Soil Heavy Metal Pollution
Cadmium pollution has become a major global challenge to farmland safety, and safeguarding the quality of farmland is of paramount importance. This paper examined the sources and speciation of cadmium in soil, summarized the efficacy and mechanisms of plant-microbe systems in remediating cadmium-contaminated soils, including root interaction, metabolite regulation and cadmium speciation transformation. This study introduced the primary sources and characteristics of both plants and microorganisms in such synergistic systems, and elucidated the underlying remediation mechanisms as well as key influencing factors. Owing to the synergistic interactions between plants and microorganisms, the combined remediation system demonstrated superior efficiency in remediating cadmium-contaminated soils compared to individual remediation approaches. Finally, in view of the future research direction, it is recommended to introduce eco-friendly functional materials (such as biochar, nanomaterials, etc.) in order to provide efficient and environmentally friendly technical solutions for the remediation of cadmium-contaminated soil.
Heavy metal contamination of soil affects soil and crop quality and poses a threat to human health. Traditional phytoremediation techniques face challenges such as prolonged remediation cycles, poor adaptability, and the complexity of pollution, thus making it crucial to explore the mechanisms of removal, decomposition, and detoxification through enhanced phytoremediation technologies in heavy metal-contaminated soils. By collecting literature on intensive phytoremediation of heavy metal-contaminated soils, we concisely described techniques such as genetic engineering, the application of plant growth regulators, microbial synergistic remediation, and the addition of chelating agents, focusing on how these techniques enhance plant tolerance to heavy metal ions and affect their transport within the plant. This paper proposed that future agricultural production should focus more on understanding the molecular mechanisms and gene regulatory networks of plants, as well as the demand and uptake capacity of different plants for specific nutrients. Additionally, it suggested exploring more in situ bioresistance resources and combinatorial modes, enriching the symbiotic systems of bacteria and plants within contamination ranges, optimizing the dosage of chelating agents, and prioritizing biodegradable chelating agents or developing environmentally friendly substitutes. These efforts aimed to provide a theoretical and practical basis for utilizing enhanced phytoremediation technologies to address soil heavy metal contamination.
As a national commercial grain base, the soil health of green rice planting areas in Jilin Province is crucial for ensuring food security and ecological safety. This study systematically analyzed the spatial distribution characteristics of soil pH and heavy metal (Cd, Hg, As, Pb, Cr) contents, along with their correlations, across 42 green rice planting areas in Jilin Province. The results indicated that the soil pH in the study area ranged from 4.6 to 10, with a mean pH value of 7.23 and significant spatial heterogeneity (standard deviation of 1.21). The analysis of heavy metal content revealed that the mean concentrations of Cd, Hg, As, Pb, and Cr were 0.1094, 0.043, 8.1, 21.79 and 49.23 mg/kg, respectively. Notably, the levels of Cd and Hg approached or exceeded the screening values for soil environmental risks in certain areas. Correlation analysis demonstrated a significant negative relationship between soil pH and heavy metal contents (P<0.01), particularly for Cd (r=-0.387) and Hg (r=-0.627), suggesting that increased pH could effectively reduce the bioavailability of heavy metals. Further spatial analysis revealed a coupling relationship between heavy metals and pH, indicating significant overlap between low pH regions and areas with high heavy metal content. Based on the findings of this study, recommendations for acidic soil amendment (with a suggested lime application rate of 1500-3000 kg/hm2) and the establishment of a comprehensive heavy metal—pH monitoring network are proposed. These measures could serve as a scientific basis for soil pollution prevention and control, as well as for sustainable agricultural development in the green rice growing areas of Jilin Province.
