Soil Cd Research Articles

Synergistic effects of arbuscular mycorrhizal fungi and biochar are highly beneficial to Ligustrum lucidum seedlings in Cd-contaminated soil.

Cadmium (Cd) contamination is a widespread environmental issue. There is a lack of knowledge about the impacts of applying arbuscular mycorrhizal fungi (AMF) and biochar, either alone or in their combination, on alleviating Cd phytotoxicity in Ligustrum lucidum. Therefore, a pot experiment was conducted in a greenhouse, where L. lucidum seedlings were randomly subjected to four regimes of AMF treatments (inoculation with sterilized AMF, with Rhizophagus irregularis, Diversispora versiformis, alone or a mixture of these two fungi), and two regimes of biochar treatments (with or without rice-husk biochar), as well as three regimes of Cd treatments (0, 15, and 150mgkg-1), to examine the responses of growth, photosynthetic capabilities, soil enzymatic activities, nutritional concentrations, and Cd absorption of L. lucidum plants to the interactive effects of AMF, biochar, and Cd. The results demonstrated that under Cd contaminations, AMF alone significantly increased plant total dry weight, soil pH, and plant nitrogen (N) concentration by 84%, 3.2%, and 13.2%, respectively, and inhibited soil Cd transferring to plant shoot by 42.2%; biochar alone significantly enhanced net photosynthetic rate, soil pH, and soil catalase of non-mycorrhizal plants by 16.4%, 9%, and 11.9%, respectively, and reduced the soil Cd transferring to plant shoot by 44.7%; the additive effect between AMF and biochar greatly enhanced plant total dry weight by 101.9%, and reduced the soil Cd transferring to plant shoot by 51.6%. Furthermore, dual inoculation with D. versiformis and R. irregularis conferred more benefits on plants than the single fungal species did. Accordingly, amending Cd-contaminated soil with the combination of mixed-fungi inoculation and biochar application performed the best than either AMF or biochar alone. These responses may have been attributed to higher mycorrhizal colonization, soil pH, biomass accumulation, and biomass allocation to the roots, as well as photosynthetic capabilities. In conclusion, the combined use of mixed-fungi involving D. versiformis and R. irregularis and biochar addition had significant synergistic effects on enhancing plant performance and reducing Cd uptake of L. lucidum plants in Cd-contaminated soil.

Insight into the mechanism of nano-TiO2-doped biochar in mitigating cadmium mobility in soil-pak choi system

Soil cadmium (Cd) pollution poses severe threats to food security and human health. Previous studies have reported that both nanoparticles (NPs) and biochar have potential for soil Cd remediation. In this study, a composite material (BN) was synthesized using low-dose TiO2 NPs and silkworm excrement-based biochar, and the mechanism of its effect on the Cd-contaminated soil-pak choi system was investigated. The application of 0.5 % BN to the soil effectively reduced 24.8 % of diethylenetriaminepentaacetic acid (DTPA) Cd in the soil and promoted the conversion of Cd from leaching and HOAc-extractive to reducible forms. BN could improve the adsorption capacity of soil for Cd by promoting the formation of humic acid (HA) and increasing the cation exchange capacity (CEC), as well as activating the oxygen-containing functional groups such as CO and CO. BN also increased soil urease and catalase activities and improved the synergistic network among soil bacterial communities to promote soil microbial carbon (C) and nitrogen (N) cycling, thus enhancing Cd passivation. Moreover, BN increased soil biological activity-associated metabolites like T-2 Triol and altered lipid metabolism-related fatty acids, especially hexadecanoic acid and dodecanoic acid, crucial for bacterial Cd tolerance. In addition, BN inhibited Cd uptake and root-to-shoot translocation in pak choi, which ultimately decreased Cd accumulation in shoots by 51.0 %. BN significantly increased the phosphorus (P) uptake in shoots by 59.4 % by improving the soil microbial P cycling. This may serve as a beneficial strategy for pak choi to counteract Cd toxicity. These findings provide new insights into nanomaterial-doped biochar for remediation of heavy metal contamination in soil-plant systems.

