Characteristics, Health Risk Assessment, and Transfer Model of Heavy Metals in the Soil-Food Chain in Cultivated Land in Karst

Stabilization mechanism and remediation effectiveness of Pb and cd in agricultural soil using nonmetallic minerals

Soil contaminated by Pb and Cd has aroused worldwide concern due to the environmental hazards they pose. The effects, mechanisms, and evaluation of Pb and Cd contaminated agricultural soil remediation by nonmetallic minerals are still poorly understood. In this study, solidification/stabilization experiments were used to screen nonmetallic mineral materials and optimize their dosages. Stabilization mechanisms of Pb and Cd by nonmetallic mineral materials were investigated by adsorption kinetics, X-ray diffraction spectroscopy, and Fourier transform infrared spectroscopy. The effectiveness of soil remediation was further confirmed through a pot experiment with pak choi (Brassica rapa L. subsp. chinensis), an important non-heading leafy vegetable. Results demonstrated that the SL composite (composed of 2.5% sepiolite and 1.5% limestone, with a total dosage of 4.0%) exhibits the optimal stabilization effect on soil contaminated with Pb and Cd. In soils with low, medium, and high contamination levels, SL reduced the bioavailability of Pb by 97.97%, 96.78%, and 95.82%, and the bioavailability of Cd by 92.96%, 91.76%, and 91.02%, respectively. SL surfaces are rich in hydroxyl (-OH) and carbonate (CO32-) groups, enabling binding with Pb and Cd ions to form hydroxide and carbonate precipitates. Such interactions suggest that chemical adsorption primarily drives Pb and Cd ion stabilization, reducing their bioavailability in soil. Pak choi grown in SL-remediated soil exhibited Pb and Cd contents compliant with China's food safety standards. These findings further validate the bioavailability reduction rate as a suitable metric for evaluating the remediation effectiveness of heavy metal pollution in agricultural soils. This study provides a new strategy for evaluating the remediation efficiency of heavy metal-contaminated agricultural soil.

Causal inference of whole-grain foods' risk based on a generative adversarial network and Bayesian network

Whole-grain foods (WGFs) constitute a large part of humans' daily diet, making risk identification of WGFs important for health and safety. However, existing research on WGFs has paid more attention to revealing the effects of a single hazardous substance or various hazardous substances on food safety, neglecting the mutual influence between individual hazardous substances and between hazardous substances and basic information. Therefore, this paper proposes a causal inference of WGFs' risk based on a generative adversarial network (GAN) and Bayesian network (BN) to explore the mutual influence between hazardous substances and basic information. The experiment results show that the proposed GAN outperformed several traditional data-imputation methods, producing at least a 13.65% reduction of the root mean square error (RMSE). The classification accuracy of the BN model reached 91%. In conclusion, we distinguish the provinces, periods, food categories, and hazardous substances cause the absolute risk of WGFs and the high risk of mycotoxins and compounds (MaCs) and cadmium. PRACTICAL APPLICATION: This research can be applied to impute missing values for whole-grain foods (WGFs) sampling data, and explore the causality among hazardous substances themselves, that between hazardous substances and basic information in WGFs. Additionally, it can be applied to infer root cause of existing or potential WGFs risk (e.g., provinces, periods, food categories, and hazardous substances).

Correlation Analysis of Ecosystem Reduction and Retention Effects and Spatial Distribution of Soil Potential Toxicity Elements

Soil contamination by potentially toxic elements (PTEs) poses a significant threat to crop quality and human health, making it a global concern. However, the distribution patterns of PTEs across different land-use types are not well understood. To investigate the relationship between the reduction and retention effects of various ecosystem types on soil PTEs, we analyzed five categories of target elements in 299 soil samples from the southeastern Yunnan Province. Using the intelligent urban ecosystem management system's surface source control (runoff) model, descriptive statistical methods, spatial interpolation analyses, and GIS, we simulated the effects of different ecosystem types on soil heavy metals. This approach allowed us to examine the spatial correlations among ecosystem reduction, retention, and PTE distribution in soils. Our results indicate that soil PTE concentrations were indicative of a high-background value area, with concentrations of arsenic, cadmium, copper, lead, and zinc exceeding risk screening values. The coefficients of variation for arsenic, cadmium, and lead were extremely high and attributable to high external anthropogenic interference. Soil heavy metal reduction and spatial distribution were affected by the ecosystem's control function, and different ecosystems had different reduction effects. The reduction simulations for As and Pb were concentrated in building areas, while those for Cd and Zn were primarily focused on water bodies. The reduction simulations for Cu were concentrated in the forested areas. In conclusion, ecosystem reduction and retention influence heavy metal distribution, which is essential when planning green ecological development and construction.

