Lead smelting effects heavy metal concentrations in soils, wheat, and potentially humans

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.

The accumulation of cadmium and lead in wheat grains is primarily determined by the soil-reducible cadmium level during wheat tillering

The significant increase in cadmium (Cd) and lead (Pb) pollution in agricultural soil has greatly heightened environmental contamination issues and the risk of human diseases. However, the mechanisms underlying the transformation of Cd and Pb in soil as well as the influencing factors during their accumulation in crop grains remain unclear. Based on the analysis of the distribution trend of Cd and Pb in soil during the growth and development stages of wheat (tillering, filling, and maturity) in alkaline heavy metal-polluted farmland in northern China, this study investigated the response mechanism of soil heavy metal form transformation to soil physicochemical properties, and elucidated the main determining periods and influencing factors for Cd and Pb enrichment in wheat grains. The results showed that an increase in CEC and SOM levels, along with a decrease in pH level, contributed to enhancing the bioavailability of Cd in the soil. This effect was particularly evident during the tillering stage and grain filling stage of wheat. Nevertheless, the effects of soil physicochemical properties on bioavailable Pb was opposite to that on bioavailable Cd. The enrichment of Cd and Pb in grain was significantly influenced by soil pH (r = -0.786, p < 0.01), SOM (r = 0.807, p < 0.01), K (r = -0.730, p < 0.01), AK (r = 0.474, p = 0.019), and AP (r = -0.487, p = 0.016). The reducible form of Cd in soil during the wheat tillering stage was identified as the primary factor contributing to the accumulation of Cd and Pb in wheat grains, with a significant contribution rate of 84.5%. This study provides a greater scientific evidence for the management and risk control of heavy metal pollution in alkaline farmland.

Foliar uptake screening: A promising strategy for identifying wheat varieties with low lead accumulation

Lead (Pb) contamination in wheat grain is of great concern, especially in North China. Atmospheric deposition is a major contributor to Pb accumulation in wheat grain. Screening low Pb accumulating wheat varieties has been an effective method for addressing Pb contamination in wheat grain. However, identifying wheat varieties with low Pb accumulation based on foliar uptake of atmospheric Pb has been neglected. Therefore, two field trials with distinct atmospheric Pb deposition were conducted to screen for stable varieties with low Pb accumulation. It was verified that YB700 and CH58, which have high thousand-grain weights and stable low Pb accumulation in field 1 (0.19 and 0.13 mg kg-1) and field 2 (0.17 and 0.20 mg kg-1), respectively, were recommended for cultivation in atmospheric Pb contaminated farmlands in North China. Furthermore, indoor experiments were conducted to investigate Pb uptake by the roots and leaves of different wheat varieties. Our findings indicate that Pb accumulation in different wheat varieties is primarily influenced by foliar Pb uptake rather than root Pb uptake. Interestingly, there was a positive correlation (p < 0.05) between the Pb concentrations in leaves and the stomatal width and trichome length of the adaxial epidermal surface. Additionally, there is a positive correlation (p < 0.01) between the Pb concentration in the wheat grain and trichome length. In conclusion, the screening of wheat varieties with narrower stomatal widths or shorter trichomes based on foliar uptake pathways is an effective strategy for ensuring food safety in areas contaminated by atmospheric Pb.

Evaluating the protective capacity of soil heavy metals regulation limits on human health: A critical analysis concerning risk assessment - Importance of localization

Heavy metal pollution of agricultural soil is a major global concern, prompting the establishment of maximum allowable limits (MALs) to ensure food safety and protect human health. This study collected and compared MALs for six heavy metals (As, Cd, Hg, Pb, Zn, and Cu) in agricultural soils from representative countries and organizations (EU and WHO/FAO). The research evaluated the critical health risks and efficacy of these MALs under the hypothetical scenario of metals concentrations reaching the maximum allowable level. Safe thresholds for heavy metals were then derived based on maximum acceptable health risk levels. The comparative analysis revealed significant variations in the specific limit values and terms of MALs across countries and organizations, even for the same metal. This suggests that there is no consensus among countries and organizations regarding the level of metal-related health risks. Furthermore, the risk analysis of metal concentrations reaching the maximum level accentuated heightened risks associated with As, suggesting that the current risk of soil As exposure was underestimated, particularly for children. However, soil Cu, Cd, and Zn limits generally resulted in low health risks, implying that the current limits may overestimate their hazard. Overall, the results highlight that the current MALs for soil heavy metals may not fully safeguard human health. There is a critical need to optimize current soil MALs based on localized risks and the actual impact of these metals on human health. It is suggested to appropriately lower the limits of metals (such as As) whose impact on health risks is underestimated, and cautiously increase the limits of metals (such as Cu, Cd, and Zn) that currently pose minor health risks. This approach aims to reduce both over and insufficient protection problems of soil heavy metal MALs, emphasizing the importance of considering the locality in setting these limits.

Exposure risks of lead and other metals to humans: A consideration of specific size fraction and methodology

Particle size is a critical influencing factor in assessing human exposure risk as fine particles are generally more hazardous than larger coarse particles. However, how particle composition influences human health risk is only poorly understood as different studies have different utilised different definitions and as a consequence there is no consensus. Here, with a new methodology taking insights of each size fraction load (%GSFload), metal bioaccessibility, we classify which specific particle size can reliably estimate the human exposure risk of lead and other metals. We then validate these by correlating the metals in each size fraction with those in human blood, hair, crop grain and different anthropogenic sources. Although increasing health risks are linked to metal concentration these increase as particle size decrease, the adjusted-risk for each size fraction differs when %GSFload is introduced to the risk assessment program. When using a single size fraction (250-50 µm, 50-5 µm, 5-1 µm, and < 1 µm) for comparison, the risk may be either over- or under-estimated. However, by considering bulk and adjusting the risk, it would be possible to obtain results that are closer to the real scenarios, which have been validated through human responses and evidence from crops. Fine particle size fractions (< 5 µm) bearing the mineral crystalline or aggregates (CaCO3, Fe3O4, Fe2O3, CaHPO4, Pb5(PO4)3Cl) alter the accumulation, chemical speciation, and fate of metals in soil/dust/sediment from the different sources. Loaded lead in the size fraction of < 50 µm has a significantly higher positive association with the risk-receptor biomarkers (BLLs, Hair Pb, Corn Pb, and Crop Pb) than other size fractions (bulk and 50-250 µm). Thus, we conclude that the < 50 µm fraction would be likely to be recommended as a reliable fraction to include in a risk assessment program. This methodology acts as a valuable instrument for future research undertakings, highlighting the importance of choosing suitable size fractions and attaining improved accuracy in risk assessment results that can be effectively compared.

Pollution levels and probability risk assessment of potential toxic elements in soil of Pb-Zn smelting areas

Soil pollution around Pb-Zn smelters has attracted widespread attention around the world. In this study, we compiled a database of eight potentially toxic elements (PTEs) Pb, Zn, Cd, As, Cr, Ni, Cu, and Mn in the soil of Pb-Zn smelting areas by screening the published research papers from 2000 to 2023. The pollution assessment and risk screening of eight PTEs were carried out by geo-accumulation index (Igeo), potential ecological risk index (PERI) and health risk assessment model, and Monte Carlo simulation employed to further evaluate the probabilistic health risks. The results suggested that the mean values of the eight PTEs all exceeded the corresponding values in the upper crust, and more than 60% of the study sites had serious Pb and Cd pollution (Igeo > 4), with Brazil, Belgium, China, France and Slovenia having higher levels of pollution than other regions. Besides, PTEs in smelting area caused serious ecological risk (PERI = 10912.12), in which Cd was the main contributor to PREI (86.02%). The average hazard index (HI) of the eight PTEs for adults and children was 7.19 and 9.73, respectively, and the average value of total carcinogenic risk (TCR) was 4.20 × 10-3 and 8.05 × 10-4, respectively. Pb and As are the main contributors to non-carcinogenic risk, while Cu and As are the main contributors to carcinogenic risk. The probability of non-carcinogenic risk in adults and children was 84.05% and 97.57%, while carcinogenic risk was 92.56% and 79.73%, respectively. In summary, there are high ecological and health risks of PTEs in the soil of Pb-Zn smelting areas, and Pb, Cd, As and Cu are the key elements that cause contamination and risk, which need to be paid attention to and controlled. This study is expected to provide guidance for soil remediation in Pb-Zn smelting areas.

