling

Characterizing the interactions between Cd and Zn with respect to the soil soluble Cd and crop Cd uptake allows the development of risk-based approaches to the performance of grain crops. By means of a three-year survey of 358 rice fields and 206 wheat fields across China, this study investigated the effect of Cd-Zn interactions on the phytoavailability of Cd to rice and wheat. The interactive nature between the Cd:Zn ratio and pH of soil affected crop Cd uptake, and the resulting grain Cd intake risk, were examined by the Free-Ion Activity-based model and probability analysis. In highly acidic rice soils (pH < 5.9), soil Zn had no effect on rice Cd uptake, whereas, under near-neutral conditions (pH > 5.9), a site-specific influence of soil Zn on grain Cd concentration was found. Soil Zn could inhibit Cd uptake and translocation by the plant in soil-wheat system when the soil Cd:Zn ratio decreased to 0.0083 and lower. Rice grain poses a significant health risk to local consumers due to its high Cd accumulation and its low Zn accumulation. In order to reduce the health risks from dietary Cd to local consumers, approximately 63.9% of the rice fields and 30.5% of the wheat fields require strategies ameliorating soil acidity in rice soils and increasing Zn concentrations in wheat soils.

Urban kitchen gardens: Effect of the soil contamination and parameters on the trace element accumulation in vegetables - A review

Trace element contaminants in kitchen garden soils can contribute to human exposure through the consumption of homegrown vegetables. In urban areas, these soils can be contaminated to various degrees by trace element (TE). They are characterized by a great variability in their physicochemical parameters due to the high anthropization level, the wide variety and combination of disturbance sources, as well as the diversity of cultivation practices and the large range of contamination levels. Pollutants can be taken up by vegetables cultivated in these soils and be concentrated in their edible parts. In this review, the behavior of vegetables cultivated in contaminated kitchen gardens is assessed through six examples of the most widely cultivated vegetables (lettuce, tomato, bean, carrot, radish, potato). The role of soil parameters that could influence the uptake of As, Cd, Cr, Ni, Pb, and Zn by these vegetables is also discussed.

Modeling and optimizing the removal of cadmium by Sinapis alba L. from contaminated soil via Response Surface Methodology and Artificial Neural Networks during assisted phytoremediation with sewage sludge

The study was aimed to model and optimize the removal of cadmium from contaminated post-industrial soil via Sinapis alba L. by comparing two modeling approaches: Response Surface Methodology (RSM) and Artificial Neural Networks (ANN). The experimental design was done using the Box-Behnken Design method. In the RSM model, the quadratic model was shown to predict the closest results in comparison to our experimental data. For ANN approach, a two-layer Feed-Forward Back-Propagation Neural Network model was designed. The results showed that sewage sludge supplementation increased the efficiency of the Sinapis alba plant in removing Cd from the soil. After 28 days of exposure, the removal rate varied from 10.96% without any supplementation to 65.9% after supplementation with the highest possible (law allowed) dose of sewage sludge. The comparison proved that the prediction capability of the ANN model was much higher than that of the RSM model (adjusted R-square: 0.98, standard error of the Cd prediction removal: 0.85 ± 0.02). Thus, the ANN model could be used for the prediction of heavy metal removal during assisted phytoremediation with sewage sludge. Moreover, such approach could also be used to determinate the dose of sewage sludge that will ensure highest process efficiency.

Bioavailability of trace metals and rare earth elements (REE) from the tropical soils of a coal mining area

