Phytoavailability Of Cd In Soil Research Articles

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.

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.

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.

Efficient models for predicting durum wheat grain Cd conformity using soil variables and cultivars

Contamination of durum wheat grain by cadmium (Cd) threatens food safety and is of increasing concern because regulations concerning Cd are becoming stricter due to its toxicity. This work aimed at using soil variables and cultivar types to build models to predict whether durum wheat grain Cd will conform with current and possibly lower regulatory thresholds. We combined multiple Gaussian and logistic regressions and the random forest algorithm to take advantage of their strength. Models tested using cross-validation produced excellent performances including for the lowest regulatory threshold of 0.1 mg Cd/kg, half of the current one: 79–85% of the non-conformity cases were detected and the reliability of predictions was 69–82%. The models enabled identification of a x1.4 variability in grain Cd content between cultivars that do not have the low Cd accumulation allele of the Cdu1 gene. The models confirmed that for the grain Cd content, the between-cultivar variability had much less influence than the phytoavailability of Cd in soil, the critical contexts of which were characterized by the models. For farmers, these models are valuable tools to predict whether durum wheat production will conform with existing and future Cd regulation in foodstuffs.

Bioavailability and Bioaccessibility of Cd in Low and High Cd Uptake Affinity Cultivars of Brassica rapa ssp. Chinensis L. (Pakchoi) using an In vitro Gastrointestinal and Physiologically-based Extraction Test

ABSTRACT In vitro oral bioaccessibility of Cadmium (Cd) in two low (XGSJ), (SHQI) and two high (CGBC), (SIYM) Cd-accumulating affinity cultivars of Brassica rapa ssp. chinensis L. (pak choi) grown on Cd-contaminated Alfisol soil was assessed. In this study, physiologically based extraction test (PBET) and in vitro gastrointestinal (IVG) were chosen to assess the bioaccessibility for Cd by stimulating human digestion of plant material. The pak choi cultivars were grown on Cd-contaminated soil with six different Cd concentrations (0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mg kg−1). The phytoavailability of Cd in soils was also measured through Mehlich-3 extraction and sequential extraction method. Plants were harvested and analyzed for their total Cd content and afterward extracted using PBET and IVG to provide the estimate of oral bioaccessibility for the human health risks of metal contamination in pak choi.

Cadmium phytoavailability evaluation in rice-soil system using a field capacity-derived soil solution extraction: An entire growth period study in subtropical China

While the evaluation of cadmium (Cd) phytoavailability in rice (Oryza sativa L.)–soil systems has attracted considerable attention in recent years, the results vary based on the evaluation method used. The objective of this work was to use field capacity-derived soil solution extraction (SSE) to evaluate the Cd phytoavailability in two typical paddy soils (purple paddy soil and red paddy soil) during an entire rice growth season. Compared to three conventional extraction methods diethylenetriaminepentaacetic acid (DTPA) extraction, toxicity characteristic leaching procedure (TCLP), and HCl extraction], field capacity-derived SSE resulted in the strongest correlation between extracted Cd and the Cd contents in different rice tissues (root, gem, leaf, ear, husk, and brown rice). When the data for the two soil types were combined, SSE was the best predictor of total accumulated Cd in rice, with linear correlation coefficients of 0.836, 0.831, 0.919, and 0.909 for the tillering stage, heading stage, filling stage, and mature stage, respectively. In contrast, TCLP was only suitable for predicting total Cd accumulation in the heading and mature stages (linear correlation coefficients of 0.813 and 0.931, respectively), while DTPA was only effective in the heading stage (linear correlation coefficient of 0.8306). These results demonstrate the potential of field capacity-based SSE to predict Cd phytoavailability in soil–rice systems with different soil types.

Evaluation of cadmium transfer from soil to leafy vegetables: Influencing factors, transfer models, and indication of soil threshold contents

Food chain contamination by soil cadmium (Cd) through leafy vegetable consumption poses a threat to human health. It is imperative to understand the relationship between Cd phytoavailability in soils and its uptake in common leafy vegetables. A large-scale field survey in Zhejiang Province, southeast China, was conducted to develop models to evaluate the Cd phytoavailability to leafy vegetables based on soil properties and to establish soil Cd thresholds based on food safety. The empirical models developed in this study explained the combined effects of soil properties and diethylenetriaminepentaacetic acid (DTPA)-extractable Cd content on Cd phytoavailability to leafy vegetables. The Cd accumulation in celery, pak choi, and amaranth was quantitatively predicted by measurement of DTPA-extractable soil Cd and soil pH, organic matter, cation exchange capacity and clay content. For predicting Cd accumulation, the DTPA-extractable Cd, pH and clay content had a major influence in lettuce; and for water spinach, the DTPA-extractable Cd, pH, and cation exchange capacity had a major influence. Soil DTPA-extractable Cd was suitable to be used as Cd thresholds in soils cultivating celery, amaranth, pak choi, lettuce, and water spinach, with values of 0.24, 0.13, 0.23, 0.32, and 0.37 mg kg−1, respectively. However, the threshold values of soil total Cd were 0.26, 0.34, and 0.83 mg kg−1 for amaranth, celery, and pak choi fields, indicating that the current soil quality standard (GB 15618-1995) for soils cultivating different types of vegetables could be overestimated or underestimated for Cd contamination and the associated risk. This study will provide a useful reference for controlling Cd contamination in common leafy vegetables and developing sustainable production of leafy vegetables.

