Source-specific risk assessment for cadmium in wheat and maize: Towards an enrichment model for China

Evaluation and Source Analysis of Plant Heavy Metal Pollution in Kalamaili Mountain Nature Reserve

Plants serve as vital components of ecosystems, with their contamination status acting as sensitive indicators of environmental pollution. Therefore, the precise assessment of plant heavy metal contamination and source identification are crucial for regional ecological conservation and sustainable development. This study investigated heavy metal pollution in four characteristic plant species (Anabasis aphylla L., Alhagi camelorum Fisch., Reaumuria songonica (PalL)Maxim., and Haloxylon ammodendron (C. A. Mey.) Bunge.) within the Kalamaili Mountain Nature Reserve, employing comprehensive methodologies including pollution indices, bioconcentration factors (BCFs), absolute principal component score-multiple linear regression (APCS-MLR), and the random forest model (RF). The key findings revealed the following: The soil exhibited severe Cd and Hg contamination. The plant Cr concentrations exceeded standard limits by 31.89 to 147 fold. The Pb, Hg, and As content in plants showed significant differences. The plants displayed differential metal enrichment capacities, ranked as Cr (BCF = 3.28) > Hg (1.22) > Cd (0.92) > Cu (0.25) > Zn (0.15) > Pb (0.125) > As (0.125), highlighting Cr, Hg, and Cd as priority ecological hazards. Complex interactions were observed, with Reaumuria songonica (PalL)Maxim. showing strong Cd soil-plant correlation (r = 0.78), whereas Alhagi camelorum Fisch. demonstrated negative associations (Cd: r = -0.21). APCS-MLR identified mining/smelting as primary contributors to Cd (63.49%), Zn (55.66%), and Cr (45.51%), while transportation dominated Pb emissions (72.92%). Mercury pollution originated from mixed sources (56.18%), likely involving atmospheric deposition, and RF modeling corroborated these patterns, confirming industrial and transportation synergies for Cd, Zn, Cr, Cu, Hg, and As, with Pb predominantly linked to vehicular emissions. This multidisciplinary approach provides scientific evidence for establishing heavy metal monitoring systems and formulating targeted remediation strategies in arid ecologically fragile regions.

Can N-Doped Biochar Achieve Safe Vegetable Production in Soil Heavily Contaminated by Heavy Metals?

Although the cultivation of food crops in farmland heavily contaminated by heavy metals is prohibited in China, vegetables can still be planted on a small-scale due to their short growth cycles and flexible sale models, posing a significant threat to local consumers. In this study, a pot culture experiment was conducted to investigate the feasibility of safe production through the in-situ stabilization of heavy metals in heavily contaminated soil. The remediation efficiency of wheat straw biochar and N-doped biochar, the growth of spinach, the heavy metal accumulation in spinach, and potential health risks were also explored. The results indicated that both biochar and N-doped biochar significantly affected the soil pH, cation exchange capacity, organic matter, available phosphorus, available potassium, alkaline nitrogen content, and spinach biomass, but the trends were variable. Additionally, the diethylenetriaminepentaacetic-extractable Pb, Cd, Cu, Zn, and Ni concentrations decreased 9.23%, 7.54%, 5.95, 7.44%, and 16.33% with biochar, and 10.46%, 12.91%, 21.98%, 12.62%, and 12.24% with N-doped biochar, respectively. Furthermore, N-doped biochar significantly reduced the accumulation of Pb, Cd, and Ni in spinach by 35.50%, 33.25%, and 30.31%, respectively. Health risk assessment revealed that the non-carcinogenic risk index for adults and children decreased from 17.0 and 54.8 to 16.3 and 52.5 with biochar and 11.8 and 38.2 with N-doped biochar, respectively, but remained significantly higher than the acceptable range (1.0). The carcinogenic risk assessment revealed that the risk posed by Cd in spinach exceeded the acceptable value (10-4) for both adults and children across all treatments. These results may imply that biochar and N-doped biochar cannot achieve the safe production of vegetables in soil heavily contaminated by heavy metals through in-situ stabilization.