Heavy metals pollution from smelting activities: A threat to soil and groundwater

Throughout the literature, the word "heavy metal" (HM) has been utilized to describe soil contamination; in this context, we characterize it as those elements with a density greater than 5 g per cubic centimeter. Contamination is one of the major global health concerns, especially in China. China's rapid urbanization over the past decades has caused widespread urban water, air, and soil degradation. This study provides a complete assessment of the soil contamination caused by heavy metals in China's mining and smelting regions. The study of heavy metals (HMs) includes an examination of their potential adverse impacts, their origins, and strategies for the remediation of soil contaminated by heavy metals. The presence of heavy metals in soil can be linked to both natural and anthropogenic processes. Studies have demonstrated that soils contaminated with heavy metals present potential health risks to individuals. Children are more vulnerable to the effects of heavy metal pollution than adults. The results highlight the significance of heavy metal pollution caused by mining and smelting operations in China. Soil contaminated with heavy metals poses significant health concerns, both carcinogenic and non-carcinogenic, particularly to children and individuals living in heavily polluted mining and smelting areas. Implementing physical, chemical, and biological remediation techniques is the most productive approach for addressing heavy metal-contaminated soil. Among these methods, phytoremediation has emerged as a particularly advantageous option due to its cost-effectiveness and environmentally favorable characteristics. Monitoring heavy metals in soils is of utmost importance to facilitate the implementation of improved management and remediation techniques for contaminated soils.

Lead, cadmium, and mercury blood levels in schoolchildren in southern Sweden: Time trends over the last decades

To prevent diseases arising from exposure to toxic metals, more knowledge about their temporal changes is needed, especially in children, the most vulnerable group. This study follows temporal changes in blood lead (BPb), mercury (BHg) and cadmium (BCd) levels in schoolchildren (8-11 years old) from two cities in southern Sweden. One blood sample per 773 children was used for time trend analyses between 2007 and 2022. One further blood sample re-sampled after 2 years, were used to assess intra-individual time trends of BPb (n = 377), BCd (n = 102) and BHg (n = 53) between 1979 and 2019. Geometric mean (range) of BPb, BCd and BHg concentrations during 2007-2022 was 9.9 (2.3-59), 0.09 (0.03-0.34) and 0.73 (0.02-8.2) μg/L, respectively. Living close to a Pb smelter resulted in higher levels of all three metals compared with living in the city or rural area. Annually, the concentrations clearly decreased for BPb (-4.9%, p < 0.001) and weakly for BCd (-0.6%, p = 0.013), while BHg slightly increased (+1.4%, p = 0.029). When stratified by residential area, the decrease of BCd and increase of BHg were significant only in the urban area (-1.8% and +2.8%, respectively; p < 0.01). The BPb decrease rate was the highest in the urban area followed by the rural and Pb smelter areas (-5.8% > -4.5% > -3.9%; p < 0.001). For children re-analysed during 1979-2019, a significant decrease was observed only for BPb (-6.8%; p < 0.001), with a 2% higher decrease rate in the period before than after the Pb-gasoline ban in 1994. The preventive measures against Pb pollution are reflected in the constant decrease of BPb levels over time. However, the area close to a Pb smelter, as indicated by a slower Pb decrease rate, might need further and stricter preventive measures. Exposure to Hg and Cd was low, however, the slight increase in BHg and only a minor decrease in BCd, indicate the need for continuous biomonitoring of children.

The Metabolomics Response of Solanum melongena L. Leaves to Various Forms of Pb

Due to activities like mining and smelting, lead (Pb) enters the atmosphere in various forms in coarse and fine particles. It enters plants mainly through leaves, and goes up the food chain. In this study, PbXn (nano-PbS, mic-PbO and PbCl2) was applied to eggplant (Solanum melongena L.) leaves, and 379 differential metabolites were identified and analyzed in eggplant leaves using liquid chromatography-mass spectrometry. Multivariate statistical analysis revealed that all three Pb treatments significantly altered the metabolite profile. Compared with nano-PbS, mic-PbO and PbCl2 induced more identical metabolite changes. However, the alterations in metabolites related to the TCA cycle and pyrimidine metabolism, such as succinic acid, citric acid and cytidine, were specific to PbCl2. The number of differential metabolites induced by mic-PbO and PbCl2 was three times that of nano-PbS, even though the amount of nano-PbS absorbed by leaves was ten times that of PbO and seven times that of PbCl2. This suggests that the metabolic response of eggplant leaves to Pb is influenced by both concentration and form. This study enhances the current understanding of plants' metabolic response to Pb, and demonstrates that the metabolomics map provides a more comprehensive view of a plant's response to specific metals.

Impacts of a lead smelter in East Java, Indonesia: degree of contamination, spatial distribution, ecological risk, and health risk assessment of potentially toxic elements in soils

This study investigates the characteristics of potentially toxic elements in soils collected from the vicinity of a lead smelter in East Java, Indonesia. The objective is to assess the impact of the lead smelter on the surrounding soil. The study involves chemical composition analysis, spatial distribution mapping, and potential ecological and health risk assessments. Soil samples were collected from the surface area (0-10 cm) and subsurface (15-30 cm) within radii of 1.5 km, 3 km, and 5 km from the lead smelter. The samples were analyzed for As, Cr, Cu, Ni, Pb, and Zn using energy-dispersive X-ray fluorescence. Principal component analysis (PCA) was performed to identify the sources of potentially toxic elements in the soil. The results indicate severe Pb contamination within a 1.5 km radius of the smelter, with an average contamination factor (Cf) value of 22.0, posing a high potential health risk. The contamination factor indicated that the soils were heavily polluted by As and Pb and moderately polluted by Cu, Ni, and Zn. The results of PCA showed that smelter releases are the main source of potentially toxic element contamination in the soil, accounting for 66.2%. The health risk assessment suggested that the children and adults in the study region were exposed to non-carcinogenic risks caused by As and Pb. Oral ingestion was identified as the primary exposure route impacting health risks. The carcinogenic risk from potentially toxic elements in soil was found to exceed the acceptable level for children and adults in the study region. Therefore, it is necessary for the government to take effective measures, including designing regulations and interventions, and improving lead smelter management to mitigate potential contamination and minimize the impact of lead smelter releases on the surrounding environment, especially to protect human health, particularly that of children.

Effects of long-term zinc smelting activities on the distribution and health risk of heavy metals in agricultural soils of Guizhou province, China

To assess the effect of zinc smelting on environment and human health, the concentration, distribution, sources and health risk of eight heavy metals (Pb, Cd, Cu, Zn, Cr, Ni, Mn, and As) were investigated from agricultural soils in a long-term Zn smelting area in Guizhou, China. Different health risk assessment methods and models were used to access health risks. The results show that the concentrations of all the eight heavy metals were significantly higher than their corresponding background values (p < 0.05). Pb, Cd, and As were the most contaminated elements, with 93.6%, 90.3% and 48.4% of agricultural soil samples higher than the risk screening values, respectively. Statistical analysis indicated that Pb, Cd, Cu, Zn, Mn, and As could be mainly accounted for Zn smelting activities, while Cr and Ni may be generally more controlled by natural sources. The geo-accumulation index (Igeo) suggested that the most seriously contaminating heavy metals were Pb, Cd, and Zn, with 96.8%, 90.3%, and 96.8%, respectively, of the soil samples classified as moderately to extremely contaminated. The non-carcinogenic health risk associated with Pb, Cd and As were observed for children, meanwhile, the carcinogenic risk due to As was found for both adults and children. Regardless of cancer risk or non-cancer risk, local children are at greater risk than adults. Therefore, Pb, Cd and As play the leading role to cause potential health risks in the study area, which need to be paid more attention and also effective control measures should be taken.

Cadmium and lead bioavailability to poultry fed with contaminated soil-spiked feed

Geophagy is common for free-range chickens, however, the relative bioavailability (RBA) of heavy metals in contaminated soils consumed by chickens has not fully investigated. In this work, chickens were fed diets increasingly spiked with a contaminated soil (Cd = 105, Pb = 4840 mg kg^-1; 3, 5, 10, 20 and 30 % of overall feed by weight), or Cd/Pb reagent spikes (from CdCl₂ or Pb(Ac)₂), for 23 d. After the study period, chicken liver, kidney, femur and gizzard samples were analyzed for Cd and Pb concentrations, and organ/tissue metal concentrations were used to calculate Cd and Pb RBA. Linear dose response curves (DRCs) were established for both Cd/Pb reagents-spiked and soil-spiked treatments. Femur Cd concentrations of soil-spiked treatments were two times of Cd-spiked treatments with similar feed Cd levels, while feed spiked with Cd or Pb also resulted in elevated Pb or Cd concentrations in some organ/tissues. Metal RBA was calculated using three different methods. Most Cd and Pb RBA values were in the range 50-70 %, with the chicken gizzard as a potential endpoint for bioaccessible Cd and Pb. Cadmium and Pb bioavailability values can help with more precise estimation of Cd and Pb accumulation in chicken following heavy metal-contaminated soil ingestion, with overall results helping to protect human health.