This study investigated the efficacy of agricultural and forestry biochar in mitigating chromium (Cr) toxicity in artificially contaminated soil through a 40-day passivation treatment. Biochars derived from different biomass sources and pyrolysis temperatures were applied to the contaminated soil at varying ratios for pot experiments with coriander. Soil and plant samples were collected and analyzed at 0, 7, 14 and 21 days after cultivation to assess Cr immobilization and bioavailability. The results demonstrated that rice straw biochar pyrolyzed at 200°C for 4 h exhibited the highest efficiency in reducing Cr toxicity, and the effect was the best at an 8% application rate. The acid-extractable Cr content in the soil decreased by 99.8% after 7 days, while the leaching concentration of Cr (VI) dropped from an initial 175.08 μg/g to undetectable levels. Furthermore, Cr was effectively stabilized in the soil, significantly inhibiting its accumulation in the roots, stems and leaves of coriander. These findings indicated a substantial reduction in both Cr toxicity and mobility. Risk Assessment Code (RAC) analysis confirmed that the environmental risks associated with Cr contamination were markedly reduced after 7 days of treatment with 4% and 8% rice straw biochar. The study highlighted that agricultural and forestry biochar could facilitate soil remediation by converting Cr into residual and less bioavailable forms, thereby reducing soil toxicity. Additionally, this approach supports the sustainable reutilization of agricultural and forestry biomass.
The aim was to explore the application effects of different water management measures in cadmium (Cd) moderately polluted farmland and ensure food safety production. In this experiment, five water management measures (conventional irrigation, whole growth period flooding, moist irrigation, periodic moist irrigation and twice field drying at tillering-heading stage) were adopted to carry out the indoor pot experiments. The experiment measured the growth status of rice, the Cd content in different parts of rice at various growth stages (tillering stage, booting stage, filling stage and maturity stage), and calculated the Cd enrichment and transport coefficients as well as changes in soil pH and organic matter. The results showed that the moist irrigation treatment increased the 1000-grain weight of rice by 8.64%, and significantly reduced the Cd content in the roots, stems and leaves of rice at tillering stage. Compared with conventional irrigation treatment, moist irrigation could significantly reduce the Cd content in mature rice grains, with a decrease of 78.83% (P<0.05), followed by the whole growth period flooding treatment (with a decrease of 39.69%). In addition, the whole growth period flooding and moist irrigation treatments mainly reduced the Cd content in rice by inhibiting the migration of Cd from stems and leaves to grains. Based on rice production and actual situation, it was recommended to use moist irrigation as a water management measure for rice planting in moderately Cd-contaminated farmland.
To effectively address the escalating heavy metal contamination in water bodies and soils, microbial-induced carbonate precipitation (MICP) technology, based on biomineralization, has recently garnered significant attention for remediating heavy metal pollution. Compared to conventional removal methods, MICP aims to induce calcium carbonate precipitation through microbial activity, offering cost-effectiveness and robust stability. This approach not only immobilizes heavy metals but also enhances the quality of contaminated matrices, demonstrating promising application prospects. This paper reviews recent advances in MICP and its applications in environmental engineering, encompassing mineral precipitation mechanisms, metabolic pathways, influencing factors, and progress in heavy metal remediation. Furthermore, it discusses the potential for large-scale implementation and three suggestions are put forward. Firstly, the internal and external factors of MICP process should be optimized to determine the optimal process conditions for microbial growth and mineral formation; the second is to further improve the treatment method of NH4+ produced in the urea hydrolysis process of MICP to reduce the negative impact on the environment; the third is to optimize the process and automation steps to reduce the cost of MICP technology and realize the large-scale application of MICP. The research is expected to provide theoretical insights to advance MICP technology in environmental restoration and biomaterial synthesis.