The C2H2 family protein ZAT17 engages in the cadmium stress response by interacting with PRL1 in Arabidopsis

Cadmium (Cd) is a heavy metal and a toxic substance. Soil Cd pollution has emerged as a significant environmental issue that jeopardizes both the safety of agricultural products and human health. PLEIOTROPIC REGULATORY LOCUS 1 (PRL1) has been identified as a crucial factor in Cd stress and a series of defence mechanisms. However, the mechanism through which PRL1 mediates its downstream signalling has remained poorly understood. Here, we discovered a prl1–2 suppressor (sup8) for prl1–2 that complemented the defective development phenotype of prl1–2 under Cd stress. Gene cloning revealed a mutation in the C2H2 transcription factor ZAT17 as the basis for the sup8 phenotype. Genetic and biochemical studies indicated that ZAT17 acts as a negative regulator of Cd tolerance. Transcriptome analysis revealed that ZAT17 influences the alternative splicing (AS) process of multiple Cd-responsive genes by interacting with members of the MAC splicing complex, including PRL1 and CDC5. In conclusion, the identification of the novel gene ZAT17 enriches the understanding of the Cd stress response pathway and provides a valuable candidate locus for breeding Cd-resistant plant varieties.

Inoculation of cadmium-tolerant bacteria to regulate microbial activity and key bacterial population in cadmium-contaminated soils during bioremediation

The perennial ryegrass Lolium perenne can be used in conjunction with cadmium (Cd)-tolerant bacteria such as Cdq4–2 (Enterococcus spp.) for bioremediation of Cd-contaminated soil. In this study, a theoretical basis was provided to increase the efficiency of L. perenne remediation of Cd-contaminated soil using microorganisms to maintain the stability of the soil microbiome. The experimental design involved three treatment groups: CK (soil without Cd addition) as the control, 20 mg·kg–1 Cd-contaminated soil, and 20 mg·kg–1 Cd-contaminated soil + Cdq4–2, all planted with L. perenne. The soil was collected on day 60 to determine the soil microbial activity and bacterial community structure and to analyze the correlation between soil variables, the bacterial community, available Cd content in the soil, Cd accumulation, and L. perenne growth. The soil microbial activity and bacterial community diversity decreased under Cd stress, and the soil microbial community composition was changed; while inoculation with Cdq4–2 significantly increased soil basal respiration and the activities of urease, invertase, and fluorescein diacetate (FDA) hydrolase by 83.65%, 79.72%, 19.88%, and 96.15% respectively; and the stability of the community structure was also enhanced. The Actinobacteriota biomass, the amount of available Cd, and the above- and belowground Cd content of L. perenne were significantly negatively correlated with the total phosphorus, total potassium, and pH. The activity of urease, invertase, and FDA hydrolase were significantly positively correlated with the biomasses of Acidobacteriota and L. perenne and significantly negatively correlated with the Chloroflexi biomass. Further, the available soil Cd content and the above- and belowground Cd levels of L. perenne were significantly positively correlated with the Actinobacteriota biomass and significantly negatively correlated with the Gemmatimonadetes biomass. Overall, inoculating Cd-tolerant bacteria improved the microbial activity, diversity, and abundance, and changed the microbial community composition, facilitating the remediation of Cd-contaminated soil by L. perenne.

Remediation of Arsenic and Cadmium Co-Contaminated Soil: A Review

The concurrent presence of arsenic (As) and cadmium (Cd) contamination in soil is widespread and severe, highlighting the need for remediation. However, remediating As and Cd co-contaminated soils is more complex than remediating soils contaminated with a single heavy metal due to the opposite properties of As and Cd in soil. Thus, the different forms of As and Cd in co-contaminated soils and their transformation rules have been systematically reviewed in this paper. Simultaneously, hyperaccumulators and immobilization amendments used in the remediation of As–Cd co-contaminated soil were reviewed. Moreover, the mechanisms of phytoremediation and chemical immobilization techniques in the treatment of As and Cd co-contaminated soil and the remediation effects were expounded in detail. To promote the development of ecological civilization, this paper proposes further remediation strategies and guidance for the remediation of As–Cd co-contaminated soil.