Evaluation of heavy metals contamination in cereals, vegetables and fruits with probabilistic health hazard in a highly polluted megacity

Heavy metals (HMs) contamination in foodstuffs could pose serious health issues for public health and humans are continually exposed to HMs through the consumption of cereals, fruits, and vegetables. The present study was conducted to assess 11 HMs in foodstuffs to investigate pollution levels and health risks to children and adults. The mean contents of Cd, Cr, Cu, Ni, Zn, Fe, Pb, Co, As, Mn and Ba in foodstuffs were 0.69, 2.73, 10.56, 6.60, 14.50, 9.63, 2.75, 0.50, 0.94, 15.39 and 0.43 mg/kg, respectively and the concentration of Cd, Cr, Cu, Ni and Pb were higher than maximum permissible concentrations (MPCs) showing that these foods may be contaminated with metals and constitute a danger to consumers. Vegetables had relatively higher metal contents followed by cereals and fruits. The average value of the Nemerrow composite pollution index (NCPI) for cereals, fruits, and vegetables were 3.99, 6.53, and 11.34, respectively indicating cereal and fruits were moderately contaminated whereas vegetables were heavily contaminated by the studied metals. The total estimated daily and weekly intakes for all studied metals were higher than the maximum tolerable daily intake (MTDI) and provisional tolerance weekly intake (PTWI) recommended by FAO/WHO. The target hazard quotients and hazard index of all studied metals exceeded the standard limit for adults and children suggesting significant non-carcinogenic health hazards. The total cancer risk value of Cd, Cr, Ni, Pb, and As from food intake exceeded the threshold range (1.0E-04), suggesting potential carcinogenic risks. Based on practical and sensible evaluation techniques, the current work will assist policymakers in controlling metal contamination in foodstuffs.

New insight into the mechanisms of preferential encapsulation of metal(loid)s by wheat phytoliths under silicon nanoparticle amendment

Silicon nanoparticles (SiNPs) have been widely used to immobilize toxic trace metal(loid)s (TTMs) in contaminated croplands. However, the effect and mechanisms of SiNP application on TTM transportation in response to phytolith formation and phytolith-encapsulated-TTM (PhytTTM) production in plants are unclear. This study demonstrates the promotion effect of SiNP amendment on phytolith development and explores the associated mechanisms of TTM encapsulation in wheat phytoliths grown on multi-TTM contaminated soil. The bioconcentration factors between organic tissues and phytoliths of As and Cr (> 1) were significantly higher than those of Cd, Pb, Zn and Cu, and about 10 % and 40 % of the total As and Cr that bioaccumulated in wheat organic tissues were encapsulated into the corresponding phytoliths under high-level SiNP treatment. These observations demonstrate that the potential interaction of plant silica with TTMs is highly variable among elements, with As and Cr being the two most strongly concentrated TTMs in the phytoliths of wheat treated with SiNPs. The qualitative and semi-quantitative analyses of the phytoliths extracted from wheat tissues suggest that the high pore space and surface area (≈ 200 m² g^-1) of phytolith particles could have contributed to the embedding of TTMs during silica gel polymerization and concentration to form PhytTTMs. The abundant SiO functional groups and high silicate-minerals in phytoliths are dominant chemical mechanisms for the preferential encapsulation of TTMs (i.e., As and Cr) by wheat phytoliths. Notably, the organic carbon and bioavailable Si of soils and the translocation of minerals from soil to plant aerial parts can impact TTM sequestration by phytoliths. Thus, this study has implications for the distribution or detoxification of TTMs in plants via preferential PhytTTM production and biogeochemical cycling of PhytTTMs in contaminated cropland following exogenous Si supplementation.

Spatial Distribution and Risk Assessment of Heavy Metal(oid)s Contamination in Topsoil around a Lead and Zinc Smelter in Henan Province, Central China

A total of 137 farmland soil samples were collected around a lead/zinc smelter within 64 km². The concentration, spatial distribution, and potential source of nine heavy metal(oid)s (As, Cd, Co, Cr, Cu, Ni, Pb, V, and Zn) in soils and their potential ecological risk were investigated in detail. The results showed that the average concentrations of Cd, Pb, Cr and Zn in these soils were higher than their background value in Henan Province, and the average content of Cd was 2.83 times of the risk screening values in the national standard of China (GB 15618-2018). According to the distribution of different heavy metal(oid)s in soils, Cd and Pb in soil decrease gradually with the increase of distance from the smelter to the surrounding area. This indicates that the Pb and Cd originate from smelters via airborne practices according to the typical air pollution diffusion model. The distribution of Zn, Cu, and As were similar to Cd and Pb. However, Ni, V, Cr, and Co were mainly affected by soil parent materials. The potential ecological risk of Cd was higher than those of other elements, and the risk grade of the other eight elements was mainly low. The polluted soils with significantly high and high potential ecological risk covered 93.84% of all the studied regions. This should be of serious concern to government. The results of a principal component analysis (PCA) and cluster analysis (CA) show that Pb, Cd, Zn, Cu, and As were the elements mainly stemmed from smelter and other types of plants, with a contribution rate of 60.08%, while Co, Cr, Ni, and V are mainly caused by nature, with a contribution rate of 26.26%.

Immobilization of Cd by mercapto-palygorskite in typical calcareous and acidic soil aggregates: Performance and differences

The microscale spatial heterogeneity and complexity of soil aggregates affect the properties and distribution of heavy metals (HMs). It has been confirmed that amendments can alter the distribution of Cd in soil aggregates. However, whether the Cd immobilization effect of amendments varies across soil aggregate levels remains unknown. In this study, soil classification and culture experiments were combined to explore the effects of mercapto-palygorskite (MEP) on Cd immobilization in soil aggregates of different particle sizes. The results showed that a 0.05-0.2% MEP application decreased soil available Cd by 53.8-71.62% and 23.49-36.71% in calcareous and acidic soils, respectively. The Cd immobilization efficiency of MEP in calcareous soil aggregates was in the following order: micro-aggregates (66.42-80.19%) > bulk soil (53.78-71.62%) > macro-aggregates (44.00-67.51%), while the efficiency in acidic soil aggregates was inconsistent. In MEP-treated calcareous soil, the percentage change in Cd speciation in micro-aggregates were higher than that in macro-aggregates, whereas there was no significant difference in Cd speciation between the four acidic soil aggregates. Mercapto-palygorskite addition in micro-aggregates of calcareous soil increased the available Fe and Mn concentrations by 20.98-47.10% and 17.98-32.66%, respectively. Mercapto-palygorskite had no effect on soil pH, EC, CEC, and DOC values, while the difference in soil properties between the four particle sizes was the main influencing factor of MEP treatments on Cd in calcareous soil. The effects of MEP on HMs varied across soil aggregates and soil types, but had strong specificity and selectivity for Cd immobilization. This study illustrates the influence of soil aggregates on Cd immobilization using MEP, which can be used to guide the remediation of Cd-contaminated calcareous and acidic soils.

Fermentation affects heavy metal bioaccessibility in Chinese mantou

Effect of different fermentation methods on heavy metal bioaccessibilities in wheat flour is undetermined. In this work, gastric and gastrointestinal heavy metal bioaccessibility in wheat flour products (control-wheat dough, T1-mantou made with normally fermented dough, T2-mantou made with over-fermented dough and T3-mantou made with over-fermented dough + Na₂CO₃) made from two wheat flour samples (NX and QD) was assessed via a modified physiologically-based extraction test. Cadmium, Zn and Mn bioaccessibility in the gastric phase (GP) was greater than in the gastrointestinal phase (GIP), yet the opposite was observed for Cu (p < 0.05). Lead bioaccessibility in the GIP of the QD sample was 1.37-4.08 times greater than that in the GP, while only the control had greater bioaccessibility in the GIP than that in the GP (p < 0.05) for the NX sample. Treatments T2 and T3 had greater Cd, Cu, Zn and Mn bioaccessibilities than the control and T1 in the GP (p < 0.05). In the GIP, however, only T3 had greater Mn bioaccessibility than the control for the NX sample. Enhanced degradation of the heavy metal-phytate following over-fermentation may have led to greater heavy metal bioaccessibility. Results should help food processors reduce human absorption of excessive heavy metals present in wheat flour foods.

Soil addition of MnSO4 reduces wheat Cd accumulation by simultaneously increasing labile Mn and decreasing labile Cd concentrations in calcareous soil: A two-year pot study

Cadmium (Cd) pollution of wheat fields is a serious environmental and health problem that warrants attention. Manganese (Mn)-containing materials are considered effective for inhibiting Cd accumulation in Cd-contaminated acidic soils. However, information on the long-term remediation effects of Mn fertilizers on Cd accumulation in wheat and on the microbial community in calcareous soils remain limited. Here, a two-year pot experiment was conducted to assess the performance of 0.05-0.2% MnSO₄ addition in Cd-contaminated calcareous soils (total Cd concentration: 3.65 mg/kg) on Cd accumulation in wheat as well as on the soil bacterial community. The formation of Mn oxides and transformation of exchangeable Cd to stable Cd fractions confirmed that the application of MnSO₄ significantly decreased CaCl₂-extractable Cd concentrations in soil (0-47.08%). In addition, MnSO₄ addition improved the antagonistic effect of Cd and Mn ions in the wheat rhizosphere by increasing the available Mn concentration in the soil (1.04-3.52 times), thereby significantly reducing wheat Cd accumulation by 24.66-54.70%. Notably, the addition of MnSO₄ did not affect the richness and diversity (P > 0.05) but altered the composition and function of bacterial communities, especially those involved in metabolism and genetic information processing. Importantly, the effects of MnSO₄ on Cd immobilization in soil (10.66-47.08%) and the inhibition of Cd accumulation in wheat (12.13-54.30%) can last for two years after one addition. Furthermore, the maximum decrease in Cd concentration in grains was found in the low-Cd wheat cultivar, with values of 31.39-54.70% and 19.94-54.30% in the first and second years, respectively. Based on the present findings, the combination of MnSO₄ with a low-Cd wheat cultivar is effective for the safe utilization of Cd-contaminated calcareous soils.