To investigate the varietal differences in cadmium (Cd) absorption and accumulation among different rice varieties, a field experiment was conducted with 10 rice varieties in slightly Cd-contaminated farmland. The variations in Cd absorption and accumulation capacities were compared. The results demonstrated that grain yields of different rice varieties ranged from 7.60 to 10.77 t/hm2, with the highest yield observed in the cultivar ‘Liangyou 5078’, which was significantly higher than other varieties (P<0.05). The Cd content in brown rice of different varieties ranged from 0.177 to 0.503 mg/kg, with the Cd concentration in ‘Zhennuo 29’ being lower than the national limit standard (0.20 mg/kg). The enrichment factors of brown rice for total soil cadmium (Cd) in different rice varieties ranged from 0.281 to 0.858, all below 1. The enrichment factor of ‘Zhennuo 29’ was significantly lower than other varieties (P<0.05). Rhizosphere Soil pH values at the maturity stage varied between 5.49 and 6.93 across varieties, with a mean value of 6.27. The total Cd and available Cd contents in soil ranged from 0.407 to 0.827 mg/kg and 0.180 to 0.293 mg/kg, respectively, with average values of 0.634 mg/kg and 0.252 mg/kg. Through input-output ratio analysis of different rice varieties, the ratio for ‘Zhennuo 29’ reached 1.81, which was significantly higher than other varieties (P<0.05). The study demonstrates that ‘Zhennuo 29’ can be cultivated as a low-Cd-accumulating rice variety in safe utilization farmland in the region with high economic value.
In order to manage the polluted farmland coordinately and precisely, this paper identified the definition of polluted agriculture land and summarized the current status of Chinese polluted farmland according to the correlated researches, laws and so on at home and abroad. The current problems of partition management of heavy metal pollution in the agriculture land were analyzed through the pollution resource, assessment and transform respectively combining with the innate character of partition. A partition management and governance system that combines multidisciplinary perspectives, coordinates the characteristics of multiple elements, integrates the strengths of multiple subjects, and establishes different levels, standards and high applicability from the bottom up is proposed to improve the level of the management of heavy metals pollution on agricultural soil in China.
To screen the wheat varieties suitable for planting in the Cd-contaminated farmland of Hebei Piedmont Plain, the field experiment was conducted to study the yield and differential characteristics of cadmium absorption of 48 local main wheat varieties. The results showed that there were significant differences in the yield and the ability to absorb and accumulate Cd among 48 wheat varieties (P<0.05). The yield of ‘Shimai 27’ was the highest (10538.6 kg/hm2), which was 6.33%-42.41% higher than that of other wheat varieties. The yield of ‘Shimai 26’ was the second highest, which was 6.77%-38.51% higher than that of other wheat varieties. The grain Cd contents and enrichment coefficients of ‘Shimai 26’, ‘Zhongxinmai 48’, ‘Malan 6’ and ‘Kenong 2011’ were relatively low, ranging from 0.115 to 0.133 mg/kg and from 0.032 to 0.038, respectively. The Cd transport coefficients of ‘Kenong 2011’, ‘Zhongxinmai 48’ and ‘Shimai 26’ were relatively low, ranging from 0.273 to 0.291. The results of cluster analysis showed that there were 2 varieties of low Cd accumulation, 19 varieties with relatively low Cd accumulation, 3 varieties with low Cd translocation, and 7 varieties with relatively low Cd translocation. By comprehensive evaluation of wheat yield, grain Cd content, enrichment coefficient and transport coefficient, ‘Shimai 26’, ‘Zhongxinmai 48’ and ‘Kenong 2011’ were identified as Cd low accumulation type wheat varieties for safe production in the Cd-contaminated farmland.