Impact of short-term soil disturbance on cadmium remobilization and associated risk in vulnerable regions

A comprehensive understanding of cadmium (Cd) migration in soils near contaminated hotspots is crucial for optimizing remediation efforts and ensuring crop health. This study investigates agricultural soils from four sites in mining and sewage-irrigation areas, assessing the impact of inorganic and organic fertilizer application on soil Cd remobilization. Results revealed that fertilization, particularly with mineral phosphorus, disrupts soil stability, substantially increases short-term Cd mobility in vulnerable regions. Random Forest analysis identified elevated dissolved organic matter and pH changes as key drivers of Cd remobilization. Monte Carlo simulation, integrating Michaelis-Menten reaction kinetics model, further accessed the potential risk of Cd remobilization. The model predicted that the probabilities of grain exceeding Cd thresholds ranged from 021.6 % for rice, 13.8 %100 % for wheat, and 084.2 % for maize in the absence of fertilizer use. Fertilization significantly increased these exceedance probabilities by 6.1 %87.4 %, with the highest risks observed in irrigation-contaminated soils, particularly under mineral phosphorus fertilization. Nevertheless, it recommended that while fertilization can elevate Cd remobilization risk in hotspots, remediation strategies might not always be necessary. This study highlights the potential of hybrid data-driven approaches, combining machine learning, mechanistic model and stochastic prediction to simplify the complex environmental process, allowing for integrated risk evaluations.

Speciation characteristics of heavy metal(loid)s in maize-wheat farmland with applying spent mushroom substrates

Spent mushroom substrates (SMS) have been increasingly applied as organic fertilizer worldwide. However, the effects of various SMS on the accumulation and speciation characteristics of soil heavy metal(loid)s (HMs) are generally overlooked. Three types of SMS, including Flammulina velutipes residue (FVR), Agaricus bisporus residue (ABR), and Auricularia auricula residue (AAR), were applied to replace 25 % and 50 % of chemical fertilizer (based on nitrogen application) used in maize-wheat farmland. Compared to chemical fertilizer, the soil Cd, Pb, and As concentrations were decreased by 20.41 %, 5.97 %, and 10.09 %, respectively. And the residual fractions of soil HMs were increased through the application of SMS, indicating a reduction in their bioavailability. Notably, 50 % ABR replacement significantly increased the proportion of residual fraction in soil Cd, Pb, and As by 23.03 %, 15.15 %, and 4.85 %, respectively (P<0.05). A significant negative correlation was observed between the concentrations of HMs in grains and the residual fractions of soil HMs. Thus, compared with chemical fertilizers, the residual fractions of soil HMs were increased by the application of SMS, thereby reducing the concentrations of HMs in grains. Ingestion of crops is the primary route for human exposure to HMs. Therefore, the application of SMS (especially ABR) reduced the accumulation and bioavailability of HMs in soil, which in turn limited the transfer of HMs to crops, resulting in lowered human health risk indices.

Exploring genotypic variation and gene expression associated to cadmium accumulation in bread wheat