Cadmium phytoavailability under greenhouse vegetable production system measured by diffusive gradients in thin films (DGT) and its implications for the soil threshold

The diffusive gradients in thin films (DGT) technique is recognized to have advantages over traditional techniques. For example, the passive measurement generally follows the principle of metal uptake by plants, and its result incorporates the influences of soil properties, which may make DGT a good protocol for improving soil quality guidelines (SQGs). However, DGT has rarely been applied to assess Cd phytoavailability in soils under greenhouse vegetable production (GVP) systems. In this study, 29 turnips (Raphanussativus L.), 21 eggplants (Solanum melongena L.) and their corresponding soils were collected from GVP systems in Dongtai and Shouguang, eastern China. Simple linear regression and stepwise regression were performed using the soil Cd content and soil properties to predict the vegetable Cd content. Soil thresholds were derived based on both total and available Cd concentrations. The results showed that total Cd, DGT-measured Cd (DGT-Cd), soil-solution Cd (Soln-Cd) and CaCl2-extractable Cd (CaCl2-Cd) were all significantly correlated with vegetable Cd. DGT-Cd had the best correlation with turnip Cd. The total Cd threshold values ranged from 4.87 (pH 6.5) to 5.18 (pH 7.5) mg kg−1 for turnips and 14.60 (pH 6.5) to 14.90 (pH 7.5) mg kg−1 for eggplants. These Cd thresholds were higher than the current SQGs. The predicted of turnip Cd by DGT-Cd was not improved significantly by further considering the soil properties. The calculated soil threshold of DGT-Cd was 5.35 μg L−1 for turnips. However, the predicted soil threshold of DGT-Cd for eggplant was improved by including SOM, with R2 values from 0.53 to 0.70. The DGT-Cd threshold was calculated as 1.81 μg L−1 for eggplant (30.0 g kg−1 SOM). In conclusion, whether DGT measurements are independent of soil properties and preferable for the evaluation of Cd phytoavailability and the generation of soil thresholds remains to be clarified in future research.

Cadmium Phytoavailability and Enzyme Activity under Humic Acid Treatment in Fluvo-aquic Soil

A pot experiment was conducted to investigate the cadmium (Cd) availability to pakchois (Brassica chinensis L.) as well as the enzyme activities in fluvo-aquic soil under humic acid treatment. The results showed that the phytoavailability of Cd in soil decreased gradually as humic acid concentration rose (0 to 12 g·kg-1), while the activities of urease (UE), alkaline phosphatase (ALP) and catalase (CAT) kept increasing (P < 0.05). The correlation analysis indicated that humic acid was effective for reducing the devastation to soil enzymes due to the Cd pollution. In conclusion, humic acid is effective for the reduction of both Cd phytoavailability and the damage to enzyme activities due to Cd pollution in fluvo-aquic soil

Phytoavailability of cadmium (Cd) to Pak choi (Brassica chinensis L.) grown in Chinese soils: a model to evaluate the impact of soil Cd pollution on potential dietary toxicity.

Food chain contamination by soil cadmium (Cd) through vegetable consumption poses a threat to human health. Therefore, an understanding is needed on the relationship between the phytoavailability of Cd in soils and its uptake in edible tissues of vegetables. The purpose of this study was to establish soil Cd thresholds of representative Chinese soils based on dietary toxicity to humans and develop a model to evaluate the phytoavailability of Cd to Pak choi (Brassica chinensis L.) based on soil properties. Mehlich-3 extractable Cd thresholds were more suitable for Stagnic Anthrosols, Calcareous, Ustic Cambosols, Typic Haplustalfs, Udic Ferrisols and Periudic Argosols with values of 0.30, 0.25, 0.18, 0.16, 0.15 and 0.03 mg kg−1, respectively, while total Cd is adequate threshold for Mollisols with a value of 0.86 mg kg−1. A stepwise regression model indicated that Cd phytoavailability to Pak choi was significantly influenced by soil pH, organic matter, total Zinc and Cd concentrations in soil. Therefore, since Cd accumulation in Pak choi varied with soil characteristics, they should be considered while assessing the environmental quality of soils to ensure the hygienically safe food production.