Landscape plants can intercept and retain atmospheric dust, which are important filters for purifying the city. In order to address the pollution issues of TSP and PM2.5, an experiment was taken using Rizhao Botanical Garden as the research object. Through the determination of the concentration of TSP and PM2.5 in the park and the survey of plant groups, it quantitatively analyzed the reduction effects of different plant groups on the concentration of TSP and PM2.5, the diurnal and seasonal changes of TSP and PM2.5 concentrations, the relationship between the changes of TSP and PM2.5 concentrations and the characteristics of plant communities, and the changes of heavy metals in PM2.5 under different populations. The results showed that: (1) the effect of plant population structure on the reduction of TSP and PM2.5 in different seasons was significantly different. However, the order was consistent as Weigela florida ‘Red Prince’> Ligustrum compactum> Platanus orientalis> Fraxinus pennsylvanica> Prunus lannesiana ‘Hatzakura’> grassland. In summer, the highest reduction rates of TSP and PM2.5 were 21.2% and 36.5%, respectively, in the pure forest of the W. florida ‘Red Prince’ belt. (2) The diurnal variation of TSP and PM2.5 concentrations showed a “W” pattern, which gradually decreased from 8:00 to 16:00, then began to rise, reached a small peak at 20:00, then decreased, and gradually increased after 24:00. The seasonal variation rule was that the concentrations of TSP and PM2.5 were the lowest in summer and the highest in winter. (3) The concentrations of TSP and PM2.5 in summer were significantly positively correlated with tree canopy density, average height and planting density. (4) The total mass concentration of 12 heavy metals in summer was grassland (813.2 ng/m3)> pure forest of P. lannesiana ‘Hatzakura’ (754.2 ng/m3)> F. pennsylvanica (724.5 ng/m3)> P. orientalis (658.9 ng/m3)> L. compactum (626.7 ng/m3)> W. florida ‘Red Prince’ (587.2 ng/m3), the changes in heavy metal concentration and PM2.5 concentration were basically consistent. The mass concentration of Zn and Pb was the highest, and the mass concentration of Cd, Ni, V and Co was relatively low. The conclusion is that the W. florida ‘Red Prince’ pure forest has a strong effect on reducing TSP and PM2.5, and the heavy metal content in PM2.5 is low. It can be used as an effective pure forest structure to improve urban air quality and reduce TSP and PM2.5 concentrations.
By identifying the distribution characteristics of heavy metal elements in Yuanmou County, we can understand the local heavy metal sources and environmental ratings, objectively grasp the environmental problems existing in the soil in this area, put forward scientific and reasonable suggestions for agricultural development and environmental governance, and improve the level of land management and environmental monitoring in this area. The method of combining traditional geochemistry and soil science was used, and the sampling was carried out according to the relevant standards of 1:250000 land quality geochemical survey. SPSS, Excel, GeolPAS.V4.5, ArcGIS10.8 and other software were used for data modeling, result integration and map production. The results showed that heavy metal elements As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were existed in the surface soil of Yuanmou County, in which Cd was enriched on the surface, and the anisotropy of Cd and Hg was higher than that of other elements. The overall distribution of Cu was balanced, with local characteristics of enrichment and depletion. Cr was highly correlated with Ni and weakly negatively correlated with Pb. There were three main sources of heavy metals: mainly rich in Zn and As, mainly rich in Cr, Ni and Cu, and mainly rich in Hg. In the comprehensive grade assessment of surface soil environment, the risk-free area was 1873 km2, accounting for 92.77%, and the risk-controlled area was 146 km2, accounting for 7.23%. The area was concentrated in Jiangyi Town, Guanyuan Town and Pingtian Town, and scattered in other areas, with no high risk area. The distribution of heavy metals As, Cr, Ni, Pb and Zn in Yuanmou County was mainly controlled by the parent material, Cu and Cd were controlled by the parent material, continuous weathering and human activities, and Hg was mainly controlled by human activities. There was no high-risk area in Environmental rating, and the risk controllable areas were mainly affected by Cu and Cd, among which the Cd risk controllable areas were highly consistent with the concentrated areas of agricultural development, and the application of relevant pesticides should be reasonably controlled and monitored in the later stage. Hg wasn’t at risk in the whole region, but there had been a slight enrichment trend in the surface soil, which required a late warning to avoid pollution.
