Cd Phytoavailability Research Articles

Efficient cadmium-resistant plant growth-promoting bacteria loaded on pig bone biochar has higher efficiency in reducing cadmium phytoavailability and improving maize performance than on rice husk biochar

Green agriculture faced challenges due to the shortage of efficient cadmium (Cd)-resistant plant growth-promoting bacteria (CdR-PGPB) and their low survival rate and activity during application. In this study, a diverse range of efficient CdR-PGPB were isolated from the rhizosphere soil of Desmodium elegans, especially those with high phosphate-solubilizing capabilities (272.87–450.45 mg L−1). Two highly efficient CdR-PGPB namely, XH1 and XH3 were loaded on to rice husk biochar (RHB) and pig bone biochar (PBB), labelled as RHBM and PBBM respectively. This study aimed to explore their effectiveness and mechanisms in promoting maize growth in a Cd-contaminated planting system. Results showed that PBBM performed best among all treatments. It significantly decreased soil phytoavailable Cd by 53.19 % and Cd content in maize shoot by 85.89 %. It also increased soil available phosphorus by 145.72 %, soil alkaline phosphatase activity by 76.34 %, maize shoot/root biomass by 47.06 %/67.98 %, Chlorophyll (a/b) content by 66.80 %/134.13 % and peroxidase activity by 171.96 %. These results were achieved through the synergistic action of efficient CdR-PGPB and PBB. Therefore, PBBM proved to be a promising and innovative application technique for sustainable agricultural development in Cd-contaminated farmland ecosystems.

Phytoavailability, translocation, and accompanying isotopic fractionation of cadmium in soil and rice plants in paddy fields

Rice consumption is a major pathway for human cadmium (Cd) exposure. Understanding Cd behavior in the soil-rice system, especially under field conditions, is pivotal for controlling Cd accumulation. This study analyzed Cd concentrations and isotope compositions (δ114/110Cd) in rice plants and surface soil sampled at different times, along with urinary Cd of residents from typical Cd-contaminated paddy fields in Youxian, Hunan, China. Soil water-soluble Cd concentrations varied across sampling times, with δ114/110Cdwater lighter under drained than flooded conditions, suggesting supplementation of water-soluble Cd by isotopically lighter Cd pools, increasing Cd phytoavailability. Both water-soluble Cd and atmospheric deposition contributed to rice Cd accumulation. Water-soluble Cd’s contribution increased from 28‐52% under flooded to 58‐87% under drained conditions due to increased soil Cd phytoavailability. Atmospheric deposition’s contribution (12‐72%) increased with potential atmospheric deposition flux among sampling areas. The enrichment of heavy Cd isotopes occurred from root-stem-grain to prevent rice Cd accumulation. The different extent of enrichment of heavy isotopes in urine indicated different Cd exposure sources. These findings provide valuable insights into the speciation and phytoavailability changes of Cd in the soil-rice system and highlight the potential application of Cd isotopic fingerprinting in understanding the environmental fate of Cd.

Comparative role of charcoal, biochar, hydrochar and modified biochar on bioavailability of heavy metal(loid)s and machine learning regression analysis in alkaline polluted soil

Pot experiment was performed aimed to assess the comparative role of charcoal, biochar, hydrochar and thiourea-vegetable modified biochar at 1 and 2 % doses, and <1 mm particle size on the bioavailability of Cd, Pb, As, Ni, Cu and Zn, and enhance NPK, and mustard growth in a slightly alkaline polluted soil. Furthermore, machine learning method was used to examine the systematic evaluation of the impact of feature selection based on Pearson's correlation on the performance of the linear regression model. The results revealed that maximum fresh and dry biomass of mustard was observed by 26.38 and 38.18 % with hydrochar 1 %, whereas lemon biochar at 2 % reduced fresh and dry biomass up to 34.0 and 53.0 % than control. The immobilization of Cd and Pb was observed by 83.70 and 71.15 % with thiourea-vegetable modified biochar at 2 %, As 71.62 % with hydrochar 2 %, Ni 80.84 % with thiourea-vegetable modified biochar 2 %, Cu 66.32 % with and Zn 36.30 % with thiourea-vegetable modified biochar at 2 % than control. However, the maximum mobilization of Cu in soil was observed by 30.3 % with lemon biochar 2 %, similarly for Zn 37.36 % with hydrochar 2 % as compared with other treatments. The phyto-availability of Cd, Pb, As and Cu in the mustard shoot and root biomass was reduced except Ni and Zn in soil than control. It was observed that using the machine learning regression analysis approach, variability in treatments effectiveness is evident across different feature correlation thresholds. This study clearly shows that the beneficial role of studied amendments on mustard growth and reduced bioavailability of heavy metal(loid)s and enhance primary macronutrients in alkaline polluted soil. It is suggested that future studies may be conducted on combined application of studies amendments on plant growth, immobilization of heavy metal(loid)s in multi-metal polluted soil under different field conditions.