In order to assess the environmental risks related to mining activities in Southern Brazil, the transfer of trace metals and rare earth elements (REE) from soils to soybeans was evaluated in a U-rich area associated with coal mining. In some samples, As, Ba, Co, Cu and Ni were higher than the guidelines proposed by the Brazilian environmental agency. Soil, coal, ash, tailings and soybean were systematically sampled so that the chemical fractionation/speciation of the elements could be related to their bioavailability. In addition to total concentrations quantified by ICP-MS after microwave digestion, elemental measurements were made following different evaluations of the bioavailable metal, including chemical extractions (10 mM Ca(NO₃)₂ and 3-step sequential extraction), diffusive gradient in thin films technique (DGT) and chemical modeling (WHAM-free ion). Lower pH and higher clay and organic matter content were reflected by higher metal assimilation by the plants, especially by the roots and leaves. The bioaccumulation factor (BF) was generally higher for the leaves (e.g. Cu, Mn, Sr, Zn, Ba, REE with exception of Tm and Yb) and roots (e.g. Cd, Th and U). The results revealed that for Ba, Cd, Sr, Pb, U and most of the REE, the free ion concentration was strongly correlated with the metal content in the plants, especially for the grains. Values obtained by DGT were also correlated with the bioavailable portion of Ba, Mn, Sr, Zn, Pb, U and REE. Measurements obtained from Ca extractions correlated well with the bioavailable metals for Ba, Cd, Sr, Rb, Pb and Th. The free or extractable metal fractions gave much better correlations of the bioavailable fractions than did the total metal concentrations from the soils, especially for the REE. The paper validates some simplified means of estimating the risks associated with metals and REE in tropical soils affected by mining activities.

Ameliorative effects of Lanthanum(Ⅲ) on Copper(Ⅱ) stressed rice (Oryza sativa) and its molecular mechanism revealed by transcriptome profiling

Rare earth elements are known to alleviate heavy metal stress. However, the potential mechanisms of the alleviation remain unclear. This study compared the effects of La(NO3)3 and La(NO3)3-amino acid chelates (La (Ⅲ)-AA) on growth, oxidative stress, ultrastructure, bioaccumulation and gene expression in rice. Results demonstrated that 20 mg/L La (Ⅲ)-AA can effectively ameliorate CuSO4 (50 mg/L) stress in rice by reducing oxidative stress and increasing chlorophyll content, thus promoting growth. ICP and TEM revealed an antagonistic effect between La (Ⅲ) and Cu(Ⅱ). Exogenous La (Ⅲ)-AA decreased Cu(Ⅱ) content in rice leaves, stems and roots by 55.56%, 59.46% and 26.29%, and ameliorated Cu(Ⅱ) damage by maintaining the ultrastructure of mesophyll cells. RNA sequencing identified 7020 differentially expressed genes, and 8 were validated by qRT-PCR. Indole-3-acetic acid (IAA) concentration was detected by HPLC. Correlation analysis between OsGH3.4-IAA-Expansin revealed that IAA content is negatively correlated with OsGH3.4 (r = -0.82, P < 0.05), and positively correlated with Expansin (r = 0.78, P < 0.05). It's assumed that La (Ⅲ)-induced OsGH3.4 could inhibit IAA-dependent Expansin expression, thereby conferring resistance to Cu stress. This work provides novel insights into the molecular basis underlying La (Ⅲ)-induced Cu(Ⅱ) tolerance in rice.

Speciation and fate of toxic cadmium in contaminated paddy soils and rice using XANES/EXAFS spectroscopy

The present study was conducted to determine the Cd distribution and speciation in contaminated paddy soils and rice kernels using XANES/EXAFS spectroscopy. The morphology and crystallization of rice and soils were investigated using FE-SEM and XRD techniques. The EXAFS spectra of Cd in soil and rice kernels showed that cadmium oxides (CdO) in soil and rice kernels formed Cd clusters with Cd-O bond distances of 2.35 Å and 2.83 Å (coordination numbers of 2.3 and 4.2), respectively. The XRD patterns show that silica oxide (SiO₂, 2θ  = 24.2) and aluminum oxide (Al₂O₃, 2θ = 35.7) were the main components detected. The FE-SEM analysis revealed that the surface characteristics and sizes of the rice kernels are smooth and uneven with particle sizes of 0.5-4 μm, while the soil particles are not uniform and aggregated. Furthermore, the distribution of toxic metals/metalloid (Cd, Pb, Cr, Ni, As, Cu, and Zn) accumulated in the contaminated paddy soils and rice crops were also examined. Interestingly, these results offered an insight into the accumulation mechanism and distribution of heavy metals in contaminated rice farming soils and rice crops.