Potentially toxic elements in human scalp hair around China's largest polymetallic rare earth ore mining and smelting area

There is a growing concern about human health of residents living in areas where mining and smelting occur. In order to understand the exposure to the potentially toxic elements (PTEs), we here identify and examine the cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn) in scalp hair of residents living in the mining area (Bayan Obo, n = 76), smelting area (Baotou, n = 57) and a reference area (Hohhot, n = 61). In total, 194 hair samples were collected from the volunteers (men = 87, women = 107) aged 5-77 years old in the three areas. Comparing median PTEs levels between the young and adults, Ni levels were significantly higher in adults living in the smelting area while Cr was highest in adults from the mining area, no significant difference was found for any of the elements in the reference area. From the linear regression model, no significant relationship between PTEs concentration, log₁₀(PTEs), and age was found. The concentrations of Ni, Cd, and Pb in hair were significantly lower in the reference area when compared to both mining and smelting areas. In addition, Cu was significantly higher in the mining area when compared to the smelting area. Factor analysis (FA) indicated that men and women from the smelting area (Baotou) and mining area (Bayan Obo), respectively, had different underlying communality of log10(PTEs), suggesting different sources of these PTEs. Multiple factor analysis quantilized the importance of gender and location when combined with PTEs levels in human hair. The results of this study indicate that people living in mining and/or smelting areas have significantly higher PTEs (Cu, Ni, Cd, and Pb) hair levels compared to reference areas, which may cause adverse health effects. Remediation should therefore be implemented to improve the health of local residents in the mining and smelting areas.

Levels of Toxic and Essential Elements and Associated Factors in the Hair of Japanese Young Children

There is growing concern regarding the effects of toxic element exposure on the development of children. However, little is known about the level of toxic elements exposure in Japanese children. The purpose of this study was to assess the concentrations of multiple elements (aluminum, cadmium, lead, calcium, copper, iron, magnesium, sodium, zinc) in the hair of 118 Japanese young children and to explore the factors associated with their element levels. The element concentration was analyzed by ICP-MS, and children's food and water intake were assessed by the questionnaire. Results showed that there were no large differences between the level of elements in the hair of Japanese children and those of children in other developed countries. Girls had significantly higher levels of aluminum, copper, and iron (p = 0.000, 0.014, and 0.013, respectively), and boys had a higher level of sodium (p = 0.006). The levels of calcium, iron, magnesium, and sodium in nursery school children were significantly higher than those in kindergarten children (p = 0.024, 0.001, 0.046, and 0.029, respectively). Multiple regression analyses with controlling the confounding variables showed significant negative associations of frequency of yogurt intake with aluminum and lead levels (p = 0.015 and 0.037, respectively). When the children were divided into three groups based on the frequency of yoghurt consumption, viz. L (≤once a week), M (2 or 3 times a week), and H (≥4 to 6 times a week) group, the mean aluminum concentration (µg/g) in the L, M, and H groups was 11.06, 10.13, and 6.85, while the mean lead concentration (µg/g) was 1.76, 1.70, and 0.87, respectively. Our results suggested the validity of hair element concentrations as an exposure measure of essential elements and frequent yogurt intake as a viable measure for protecting children from toxic elements. However, these findings will need to be confirmed in more detailed studies with larger sample sizes in the future.

Distribution, Risk Assessment and Source of Heavy Metals in Mangrove Wetland Sediments of Dongzhai Harbor, South China

Heavy metals are common environmental contaminants that are toxic, non-biodegradable, and bioaccumulative. They can bioaccumulate through the food chain and present a risk to both public health and ecology. Therefore, this study takes the mangrove wetland of Dongzhai Harbor as an example. The concentrations of heavy metals such as As, Cd, Cr, Cu, Ni, Pb, and Zn in the surface sediments of mangrove wetlands were measured to reveal their distribution, the contamination level was assessed, and the sources of contamination were analyzed. The distribution of Cr, Zn, Ni, Pb, Cu, and Cd concentrations are: Yanfeng East River > Sanjiang River > Yanzhou River > Yanfeng West River, while the As concentration in the Yanfeng West River is greater than that in the Yanfeng East River. According to the correlation analysis, the concentrations of Cr, Zn, Ni, Cu, and Cd are significantly and positively correlated with total organic carbon (TOC), total phosphorus (TP), total nitrogen (TN), and salinity (SAL) and shared a significantly negative correlation with pH. There is moderate contamination risk of As and slight contamination risk of Cd, Cr, Cu, Ni, Pb, and Zn in most regions within the study area. Cd, Cr, Cu, Ni, Pb, and Zn exhibit the same sources, which are mainly influenced by human sources such as aquaculture, agricultural cultivation, and livestock farming, while the source of As comes from aquaculture.

Distribution Characteristics and Influencing Factors of Bio-elements in the Human Hair of Uyghur Communities in an Oasis Area of Xinjiang, China

Located in central Asia, Xinjiang is characterized as a diverse environment in China, consisting of vast deserts, dotted oases, and high mountains. Due to the combined effect of climate conditions under such a diverse environment, there are large differences in human activities, living styles, and eating habits in farmland and grazing pastures between Xinjiang and other regions of China. This study aimed to investigate the variations and mechanisms of elemental distribution in the hair of Uyghur communities among different ages and genders and under different land use backgrounds in an oasis region in Xinjiang. Hair samples from 524 residents from four traditional farmland areas and two grazing pasture areas in Bai Cheng County in Xinjiang were collected, and the levels of thirteen elements were analyzed. The results indicated that the average levels of Cu, Mg, Mn, Zn, Ni, Co, Pb, Fe, Ca, Cd, Cr, As, and Se in the hair of Uyghur communities were within the background levels of Chinese and global residents' hair. Overall, the levels of elements in the hair of women residents were higher than those of men residents. The levels of elements in the human hair of the middle-aged group were higher than those of child and older-aged groups. Elements Cr and Se in the hair of grazing pastures were higher than those of farmland areas. The levels of Cd, Pb, As, and Zn in the hair of farmland areas were higher than those of grazing pasture areas. The levels of Ca, Mg, Cu, and Fe in the hair of Uyghur communities were higher than those of other ethnic groups, while the toxic elements in the hair of residents in Bai Cheng were lower than those in other regions of China. Middle-aged people were exposed to higher levels of toxic elements in their daily activities compared to elderly and child groups. Also, adult groups need much more nutrients for their growth and intellectual development compared to child and elderly groups. The change in land use from grazing pastures to farmland increased the toxic trace element concentration levels in human hair. The significant differences in the overall concentration levels of elements in human hair among the different ethnic groups and regions can be attributed to the differences in lifestyles, cultural customs, dietary habits, and internal and external exposure routes.

Bioaccessibility, source and human health risk of Pb, Cd, Cu and Zn in windowsill dusts from an area affected by long-term Pb smelting

Non-ferrous metal smelting results in heterogenous spatial distribution of potentially toxic metals (PTM) near smelters. In this work, windowsill dusts were collected from smelting (SA) and urban (UJ) sub-areas of Jiyuan (a city affected by >70 years of Pb smelting) to investigate PTM source and bioaccessibility. The <10 μm fraction of dusts were analyzed for total and bioaccessible Pb, Cd, Cu and Zn concentrations; bioaccessibility was analyzed by a three-stage assay (i.e., lung phase, gastric phase and gastrointestinal phase) using artificial lysosomal fluid (ALF, L phase) followed by simulated gastric and gastrointestinal fluids (G and GI phases). This assay mimicked the movement of particles phagocytosed by alveolar macrophages in the respiratory system, then transported up the oropharynx and subsequently swallowed and transported into the digestive system. Zinc had greater bioaccessible concentrations in L and GI phases than other metals, and the mean L phase bioaccessible PTM concentrations in SA were greater than in UJ. The mean L + GI phase bioaccessible concentrations of Pb, Cd, Cu and Zn in SA were 280, 79, 124 and 1458 mg kg^-1, while those in UJ were 215, 54, 116 and 598 mg kg^-1, respectively. The L phase extracted 87.7 to 98.8 % of PTM within the L + GI assay. Lead had a lower L + GI bioaccessibility than Cd, Cu and Zn (70-76 % vs. 82-92 %). Higher tolerable Cd carcinogenic risks based on bioaccessibility were found in SA sub-area than in UJ while no carcinogenic or non-carcinogenic risk was found for other metals. Lead isotopic ratios indicated that both Pb ore and smelting bottom ash contributed to dust Pb accumulation in SA, while coal burning, lead ore, Pb smelting bottom ash and diesel engine exhaust contributed to dust Pb accumulation in UJ. Overall, results indicated heterogenous distribution of PTM source and bioaccessibility in the vicinity of Pb smelters.