Cadmium accumulation in wastewater-irrigated vegetables: Exploring factors, thresholds, health implications, and transfer modeling

The Introduction of cadmium (Cd) into the soil-crop system through wastewater (WW) irrigation poses a significant challenge to environmental safety. However, the understanding of the relationship between Cd phytoavailability in WW-irrigated soil and its uptake characteristics in edible vegetables remains largely unknown. This study aims to analyze the influence of WW irrigation on the accumulation characteristics and health risks associated with Cd in the soil-vegetables system. Soil and corresponding vegetable samples were collected from 12 vegetable farms including cabbage, lettuce, green beans, and pepper were studied under wastewater (WW) and freshwater (FW) irrigation. WW irrigation led to a significant increase in soil Cd levels, with enrichment factor, and contamination factor values ranging from 2.9 to 3.1 and 2.7 to 3.3 times higher, respectively, compared to the control. Across the study farms, WW irrigation increased Cd concentrations in cabbage, green beans, lettuce, and pepper by 62–220%, 55–100%, 25–68%, and 29–80%, respectively, compared to FW-irrigated farms. The average hazard quotient (HQ) and carcinogenic risk (CR) scores for Cd in WW-irrigated vegetables indicated low risk (0.1 < HQ) and fell within the permissible range (1.00E-06 < CR < 1.00E-04) for children and adults. The soil DTPA-extractable Cd thresholds for WW-irrigated farms cultivating cabbage, lettuce, green beans, and pepper were 0.62, 0.72, 0.85, and 0.83 mg kg−1, respectively. The results provide insight into the management strategies along with developing sustainable production practices for common leafy vegetables in Cd-enriched soil resulting from WW irrigation.

Revealing the Sources of Cadmium in Rice Plants under Pot and Field Conditions from Its Isotopic Fractionation.

The highly excessive uptake of cadmium (Cd) by rice plants is well known, but the transfer pathway and mechanism of Cd in the paddy system remain poorly understood. Herein, pot experiments and field investigation were systematically carried out for the first time to assess the phytoavailability of Cd and fingerprint its transfer pathway in the paddy system under different treatments (slaked lime and biochar amendments), with the aid of a pioneering Cd isotopic technique. Results unveiled that no obvious differences were displayed in the δ114/110Cd of Ca(NO3)2-extractable and acid-soluble fractions among different treatments in pot experiments, while the δ114/110Cd of the water-soluble fraction varied considerably from -0.88 to -0.27%, similar to those observed in whole rice plant [Δ114/110Cdplant-water ≈ 0 (-0.06 to -0.03%)]. It indicates that the water-soluble fraction is likely the main source of phytoavailable Cd, which further contributes to its bioaccumulation in paddy systems. However, Δ114/110Cdplant-water found in field conditions (-0.39 ± 0.05%) was quite different from those observed in pot experiments, mostly owing to additional contribution derived from atmospheric deposition. All these findings demonstrate that the precise Cd isotopic compositions can provide robust and reliable evidence to reveal different transfer pathways of Cd and its phytoavailability in paddy systems.