Sepiolite-supported nanoscale zero-valent iron alleviates Cd&As accumulation in rice by reducing Cd&As bioavailability in paddy soil and promoting Cd&As sequestration in iron plaque

Cadmium and arsenic (Cd&As) co-contaminated paddy soil is the main reason for excessive Cd&As in rice. However, the opposite chemical behaviors of Cd&As posed a challenge to the simultaneous remediation of Cd&As and the reduction of Cd&As content in rice. The synthesized sepiolite-supported nanoscale zero-valent iron (S-nZVI) exhibits exceptional efficacy in Cd&As adsorption. The effects of S-nZVI on Cd&As availability in soil and Cd&As accumulation in rice need to be further investigated. This study applied different amounts of S-nZVI (0.1%−0.6%) to paddy soils for rice cultivation. The findings revealed that the Cd&As concentrations in rice grains reduced by 46.18%− 68.13% and 24.26%− 57.16%, respectively, under 0.1%− 0.6% S-nZVI application. S-nZVI significantly decreased Cd&As concentrations (Cd: 8.23%−86.70%, As: 5.69%−82.03%) in pore water and transformed Cd&As chemical speciation to immobile fractions, reducing the Cd&As availability to rice. Moreover, S-nZVI facilitated iron plaque formation and Cd&As sequestration in iron plaques, inhibiting the absorption of Cd&As by rice roots. Notably, the lower application of S-nZVI (0.1%−0.2%) improved soil pH, more effectively inhibited rice uptake of soil Cd, and increased rice yield. The increased soil pH, decreased Eh, and surface complexation with iron oxyhydroxide were responsible for Cd immobilization, while the formation of inner-sphere chelates with iron oxyhydroxide predominated As immobilization. These findings suggest S-nZVI has the potential to be an effective material for remediating Cd&As co-contaminated paddy soil and alleviating Cd&As accumulation in rice.

Accumulation of cadmium in soils, litter and leaves in cacao farms in the North Sierra Nevada de Santa Marta, Colombia

Cadmium (Cd) accumulation in Colombian cacao is a growing concern due to its potential health impacts and EU regulations on Cd content in chocolate products. Furthermore, cacao plays a significant role as an agricultural commodity and a tool for illegal crop replacement, yet our regional understanding of Cd dynamics in cacao cultivation in the north flank of the Sierra Nevada de Santa Marta is still limited. This research provides the first comprehensive investigation of cadmium biogeochemistry in cacao agroecosystems by analyzing the interactions between subsurface soils, topsoil, rock fragments, litter, and cacao leaf Cd concentrations from 30 farms. Results reveal generally low mean total soil Cd concentrations for topsoil and subsurface soils at 0.12 mg kg−1 and 0.05 mg kg−1, respectively. Leaf and litter Cd concentrations are significantly higher (p < 0.05) than soil Cd, with a mean of 0.42 and 0.4 mg kg−1, respectively. Our results suggest that age dependent surface-level processes such as the bioaccumulation and biocycling of Cd over time through the leaves, litter, and topsoil, govern Cd in the topsoil, leading to older cultivars and trees exhibiting higher Cd concentrations in leaves, litter, and soils. Subsurface soil Cd is primarily driven by geogenic Cd coming from the weathering of the underlying bedrock with a hypothesized contribution from pedogenic Cd being translocated to deeper soil horizons from the topsoil via clay and oxide illuviation. Our research provides insights into the accumulation of Cd in cacao plants and soils, which can lead to long-term preferential accumulation of cadmium on soil layers and thus increase plant uptake through roots.