Insights into site-specific influences of emission sources on accumulation of heavy metal(loid)s in soils by wheat grains

Excessive accumulation of heavy metal(loid)s in agricultural environment usually originates from anthropogenic activities. Both large diversities of emission sources and complexity of plant accumulation challenge the understanding of the site-specific effects of emission sources on heavy metal(loid)s in wheat grains. Herein, both soil samples and wheat grain samples (n = 80) were collected from the farmland of Jiyuan City, China. Soil and grain burdens of heavy metal(loid)s were determined by inductively coupled plasma mass spectrometry (ICP-MS) and/or X-ray fluorescence spectrometry (XRF). The quotients (Q) were developed to indicate relative impacts of industrial plants and traffic to soil sites. Principal component analysis-absolute principal component scores-multivariate linear regression (PCA-APCS-MLR) analysis was conducted to reveal the source contributions to heavy metal(loid)s in grains, considering Q values, soil, and wheat grain data. Results showed that contributions of main sources and factors drastically varied with soil sites, and usually overlapped to different extents. For grain Cd and grain Pb, natural soil silicate (0.066/0.104 mg/kg) and iron-bearing minerals (- 0.044/ - 0.174 mg/kg) contributed to high extents, while metal smelting activities (0.018/0.019 mg/kg) and agronomic activities (- 0.017/ - 0.019 mg/kg) unexpectedly posed low or moderate contributions. The pH-mediated availability of soil Cd (0.035 mg/kg) and the sand-dust weather (0.028 mg/kg) also made considerable contributions to grain Cd. For grain As, both natural soil iron-bearing (- 0.048 mg/kg) and silicate minerals (- 0.013 mg/kg) made negative contributions. The results benefit to the decision-making of pollution remediation of farmland soils in the regional scales.

Evaluation of the water pollution risk of dam and dike-break floods in the inundated area

The inundated area of dam and dike-break floods includes various types of land and factories that release considerable amounts of pollutants into floods, causing serious water pollution and further endangering human health. Many pollution sources and factors affect the water pollution risk in inundated areas. Accurate assessment of the water pollution risk for dam and dike-break floods enables people to take measures in advance to reduce public health problems. The existing evaluation methods cannot effectively analyze the water pollution risk for dam and dike-break floods because partial or all pollution sources and influencing factors are ignored. The main factors affecting flood water quality were summarized into point source (PS), non-point source (NPS), flood depth, velocity, duration, and temperature. The water pollution risk caused by NPSs and PSs were quantified, as well as the impact of all main factors on water pollution risk. The evaluation model proposed for water pollution risk in inundated areas of dam and dike-break floods considers all pollution sources and influencing factors. The WPR was proposed to represent the water pollution risk value. The dam-break flood of Luhun Reservoir was simulated to verify the feasibility of the evaluation model. We concluded that (1) WPR varied with space and time in the inundated area and was seriously affected by PS in local areas; (2) the annual average WPR of different land use types from high to low were construction land, cropland, urban, water, rural area, woodland, and grassland. The evaluation model can be used to evaluate the water pollution risk for dam and dike-break floods at macro and micro scales. People can use this method to evaluate the impact, range, and degree of specific pollution sources or pollutants in the inundated area, thus allowing for measures to be taken in advance to reduce associated damages.

Comparison of Pb and Cd in wheat grains under air-soil-wheat system near lead-zinc smelters and total suspended particulate introduced modeling attempt

The excessive accumulation of wheat grain metals and metalloids caused by ambient air contamination has drawn an increasing concern. However, at present, the differences in the pathways of cadmium and lead accumulation in wheat grains in an air-soil-wheat system are not clear. In this study, wheat was grown around a lead‑zinc smelting area and exposed to different soil Pb and Cd levels and different ambient air Pb and Cd levels. Lead and Cd accumulation in wheat grains was examined in this study. Two models of wheat grain Pb and Cd concentrations were established based on the 3 variables including soil Pb and Cd concentration, ambient air Pb and Cd concentration, and soil pH. The results showed that total suspended particulate (TSP), soil, and wheat grains exhibited different degrees of Pb and Cd contamination in the study area, and the contamination of Cd is more serious than Pb contamination. The Pb in wheat grains was more likely to derive from ambient air than from soil, whereas the impact of ambient air on the accumulation of Cd in wheat grains might be very limited. This speculation was confirmed by the results of the predictor variable relative weight method based on the multiple regression analysis. Introduction of ambient air factor (TSP Pb and Cd) greatly improved the modeling effect of wheat grains Pb, while the modeling of grain Cd was more dependent on soil pH and total soil Cd. This research suggests that the reduction in wheat grain Pb is likely to be achieved by the control over ambient air Pb, whereas the reduction in the wheat grain Cd by the remediation of soil pollutants.

Physiological and metabolomics responses of Hydrangea macrophylla (Thunb.) Ser. and Hydrangea strigosa Rehd. to lead exposure

Hydrangea is a potential remediation plant for lead (Pb) pollution. Plant roots communicate with soil through the release of root exudates. It is crucial to study rhizoremediation mechanisms to understand the response of root exudates to contamination stress. Here, we investigated the physiological responses and metabolomic profiling of two Hydrangea species, a horticultural cultivar (Hydrangea macrophylla (Thunb.) Ser.) and a wild type (Hydrangea strigosa Rehd.), under Pb-free and Pb-stressed conditions for 50 days. The results showed that Pb treatment adversely affected the biomass and root growth of the two species. H. strigosa was a Pb-tolerant species with higher superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities and more ascorbic acid (AsA) content in roots. Metabolomic profiling showed that 181 and 169 compounds were identified in H. macrophylla and H. strigosa root exudates, respectively, among which 18 showed significant differences between H. macrophylla and H. strigosa under Pb exposure. H. strigosa showed significantly (P < 0.05) higher secretion of sucrose, glycolic acid, and nonanoic acid than H. macrophylla after Pb treatment. Pb stress promoted fatty acid metabolism in H. strigosa, suppressed amino acid metabolism in H. macrophylla, and promoted a higher carbohydrate metabolism in H. strigosa compared with H. macrophylla. This study provides a possible mechanism for the high Pb absorption potential of Hydrangea.

Evaluating the contributions of leaf organ to wheat grain cadmium at the filling stage

Cadmium (Cd) is an element of global concern in agricultural fields owing to its high bioavailability and its risk to human health via the consumption of wheat products. However, whether wheat leaves can directly absorb atmospheric Cd and transport them to the grains along with the contribution of leaves to Cd accumulation in the grains is not clear. We evaluated this mechanism through three comparative treatments: 1) exposure to atmospheric deposition (CK), 2) no exposure to atmospheric deposition (T1), and 3) exposure to atmospheric deposition with leaf cutting (T2). The Cd accumulation rate of grains in the CK, T1, and T2 groups all showed an increasing trend, followed by a decreasing trend, which was consistent with the trend of filling rate. Moreover, the critical period for leaf Cd accumulation in the grains was the early filling period, and its contribution decreased gradually as filling progressed. The contribution of the leaves to grain Cd reached 31.73% at maturity, with the reactivation of stored Cd in leaves pre-flowering and the newly absorbed atmospheric Cd by leaves post-flowering contributing 19.76% and 11.97% to Cd accumulation in grains, respectively, at maturity. Sub-microstructure analysis of the leaves further confirmed that the direct Cd absorption by leaves from atmospheric deposition through stomata contributed to Cd accumulation in wheat grains. Therefore, controlling the sources of atmospheric Cd pollution and reducing Cd absorption by leaves during grain filling can effectively control Cd pollution of wheat grains. This study provides significant insights on how to more effectively control the Cd content of edible part of wheat and ensure food security.

Research Progress on Heavy Metals Pollution in the Soil of Smelting Sites in China

Contamination by heavy metals is a significant issue worldwide. In recent decades, soil heavy metals pollutants in China had adverse impacts on soil quality and threatened food security and human health. Anthropogenic inputs mainly generate heavy metal contamination in China. In this review, the approaches were used in these investigations, focusing on geochemical strategies and metal isotope methods, particularly useful for determining the pathway of mining and smelting derived pollution in the soil. Our findings indicate that heavy metal distribution substantially impacts topsoils around mining and smelting sites, which release massive amounts of heavy metals into the environment. Furthermore, heavy metal contamination and related hazards posed by Pb, Cd, As, and Hg are more severe to plants, soil organisms, and humans. It's worth observing that kids are particularly vulnerable to Pb toxicity. And this review also provides novel approaches to control and reduce the impacts of heavy metal pollution. Hydrometallurgy offers a potential method for extracting metals and removing potentially harmful heavy metals from waste to reduce pollution. However, environmentally friendly remediation of contaminated sites is a significant challenge. This paper also evaluates current technological advancements in the remediation of polluted soil, such as stabilization/solidification, natural attenuation, electrokinetic remediation, soil washing, and phytoremediation. The ability of biological approaches, especially phytoremediation, is cost-effective and favorable to the environment.