Cadmium (Cd) contamination poses significant risks to agricultural productivity and human health, particularly through its accumulation in staple crops such as bread wheat (Triticum aestivum L.). This study evaluated Cd accumulation and tolerance among six bread wheat cultivars exposed to six Cd concentrations (0, 2.5, 5, 10, 15, 20, and 25 mg kg-1 soil). Phenotypic assessments and quantitative real-time PCR (qRT-PCR) were conducted to analyze the expression patterns of TaNRAMP and TaZIP genes in various tissues and developmental stages of wheat, which play crucial roles in Cd uptake and transport. Results demonstrated significant variability in Cd accumulation. The Barat cultivar exhibited the lowest accumulation in grain (ranging from 0.21 to 8.8 mg kg-1) and the highest tolerance. In contrast, Kavir and Pishtaz displayed elevated Cd levels in both grain and straw, while Parsi accumulated more Cd in straw at lower concentrations (56.9 mg kg-1 in Cd concentration of 10 mg kg-1 soil). The gene expression analysis revealed that most cultivars showed increased expression of TaNRAMP genes, particularly TaNRAMP2 in Cd concentration of 10 mg kg-1 soil, which facilitates Cd uptake from the soil, and TaZIP genes, such as TaZIP4 and TaZIP7, involved in transporting Cd within the plant. Notably, the expression of TaZIP1 was significantly lower in cultivars with high Cd accumulation, suggesting a potential regulatory mechanism for Cd tolerance. Furthermore, cultivars exhibiting higher Cd levels correlated with increased expression of stress-responsive genes, indicating a broader response to Cd stress. These findings highlight Barat's potential for bread-making applications due to its low Cd accumulation, while Morvarid and Pishtaz which show reduced Cd content in the straw even under high Cd exposure are better suited for animal feed. This research underscores the genetic variability of wheat cultivars in response to Cd stress and provides essential insights into the molecular mechanisms underlying Cd accumulation, offering valuable information for breeding programs aimed at developing Cd-tolerant varieties to ensure food security in contaminated regions.

Integrated proteomics, transcriptomics, and metabolomics offer novel insights into Cd resistance and accumulation in Poa pratensis

Kentucky bluegrass (Poa pratensis L., KB) demonstrates superior performance in both cadmium (Cd) accumulation and tolerance; however, the regulatory mechanisms and detoxification pathways in this species remain unclear. Therefore, phenotype, root ultrastructure, cell wall components, proteomics, transcriptomics, and metabolomics were analyzed under the hydroponic system to investigate the Cd tolerance and accumulation mechanisms in the Cd-tolerant KB variety 'Midnight (M)' and the Cd-sensitive variety 'Rugby II (R)' under Cd stress. The M variety exhibited higher levels of hydroxyl and carboxyl groups as revealed by Fourier transform infrared spectroscopy spectral analysis. Additionally, a reduced abundance of polysaccharide degradation proteins was observed in the M variety. The higher abundance of glutathione S-transferase and content of L-cysteine-glutathione disulfide and oxidized glutathione in the M variety may contribute to better performance of the M variety under Cd stress. Additionally, the R variety had an enhanced content of carboxylic acids and derivatives, increasing the Cd translocation capacity. Collectively, the down-regulation of cell wall polysaccharide degradation genes coupled with the up-regulation of glutathione metabolism genes enhances the tolerance to Cd stress in KB. Additionally, lignification of the endodermis and the increase in carboxylic acids and derivatives play crucial roles in the redistribution of Cd in KB.

Bayesian risk prediction model: An accessible strategy to predict cadmium contamination risk in wheat grain grown in alkaline soils

Excessive cadmium (Cd) concentration in wheat grain is becoming a widespread concern in China. Considering the complexity of Cd transfer in the soil-wheat system, how the Cd risk in wheat grain be accurately predicted from the limited details available is of great significance for the risk management of Cd. Bayes' theory could leverage existing data by combining prior information and observational data, providing a promising strategy with which to calculate a more robust posterior probability of a grain sample exceeding the food safety standard (FSS) for Cd (0.1 mg kg-1). In the current study, a risk prediction model, based on Bayes' theory, was established to achieve a more accurate prediction of the wheat grain Cd risk from a limited number of soil parameters. The risk prediction model could predict the risk probability of wheat grain with a Cd concentration exceeding the FSS under a given soil concentration of either total Cd or diethylenetriaminepentaacetic acid (DTPA)-extractable Cd. Soil total Cd concentration proved to be a better variable for the model with greater predictive accuracy. The model predicted that fewer than 5% of the wheat grain would have a Cd concentration exceeding the FSS when grown in soil with a total Cd concentration of less than 0.299 mg kg-1. The risk probability rose significantly to 50% when the soil total Cd reached 0.778 mg kg-1. The accuracy of the model was greater than the widely applied multiple linear regression model, whereas previously published data from similar soil conditions also confirmed that the Bayesian model could predict wheat Cd risk with minimal error. The proposed model provides an accurate, accessible and cost-effective methodology for predicting Cd risk in wheat grown in alkaline soils before harvest. The wider application to other soil conditions, crops or contaminants using the Bayesian model is also promising for risk management authorities.