Regulation Effects of Humus Active Components on Soil Cadmium Availability and Critical Threshold for Rice Safety

Organic materials containing humic acids (HAs) play important roles in regulating the bioavailability of cadmium (Cd) in soils and thus its accumulation in crops. The effects of the two active components of HAs, humic acid (HA) and fulvic acid (FA), in organic materials and their different ratios (HA/FA) on Cd uptake and accumulation in rice were investigated using a field plot experiment, and their relationships with the Cd fractions and availability in paddy soil as influenced by the use of these organic materials were analyzed in combination with the fractionation method of chemical continuous extraction. The results showed that the effects of HAs on Cd availability in soil and Cd accumulation in rice grains were controlled by the ratios of the active components in the organic materials. The treatments with an HA/FA ratio ≥ 4/6 had a passivating effect on soil Cd, resulting in a significant reduction in Cd availability. Compared with that in the control without the application of HAs (CK), rice grain Cd concentration was reduced by 15.2%-33.3%, whereas those with an HA/FA ratio ≤ 2/8 activated Cd in soil, and the available Cd content was significantly increased. Compared with that in CK, rice grain Cd concentration was increased by 24.2%-42.4%. The ratios of HA/FA in HAs affected the morphological transformation of soil Cd. Compared with the CK treatment, the treatments with ratios of HA/FA ≥ 4/6 promoted the transformation of soil Cd from the exchangeable form (EX-Cd) with high activity to the carbonate bound form (CA-Cd) and Fe and Mn oxide-bound forms (FM-Cd) with low activity, whereas those with ratios of HA/FA ≤ 2/8 showed the opposite effects. The effects of HA and FA on soil pH and available sulfur concentration differed. Soil pH had a significant positive correlation with HA addition but a negative correlation with FA addition, and soil available sulfur content had a significant positive correlation with FA addition at the rice tillering stage. Therefore, to ensure the quality and safety of rice, organic materials with an HA/FA ratio ≥ 4/6 should be selected. The results provided a scientific basis for the directed utilization of organic materials containing HAs.

Prediction of Spatial Distribution of Heavy Metals in Cultivated Soil Based on Multi-source Auxiliary Variables and Random Forest Model

Spatial prediction of the concentrations of soil heavy metals (HMs) in cultivated land is critical for monitoring cultivated land contamination and ensuring sustainable eco-agriculture. In this study, 32 environmental variables from terrain, climate, soil attributes, remote-sensing information, vegetation indices, and anthropogenic activities were used as auxiliary variables, and random forest (RF), regression Kriging (RK), ordinary Kriging (OK), and multiple linear regression (MLR) models were proposed to predict the concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in cultivated soils. In comparison to those of RK, OK, and MLR, the RF model had the best prediction performance for As, Cd, Cr, Hg, Pb, and Zn, whereas the OK and RK models had highest prediction performance for Cu and Ni, respectively, showing that R2 was the highest, and mean absolute error (MAE) and root mean square error (RMSE) were the lowest. The prediction performance of the spatial distribution of soil HMs under different prediction methods was basically consistent. The high value areas of eight HMs concentrations were all distributed in the southern plain area. However, the RF model depicted the details of spatial prediction more prominently. Moreover, the importance ranking of influencing factors derived from the RF model indicated that the spatial variation in concentrations of the eight HMs in Lanxi City were mainly affected by the combined effects of Se, TN, pH, elevation, annual average temperature, annual average rainfall, distance from rivers, and distance from factories. Given the above, random forest models could be used as an effective method for the spatial prediction of soil heavy metals, providing scientific reference for regional soil pollution investigation, assessment, and management.