Accumulation and risk assessment of heavy metals in different varieties of leafy vegetables

A pot experiment was conducted to investigate the differences in heavy metal accumulation in different varieties of leafy vegetables (five leafy vegetables four or five varieties of each) and their potential risk. The results revealed that the concentrations of Cd in all the vegetables exceeded the limit for China (0.2 mg/kg) and that the As and Pb concentrations were within the limit. The bioaccumulation of Pb, Cd, and As in spinach (0.01, 1.08, and 0.02) and rape seedlings (0.004, 0.43, and 0.03) were the highest and lowest, respectively. Health risk assessments indicate that the hazard index (HI) ranged from 0.66 to 3.37 and 2.86 to 14.64 for adults and children, respectively, and the total carcinogenic risk (TCR) ranged from 2.13E-03 to 1.86E-02 and 9.27E-03 to 8.07E-02. Probabilistic health risk assessment revealed that the HI was 3.06 and 4.75, and the TCR was 2.5E-03 and 8.88E-04 for adults and children, respectively. More importantly, heavy metal accumulation significantly differed among varieties of leafy vegetables, especially spinach. The BF of Pb, Cd, and As in spinach ranged from 0.003 to 0.01, 0.77 to 1.39, and 0.01 to 0.02, respectively. Geodetector analysis revealed that oxalic acid, available As, and organic matter are the key factors that affect Pb, Cd, and As accumulation, respectively, in these vegetables. These results suggest that the planting of suitable types and varieties of vegetables can reduce the potential health risk to a certain extent and that more effective measures should be implemented to ensure the safety of local residents in areas contaminated with heavy metals.

Selenium and Bacillus proteolyticus SES increased Cu-Cd-Cr uptake by ryegrass: highlighting the significance of key taxa and soil enzyme activity

Many studies have focused their attention on strategies to improve soil phytoremediation efficiency. In this study, a pot experiment was carried out to investigate whether Se and Bacillus proteolyticus SES promote Cu-Cd-Cr uptake by ryegrass. To explore the effect mechanism of Se and Bacillus proteolyticus SES, rhizosphere soil physiochemical properties and rhizosphere soil bacterial properties were determined further. The findings showed that Se and Bacillus proteolyticus SES reduced 23.04% Cu, 36.85% Cd, and 9.85% Cr from the rhizosphere soil of ryegrass. Further analysis revealed that soil pH, organic matter, soil enzyme activities, and soil microbial properties were changed with Se and Bacillus proteolyticus SES application. Notably, rhizosphere key taxa (Bacteroidetes, Actinobacteria, Firmicutes, Patescibacteria, Verrucomicrobia, Chloroflexi, etc.) were significantly enriched in rhizosphere soil of ryegrass, and those taxa abundance were positively correlated with soil heavy metal contents (P < 0.01). Our study also demonstrated that in terms of explaining variations of soil Cu-Cd-Cr content under Se and Bacillus proteolyticus SES treatment, soil enzyme activities (catalase and acid phosphatase) and soil microbe properties showed 42.5% and 12.2% contributions value, respectively. Overall, our study provided solid evidence again that Se and Bacillus proteolyticus SES facilitated phytoextraction of soil Cu-Cd-Cr, and elucidated the effect of soil key microorganism and chemical factor.

Exploring the mechanism of Cd uptake and translocation in rice: Future perspectives of rice safety

Cadmium (Cd) contamination in rice fields has been recognized as a severe global agro-environmental issue. To reach the goal of controlling Cd risk, we must pay more attention and obtain an in-depth understanding of the environmental behavior, uptake and translocation of Cd in soil-rice systems. However, to date, these aspects still lack sufficient exploration and summary. Here, we critically reviewed (i) the processes and transfer proteins of Cd uptake/transport in the soil-rice system, (ii) a series of soil and other environmental factors affecting the bioavailability of Cd in paddies, and (iii) the latest advances in regard to remediation strategies while producing rice. We propose that the correlation between the bioavailability of Cd and environmental factors must be further explored to develop low Cd accumulation and efficient remediation strategies in the future. Second, the mechanism of Cd uptake in rice mediated by elevated CO2 also needs to be given more attention. Meanwhile, more scientific planting methods (direct seeding and intercropping) and suitable rice with low Cd accumulation are important measures to ensure the safety of rice consumption. In addition, the relevant Cd efflux transporters in rice have yet to be revealed, which will promote molecular breeding techniques to address the current Cd-contaminated soil-rice system. The potential for efficient, durable, and low-cost soil remediation technologies and foliar amendments to limit Cd uptake by rice needs to be examined in the future. Conventional breeding procedures combined with molecular marker techniques for screening rice varieties with low Cd accumulation could be a more practical approach to select for desirable agronomic traits with low risk.