Temporal Changes in Cd Sorption and Plant Bioavailability in Compost-Amended Soils

The application of Cd-contaminated phosphate fertiliser has enriched concentrations of this non-essential element in many agricultural soils. Consequently, concentrations of the metal in some agricultural products exceed the Maximum Limit in foods. Composts can reduce the transfer of Cd from soil to plants; however, it is unclear how long this beneficial effect endures. We aimed to determine temporal changes of phytoavailable Cd in two market garden soils (an Allophanic Orthic Granular Soil and a Recent Silt Loam). Soils were amended with either municipal green waste compost or sawdust and animal waste compost at a rate of 2.5% w/w under three incubation regimes: at 19 °C, at 30 °C, and at 30 °C with additional N added as urea at 0.6 g urea/kg soil added over 1 year. Each replicate was sampled after 1, 5, 9, 13, 21, 31, and 49 weeks, and phytoavailable Cd was estimated through 0.05 M Ca(NO3)2 extraction. Seed potato (Solanum tuberosum), ‘Nadine’ variety, was grown in the Pukekohe Allophanic Orthic Granular Soil, freshly amended with municipal compost and the same soil aged for one year. The concentration of Cd in all samples was analysed using an ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer). The C concentration in the soil—compost mixtures decreased over the year, with the greatest decreases occurring in the soils incubated at 30 °C with added N. Unexpectedly, the concentration of Ca(NO3)2-extractable Cd in the compost-amended soils did not increase over time and in some cases even decreased. This was confirmed through a pot experiment, which showed the Cd concentration in potato was reduced by 50% in both the freshly amended soil and the amended soil aged for one year. Cadmium immobilisation in soils might be due to both the sorption of Cd by organic matter and the occlusion of sorbed Cd by oxy-hydroxides of iron and aluminium. Over 49 weeks, soluble Cd does not increase as organic matter oxidises. The application of municipal compost to soil will reduce both plant Cd solubility and plant Cd uptake for at least one year in the soils tested.

Quantitative relationship between soil pH and electrical conductivity values and cadmium phytoavailability for Chinese cabbage under simulated conditions

Pot experiments were conducted to investigate the impacts of continuous addition of different concentrations of calcium chloride (CaCl2) and/or low-molecular-weight organic acids (LMWOAs) on soil pH, electrical conductivity (EC), and cadmium (Cd) transformation. These factors subsequently affected Cd phytoavailability in a system consisting of Cd-contaminated soil and Chinese cabbage (Brassica chinensis L.). The results indicate that CaCl2 addition had a greater impact on reducing soil pH value, increasing soil EC value, and enhancing Cd phytoaccumulation in Chinese cabbage compared to LMWOAs. When soil pH dropped by 0.3 unit and the soil EC increased by 500 µS cm−1, the Cd concentration in the Chinese cabbage shoots was 3 times higher than that in the control group. Throughout two planting terms of Chinese cabbage, the addition of CaCl2 (1.6–3.2 g kg−1) and LMWOAs (≤ 1.0 g kg−1) led to phytoextracted Cd concentration exceeding exchangeable Cd concentration in soil samples before the pot experiment. Regarding phytoextracted Cd, desorption from carbonate-bound Cd contributes more than desorption from bound to organic matter Cd and adsorption to Fe/Mn oxide Cd. This study underscores the influence of soil pH and EC value variations and Cd transformation on Cd phytoavailability. Special attention should be given to leafy vegetables grown in Cd-contaminated soil, as the phytoavailable Cd concentration reaches approximately 2.0 µg kg−1, which may lead to Cd levels surpassing acceptable limits for Chinese cabbage.

Phytoavailability of cadmium in rice amended with organic materials and lime: Effects of rhizosphere chemical changes and cadmium sequestration in iron plaque