Evaluation of the uptake capacities of heavy metals in Chinese cabbage

Heavy metal (HM) contamination in soil result in second pollution damage to Chinese cabbage, leading to deleterious health impacts. To elucidate the common transfer and accumulation characteristics of HMs in Chinese cabbage cultivar is important for safety breeding and consumption. In this case, concentrations and transfer capacities of HMs (Cd, Cr, Hg, Pb and As) in 35 common Chinese cabbage genotypes and their genotypic difference were investigated in this work. Results indicate that Chinese cabbage cultivar was more susceptible to Cd pollution, Hg was easily sifted from underground part to aerial part, Cr and Pb have similar enrichment and translocation characteristics, and Chinese cabbage cultivar had tolerance to As toxicity to some extent. Moreover, genotypic difference in HM accumulation in different parts of Chinese cabbage cultivar was also observed, and for edible part, followed by Hg>As>Cd>Pb>Cr. Referring to overall HM pollution level and biomass yield of edible part of 35 tested Chinese cabbages, B18, B6, B2 and B3 could be considered as the potential HMs pollution-safe Chinese cabbage cultivars. Information founded in this work may be used to provide referential strategies and methods to minimize the influx of HMs pollutants to human being through consumption and cultivation of Chinese cabbages.

Ecological risk assessment of cerium for tropical agroecosystems

Cerium (Ce) is present in high technology materials and in mineral P fertilizers and the use and discharge of such resources may change the natural status of Ce in the soil environment. Brazilian soils in farming areas are significantly exposed to increased levels of unintentionally-added Ce through intensive input of phosphate fertilizers. The aims of this study were to evaluate the ecotoxicological risk to plants growing in tropical soils contaminated with Ce, as well as to create a database to support future legislation regulating the limits of this element in Brazilian and conceivably other tropical soils. Eight crop species (corn, sorghum, rice, wheat, soybeans, sunflower, radish, and beans) were exposed to a Ce concentration gradient in two typical tropical soils (Oxisol and Inceptsol), and an artificial soil. Our findings showed that among the endpoints measured, Ce phytotoxicity was more pronounced on shoot dry matter than on percent germination and germination speed index. Sensitivity of plants is species specific and our data showed that sunflower and radish exposed to Ce were the most sensitive crop species. Soil properties such as pH, cation exchange capacity, and organic carbon may have influenced the severity of Ce phytotoxicity. Because of that, the Oxisol contaminated with this element caused higher phytotoxicity than the other soils tested. Our risk assessment results (hazardous concentration, HC₅ = 281.6 mg Ce kg^-1) support the idea that unintentional Ce input through P fertilizers does not pose a risk to soils of Brazilian agroecosystems.

Heavy metals in food crops: Health risks, fate, mechanisms, and management

Food security is a high-priority issue for sustainable global development both quantitatively and qualitatively. In recent decades, adverse effects of unexpected contaminants on crop quality have threatened both food security and human health. Heavy metals and metalloids (e.g., Hg, As, Pb, Cd, and Cr) can disturb human metabolomics, contributing to morbidity and even mortality. Therefore, this review focuses on and describes heavy metal contamination in soil-food crop subsystems with respect to human health risks. It also explores the possible geographical pathways of heavy metals in such subsystems. In-depth discussion is further offered on physiological/molecular translocation mechanisms involved in the uptake of metallic contaminants inside food crops. Finally, management strategies are proposed to regain sustainability in soil-food subsystems.

Distribution, pollution, bioaccumulation, and ecological risks of trace elements in soils of the northeastern Qinghai-Tibet Plateau