Effects of exogenous additives on wheat Cd accumulation, soil Cd availability and physicochemical properties in Cd-contaminated agricultural soils: A meta-analysis

Cadmium (Cd) contamination in wheat is a serious issue. The application of exogenous additives can effectively inhibit Cd bioavailability in soil and decrease Cd accumulation in wheat. However, a comprehensive and quantitative analysis of how additives affect wheat Cd accumulation, wheat yield, soil Cd availability, and soil properties is lacking. We conducted a meta-analysis of 65 peer-reviewed papers published before April 2021 to investigate how additives application affects Cd accumulation in wheat and soil Cd availability. The results indicated that most additives application decreased the diethylenetriaminepentaacetic acid extractable-Cd content (5.27-56.33%) in the soil, and wheat grain and root Cd concentrations (0.03-129.87% and 0.42-52.84%, respectively); the pH values of wheat-grown soil and the properties of the additives affected the reduction percentage. Overall, most wheat-grown soils were calcareous soil (42 peer-reviewed papers); in calcareous soil, the magnitude of the Cd reduction in wheat grain was the highest under treatments with clay minerals (129.87%) due to clay modification, followed by composite (75.36%) and phosphorus materials (73.55%). Moreover, most additives application increased wheat grain yield by 0.03-51.84%, which was attributed to the positive effects of additives on wheat antioxidant capacity, photosynthesis, respiration, and nutrient uptake. Additives application increased the pH value of acidic wheat soil, and positively affected the electrical conductivity, cation exchange capacity, and organic carbon content of the wheat grown soil. In addition, regression analysis showed that soil available Cd was negatively correlated with the pH value with additives application in acidic soil (r² = 0.43), while a non-significant correlation was observed in neutral and calcareous wheat soils (r² = 0.017 and 0.016, respectively). The results of this study can assist in the selection, modification, and utilisation of additives to remediate Cd-contaminated wheat soils.

Metal Accumulation and Biomass Production in Young Afforestations Established on Soil Contaminated by Heavy Metals

The restoration of forest ecosystems on metal-contaminated sites can be achieved whilst producing valuable plant biomass. Here, we investigated the metal accumulation and biomass production of young afforestations on contaminated plots by simulating brownfield site conditions. On 16 3-m² plots, the 15 cm topsoil was experimentally contaminated with Zn/Cu/Pb/Cd = 2854/588/103/9.2 mg kg⁻¹ using smelter filter dust, while 16 uncontaminated plots (Zn/Cu/Pb/Cd = 97/28/37/< 1) were used as controls. Both the calcareous (pH 7.4) and acidic (pH 4.2) subsoils remained uncontaminated. The afforestations consisted of groups of conifers, deciduous trees, and understorey plants. During the four years of cultivation, 2254/86/0.35/10 mg m⁻² Zn/Cu/Pb/Cd were extracted from the contaminated soils and transferred to the aboveground parts of the plants (1279/72/0.06/5.5 mg m⁻² in the controls). These extractions represented 3/2/3% of the soluble soil Zn/Cu/Cd fractions. The conifers showed 4–8 times lower root-to-shoot translocation of Cu and Zn than the deciduous trees. The contamination did not affect the biomass of the understorey plants and reduced that of the trees by 23% at most. Hence, we conclude that the afforestation of brown field sites with local tree species is an interesting option for their reclamation from an ecological as well as economic perspective.

Toxicological assessment of low-dose bisphenol A, lead and endosulfan combination: chronic toxicity study in male rats

In the present study, toxic effects, both alone and combined, of bisphenol A (BPA), lead (Pb) and endosulfan (ES) in the low doses were investigated in rat liver and kidney functions. In the study, bisphenol A (BPA), lead (Pb) and endosulfan (ES) were chosen because although they are the chemicals people are most frequently exposed to, no combined toxic effect studies were conducted with these chemicals. Sixty-four male Wistar albino rats were used in the study, and they were randomly divided into eight groups (n = 8 per group); control, BPA (5 mg/kg), Pb (100 ppm), ES (0.61 mg/kg), BPA+Pb, BPA+ES, Pb+ES and BPA+P+ES. The rats were sacrificed after 65 days of treatment. Severe histopathological changes in the liver and kidney tissues were observed in the rats exposed to BPA+Pb+ES combination. Elevated malondialdehyde (MDA) in the liver and decreased superoxide dismutase activity (SOD) in the kidney tissue were detected in the BPA+Pb+ES group compared to those of the control group. It was found that serum alanine aminotransferase (ALT) and blood urea nitrogen (BUN) and creatinine (CREA) levels were higher in the BPA+Pb+ES combination group than the control group. Also, combined exposure of BPA, Pb and ES caused apoptotic cell numbers and inducible nitric oxide (iNOS) to increase in the liver and kidney tissues. The results of the present study suggested that the BPA, Pb and ES caused more dramatic changes to both histological architecture and cell apoptosis in the liver and kidney tissues when there was a combined exposure.

Accumulation and partitioning of toxic trace metal(loid)s in phytoliths of wheat grown in a multi-element contaminated soil

Cropland contamination by toxic trace metal (loid)s (TTMs) has attracted increasing attention due to the serious consequential threat to crop quality and human health. Mitigation of plant TTM stress by silica amendment has been proposed recently. However, the relationship between the siliceous structure of phytoliths and TTMs in plants, and the environmental implications of phytolith-occluded trace metal (loid)s (PhytTMs) remain unclear. This study assessed the accumulation of five metal (loid)s, including lead (Pb), zinc (Zn), cadmium (Cd), copper (Cu) and arsenic (As), in the organic tissues and phytoliths of wheat grown in a mixed-TTM contaminated soil under both lightly and heavily contaminated conditions. The results show that the concentrations of plant TTMs and PhytTMs were significantly (p < 0.05) positively correlated, and higher in heavily contaminated wheats than those in lightly contaminated ones. The bio-enrichment factors between phytoliths and organic tissues were higher for As (1.83), Pb (0.27) and Zn (0.30) than for Cd (0.03) and Cu (0.14), implying that As, Pb and Zn were more readily co-precipitated with silicon (Si) in phytolith structures than Cd and Cu. Network analysis of the relationship between soil and plant elements with PhytTMs showed that severe contamination could impact the homeostasis of elements in plants by altering the translocation of TTMs between soils, plants, and phytoliths. The accumulation of TTMs in phytoliths was affected by the capacity of Si deposition in tissues and chelation of TTMs with silica, which could impact the role of PhytTMs in global biogeochemical TTM cycles.

Effect of insect feces (Hermetia illucens) on rice growth and heavy metal migration from polluted soil to rice plant

Insect feces are a new kind of biological organic fertilizer. Little is known about the influences of insect feces on rice growth and heavy metal migration from soil to rice plant. In this study, the effects of different amounts (CK (0%), T1 (2%), T2 (4%), T3 (6%), and T4 (8%)) of black soldier fly larvae (BSFL) feces on the rice growth and the migration/accumulation of heavy metals (Cd and Pb) were investigated by pot experiments within 2 years. The application of insect feces remarkably increased the contents of soil pH, organic matter, ammonium nitrogen, available phosphorus, and potassium. Meanwhile, the insect feces application reduced the weak acid-soluble contents of soil Cd and Pb by 8.3-56.8%, but increased those in the oxidizable (by 22.4-165.7%) and residual (by 1.8-225.6%) states. Except for the T4 treatment in the first year, all fertilization treatments increased the rice yield (up to 43.7% and 195.5% higher than those of CK within 2 years). Moreover, the insect feces application reduced the contents of Cd (8.3-66.7%) and Pb (6.4-61.8%) in different parts of rice. Under the same treatment, the metal contents in each part of rice in the second year were lower than those in the first year. The insect feces application decreased the absorption coefficients (24.4-57.5%) and secondary transport coefficients (3.6-44.1%) of Cd and Pb by rice plant. The findings implied that the insect feces might act as effective organic fertilizers for rice plants as well as reducing heavy metal accumulation in rice plants growing in polluted soil.

Derivation of human health risk-based thresholds for lead in soils promote the production of safer wheat and rice

A reliable and accurate soil threshold helps prevent excessive dietary Pb intake risks to consumers of locally grown wheat and rice crops. Based on a three-year investigation of 206 wheat fields and 358 rice fields throughout China, this study aimed to improve the soil protection guidelines by investigating Pb accumulation in soil-wheat and soil-rice systems and by assessing Pb exposure risks through the soil-grain-human pathway. A site-specific bioconcentration factor (BCF, ratio of Pb concentration in plant to that in soil) was calculated and used to assess grain Pb intake risks instead of a generic BCF value to reduce data uncertainty. In addition to soil pH, cation-exchange capacity exerted a major influence on the Pb BCF variations in wheat, whereas the organic carbon dynamics affected the BCF variations in rice. Once normalized BCF against those soil variables, the distributions of BCF were log-normal in nature. Optimizing the pH and cation-exchange capacity of wheat soils would help protect 49.8% of local adults from excessive Pb dietary intake. The scenario soil thresholds linked to soil variables and grain Pb intake risks were then derived and validated by independent data from field surveys and published articles. Poor production practices in the wheat fields under study included using soils with low fertility.