Determining the safety threshold of heavy metals in soil is an important measure to ensure the quality and safety of agricultural products in China. By studying the accumulation and transportation characteristics of five heavy metals (Cr, Cd, Pb, As, and Hg) in different organs of corn and wheat in the cities of Jinchang, Zhangye and Baiyin in Gansu Province and establishing the relationship between the effective content of Cr, Cd, Pb, As, and Hg in soil and crop grains, this study identified the safety threshold of effective heavy metals in soil for corn and wheat systems. This study employed the method and principles of species sensitivity distribution (SSD) and derived the safety threshold of effective heavy metals in soil for corn and wheat planting systems based on the cumulative probability distribution curve of the Logistic function distribution model. The results showed that the accumulation pattern of Cr, Cd, Pb, As and Hg in wheat plants was consistent, namely, roots>stems>grains, and similarly, the accumulation pattern of Cr, Pb, As and Hg in corn plants was roots>stems>grains, while the accumulation pattern of Cd was stems>roots>grains. Utilizing the Logistic function distribution model to fit the cumulative probability distribution curve based on the effective content of heavy metals, the safety thresholds of effective Cr, Cd, Pb, As and Hg in wheat soil were determined to be 0.019, 0.771, 35.294, 2.777 and 0.133 mg/kg, respectively. Meanwhile, the safety thresholds of effective Cr, Cd, Pb, As and Hg in corn soil were determined to be 0.296, 7.90, 52.363, 12.462 and 0.119 mg/kg, respectively. The results of this study indicate that estimating the safe threshold of effective heavy metal content based on the cumulative probability distribution curve method was scientific, providing a scientific basis and support for the safe planting and risk control of wheat and corn.
In order to explore the pollution status and health risks of heavy metals in rice grains in a county of southern Henan, 68 rice grain samples were collected in the area in September 2021. The contents of chromium, arsenic, cadmium, lead, and mercury were determined by inductively coupled plasma mass spectrometry (ICP-MS-TQ) and direct mercury detection. The risk degree of heavy metals in rice was evaluated by single factor and Nemerowcomprehensive pollution index method, and the potential health risk of heavy metals from rice grains was evaluated by target hazard quotient (THQ) promoted by US EPA. The results showed that the average content of heavy metals in 68 rice grains did not exceed the Chinese Food Hygiene Standards, but the arsenic and cadmium contents in some samples exceeded the standards. The comprehensive pollution index (PN) of heavy metals in rice grain was 0.49, which was safe. ADD of adults and children was higher than RfD, and hazard quotients (HQ) of As were 3.11 and 4.80, which indicated that there was a certain risk of arsenic content in rice grains. The total hazard index (HI) of heavy metals to the exposed population was greater than 1, indicating that the long-term consumption of the rice by local residents may cause adverse health effects. In summary, the rice grain samples in the research area have been contaminated with arsenic, posing certain health risks. The local government needs to strengthen dynamic monitoring of the rice planting process, pay attention to the changes in the form and effective state of arsenic, ensuring food security.
To study the environmental pollution of paddy fields in a region of Sichuan, this paper focused on paddy soil and rice as the main research objects. A total of 216 soil and rice samples were collected from the area, and the heavy metal pollutants in soil and rice in the study area were evaluated by testing the content of eight heavy metal elements, namely arsenic, lead, cadmium, chromium, mercury, copper, zinc and nickel in soil, and the content of five heavy metals, namely arsenic, lead, cadmium, chromium, and mercury in rice, using the single-factor pollutant index method and the Nemero composite pollutant index method, as well as performing the quantitative analysis of the association between various heavy metal elements in soil and rice. The results showed that: (1) the average content of cadmium and mercury in the soil of this study area was 0.47 and 0.98 mg/kg, respectively, which exceeded the standard, and their exceedance rates were 27.78% and 34.26%, respectively. The combined pollution index of Nemero in this study area was 1.11 mg/kg and the pollution level was mild. (2) There were significant correlations between the eight elements in the soil and the pathways of heavy metal accumulation might be the same. The coefficient of variation of soil Hg was 163.20%, which was highly variable, indicating that local pollution sources had a strong influence on heavy metals in soil, and the exceeding of Hg content in soil was mainly anthropogenic. (3) Cadmium, chromium and lead in rice had exceeded the standards, with exceedance rates of 19.44%, 3.70% and 19.44%, respectively. The study shows that the degree of heavy metal enrichment in rice has some correlation with soil heavy metal content and is related to the chemical form of heavy metals. It has certain guiding significance for food safety and heavy metal pollution remediation and treatment.