Health risk assessment of trace metal(loid)s in agricultural soil using an integrated model combining soil-related and plants-accumulation exposures: A case study on Hainan Island, South China

Traditional health risk assessment of trace metal(loid)s (TMs) in agricultural soil exclusively considers direct soil-related exposure and may underestimate the health risks they pose. In this study, the health risks of TMs were evaluated using an integrated model that combined soil-related and plant-accumulating exposures. A detailed investigation of common TMs (Cr, Pb, Cd, As, and Hg) coupled with probability risk analysis based on a Monte Carlo simulation was conducted on Hainan Island. Our results showed that, except for As, the non-carcinogenic risk (HI) and carcinogenic risk (CR) of the TMs were all within the acceptable ranges (HI < 1.0, and CR < 1E-06) for direct soil-related exposure to bio-accessible fractions and indirect exposure via plant accumulation (CR substantially lower than the warning threshold 1E-04). We identified crop food ingestion as the essential pathway for TM exposure and As as the critical toxic element in terms of risk control. Moreover, we determined that RfDo and SFo are the most suitable parameters for assessing As health risk severity. Our study demonstrated that the proposed integrated model combining soil-related and plant-accumulating exposures can avoid major health risk assessment deviations. The results obtained and the integrated model proposed in this study can facilitate future multi-pathway exposure research and could be the basis for determining agricultural soil quality criteria in tropical areas.

Ecological Risk Assessment and Source Identification of Heavy Metals in Soils from Shiyang River Watershed in Northwest China

Shiyang River Watershed is an important ecological barrier and agricultural production area in Northwest China, and the study of soil heavy metal content, distribution, and sources is important for agricultural product safety, pollution control, and ecosystem health. In this paper, 140 soil samples were collected from 28 stations to assess the level of heavy metal (Arsenic (As), Copper (Cu), Lead (Pb), Cadmium (Cd), Chromium (Cr), Mercury (Hg), Nickel (Ni), Zinc (Zn)) contamination, pollutant sources and influencing factors of soil in Shiyang River Watershed through determination of the metal contents and statistical analysis. The results indicated that the soils in the study area are typical saline soils in arid zones. The enrichment factors (EF) of As, Cr, Cu, Ni, Zn, and Pb indicate no contamination, and the EFs of Cd and Hg suggested minor contamination. Although the concentrations of Cd and Hg in soil are lower than others, they are more biotoxic and exhibit a moderate-high ecological risk. The index of geoaccumulation (Igeo) values reflect that most of the stations, especially the three groups of samples from depths of 10-20 cm, 20-40 cm, and 40-80 cm, are below the contamination threshold for all heavy metals. The chemical speciation of heavy metals, principal component analysis, and correlation analysis showed that Cr, Cu, Pb, Cd, Ni, and Zn mainly come from the natural accumulation upon weathering of soil-forming matrices. Hg and As mainly come from anthropogenic contributions. The effect of agricultural crop cultivation on soil heavy metal contamination is mainly through farm irrigation and crop-soil interactions, which accelerate the release of heavy metals through the weathering of soil-forming parent material and irrigation, which transports the heavy metals below the surface. The results of this study can provide a scientific basis for the involved authorities to formulate reasonable policies on environmental protection and pollution control.

The Distribution of Selected Toxic Elements in Sauced Chicken during Their Feeding, Processing, and Storage Stages

Sauced chicken is popular food worldwide. However, the elemental pollution of poultry industrialization has led to an increasing health risk concern. In this study, four typical toxic elements, including chromium (Cr), arsenic (As), lead (Pb), and cadmium (Cd), were selected and detected in whole industry chains of sauced chicken preparation by inductively coupled plasma-mass spectrometry. The detection method was optimized and verified with an average recovery of 93.96% to 107.0%. Cr has the highest proportion among the elements during the three stages, while the content of Cd was the least. In the feeding stages, elements were at the highest level in the starter broiler, and the grower broiler was considered to have a good metabolic capacity of them. In addition, the elements were mainly distributed in the chicken kidney, gizzard, liver, leg, wing, and lung. In the processing stage, the elements continued to accumulate from the scalding to the sterilization process. The elements were mainly distributed in the chicken wing, leg, head, and breast. In the storage stage, the elements almost kept constant in the polyamide and polyethylene packaging, while it showed irregular small-range fluctuations in the other two packages. This study provides beneficial references for the toxic element risk management in the whole industry chain.