Environmental quality of the northeastern Qinghai-Tibet Plateau has attracted more attention due to increasing anthropogenic disturbance. Therefore, this study investigated the distribution, pollution, ecological risks, and bioaccumulation of 12 target heavy metals and 16 rare earth elements (REEs) in soils of this area. The average concentrations of target trace elements in soils ranged from 0.16 (Hg) to 500.46 (Cr) mg/kg. Pb caused more serious pollution than the other elements based on geo-accumulation index evaluation. Hg exhibited the strongest enrichment feature with the average enrichment factor of 8.41. Compare with modified contamination degree and pollution load index, Nemerow pollution index method obtained the most serious evaluation results that 45.67% and 16.54% of sampling sites possessed high and moderate pollution. Evaluation results of potential ecological risk index showed that trace elements in soils posed very high and considerable ecological risks in 34.65% and 7.09% of sampling sites, respectively. Mining area was the region with the most serious pollution and ecological risks. Average bioaccumulation factor (BCF) values of target trace elements ranged from 0.05 (REEs) to 2.67 (Cr). Cr was the element that was easier to bio-accumulate in plants of the study area than the other target elements. It is in urgent need to take effective measures for controlling current pollution and potential ecological risks of trace elements in soils of the northeastern Qinghai-Tibet Plateau.

Dietary cadmium intake from rice and vegetables and potential health risk: A case study in Xiangtan, southern China

Soil contamination in some areas of southern China has resulted in elevated dietary intake of cadmium (Cd), posing a potential risk to human health. A survey of paired soil-rice (n = 200) and soil-vegetable (n = 142) samples was conducted in Xiangtan county of Hunan province, southern China. The concentrations of Cd in all the samples were determined by inductively coupled plasma mass spectrometry. Dietary intakes of Cd from the consumption of locally produced rice and vegetables were estimated for different age groups. Among the 342 crop samples collected in the survey, 88% and 29% of rice grain and vegetable samples, respectively, exceeded the Chinese maximum permissible limit for Cd (0.2 mg dry weight kg^-1, 0.2 mg fresh weight kg^-1 and 0.1 mg fresh weight kg^-1 for rice, leafy vegetables and for rootstalk and legume vegetables, respectively). The median dietary Cd intake varied from 66.5 to 116 μg Cd kg^-1 body weight (BW) month^-1, with children (4-11 years) exhibiting the highest intake. These values are 2.7-4.6 times the tolerable dietary intake of 25 μg kg^-1 BW month^-1 recommended by the Joint FAO/WHO Expert Committee on Food Additives. For the general population in Xiangtan county, rice contributed the majority (81%) of the Cd intake with vegetables contributing only 19%. The median hazard quotient calculated from dietary Cd intake was 2.4 times the permissible level, indicating a high risk to the local residents. This study highlights an urgent need to reduce the transfer of Cd from soil to the food chain in the investigated region.

Assessing cadmium exposure risks of vegetables with plant uptake factor and soil property

Plant uptake factors (PUFs) are of great importance in human cadmium (Cd) exposure risk assessment while it has been often treated in a generic way. We collected 1077 pairs of vegetable-soil samples from production fields to characterize Cd PUFs and demonstrated their utility in assessing Cd exposure risks to consumers of locally grown vegetables. The Cd PUFs varied with plant species and pH and organic matter content of soils. Once normalized PUFs against soil parameters, the PUFs distributions were log-normal in nature. In this manner, the PUFs were represented by definable probability distributions instead of a deterministic figure. The Cd exposure risks were then assessed using the normalized PUF based on the Monte Carlo simulation algorithm. Factors affecting the extent of Cd exposures were isolated through sensitivity analyses. Normalized PUF would illustrate the outcomes for uncontaminated and slightly contaminated soils. Among the vegetables, lettuce was potentially hazardous for residents due to its high Cd accumulation but low Zn concentration. To protect 95% of the lettuce production from causing excessive Cd exposure risks, pH of soils needed to be 5.9 and above.

Modulation of hexavalent chromium toxicity on Οriganum vulgare in an acidic soil amended with peat, lime, and zeolite