Drip irrigation reduces the toxicity of heavy metals to soybean: By moving heavy metals out of the root zone and improving physiological metabolism

Excessive heavy metal content in soil can seriously hinder plant physiological metabolism and growth. This study, with soybean, examined how drip irrigation reduced heavy metal toxicity. The drip irrigation experiments with four irrigation frequencies were conducted by controlling the lower limit of the soil matric potential (D1: −10 kPa; D2: −20 kPa; D3: −30 kPa; D4: −40 kPa). Through comparison with traditional surface irrigation, the effects of drip irrigation on heavy metal distribution, soybean growth status, physiological metabolism and transcriptome under Cd, Pb and Cr(VI) composite pollution were comprehensively analyzed. The results show that (i) The Cd, Pb and Cr(IV) in soil migrated away from the plant under drip irrigation, thereby reducing the inhibition of heavy metal stress on soybean growth at the root, among which D1 had the best improvement effect on soybean growth. (ii) Drip irrigation improved the resistance of soybean to heavy metal stress, and promoted the transport and fixation of free Cd2+, Pb2+ and Cr6+ in cells, thereby reducing the damage of oxidative stress and heavy metal ions to cell structure. (iii) Drip irrigation was conducive to the energy supply and protein stability of cell physiological metabolism, which helped the improvement of soybean physiological activity. Overall, compared with surface irrigation, drip irrigation reduced the toxicity of heavy metals to soybeans by moving heavy metals out of the root zone and enhancing physiological activity. The results of this study can provide a theoretical basis for the application of drip irrigation technology in the prevention and control of heavy metal pollution, and provide a new strategy for the safe production of agriculture.

Organic matter and Bacillus niescheri amendments mitigate cadmium toxicity by regulating physiology and transcription of Diospyros lotus L., and soil bio-chemical properties

Cadmium (Cd) is a hazardous heavy metal that threaten fruit safety and soil quality. The remediated effects of wheat straw and fruit pruning branch, with or without Bacillus niescheri, on the physiology and transcriptome of Diospyros lotus L., and soil bio-chemical properties in Cd condition were assessed in this study. Wheat straw and persimmon branch residue addition decreased the Cd availability in soil and Cd accumulation in tissues and alleviated oxidative damage caused by Cd as exhibited by the reduced O2•-, H2O2 and malondialdehyde contents in roots of D. lotus, especially following B. niescheri inoculation. Different expressed genes of ion uptake and translocation were mostly downregulated, whereas cell wall formation/modifications, amino acid metabolism, and phytohormone biosynthesis in roots were upregulated by organic matter plus B. niescheri. Furthermore, organic matter plus B. niescheri improved soil pH, electrical conductivity, cation exchange capacity, enzyme activity (urease, dehydrogenase, catalase), nutrients (nitrogen, phosphorus, potassium) and organic carbon contents. Soil Cd availability was negatively correlated with the relative abundance of Bacteroides, Cellvibrio, Bacillus, Sphingomonas, Vicinamibacteraceae, and Faecalibacterium. Therefore, the organic waste such as wheat straw and branch residues are eco-friendly methods of remediating Cd-contaminated soil and mitigating toxicity for D. lotus, especially following B. niescheri inoculation.

Impact of iron and sulfur cycling on the bioavailability of cadmium and arsenic in co-contaminated paddy soil

The biogeochemical cycling of iron (Fe) or sulfur (S) in paddy soil influences the cadmium (Cd) and arsenic (As) migration. However, the influence of coupled reduction effects and reaction precedence of Fe and S on the bioavailability of Cd and As is still not fully understood. This study aimed to reveal the influence of Fe and S reduction on soil Cd and As mobility under various pe + pH conditions and to elucidate the related mechanism in subtropical China. According to the findings, higher adsorption from Fe reduction caused high-crystalline goethite (pe + pH > 2.80) to become amorphous ferrihydrite, which in turn caused water-soluble Cd (62.0%) to first decrease. Cd was further decreased by 72.7% as a result of the transformation of SO42- to HS-/S2- via sulfate reduction and the formation of CdS and FeS. As release (an increase of 8.1 times) was consequently caused by the initial reduction and dissolution of iron oxide (pe + pH > 2.80). FeS had a lesser impact on the immobilization of As than sulfate-mediated As (V) reduction in the latter stages of the reduction process (pe + pH < 2.80). pe + pH values between 3 and 3.5 should be maintained to minimize the bioavailability of As and Cd in moderate to mildly polluted soil without adding iron oxides and sulfate amendments. The practical remediation of severely co-contaminated paddy soil can be effectively achieved by using Fe and S additions at different pe + pH conditions. This technique shows promise in reducing the bioavailability of Cd and As.