Ecological and health risk assessment of heavy metals in agricultural soils from northern China

Soil pollution by heavy metals can cause continuing damage to ecosystems and the human body. In this study, we collected nine fresh topsoil samples and 18 maize samples (including nine leaf samples and nine corn samples) from agricultural soils in the Baiyin mining areas. The results showed that the order of heavy metal concentrations (mg/kg) in agricultural soils was as follows: Zn (377.40) > Pb (125.06) > Cu (75.06) > Ni (28.29) > Cd (5.46) > Hg (0.37). Cd, Cu, Zn, and Pb exceeded the Chinese risk limit for agricultural soil pollution. The average the pollution load index (4.39) was greater than 3, indicating a heavy contamination level. The element that contributed the most to contamination and high ecological risk in soil was Cd. Principal component analysis (PCA) and Pearson's correlation analysis indicated that the sources of Ni, Cd, Cu, and Zn in the soil were primarily mixed, involving both industrial and agricultural activities, whereas the sources of Hg and Pb included both industrial and transportation activities. Adults and children are not likely to experience non-carcinogenic impacts from the soil in this region. Nonetheless, it was important to be aware of the elevated cancer risk presented by Cd, Pb, and especially Ni. The exceedance rates of Cd and Pb in corn were 66.67% and 33.3%, respectively. The results of this research provide data to improve soil protection, human health monitoring, and crop management in the Baiyin district.

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.

Variability in cadmium stress tolerance among four maize genotypes: Impacts on plant physiology, root morphology, and chloroplast microstructure

Cadmium (Cd) is detrimental to both plants and humans. Maize (Zea mays L.) genotypes exhibit variations in Cd accumulations. This study examined variations in Cd accumulation and tolerance among four maize genotypes with contrasting root morphology. The four maize genotypes were cultivated in a semi-hydroponic system with three Cd concentrations (0, 10, 20 μmol L-1). The effects of Cd on plant growth and physiology were assessed 39 days after transplanting. Results showed that root characteristics were positively correlated with root Cd accumulation and the bioconcentration factor under Cd20 treatment. Genotypes Shengrui999 and Zhengdan958 exhibited higher total Cd content than Xundan29 and Zhongke11 under Cd20 conditions. Cd toxicity led to membrane degradation of chloroplast mesophyll cells, loosening and swelling of grana lamella, and reduced starch reserves. The greater tolerance of Shengrui999 and Zhengdan958 was contributed to factors such as root biomass, shallower root depth, higher Cd content, accumulation of osmolyte such as soluble protein, antioxidant activities such as catalase (CAT), and the presence of phytohormone gibberellic acid. The study establishes a link between root morphology, Cd accumulation, and tolerance in maize plants, as demonstrated by the higher Cd accumulation and shallower root system in Cd-tolerant genotypes. This research provides a foundation for breeding maize cultivars better suited for adaptation to moderate Cd-contaminated environments.