Bioimaging of Pb by LA-ICP-MS and Pb isotopic compositions reveal distributions and origins of Pb in wheat grain

Atmospheric heavy metal deposition in agroecosystems has increased recently, especially in northern China, which poses serious risks to crop safety and human health via food chain. Wheat grains can accumulate high levels of Pb even when wheat is planted in soils with low levels of Pb. However, the influence of atmospheric deposition on the accumulation and distribution of Pb in wheat grain is still unclear. A field survey was conducted in three districts (A: a district with industrial and traffic pollution; B: a district with traffic pollution; and C: an unpolluted district) in Hebei Province, North China. The grain of wheat cultivated in district A accumulated more Pb from soil and atmospheric deposition than those in other districts, and the bran from district A contained 3.50 and 2.04 times more Pb than those from districts B and C, respectively. The Pb distribution pattern in wheat grain detected by laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was characterized by accumulation mostly in the pericarp and seed coat rather than in the crease, embryo and endosperm. Furthermore, Pb isotopic data showed that airborne Pb was the major source (>50%) of Pb in wheat grain. Interestingly, average contributions of Pb from atmospheric deposition to white flour (78.22%) were higher than its contributions to bran (56.27%). In addition, wheat flag leaves were exposed to PbSO₄ at the booting stage, and much greater Pb accumulation (0.33-0.48 mg/kg) was observed in exposed wheat grain than in the control (P < 0.05), PbSO₄ constituted most (82.80-100%) of the Pb in the wheat grain. In summary, the results confirmed the efficient foliar Pb uptake and transfer from atmospheric deposition into wheat grain. It would be a new sight for understanding the contribution of airborne Pb to Pb accumulation in wheat grains.

Quantifying source-specific intake risks of wheat cadmium by associating source contributions of soil cadmium with human health risk

Sources of cadmium (Cd) contamination of farmlands and the potential risk to human health via dietary intake of wheat Cd are of great concern to consumers. A source-specific risk assessment (SSRA) model, which combined a positive matrix factorization receptor model and spatial analysis with a health risk assessment model, was developed based on a wheat field investigation in northern China. It was used to estimate the daily intake risk from different sources of ingesting Cd from wheat. The mixed source of wastewater and residues from industrial activities and atmospheric deposition were identified as the dominant sources of Cd contamination. Wheat Cd uptake could be predicted reliably from the pH and total Cd concentration of field soil. Based on the predictive model of Cd transfer from soil to wheat, the SSRA model then linked sources to the Cd intake risk from wheat grain. Results showed that the mixed source and the atmospheric deposition source accounted for 52.8% and 29.3%, respectively, of the wheat Cd intake risk. In combination with the spatial analysis, the potential risk of Cd contamination in western and central eastern areas was mainly attributed to the mixed source of wastewater and industrial residues, whereas the risk in the northwestern area was associated mainly with atmospheric deposition. Regionalized risk management strategies, focusing on different sources, were proposed to minimize the Cd input to field cropping system and to mitigate health risk for local residents.

Heavy metal phytoremediation potential of the roadside forage Chloris barbata Sw. (swollen windmill grass) and the risk assessment of the forage-cattle-human food system

This study presents the assessment of the risks incidental to the growth of the common tropical grass species Chloris barbata Sw. (swollen windmill grass) on road margins contaminated with Pb and Cd. Pot experiments were first carried out to quantify the Pb and Cd accumulation potential of the plant species in various plant parts as a function of the metal concentration in soil. C. barbata was found to be a hyperaccumulator for Cd (BCF>1, for aerial parts) and an excluder of Pb (BCF<1, for aerial parts). As the plant was found to accumulate Pb in its roots with TF<1, it can be considered a phytostabilizer of Pb. The mathematical relationship developed between soil concentrations of Pb and Cd and their corresponding concentrations in aerial parts were used in combination with the concentrations of these heavy metals reported in roadside soils to obtain estimates of their accumulation in the forage and consequently in the animal organs. Risk to the consumers of offal was estimated. It was found that the consumption of kidney meat was riskier than the consumption of liver meat. Furthermore, it was seen that despite the nearly two order less concentrations of Cd in roadside soils compared to Pb, it was posing a higher risk. For the median concentrations of Pb reported in roadside soils and cattle feeding exclusively on C. barbata growing on roadside soils, the HQ exceeded 1 for weekly consumption of kidney meat above 650 g. For median Cd concentrations, consumption of kidney meat above 230 g/week resulted in HQ>1. The scenario considered for risk assessment is significant for India, where stray grazing of cattle on road margins is common and offal offers a cheap source of animal protein for the economically poor.

Comparative effects of Tagetes patula L. extraction, mercapto-palygorskite immobilisation, and the combination thereof on Cd accumulation by wheat in Cd-contaminated soil

Phytoextraction and in situ immobilisation are two of the most commonly used remediation techniques for Cd-contaminated farmland. In theory, phytoextraction followed by immobilisation can reduce the total Cd and available Cd contents of the soil, making it suitable for the remediation of heavily Cd-contaminated alkaline soil. However, the real remediation efficiency is uncertain, and it is also unknown whether phytoextraction affects subsequent wheat Cd accumulation. In this study, two seasonal pot experiments were conducted to determine the effects of S,S-ethylenediamine disuccinic acid (EDDS)-assisted Tagetes patula L. (T. patula) extraction, mercapto-palygorskite (MPAL) immobilisation, and the combination thereof on subsequent Cd accumulation in wheat. EDDS application significantly increased the Cd content in the subsequent-soil solution, but the EDDS-activated Cd could not be absorbed by wheat roots. T. patula extraction decreased the subsequent soil pH value by 0.1-0.2 pH units, increased the available Cd content by 0.19 mg/kg, but had no effect on subsequent wheat Cd accumulation. The Cd absorption capacity of wheat roots and the Cd translocation capacity of wheat stems to grains of high-Cd wheat were higher than that of low-Cd wheat cultivar. The application of MPAL had no effect on soil pH value, but significantly decreased soil available Cd and exchangeable Cd contents by 17.78-36.76% and 21.13-52.63%; it also increased the Fe/Mn oxide-bound Cd fraction by 14.02-64.00%. MPAL application decreased the wheat grain Cd concentrations from 0.51 to 0.13 mg/kg (high-Cd wheat) and 0.35 to 0.05 mg/kg (low-Cd wheat), but had no negative effect on Fe, Mn, Cu, and Zn elements. Compared with the single MPAL application treatments, the combination treatments had no inhibition effect on Cd accumulation in wheat. MPAL is an efficient amendment, and considering the remediation efficiency, stability, and time of these methods, the combination of MPAL application with a low-Cd accumulation wheat cultivar represents a suitable proposal to ensure the safe production of wheat in Cd-contaminated alkaline soil.

Investigation of plant contamination to Ni, Pb, Zn, and Cd and its relationship with spectral reflections

This study aims to investigate the toxicity of the plant to heavy elements (HMs). For this purpose, the estimated daily intake (EDI) parameters of potentially toxic elements (PTE) per kilogram of body weight, target hazard quotient (THQ) for non-carcinogenic disorders, total hazard index (HI), and bioconcentration factor (BCF) are determined in the plant at different stages of growth. In this study, the reaction of the plant to different electromagnetic waves at different stages of growth (DSG) is also investigated, and the relationship between the THQ values and electromagnetic waves is prepared. The results show that Pb has the highest EDI value (5.97), Pb (74.67) and Cd (9.75) have the highest THQ values, and Cd has the highest BCF value (30.44). Also, the results show that HI values are higher than the threshold in the growth (69.98), flowering (71.38), and fruiting (68.06) stages. Results of BCF indicate Pb, and Cd has absorption rate in Capsicum towards. Contaminated Capsicum plants submitted to electromagnetic waves showed a significant relationship between Pb and the b490, and b560 spectra, Cd and Ni the b450 spectrum, and Zn the b460 spectrum. This finding highlights the salience of employing electromagnetic waves in assessing contamination in plants. Put differently, THQ can be estimated using electromagnetic waves without any need for laboratory studies.