Excessive Cd in rice grains produced with acidic paddy soil is receiving increasingly widespread attention because it endangers human health. Applying organic materials (OM) and lime (L) is a common technique used to reduce Cd concentration in grains (CdG). Nevertheless, the mechanism by which their simultaneous application affects the Cd phytoavailability in soilrice systems remains ambiguous. In the current study, we adopted a rhizobag pot culture test to explore the influences of single application of OM [rice straw (RS), milk vetch (MV)], L, and their co-utilization on Cd phytoavailability and the associated mechanisms. The results showed that the application of RS, MV, L, L + RS (LRS), and L + MV (LMV) significantly decreased CdG by 26.9%, 38.2%, 48.6%, 50.0%, and 53.0%, respectively. Fe plaque (IP) formation was not affected by these treatments; however, Cd sequestration in IP (CdIP) was significantly reduced. CdIP was significantly reduced by 18.3%, 23.6%, 43.8%, 33.1%, and 41.4%, after RS, MV, L, LRS, and LMV treatments, respectively. Additionally, available Cd concentrations in rhizospheric soil (RHS) were significantly reduced by 11.5%, 14.8%, 15.1%, and 18.4%, after MV, L, LRS, and LMV treatments, respectively. Cd availability in RHS was significantly influenced by pH, dissolved organic carbon concentration, and Zn, Fe, and Mn availability. The results of the structure equation mode showed that CdG was mainly affected by CdIP, followed by Cd availability and the pH of RHS. In conclusion, the reduction of CdG by OM, L, and their co-utilization was the results of their combined effects of reducing Cd availability in RHS, CdIP, and Cd uptake by the roots. This study emphasizes that the reduction of CdG is a result of the dual effects of reducing Cd availability in RHS and CdIP after amendments application. L application alone or in conjunction with OM is an efficient practice to reduce CdG in acidic Cd-contaminated paddy fields.

Identification of cadmium phytoavailability in response to cadmium transformation and changes in soil pH and electrical conductivity

Owing to complex changes in the soil environment, determining cadmium (Cd) phytoavailability is challenging. We devised a soil-wheat system to monitor alterations in soil pH, electrical conductivity (EC), and Cd transformation under various rates of calcium chloride and/or low-molecular-weight organic acids (LMWOAs) addition. The findings indicate that decreasing soil pH value, increasing soil EC value, and Cd transformation affect the phytoextraction of Cd. The exchangeable Cd and transformation of Cd under shifts in soil pH and EC contribute differentially to the phytoextracted Cd. The level of potentially phytoavailable Cd was identified through complete wheat cultivation in which the soil pH decreased by 0.47 unit and soil EC increased by 600-1000 μS cm−1, resembling the concentration of 0.01 M LMWOAs extractable Cd, when transitioning from paddy to dryland soil. Based on considering the phytoextracted Cd as the phytoavailable Cd throughout a complete wheat growth term, the threshold for phytoavailable Cd in soil, ensuring the safety of wheat grain (limit: 0.1 mg kg−1), is determined to be 2.90 μg kg−1. Maintaining control over Cd phytoavailability in soil emerges as the key factor in ensuring the safety of wheat grain cultivation.

English

Phytoavailable cadmium (Cd) refers to the fraction of total cadmium in soil that is easily taken up by plants, which degrades the environmental quality and can cause contamination in the food chain. Cd contamination causes high carcinogenicity and toxicities, which harm both the environment and human health, including damage to the kidneys, bones, and respiratory system. In this study, seven extracting agents like ammonium bicarbonate diethylene triamine penta acetic acid (ABDTPA) and neutral salts having low and higher concentrations were used for the determination of phytoavailable Cd in sandy clay loam (SCL) and clay loam (CL) soils contaminated with Cd at naturally-Cd, Cd-20, Cd-40, and Cd-60 mg kg-1 and correlate it with Cd contents in roots, shoots, and grains of maize crop. Extraction efficiency of extractants remains in order: 10 M NH4AOc &gt; ABDTPA &gt; 1 M NH4AOc &gt; 0.1 M CaCl2 &gt; 0.01 M CaCl2 &gt; 1 M NaNO3 &gt; 0.1 M NaNO3. ABDTPA showed significantly the highest positive correlation with maize roots, shoots, and grains Cd contents in naturally Cd contaminated SCL and CL soils. While for artificially contaminated SCL and CL soils contaminated with Cd at Cd-20, Cd-40, and Cd-60 contamination levels, 0.1 M CaCl2 extractable Cd showed a stronger positive significant correlation with Cd contents in roots, shoots, and grains of maize crop. Overall results concluded that 10 M NH4AOc has the highest efficiency to extract Cd and 0.1 M NaNO3 has the lowest Cd extraction efficiency. Correlation results showed that ABDTPA and 0.1 M CaCl2 were found to be the most suitable extractants for predicting the bioavailability of Cd. Highly concentrated extractants give a stronger positive correlation as compared to low concentrated extractants. SCL soil showed stronger positive correlations as compared to CL soil