It is valuable to compare the effects of different amounts of tobacco stalk biochar on Cd bioactivity in acidic soil, which may contribute to the safe planting of polluted farmland, and provide theoretical support for the resource utilization of a large amount of tobacco stalk waste as well. In this study, a series of tobacco stalk biochar (0, 5, 15 and 30 g/kg, denoted as B0, B5, B15 and B30, respectively) were applied to typical Cd-polluted acidic soil collected from the local region, and then C. coronarium and C. endivia were planted continuously in pots. The results showed that the biochar amendment significantly improved the soil physiochemical characters. All the parameters such as pH, TOC, CEC, available P and K in the biochar-amended soil were significantly higher than those of the control soil (P<0.05). Biochar addition promoted the transition from acid-soluble (Cdacid) to the reducible Cd fraction (Cdred) in the soil. The proportion of Cdacid in the total was decreased from 64.03%-71.91% to 52.94%-56.51%, which indicated the large reduction of Cd bioavailability. Cd content in both above- and below-ground tissues of C. coronarium and C. endivia were significantly decreased by 53.47%-91.71% and 56.32%-87.95%, respectively. The biological cumulative factor (BCF) values for both crops were also significantly decreased by 54.47%-89.54%. The transfer factor (TF) values of C. coronarium in all treatments were highly similarity, no significant difference was observed. However, TF of C. endivia increased by 2.94%-86.76% compared to those in control. In addition, the larger rate of biochar amendment induced the greater changes in those parameters. The crop of C. coronarium is more sensitive to biochar addition than C. endivia. With the addition of 30 g/kg biochar (B30), Cd content in edible parts of both C. coronarium and C. endivia were decreased to 0.11 mg/kg and 0.20 mg/kg respectively, which were lower than the national limit for food. It was concluded that adding suitable rate of tobacco stalk biochar (5-15 g/kg) could not only improve soil properties like pH, organic C and CEC, but also promote the transformation of acid-extractable Cd to reducible Cd, and reduce the Cd bioavailability. Biochar addition reduced the Cd content in both C. coronarium and C. endivia, and strongly enhanced vegetable biomass production. C. coronarium was more sensitive to the biochar addition than that of C. endivia.
To accurately assess the levels of heavy metal pollution, health risks and pollution sources in the surface soil of orchards in Qingyang City, the research team collected 16 surface soil samples at 0-40 cm soil layer from orchards in Qingyang City. The concentrations of chromium (Cr), cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), arsenic (As) and mercury (Hg) were determined. Based on the single factor pollution index, the Nemerow comprehensive pollution index, geo-accumulation index, potential ecological risk index and health risk appraisal model were used to evaluate the degree of heavy metal pollution and health risks. In addition, principal component analysis was applied to analyze the sources of heavy metal pollution. The results indicated that the soil of orchards in Qingyang City was severely polluted by cadmium (Cd), reaching a moderate pollution level. The geo-accumulation index for mercury (Hg) was greater than 5, indicating extreme pollution, while the geo-accumulation indices for other heavy metals were all below 0, indicating no pollution. The potential ecological risk index (RI) for the seven elements ranged from 1694.28 to 5158.06, indicating extreme pollution. The total non-carcinogenic risks for young adults (aged from 18 to 40) and middle-aged adults (aged from 41 to 60) were 0.12 and 0.09, respectively, indicating no non-carcinogenic risk to local orchard farmers from soil heavy metals. However, the total carcinogenic risks for young adults and middle-aged adults were 9.21×10-5 and 7.45×10-4, respectively, exceeding the acceptable level (1×10-6), indicating a carcinogenic risk from soil heavy metals to local orchard farmers. Source analysis suggested that the main sources of soil heavy metal pollution may be a combination of traffic and plastic mulch, pesticides, fertilizers, and atmospheric deposition.