Field evidence of cadmium phytoavailability decreased effectively by rape straw and/or red mud with zinc sulphate in a Cd-contaminated calcareous soil.

To reduce Cd phytoavailability in calcareous soils, the effects of soil amendments of red mud, rape straw, and corn straw in combination with zinc fertilization on Cd extractability and phytoavailability to spinach, tomato, Chinese cabbage and radish were investigated in a calcareous soil with added Cd at 1.5 mg kg−1. The results showed that water soluble and exchangeable Cd in soils was significantly decreased by the amendments themselves from 26% to 70%, which resulted in marked decrease by approximately from 34% to 77% in Cd concentration in vegetables. The amendments plus Zn fertilization further decreased the Cd concentration in vegetables. Also cruciferous rape straw was more effective than gramineous corn straw. In all treatments, rape straw plus red mud combined with Zn fertilization was most effective in decreasing Cd phytoavailability in soils, and it is potential to be an efficient and cost-effective measure to ensure food safety for vegetable production in mildly Cd-contaminated calcareous soils.

Phytoavailability of cadmium to cherry-red radish in soils applied composted chicken or pig manure

The aim of this study was to assess phytoavailability of cadmium to crop in soils applied composted animal manures. In a greenhouse experiment cherry-red radish ( Raphanus sativus) was grown in two soils applied with different levels of Cd with chicken manure or pig manure compost, compared with those of Cd applied in metal salt. Phytoavailable Cd was determined as Cd concentration in radish leaf or root. Results indicated that phytoavailability of Cd applied through manure composts was significantly ( P < 0.001) less than the same rate of Cd amended with soluble CdCl 2 suggesting the lower potential hazard of composted manure-applied Cd. Radish leaves had higher concentrations of Cd than the roots. Phytoavailability of applied Cd in acidic Ferralsols was significantly ( P < 0.001) greater than that in Calcaric Cambisols. The risk of applied Cd from composted manures to radish was also assessed by bioconcentration factors (BCF values) and uptake coefficients (UCs). The relationships between Cd concentrations of plant and Cd loading rates could be expressed by quadratic equation and suggested that uptake of metals by radish plant become less efficient at higher Cd loadings. Sequential extraction scheme indicated that increasing rates of Cd applied through chicken or pig manure compost did not increase exchangeable fraction of Cd, but mainly increase its inorganic precipitated and residual fractions. The precipitated and/or residual fraction of Cd combined with soil pH could explain significantly 95% or 92% of the variation in phytoavailable Cd expressed as Cd content in radish leaves or roots when chicken manure compost was applied, and 88% or 84% of the variation in phytoavailable Cd when pig manure compost was applied. However, for soluble CdCl 2 amendment, the phytoavailable Cd in radish leaves or roots could be explained significantly (89% or 92%) by exchangeable Cd and soil pH. The results of this experiment point to the fact that the Cd source, loading rate, soil pH, and plant tissue are important factors in evaluation of Cd phytoavailability. Results also demonstrated the importance of solid-phase Cd fractions, EDTA fraction and/or HNO 3 fraction, in predicting phytoavailability of Cd in soils applied manure compost.

Cadmium Solubility and Phytoavailability in Sludge‐Treated Soil: Effects of Soil Organic Carbon

AbstractSlow mineralization of organic matter in sewage sludge‐treated soil could release metals into more labile forms, which would then be more available for plant absorption. We examined the effect of soil organic matter decomposition on the phytoavailability of Cd in soils which, prior to this experiment, received 0 (control), 22.5, 45, 90, 180 Mg ha−1 yr−1 of sewage sludge for 6 yr. At the commencement of the experiment, one‐half of the experimental plots continued to receive sewage sludge application`at the prescribed rates. Sewage sludge application in the other half of the plots was terminated. All treated soils were cropped to Swiss chard (Beta vulgaris) twice each year for 10 yr and the soil was sampled after each crop harvest. When sewage sludge applications were teenated, the soluble Cd concentrations of the sludge‐treated soil were higher than those in the control soils and did not decline significantly over the next 10 yr. With continuous sludge applications, the soluble Cd concentration of sludge‐treated soils increased with each incremental addition of sludge for the same 10 yr. In soils receiving continuous sewage sludge inputs, the organic C content continued to rise with sludge inputs. After the termination of sludge application, organic C content of the sludge‐treated soils decreased by approximately 40% over the 10‐yr study. There was no indication that the soluble Cd concentration or the phytoavailability of Cd in the sludge‐treated soils increased as the organic C in these soils declined over the 10 yr following termination of sewage sludge application.