Dynamics of chromate (Cr(VI)) in contaminated soils may be modulated by decreasing its phytoavailability via the addition of organic matter-rich amendments, which might accelerate Cr(VI) reduction to inert chromite (Cr(III)) or high-cation exchange capacity amendments. We studied Cr(VI) phytoavailability of oregano in a Cr(VI)-spiked acidic soil non-treated (S) and treated with peat (SP), lime (SL), and zeolite (SZ). The addition of Cr(VI) increased the concentrations of Cr(VI) and Cr(III) in soils and plants, especially in the lime-amended soil. The plant biomass decreased in the lime-amended soil compared to the un-spiked soil (control) due to decreased plant phosphorus concentrations and high Cr(VI) concentrations in root at that treatment. Oregano in the peat-amended soil exhibited significantly less toxic effects, due to the role of organic matter in reducing toxic Cr(VI) to Cr(III) and boosted plant vigour in this treatment. In the lime-amended soil, the parameters of soil Cr(VI), soil Cr(III), and root Cr(III) increased significantly compared to the non-amended soil, indicating that Cr(VI) reduction to Cr(III) was accelerated at high pH. Added zeolite failed to decreased Cr(VI) level to soil and plant. Oregano achieved a total uptake of Cr(III) and Cr(VI) of 0.275 mg in plant kg^-1 soil in a pot in the non-amended soil. We conclude that peat as soil amendment might be considered as a suitable option for decreasing Cr(VI) toxicity in soil and plant, and that oregano as tolerant plant species has a certain potential to be used as a Cr accumulator.

Soil contamination with cadmium, consequences and remediation using organic amendments

Cadmium (Cd) contamination of soil and food crops is a ubiquitous environmental problem that has resulted from uncontrolled industrialization, unsustainable urbanization and intensive agricultural practices. Being a toxic element, Cd poses high threats to soil quality, food safety, and human health. Land is the ultimate source of waste disposal and utilization therefore, Cd released from different sources (natural and anthropogenic), eventually reaches soil, and then subsequently bio-accumulates in food crops. The stabilization of Cd in contaminated soil using organic amendments is an environmentally friendly and cost effective technique used for remediation of moderate to high contaminated soil. Globally, substantial amounts of organic waste are generated every day that can be used as a source of nutrients, and also as conditioners to improve soil quality. This review paper focuses on the sources, generation, and use of different organic amendments to remediate Cd contaminated soil, discusses their effects on soil physical and chemical properties, Cd bioavailability, plant uptake, and human health risk. Moreover, it also provides an update of the most relevant findings about the application of organic amendments to remediate Cd contaminated soil and associated mechanisms. Finally, future research needs and directions for the remediation of Cd contaminated soil using organic amendments are discussed.

Bioaccessibility and Human Exposure Assessment of Cadmium and Arsenic in Pakchoi Genotypes Grown in Co-Contaminated Soils

In many countries cadmium (Cd) and arsenic (As) commonly coexist in soils contaminated by mining activities, and can easily enter the human body via consumption of leafy vegetables, like the popularly consumed pakchoi (Brassica chinensis L.), causing major health concerns. In the present study, bioaccessibility and human exposure of Cd and As were assessed in twenty genotypes of pakchoi cultured at two different levels of co-contamination to identify low health risk genotypes. The bioaccessibilities of Cd and As represent a fraction of the total metals content could be bioaccessible for human, in the present study, significant differences in pakchoi Cd and As bioaccessibility were observed among all tested genotypes and co-contaminated levels. Cd and As bioaccessibility of pakchoi were in the ranges of 24.0-87.6% and 20.1-82.5%, respectively, for in the high level co-contaminated soils, which was significantly higher than for low level co-contaminated soils with 7.9-71.8% for Cd bioaccessibility and 16.1-59.0% for As bioaccessibility. The values of bioaccessible established daily intakes (BEDI) and the total bioaccessible target hazard quotients (TBTHQ) of Cd and As were also considerably higher in high level co-contaminated soils than in low level co-contaminated soils. Two genotypes (Meiguanqinggengcai and Zhenqing60F1) contained relatively low concentrations and bioaccessible Cd and As and, their BEDI and TBTHQ for Cd and As ranged below the tolerable limits set by the FAO/WHO (BEDI of Cd < 0.83 μg kg^-1 bw day^-1, BEDI of As < 3 μg kg^-1 bw day^-1) and United States Environmental Protection Agency (TBTHQ for Cd and As < 1), this applied for both levels of co-contaminated soils for adults and children. Consequently, these findings suggest identification of safe genotypes in leafy vegetable with low health risk via genotypic screening and breeding methods could be a useful strategy to ensure the safety of food crops grown in those Cd and As co-contaminated fields due to mining activities.