Application of oyster shell powder reduces cadmium accumulation by inhibiting the expression of genes responsible for cadmium uptake and translocation in rice.

The application of waste oyster shell in agriculture is of extensive concern due to its benefits on improving yields and inhibiting cadmium (Cd) accumulation in edible parts of crops. However, the underlying mechanisms responsible for oyster shell powder (OSP) that decreases Cd accumulation in crops remain poorly understood. This study explored the effects of OSP on growth and Cd accumulation in rice via pot experiments and hydroponics. Pot experiments showed that the application of 1g·kg-1 OSP improved rice yields and decreased Cd concentrations in all tissues of rice, especially in grains, which was reduced by 43.5%. The pH was increased and the phytoavailability of Cd in soil was reduced by OSP supplementation. In addition, OSP also exhibited high dissolution of Ca, Fe, Zn, and Se. In hydroponics, OSP supply also suppressed Cd accumulation in rice and increased plant growth. Pretreatment with OSP inhibited the accumulation of Cd in the roots and shoots. Simultaneously, OSP reduced the content of Cd in the root cell sap, cell wall, and xylem sap, and downregulated the expression of OsNramp5, OsNramp1, OsIRT1, and OsHMA2. These findings suggested that the application of OSP could reduce Cd accumulation by inhibiting the expression of genes responsible for Cd absorption and xylem loading in rice.

Stabilization of cadmium in a fluvo-aquic soil-Chinese chive system using loess and chicken manure compost.

The stabilization of heavy metals in soil has been increasingly applied in China in recent years due to its quick effect and low cost. In this study, loess and chicken manure compost (a commercial organic fertilizer) were used to stabilize Cd in slightly polluted fluvo-aquic soil from the North China Plain, and the driving factors for stabilization were investigated through ridge regression. The additives significantly reduced the total concentration of Cd in soil through dilution. The addition of loess and compost increased carbonates and organic matter in soil, respectively. This caused exchangeable Cd to be transformed to fractions bound to carbonates or organic matter, thereby decreasing the concentration of Cd in the roots and leaves of Chinese chive. The decreasing exchangeable Cd in soil was the direct cause of decreased uptake of Cd by plants, and the increasing fractions bound to carbonates or organic matter were indirect influencing factors. However, adding loess decreased soil fertility and retarded plant growth. The addition of compost compensated for these defects. This study suggests that the combined addition of loess and chicken manure compost was able to effectively reduce the total concentration and phytoavailability of Cd in soil and guarantee crop yield and quality.

Green synthesized hydroxyapatite for efficient immobilization of cadmium in weakly alkaline environment

The development of cost-effective passivators for the remediation of heavy metal-contaminated soils has been a research hotspot and an unsolved challenge. Herein, a novel hydroxyapatite (GSCH) was synthesized by co-precipitating distiller effluent-derived Ca with (NH4)2HPO4 using straw-derived dissolved organic matter (S-DOM) as the dispersant. Batch adsorption experiments and soil incubation tests were performed to assess the immobilization efficiency of GSCH for Cd in weakly alkaline environments. As a result, GSCH showed an excellent adsorption efficiency to Cd with a maximum adsorption amount of ∼222 mg g−1, which was fairly competitive compared to other similar previously materials reported. The kinetic data indicated that the adsorption of Cd on GSCH was a chemical and irreversible process, while the thermodynamic data revealed a spontaneous (ΔG° < 0) and endothermic (ΔH° > 0) adsorption process. Based on mechanism analysis, both physisorption (e.g., electrostatic attraction and pore filling) and chemisorption (e.g., ion exchange and complexation) were responsible for Cd adsorption on GSCH. Particularly, the incorporated S-DOM and hydroxyapatite phase in GSCH acted synergistically in the adsorption process. The incubation results showed that GSCH application could significantly reduce the bioavailability, phytoavailability and bioaccessibility of Cd in soil by 48.4%–57.8%, 20.4%–28.6% and 12.6%–24.0%, respectively. Moreover, GSCH application also improved soil bacterial communities and enhanced soil nutrient availability. Overall, this is the first study to demonstrate the potential application value of GSCH in Cd immobilization, providing promising insights into the development of green and cost-effective hydroxyapatite-based passivators for the remediation of heavy metal-contaminated soils.