To study the effect of the application of soil amendment on the Cd availability in soil and the Cd content in brown rice, a continuous three-year field experiment was conducted in two different textures of Cd contaminated paddy soil in Xiaojia Town, Hengyang City, Hunan Province. The results indicated that: (1) continuous application of soil amendment (2250 kg/hm2 and 3000 kg/hm2) for three years significantly increased the paddy soil pH in Jinxing Village and Niuling Village, and reduced the content of available Cd in soil by 14.1%-50.0% and 16.9%-49.4%, respectively; (2) continuous application of soil amendment for three years significantly increased the rice yield in Jinxing Village and Niuling Village, and reduced the Cd content in brown rice by 40.4%-62.9% and 40.0%-64.1%, respectively. Moreover, the Cd content in brown rice in both areas was 0.15-0.18 mg/kg under the treatment of applying 3000 kg/hm2 amendment, lower than the National Standards for Food Safety (GB2762—2022); (3) the net income of farmers in both areas increased significantly by 1603-2912 and 2282-3408 yuan/hm2, respectively, under the treatment of applying 3000 kg/hm2 amendment. Therefore, the application of soil amendment was a remediation technology that can achieve safe production in mildly Cd contaminated paddy soil.
This study briefly describes the impact of pollution by five heavy metal elements, namely cadmium, chromium, arsenic, vanadium, and copper, on the growth and quality of Lycium barbarum and other crops. It summarizes the mechanisms of L. barbarum to cope with the stress of cadmium, chromium, arsenic, and other five heavy metals, as well as the research progress on detoxification of heavy metal stress at the subcellular level in L. barbarum. The study points out the existing problems in current research on L. barbarum response to heavy metal stress and future research directions, such as the migration and transformation of heavy metal content between soil and various parts of the L. barbarum, including roots, stems, branches, leaves, and fruits, the response mechanisms of L. barbarum to heavy metal stress, and molecular mechanisms, in order to provide references for the application and improvement of clean cultivation of L. barbarum.
To investigate the efficiency of Sedum alfredii in extracting heavy metals from farmland under intercropping systems, this study employed the technique of intercropping the Cd-hyperaccumulator Sedum alfredii with sweet corn to conduct experiments in moderately cadmium-contaminated farmland in South China. The results indicated that under the intercropping system, the yield of sweet corn increased, and the Cd content in the kernels significantly decreased by 8.3% compared to monoculture. Additionally, under the intercropping system, the biomass of Sedum alfredii increased by 16.5%, with Cd accumulation in the roots and shoots increasing by 8.8% and 3.6%, respectively. The enrichment coefficients improved by 15.7 and 6.6 units, respectively. After intercropping sweet corn with Sedum alfredii, the Cd content in the top soil significantly decreased. The experiment demonstrated that the phytoremediation model of intercropping Sedum alfredii with sweet corn not only allowed for the simultaneous remediation and production of polluted farmland but also enhanced the extraction efficiency of the hyperaccumulator plant. This approach presented a practical and green remediation technology for moderately heavy metal-contaminated farmland.
Winter wheat is one of the main food crops in China. The enrichment characteristics and potential risks of heavy metals were discussed to provide reference for rational planting of wheat and grain safety and quality. The contents of Fe, Mn, Cu, Zn, Cr, Ni in soil and wheat grain samples collected from typical farmland in northern Henan were determined, and the pollution and ecological risk of heavy metals were evaluated. The results showed that the average contents of Fe, Mn, Cu, Zn, Cr, Ni in soil were 11397.33, 287.83, 23.33, 7.41, 31.41 and 8.56 mg/kg, respectively. Most of the elements showed a significant positive correlation; the single pollution evaluation and comprehensive pollution evaluation of Cu, Zn, Cr, Ni were clean. The average contents of Fe, Mn, Zn, Cu, Cr, Ni in wheat grains were 30.42, 61.75, 23.17, 1.52, 0.28 and 0.16 mg/kg, respectively. There was a significant positive correlation between individual elements. The contents of Fe, Zn, Cu were lower than the maximum tolerable content of wheat, and the content of Mn was higher than the maximum tolerable content of wheat. The comprehensive pollution evaluation of Cr was mild pollution, and the pollution evaluation of Ni was clean. There was a synergistic or antagonistic effect between heavy metals in the soil-wheat system. The enrichment coefficient of wheat grain to soil heavy metals was Zn > Mn > Cu > Ni > Cr > Fe. The risk of heavy metal pollution in farmland soil in northern Henan is low.
Soil Heavy Metal Pollution