Ectopic expression of SaCTP3 from the hyperaccumulator Sedum alfredii in sorghum increases Cd accumulation for phytoextraction

The Cd tolerance protein SaCTP3, which responds to Cd stress, was identified in Sedum alfredii; however, how to improve the efficiency of phytoremediation of Cd–contaminated soil using the CTP gene remains unknown. In this study, the phytoremediation potential of SaCTP3 of Sedum alfredii was identified. In the yeast Cd–sensitive strain Δycf1 overexpressing SaCTP3, the accumulation of Cd was higher than that in the Δycf1 strain overexpressing an empty vector. Transgenic sorghum plants overexpression SaCTP3 were further constructed to verify the function of SaCTP3. Compared to wild–type plants, the SaCTP3–overexpressing lines exhibited higher Cd accumulation under 500 μM Cd conditions. The average Cd content inSaCTP3–overexpressing plants is more than four times higher than that of WT plants. This was accompanied by an enhanced ability to scavenge ROS, as evidenced by the significantly increased activities of peroxidase, catalase, and superoxide dismutase in response to Cd stress. Pot experiments further demonstrated that SaCTP3 overexpression resulted in improved soil Cd scavenging and photosynthetic abilities. After 20 days of growth, the average Cd content in the soil planted with SaCTP3–overexpressing sorghum decreased by 19.4%, while the residual Cd content in the soil planted with wild–type plants was only reduced by 5.4%. This study elucidated the role of SaCTP3 from S.alfredii, highlighting its potential utility in genetically modifying sorghum for the effective phytoremediation of Cd.

Elevated CO2 and nitrogen addition enhance the symbiosis and functions of rhizosphere microorganisms under cadmium exposure

Soil microbes are fundamental to ecosystem health and productivity. How soil microbial communities are influenced by elevated atmospheric carbon dioxide (eCO2) concentration and nitrogen (N) deposition under heavy metal pollution remains uncertain, despite global exposure of terrestrial ecosystems to eCO2, high N deposition and heavy metal stress. Here, we conducted a four year's open-top chamber experiment to assess the effects of soil cadmium (Cd) treatment (10 kg hm−2 year−1) alone and combined treatments of Cd with eCO2 concentration (700 ppm) and/or N addition (100 kg hm−2 year−1) on tree growth and rhizosphere microbial community. Relative to Cd treatment alone, eCO2 concentration in Cd contaminated soil increased the complexity of microbial networks, including the number links, average degree and positive/negative ratios. The combined effect of eCO2 and N addition in Cd contaminated soil not only increased the complexity of microbial networks, but also enhanced the abundance of microbial urealysis related UreC and nitrifying related amoA1 and amoA2, and the richness of arbuscular mycorrhiza fungi (AMF), thereby improving the symbiotic functions between microorganisms and plants. Results from correlation analysis and structural equation model (SEM) further demonstrated that eCO2 concentration and N addition acted on functions and networks differently. Elevated CO2 positively regulated microbial networks and functions through phosphorus (P) and Cd concentration in roots, while N addition affected microbial functions through soil available N and soil organic carbon (SOC) concentration and microbial network through soil Cd concentration. Overall, our findings highlight that eCO2 concentration and N addition make microbial communities towards ecosystem health that may mitigate Cd stress, and provide new insights into the microbiology supporting phytoremediation for Cd contaminated sites in current and future global change scenarios.