Lactic acid bacteria promoted soil quality and enhanced phytoextraction of Cd and Zn by mustard: A trial for bioengineering of toxic metal contaminated mining soils

Microbial-assisted phytoremediation provides a green approach for remediation of metal contaminated soils. However, the impacts of mono and co-applications of lactic acid bacteria (LAB) on soil biochemical properties and phytoavailability of toxic metals in contaminated mining soils have not yet been sufficiently examined. Consequently, here we studied the effects of Lactobacillus plantarum (P), Lactobacillus acidophilus (A), and Lactobacillus rhamnosus (R) applications alone and in combination on soil enzyme activities and bioavailability and uptake of Cd and Zn by mustard (Brassica juncea) in a smelter-contaminated soil under greenhouse conditions. Among the studied bacteria, P was the most tolerant to Cd-and-Zn contamination. As compared to control, R increased the fresh and dry weight of mustard plants by 53.5% and 63.2%, respectively. Co-application of P + A increased the chlorophyll content by 28.6%, as compared to control. Addition of LAB to soil increased the activity of soil urease, alkaline phosphatase and β-D glucosidase increased by 1.86-fold (P + R), 1.80-fold (R) and 55.16% (P + R), respectively. Application of P + A + R enhanced catalase activity (19.3%) and superoxide dismutase activity (51.2%), while addition of A alone increased peroxidase activity (POD: 15.7%). Addition of P alone and together with A (P + A) enhanced Cd and Zn phytoextraction by mustard shoots up to 51.5% and 52.5%, respectively. We conclude that the single and/or co-application of LAB decreased soil pH, promoted plant growth, antioxidant and enzyme activities, and enhanced the phytoavailability of Cd and Zn in the studied contaminated soil. These findings might be an aid for enhancing the phytoremediation of Cd and Zn using LAB and mustard as a bioenergy crop, which may offer new ideas for field treatment of toxic metals contaminated soils.

Novel Fuller Earth, Rock Phosphate, and Biochar for Phytomanagement of Toxic Metals in Polluted Soils

The present study was aimed to assess the efficacy of individual and combined effects of novel fuller earth, rock phosphate, and biochar (grapefruit peel) at 1% dosage on maize plant growth, soil chemical properties anduptake of toxic metals (TMs), such as Cu, Zn, Fe, and Cd, by maize plant sown in Korangi (district of Karachi, Pakistan) heavily polluted and Korangi less polluted (K-HP and K-LP) soils. The obtained results indicate that the dry biomass of maize crop increased by 14.13% with combined (FE1% + GBC1%) on K-HP soil and 18.24% with combined (FE 1% + GBC 1%) effects on K-LP soil. The maximum immobilization of Cu, Zn, Fe, and Cd was observed by 36% with GBC1%, 11.90% with FE1%, 98.97% with combined RP1% + GBC1%, 51.9% with FE1% + GBC1% for K-HP, 11.90% with FE1%, 28.6% with FE1%, 22.22% with RP1% + GBC1%, and 57.05% with FE 1% + GBC 1% for K-LP soil. After the addition of proposed substances, modification of soil OM, SOC, TOC, and pH level appeared this lead to the changes in the phyto-availability of Cu, Zn, Fe, and Cd in maize plant. It was concluded that the application of individual and combined effects of novel fuller earth, rock phosphate, and biochar (grapefruit peel) have potential to stabilize pollutants from multi-metal polluted soils for safe crop production.