Heavy metals contamination, receptor model-based sources identification, sources-specific ecological and health risks in road dust of a highly developed city

The present study quantified Ni, Cu, Cr, Pb, Cd, As, Zn, and Fe levels in road dust collected from a variety of sites in Tangail, Bangladesh. The goal of this study was to use a matrix factorization model to identify the specific origin of these components and to evaluate the ecological and health hazards associated with each potential origin. The inductively coupled plasma mass spectrometry was used to determine the concentrations of Cu, Ni, Cr, Pb, As, Zn, Cd, and Fe. The average concentrations of these elements were found to be 30.77 ± 8.80, 25.17 ± 6.78, 39.49 ± 12.53, 28.74 ± 7.84, 1.90 ± 0.79, 158.30 ± 28.25, 2.42 ± 0.69, and 18,185.53 ± 4215.61 mg/kg, respectively. Compared to the top continental crust, the mean values of Cu, Pb, Zn, and Cd were 1.09, 1.69, 2.36, and 26.88 times higher, respectively. According to the Nemerow integrated pollution index (NIPI), pollution load index (PLI), Nemerow integrated risk index (NIRI), and potential ecological risk (PER), 84%, 42%, 30%, and 16% of sampling areas, respectively, which possessed severe contamination. PMF model revealed that Cu (43%), Fe (69.3%), and Cd (69.2%) were mainly released from mixed sources, natural sources, and traffic emission, respectively. Traffic emission posed high and moderate risks for modified NIRI and potential ecological risks. The calculated PMF model-based health hazards indicated that the cancer risk value for traffic emission, natural, and mixed sources had been greater than (1.0E-04), indicating probable cancer risks and that traffic emission posed 38% risk to adult males where 37% for both adult females and children.

Phytoremediation strategies for heavy metal-contaminated soil by selecting native plants near mining areas in Inner Mongolia

Phytoremediation technology, as an eco-friendly and cost-effective approach, is widely used to restore soil contaminated by heavy metal(loid)s. However, the adaptability and absorption capacity of plants to multiple elements are the crucial factors affecting the application of phytoremediation in mining areas. In this study, dominant native plant species and their paired soils were collected near a lead-zinc mine in Inner Mongolia, to assess the ecological risk of heavy metal(loid)s and phytoremediation potential. The results showed that Cd and As were the dominant soil pollutants, with levels of 90.91% and 100%, respectively, exceeding the risk intervention values for soil contamination of agricultural land. The rates of Pb, Cu, and Zn exceeding the risk screening values were 69.70%, 60.61%, and 96.97%, respectively. Extremely high ecological risk of heavy metal(loid)s was observed in this area. The ability of native plants accumulating heavy metals varied among species. The bioconcentration factor (BCF) varied from 0.14 to 2.59 for Cd, 0.02 to 0.45 for As, 0.06 to 0.76 for Pb, 0.05 to 2.69 for Cr, 0.15 to 1.00 for Cu, and 0.22 to 4.10 for Zn. Chinese Cinquefoil Herb (Potentilla chinensis Ser.) showed the potential to accumulate multiple toxic elements based on the biomass, shoot content, translocation factor (TF), BCF, and metal extraction rate (MER), while, other species showed the potential to accumulate single toxic element: goosefoot (Chenopodium album L.), Lespedeza daurica (Laxm.) Schindl. and peashrubs (Caragana korshinskii Kom.), Herba Artemisiae Scopariae (Artemisia capillaris Thunb.), alfalfa (Medicago sativa L.), and Moldavian Dragonhead (Dracocephalum moldavica L.) for Cd, As, Cr, Cu, and Zn, respectively. Furthermore, wild leek (Allium ramosum L.), cogongrass (Imperata cylindrica (L.) Beauv.), fringed sagebrush (Artemisia frigida Willd.), and field bindweed (Convolvulus arvensis L.) were selected for phytostabilization of specific elements, considering the heavy metal contents in the roots and low TF values. This study provides a reference for selecting appropriate species for the remediation of heavy metal-contaminated soils in certain mining areas.