Remobilization of Cd caused by iron oxide phase transformation and Mn2+ competition after stabilization by nano zero valent iron

Stabilization techniques are vital in controlling Cd soil pollution. Nano zero valent iron (nZVI) has been extensively utilized for Cd remediation owing to its robust adsorption and reactivity. However, the environmental stress-induced stability of Cd after nZVI addition remains unclear. A pot experiment was conducted to evaluate the Cd bioavailability in continuously flooded (130 d) soil after stabilization with nZVI. The findings indicated that nZVI application did not result in a decline in Cd concentration in rice, as compared to the no-nZVI control. Additionally, nZVI simultaneously increased the available Cd concentration, iron-manganese oxide-bound (OX) Mn fraction, and relative abundance of Fe(III)-reducing bacteria, but it decreased OX-Cd and Mn availability in soil. Cadmium in rice tissues was positively correlated with the available Cd in soil. The results of subsequent adsorption tests demonstrated that CdO was the product of Cd adsorption by the nZVI aging products. Conversely, Mn2+ decreased the adsorption capacity of Cd-containing solutions. These results underscore the crucial role of both biotic and abiotic factors in undermining the stabilization of nZVI under continuous flooding conditions. This study offers novel insights into the regulation of nZVI-mediated Cd stabilization efficiency in conjunction with biological inhibitors and functional modification techniques.

Alternating Direct Current Field Assistant Promoting Chemical Stabilization of Combined Heavy Metals Contaminated Soil

To enhance the remediation efficiency and reduce the chemicals consumption, the combined heavy metals Lead (Pb), Copper (Cu) and Cadmium (Cd) contaminated soil were stabilized by chemical passivators with alternating direct current field (ADC) assistant. The results showed that ADC treatment activated initial heavy metal compounds in the soil. The leaching concentrations of Pb, Cu and Cd in soil under ADC condition increased by 19.61%, 38.77% and 49.10% in comparison with no electric field, respectively. The exchangeable fractions of Pb, Cu and Cd increased while the reducible, oxidizable and residual fractions decreased substantially. Thus, the chemical passivators addition companied with ADC treatment in the beginning increased stabilization efficiency of heavy metals in the soil and reduced over 30% amount of chemical agent consumption, comparing with only chemical passivator stabilization. The mechanism can be speculated that ADC assistant facilitated more heavy metal ions in the soil reacting with phosphorus- containing passivator to formed more complex and stable metal phosphates. It was confirmed by XRD measurement that silicon element in the crystal structure of metallic compound was replaced by phosphorus element.

Influence of biochar on the remediation of cadmium-contaminated soil in an Eisenia fetida–Solanum nigrum system

Biochar, plants, and earthworms have good remediation effects on cadmium (Cd)-contaminated soils. However, few studies have combined all three technologies to explore the treatment of Cd-contaminated soils. This study investigated the effect of corn straw biochar addition (1% and 5% mass ratios) on soil Cd treatment in an Eisenia fetida–Solanum nigrum system. The addition of corn straw biochar increased soil pH, total nitrogen (TN), total phosphorus (TP), and soil organic carbon (SOC); adding 5% (w/w) biochar under Cd stress resulted in significant increases (P < 0.05) of soil pH, TN, TP, and SOC. Adding 5% (w/w) biochar under Cd stress increased Cd enrichment by E. fetida and S. nigrum and significantly reduced the soil total and available Cd contents (P < 0.05). The addition of biochar increased the metallothionein content of E. fetida, which functions to resist Cd stress in high-Cd environments (P < 0.05); with the addition of 5% (w/w) biochar, the metallothionein content was 1.55 times higher than in the 1% (w/w) biochar treatment, at 23.78 ng L−1. Adding 5% (w/w) biochar significantly increased the Cd enrichment coefficient and transfer coefficient values of S. nigrum under high-Cd stress (P < 0.05), reaching 7.37 and 1.89, respectively. Adding 5% (w/w) biochar significantly reduced the exchangeable and acid-soluble fraction of Cd, increased the oxidizable fraction, reduced Cd bioavailability, and mitigated physiological damage (P < 0.05). The present study demonstrated that adding biochar to the E. fetida–S. nigrum system could effectively reduce the soil Cd pollution level, providing a new method and scientific guidance for the remediation of heavy metal-polluted soil.