Combined effects of green manure and zinc oxide nanoparticles on cadmium uptake by wheat (Triticum aestivum L.)

Cadmium (Cd) toxicity in agricultural soils is serious concern these days which needs continuous attention. Little is known about the combined use of berseem and/or maize residues soil applied as a green manure alone or along with foliar dressing of zinc oxide nanoparticles (ZnONPs) on Cd accumulation in wheat (Triticum aestivum L.). A pot experiment under ambient conditions with wheat grown in Cd-contaminated soil was performed after soil applied different green manure amendments and foliar dressing of ZnONPs was done during plant growth and plants were harvested at full maturity. Compared with control, plant growth attributes and biomass of above ground parts substantially increased with applied amendments being maximum with combined use of ZnONPs + B75 (berseem residue, 75 mg/kg) followed by ZnONPs + M75 (maize residue, 75 mg/kg). All the treatments improved the leaf chlorophyll contents and improved the leaf antioxidant enzyme activities thereby reduced the leaf electrolyte leakage. The Cd accumulation in roots and aboveground parts of the wheat was reduced especially in ZnONPs + B75 followed by ZnONPs + M75. The higher rate of soil applied amendments along with NPs minimized the available Cd in soil extracts but soil post-harvest pH was not much affected by the applied amendments. In conclusion, incorporation of berseem and maize residues as a green manure applied in Cd-contaminated soil combined with foliar NPs may decrease Cd phytoavailability and its accumulation in wheat grains. However, substantial field studies are required under various environmental conditions before final recommendations at field levels.

Role of Organic Amendments to Mitigate Cd Toxicity and Its Assimilation in Triticum aestivum L.

In soil biota, higher and enduring concentration of heavy metals like cadmium (Cd) is hazardous and associated with great loss in growth, yield, and quality parameters of most of the crop plants. Recently, in-situ applications of eco-friendly stabilizing agents in the form of organic modifications have been utilized to mitigate the adverse effects of Cd-toxicity. This controlled experiment was laid down to appraise the imprints of various applied organic amendments namely poultry manure (PM), farmyard manure (FYM), and sugarcane press mud (PS) to immobilize Cd in polluted soil. Moreover, phytoavailability of Cd in wheat was also accessed under an alkaline environment. Results revealed that the addition of FYM (5–10 ton ha-1 ) in Cd-contaminated soil significantly increased germination rate, leaf chlorophyll content, plant height, spike length, biological and grain yield amongst all applied organic amendments. Moreover, the addition of FYM (5–10 ton ha-1 ) also reduced the phytoavailability of Cd by 73–85% in the roots, 57–83% in the shoots, and 81–90% in grains of wheat crop. Thus, it is affirmed that incorporation of FYM (5–10 ton ha-1 ) performed better to enhance wheat growth and yield by remediating Cd. Thus, the application of FYM (5–10 ton ha-1 ) reduced the toxicity induced by Cd to plants by declining its uptake and translocation as compared to all other applied organic amendments to immobilize Cd under sandy alkaline polluted soil.

Organic/inorganic amendments for the remediation of a red paddy soil artificially contaminated with different cadmium levels: Leaching, speciation, and phytoavailability tests

In the present study, the viability of using manure (M), lime (L), and sepiolite (S) alone and in combinations (M/L, M/S, and M/L/S) was evaluated for the remediation of a red paddy soil artificially contaminated with three levels of cadmium (Cd- 0.6, 1, and 2 mg kg−1 soil). Experiments were performed in columns (to evaluate Cd leaching) and pots by growing rice plants (to study Cd accumulation in plants). Before their application, the tested amendments were thoroughly characterized using SEM, EDS and FT-IR spectroscopy. The leaching experiment indicates that the application of L or M/L significantly improved the pH of soil leachate collected at different time intervals. However, the use of M/L/S was found better in decreasing the Cd contents in collected leachate. The use of M/L efficiently decreased the DTPA metal extraction (0.19, 0.41, and 0.55 mg kg−1) as compared to the CK (0.35, 0.63, and 1.13 mg kg−1, respectively). The Cd speciation results depicted a 33% decrease in exchangeable Cd with M/L/S treatment when compared with control (55%). Moreover, the M/L/S treatment was more efficient in lowering the Cd phytoavailability and subsequent accumulation in rice grains (0.05, 0.09, and 0.08 mg kg−1). These findings demonstrate that the use of composite amendments is categorically effective as an in-situ remediation tool to decrease Cd leaching and availability in diverse contaminations.