Nodes play a major role in cadmium (Cd) storage and redistribution in low-Cd-accumulating rice (Oryza sativa L.) cultivars

Rice cadmium (Cd) contamination is one of the critical agricultural issues. Breeding of low-Cd-accumulating cultivar is an effective approach to reduce Cd bioaccumulation in rice. To investigate the molecular mechanism underlying Cd transport in rice, the functions of nodes in Cd transport are explored. The results show that different nodes have different functions of Cd transport in the rice plant and the physiological structure of the first node under panicle (N1) determine the Cd accumulation in the brown rice. The upper nodes can redistribute the Cd transport in aboveground tissues. The expressions of Cd-efflux transporter genes (OsLCT1 and OsHMA2) located on the plasma-membrane are the main factors affecting the Cd transport form node to brown rice, which are more depended on the node functions but not the node Cd concentrations. Lower expressions of OsLCT1 and OsHMA2 in N1 result in lower Cd transport from node to brown rice. The size of vascular-bundle (VB) areas in the junctional node with the flag leaf can determine the expression of OsHMA2 and the expression of OsLCT1 positively correlated with the Cd transport ability of first node (N1). The expressions of OsVIT2 and OsABCC1 cannot allow Cd to be immobilized into the vacuoles in node. The VB structure and Cd transporter gene expression level of N1 proved that the Cd concentration of N1 can be used as an important indicator for screening low-Cd-accumulating cultivars. The major implication is that selecting or breeding cultivars with lower Cd accumulations in N1 could be an effective strategy to reduce Cd accumulation in rice grains.

Effects of vegetation restoration on distribution characteristics of heavy metals in soil in Karst plateau area of Guizhou

In southwest China, vegetation restoration is widely used in karst rocky desertification control projects. This technology can effectively fix the easily lost soil, gradually restore the plant community and improve soil fertility. However, the change law of soil heavy metals in the restoration process remains to be further studied. Therefore, in this work, Guizhou Caohai Nature Reserve as a typical karst area was taken as the research object to investigate the influence of vegetation restoration technology on repairing soil heavy metal pollution. The spatial distribution characteristics of soil heavy metals (chromium, nickel, arsenic, zinc, lead) before and after vegetation restoration in karst area were studied by comparative analysis and linear stepwise regression analysis. The main influencing factors and spatial distribution characteristics of heavy metals in karst area were further discussed. The results showed that: (1) heavy metals in karst soils are affected by surface vegetation, root exudates, microorganisms and leaching. Only heavy metals nickel (Ni) and lead (Pb) showed the tendency of surface enrichment and bottom precipitation enrichment in non-karst soils. Path analysis suggested that non-metallic soil factors such as soil bulk density (BD), total nitrogen (TN) and ammonium nitrogen (NH₄ ⁺-N) had direct effect on the content of heavy metals in soil. (2) The proportion of 0.25-2 mm aggregates in the surface soil of vegetation restoration belt was more than 40%, and the proportion of surface soil ≤2 mm aggregates in this increased to 83% and 88%, respectively, which could improve the soil structure and properties effectively. (3) Vegetation restoration effectively restored the nutrient elements such as carbon and nitrogen in the soil, and enhanced the soil material circulation. Furthermore the content of heavy metals in the surface soil higher than that in the 10-20 cm soil layer. Plant absorption, biosorption mechanism of microorganisms, coupling of root exudates, dissolution of soil soluble organic carbon and pH make the contents of heavy metals Cr, Ni and Pb in vegetation restoration belt slightly lower than those in karst soil. At the same time, affected by vegetation coverage, residual heavy metals in soil are further leached by surface runoff. Therefore, the content of heavy metals in soil could reduce combined heavy metal enrichment plants for extraction with remediation. This study elucidates the advantages and remedy mechanism of vegetation restoration in the remediation of heavy metal contaminated soils in Caohai area of Guizhou, and this plant activation and enrichment extraction remediation technology would be popularized and applied in the remediation of heavy metal contaminated soils in other karst areas.

How Does the Concept of Guanxi-circle Contribute to Community Building in Alternative Food Networks? Six Case Studies from China

As social innovations that help to transition towards a more sustainable food system, alternative food networks (AFNs) in China have attracted much scholarly attention in recent years. However, studies of the community building behavior of AFNs at the micro-level in the Chinese social context are scant. Through in-depth case studies conducted between 2017 and 2021 and social network analysis, our study examines how founders of AFNs successfully facilitate community building among their customers. We find that in China, the traditional social-cultural construct, guanxi, plays a critical role in AFNs’ community formation and expansion. The study identifies a three-stage framework for understanding the community building process of AFNs. First, a group of guanxi of the same kind would form a guanxi-circle. Second, the initial guanxi-circle is enhanced and expanded to multiple secondary guanxi-circles. Third, these multiple guanxi-circles together and the interactions among them constitute the community of AFNs. We argue that to strengthen the community, AFNs operators should inspire key members to form secondary guanxi-circles by enhancing their cognitive trust and emotional trust.