Assessment of Physicochemical Properties and Heavy Metal Content of Floriculture Soil in Amhara Region of Northwest Ethiopia.

Floriculture is a new and rapidly expanding sector in Ethiopia that aids economic growth but has also come under blame for pollution of the surrounding soil. The purpose of this study was to assess the soil physicochemical properties and heavy metal contents in floriculture in the Amhara Region of Northwest Ethiopia. Soil samples were collected from seven different greenhouses (2ABC, 4DEF, 5ABC, 7DEF, 8ABC, 9DEF, and 11DEF), and a control soil sample was taken on the 15-cm depth from a nearby agricultural area. They were analyzed for soil physicochemical parameters and heavy metal compositions. Soil texture showed a significant difference between the soils sampled from the greenhouses and the control group. The highest average clay, silt, and sand contents were recorded in the control group, 4DEF, and 9DEF, respectively. The lower clay content was at 9 DEF, silt at 11 DEF, and sand in the control group. Clay was positively correlated to soil pH (r = 0.66) and TN (r = 0.38) but showed significant negative correlation with the sand fraction (r = -0.96). The average bulk density (BD) values of the soils from the greenhouses were within acceptable ranges; however, the mean BD value of 7DEF was relatively highest (1.34 g/cm3). There were significant (P < 0.05) changes in soil pH and electrical conductivity, with pH values ranging from 5.8 to 7.17 and EC from 0.08 to 1.72 mScm-1. Soil organic carbon, available phosphorus, total nitrogen, and carbon-to-nitrogen ratio of the soil samples from the greenhouses and the control group were significantly different. There were also significant differences in soil exchangeable aluminum and acidity between greenhouse soil samples and the control group. Soil contents of some of the heavy metals (Pb, Cd, Mn, and Cu) in the floriculture soil were above the permissible limits, while Cr, Zn, and Ni contents were below. The soil in floriculture showed low quality compared to the control group and international standards, indicating the need for improved soil quality management. This study recommends reducing agrochemical use, increasing bio-fertilizers, using botanicals, and transitioning to organic farming. Further studies are needed to assess soil microbial diversity and abundance for soil fixation.

Anthropogenic effect on the pedochemical variability of potentially toxic elements at the vicinity of an Antarctic research station.

Antarctica represents an isolated continent devoted to conservation and scientific research, although it accumulates records of increasing anthropic contamination. The historical continued use of fuel for power generation in Antarctic settlements is a potential source of toxic elements to the soil. We investigate Cd, Cr, Cu, Mn, Ni, Pb, V and Zn levels in surface soils in the vicinity of the Henryk Arctowski Antarctic Station, aiming to identify anthropic effects on their local pedochemical variability. Pollution indices were used and compared to evaluate possible cumulative anthropic impacts, whereas correlation analyzes were explored to identify potential sources of contamination. High concentrations of Pb and Zn were locally observed near fuel tanks and machinery facilities. Correlation and principal component analysis suggest that old fuel tanks, vehicle traffic and machinery disturbance are key, and contrasting, sources of contamination. Among the eight indices we compared, Enrichment Factor and Modified Degree of Contamination were chosen, showing very high enrichment for Pb and moderate for Zn. All other elements presented minimal or null enrichment. The evidence of potentially toxic elements enrichment on Antarctic soils associated with the long-term occupation of Antarctic research stations highlights the need for further monitoring and mitigation measures, especially in energy-generating systems.

Synergistic effects of potassium-silicon-calcium mineral fertilizer combined with rice husk biochar on the immobilization of Cd and Pb in soil

Synergistic effects of potassium-silicon-calcium mineral fertilizer combined with rice husk biochar on the immobilization of Cd and Pb in soil