Inter-annual reduction in rice Cd and its eco-environmental controls in 6-year biannual mineral amendment in subtropical double-rice cropping ecosystems

The alkaline mineral amendment is a practical means of alleviating Cd concentration in rice grain (CdR) in the short-term; however, the long-term remediation effect of mineral amendment on the CdR and the eco-environmental controls remains unknown. Here a mineral (Si–Ca–Mg) amendment, calcined primarily from molybdenum tailings and dolomite, was applied biannually over 6 years (12 seasons) to acidic and moderately Cd-contaminated double-rice cropping ecosystems. This study investigated the inter-annual variation of Cd in the rice-soil ecosystem and the eco-environmental controls in subtropical rice ecosystems. CdR was reduced by 50%–86% following mineral amendment. The within-year reduction in CdR was similar between early rice (50%–86%, mean of 68%) and late rice (68%–85%, mean of 74%), leading to CdR in all early rice and in 83% of late rice samples below the upper limit (0.2 mg kg−1) of the China National Food Safety Standards. In contrast, the inter-annual reduction in CdR was moderately variable, showing a greater CdR reduction in the later 3 years (73%–86%) than in the former 3 years (54%–79%). Three years continuous mineral amendment was required to guarantee the safety rice production. The concentrations of DTPA-extractable and exchangeable Cd fractions in soil were reduced, while the concentration of oxides-bound Cd was increased. In addition, the soil pH, concentrations of Olsen-P and exchangeable Ca and Mg were elevated. These imply a lower apparent phytoavailability of Cd in the soil following mineral amendment. An empirical model of the 3-variable using soil DTPA-Cd, soil Olsen-P, and a climatic factor (precipitation) effectively predicted temporal changes in CdR. Our study demonstrates that Cd phytoavailability in soil (indexed by DTPA-extractable Cd) and climatic factors (e.g., temperature and precipitation) may directly/indirectly control the inter-annual reduction in CdR following mineral amendment in slightly and moderately Cd-contaminated paddy ecosystems.

Consistent inter–annual reduction of rice cadmium in 5–year biannual organic amendment

Organic fertilizers may contain cadmium (Cd) and the transformation of organic materials in soil also has a role in soil-plant Cd distribution, both of which lead to Cd accumulation in plant edible parts. However, the advisability of applying organic fertilizer to remediate soils that are moderately and slightly contaminated with Cd has not been clarified. In this study, we investigated the impacts of an organic amendment (chicken manure) on the Cd concentration in rice grains (CdR) and the soil chemical properties over a five year period (10 rice seasons) within a slightly contaminated paddy soil in Hunan Province, subtropical China. We found that the CdR was reduced by 28%–56% as a result of the organic amendment. The within-year reduction in CdR was higher in late rice (43%–56%, averaging 51%) than in early rice (28%–45%, averaging 38%); however, the inter-annual reduction in CdR was fairly stable (40%–49%), which suggests that chicken manure amendment has a long-term and persistent remediation potential. The concentrations of DTPA-extractable Cd and exchangeable plus water-soluble Cd fractions in soil were reduced, whereas soil pH and the concentrations of soil organic C and its labile fractions increased. These results indicate a lower apparent phytoavailability of Cd in soil following organic amendment. A two-variable empirical model using DTPA-Cd extracted from the soil at the full heading stage of rice and a climatic factor (total precipitation during the rice growing season) showed great potential in effectively predicting CdR. Our study suggests that Cd phytoavailability in soil (indexed by DTPA-extractable and exchangeable Cd) and climatic factors (such as temperature and precipitation) may control inter-annual reductions in CdR following organic amendment in slightly contaminated paddy soils.