Accumulation characteristics, driving factors, and model prediction of cadmium in soil-highland barley system on the Tibetan Plateau

Cadmium (Cd) poses major human health problems due to its high toxicity and organ bioaccumulation potential. This study collected and analysed 130 pairs of representative soil-highland barley samples on the Tibetan Plateau. The total soil Cd content (Cd-soil), available soil Cd (Cd-ava), and highland barley Cd contents (Cd-barley) ranged from 0.03 to 0.46 mg kg-1, 0.006-0.185 mg kg-1, and 0.57-13.62 μg kg-1, with mean values of 0.19 ± 0.01 mg kg-1, 0.045 ± 0.003 mg kg-1, and 4.57 ± 0.17 μg kg-1, respectively. Redundancy analysis (RDA) demonstrated that geographic factors and soil properties explained 28.46% of the variation in Cd-soil and Cd-ava, and precipitation (14.6%) and pH (9.1%) were the dominant factors. The structural equation model (SEM) indicated that Cd-soil and Cd-ava were predominantly controlled by pH. Furthermore, the Cd-soil, Cd-ava, and Cd-barley with significantly different environmental conditions were more accurately predicted by conditional inference trees-multiple linear regression (CITs-MLR). When Cd-soil is more than 0.376 mg kg-1, Cd-ava obtains the most accurate predictor (R2 =0.64, P < 0.01). This study provides new scientific insight into understanding the environmental biogeochemical nexus of Cd in the complex and fragile plateau environment and evaluating food security on the Tibetan Plateau under the self-sufficiency model of highland barley.

The effect of polystyrene microplastic and biosolid application on the toxicity and bioaccumulation of cadmium for Enchytraeus crypticus

Plastics smaller than 5 mm that end up in a soil environment are known as microplastics (MPs). Microplastics have become a common contaminant in agricultural areas in addition to metals. However, the effect of cadmium (Cd) on soil organisms has not been clearly defined in the presence of MPs. In addition to MPs, biosolid application as a soil amendment in agricultural lands is also leading to shifts in soil conditions, such as the concentrations of nutrients and organic matter. Therefore, the aim of this study is to investigate the toxicity and bioaccumulation of Cd for Enchytraeus crypticus in the presence of polystyrene (PS)-MPs and biosolids to provide insight into their possible interactions. The lethal toxic concentration (LC50) for Cd was higher than 650 mg Cd/kg dry soil for all conditions. The presence of PS-MPs increased the toxicity of Cd for which EC50 was 102 and 38 mg Cd/kg dry soil without and with Cd, respectively, which may be the result of an increased exposure rate through adsorption of Cd on PS-MPs. On the contrary, the presence of biosolids decreased the toxicity of Cd where EC50 was 193 and 473 mg Cd/kg dry soil for the sets applied with 0.6 and 0.9 g biosolids, respectively. Coexistence of biosolids and PS-MPs decreased the reproduction toxicity of Cd, which is similar to the biosolid effect (EC50 is 305 mg Cd/kg dry soil). Bioaccumulation of Cd only positively correlated with its initial concentration in soil and was not affected by the presence of PS-MPs or biosolids. Integr Environ Assess Manag 2023;19:489-500. © 2022 SETAC.

The effects of biochar and its applications in the microbial remediation of contaminated soil: A review

The amendment of biochar for soil bioremediation can improve soil conditions, influence soil microbial community, and achieve co-application of biochar-microbe to promote the removal of pollutants. This paper summarizes the positive effects of biochar on microorganisms, including acting as a shelter, providing nutrients, and improving soil conditions (soil aggregation, pH, cation exchange capacity (CEC), and enzymatic activity). These effects will cause variations in microbial abundance, activity, and community structure. Biochar can act as an electron mediator to promote electron transfer in the process of microbial degradation. And the application of biochar in soil bioremediation is also introduced. Nevertheless, toxic substances carried by biochar that may threaten microbial community shouldn't be overlooked. With this review, we can better understand biochar's involvement in soil bioremediation, which will help us choose and modify biochar in a targeted manner for the desired purpose in practical applications.