Remediation of Metal/Metalloid-Polluted Soils: A Short Review

The contamination of soil by heavy metals and metalloids is a worldwide problem due to the accumulation of these compounds in the environment, endangering human health, plants, and animals. Heavy metals and metalloids are normally present in nature, but the rise of industrialization has led to concentrations higher than the admissible ones. They are non-biodegradable and toxic, even at very low concentrations. Residues accumulate in living beings and become dangerous every time they are assimilated and stored faster than they are metabolized. Thus, the potentially harmful effects are due to persistence in the environment, bioaccumulation in the organisms, and toxicity. The severity of the effect depends on the type of heavy metal or metalloid. Indeed, some heavy metals (e.g., Mn, Fe, Co, Ni) at very low concentrations are essential for living organisms, while others (e.g., Cd, Pb, and Hg) are nonessential and are toxic even in trace amounts. It is important to monitor the concentration of heavy metals and metalloids in the environment and adopt methods to remove them. For this purpose, various techniques have been developed over the years: physical remediation (e.g., washing, thermal desorption, solidification), chemical remediation (e.g., adsorption, catalysis, precipitation/solubilization, electrokinetic methods), biological remediation (e.g., biodegradation, phytoremediation, bioventing), and combined remediation (e.g., electrokinetic–microbial remediation; washing–microbial degradation). Some of these are well known and used on a large scale, while others are still at the research level. The main evaluation factors for the choice are contaminated site geology, contamination characteristics, cost, feasibility, and sustainability of the applied process, as well as the technology readiness level. This review aims to give a picture of the main techniques of heavy metal removal, also giving elements to assess their potential hazardousness due to their concentrations.

Lead smelting alters wheat flour heavy metal concentrations and health risks

Wheat (Triticum aestivum L.) flour consumption may be a major source of human metal intake, especially when wheat is cultivated in metal-contaminated soils. This work investigated Cd, Cu, Pb, and Zn distribution in whole wheat flour, wheat flour, and wheat bran when grown in an area polluted by Pb smelting. Wheat product heavy metal concentrations were analyzed, and the (non)carcinogenic risks were assessed. Mean Cd, Cu, Pb, and Zn concentrations in whole wheat flour were 0.38, 3.83, 0.48, and 29.3 mg kg^-1 , respectively; those in flour were only slightly reduced. The ratios between noncarcinogenic average daily dose of whole wheat flour and wheat flour consumption ranged from 1.06 to 3.76, with Pb having the greatest values compared with other metals. For children, the average hazard quotients (HQs) of whole wheat flour consumption of Cd, Cu, Pb, and Zn were 4.19, 1.06, 1.53, and 1.07; those for wheat flour consumption were 3.81, 0.68, 0.70, and 0.98, respectively. The HQs of adults were less than those of children. Overall results indicated that consumption of wheat products may lead to health concerns in the heavy metal contaminated area, yet when wheat flour rather than whole wheat flour is consumed, only the human health risk from Pb ingestion is reduced. Altering or removing human edible crops in the most contaminated areas should be considered.

Chronic Exposure to Lead and Cadmium in Residents Living Near a Zinc Smelter

This study aimed to measure lead (Pb) and cadmium (Cd) exposure levels in residents living near a zinc (Zn) smelter in Seokpo-myeon, Bonghwa-gun, South Korea, and identify factors affecting exposure. Residents aged ≥20 years living within 3 km and ≥30 km away from the smelter were classified as the exposure group (n = 549), and the control group (n = 265), respectively. Data were obtained through a questionnaire survey. Blood Pb levels in the exposure group (4.19 µg/dL) were higher than in the control group (2.70 µg/dL). The exposure group (1.32 µg/L) also had higher urinary Cd concentrations than the control group (0.80 µg/L). Male sex, older age, previous work at the smelter, smoking, and proximity to the smelter were associated with higher blood Pb levels on multivariate analysis; urinary Cd concentration was significantly higher in women, those who were older, those with experience of working in a Zn smelter or mine, those with proximity to the Zn smelter, and those who consumed locally grown vegetables. In conclusion, Zn smelters are major source of Pb and Cd pollution and require ongoing public health management to prevent potential adverse health effects.

Spatial assessment models to evaluate human health risk associated to soil potentially toxic elements

Quantifying source apportionment of potentially toxic elements (PTEs) in soils and associated human health risk (HHR) is essential for soil environment regulation and pollution risk mitigation. For this purpose, an integrated method was proposed, and applied to a dataset consisting of As, Cd, Cr, Cu, Hg, Ni, Pb, Se, and Zn in 273 soil surface samples. Positive matrix factorization (PMF) was used to quantitatively examine sources contributions of PTEs in soils; and the HHR arising from the identified source was determined by combining source profiles and health risk assessment; at last, sequential Gaussian simulation (SGS) was used to identify the areas with high HHR. Four sources were identified by PMF. Natural and agricultural sources affected all 9 PTEs contents with contributions ranging from 19.2% to 62.9%. 41.9% of Cd, 40.8% of Pb, 58.6% of Se, and 29.8% of Zn were controlled by industrial and traffic emissions. Metals smelting and mining explained 35.5%, 30.5%, and 24.9% of Cr, Cu, and Ni variations, respectively. Hg was dominated by atmospheric deposition from coal combustion and coking (58.7%). The mean values of the total non-carcinogenic risks of PTEs were 1.55 × 10^-1 and 9.40 × 10^-1 for adults and children, and the total carcinogenic risk of PTEs had an average value of 8.86 × 10^-5. Based on source-oriented HHR calculation, natural and agricultural sources were the most important factor influencing HHR, explaining 51.0% and 49.1% of non-carcinogenic risks for children and adults, and 44.2% of carcinogenic risk. SGS indicated that 1.1% of the total area was identified as hazardous areas with non-carcinogens risk for children.

Removal of lead and other toxic metals in heavily contaminated soil using biodegradable chelators: GLDA, citric acid and ascorbic acid

In this study, we investigated the level of contamination of agricultural soil near an old recycling lead smelter in Vietnam and proposed an effective treatment for the remediation of the soil. The analysis of soil samples using an ICP-MS method revealed that the soil in the area was heavily contaminated by heavy metals, especially lead (Pb) with concentrations in surface soil of >3000 μg g^-1. High concentrations of metals, including Pb, copper (Cu) and zinc (Zn), were found in whole soil profile. The FE-EPMA and Laser-Raman spectrometer results suggested that iron minerals and carbon materials in the soil are the important hosts of the toxic metals. Subsequently, a series of washing experiment were performed on the soil using biodegradable chelators, including N, N-dicarboxymethyl glutamic acid tetrasodium salt (GLDA), ascorbic acid and citric acid. The results showed that the mixture of GLDA-ascorbic (100 mM: 100 mM) can be considered as a potential candidate for Pb and Zn removal, which removes approximately 90% of Pb and 70% of Zn. Meanwhile, a mixture of GLDA-citric would be preferred for Cu removal based on its greater extraction efficiency compared to other mixtures.

Lead source and bioaccessibility in windowsill dusts within a Pb smelting-affected area

Windowsill, heavy metal-containing dust samples, collected at different building heights, may provide some insight into both source and human health risk. Windowsill dust samples were collected from the 1st to 9th floor (1.4-23.2 m above ground) near a lead smelter (1 km to the smelter) and in urban areas (4.2-7.3 km to the smelter) and separated into <10, 10-45 and 45-125 μm size fractions. Samples were extracted with artificial lysosomal fluid (ALF) and the physiologically based extraction test (PBET) (<10 μm fractions only), subjected to scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDS) and Pb isotopic analysis. Greater Pb concentrations were found in 10-45 μm fraction than the other size fractions; at the PX site, dust Pb concentrations increased with windowsill height, while an opposite trend was found at other sites. Isotopic analysis and SEM-EDS results supported this contention. Higher floor samples collected near the smelter were more affected by lead smelting than lower floor samples; lower floor samples collected at urban sites were more affected by resuspended Pb-laden particles from the ground than higher floors. The Pb bioaccessible fraction (BAF) in the ALF and PBET ranged between 68.9-90.1 and 1.3-17.0%, respectively; urban samples had greater BAF values than samples collected near the smelter. This, first of its kind investigation regarding Pb in dusts at different building heights, provides further insight for reducing human health risks within Pb smelter vicinities.

Atmospheric deposition of arsenic, cadmium, copper, lead, and zinc near an operating and an abandoned lead smelter

Atmospheric deposition samples were collected over 15 mo at several locations near an operating smelter and an abandoned Pb smelter to investigate the contribution of Pb smelting to depositional fluxes and potential local air quality degradation. Samples were analyzed for As, Cd, Cu, Pb, and Zn and subjected to scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS). Concentrations of Cd and Pb at both sites were greater than at the control site (p < .05), and significant correlations existed between Cd and Pb concentrations at both sites (p < .05). Monthly depositional flux variations at both sites were similar, with greater deposition during cold and dry periods. Heavy metal(loid)s deposition during these periods was correlated with wind speed. Greater Cd depositional flux differences were found between the smelter and control sites compared with other elements. The SEM images suggested that some particles at the operating smelter site were from Pb smelting material. However, most particles at both sites had no characteristics of smelting, suggesting reactions occurred between the smelter-emitted particles and soil components. The EDS results indicated that atmospheric deposition from both sites had lower Pb concentrations than smelting material or ash. The main atmospheric deposition source at the operating and abandoned sites was likely from the resuspension of heavy metal(loid)-enriched soil particles. Greater risk of air pollution from historical Pb smelting facilities exists years after closing down. Reducing soil wind erosional losses may help reduce heavy metal(loid)s dispersion across environments.