Available Concentrations Of Cd Research Articles

Variations in Root Characteristics and Cadmium Accumulation of Different Rice Varieties under Dry Cultivation Conditions.

Variations in the cadmium (Cd) accumulation and root characteristics of different genotypes of rice during three developmental periods of dry cultivation were investigated in pot experiments in which two levels of Cd were added to the soil (0 and 10 mg kg-1). The results show that the Cd concentration in each organ of the different rice genotypes decreased in both the order of roots > shoots > grains and during the three developmental periods in the order of the maturity stage > booting stage > tillering stage. The lowest bioaccumulation factor (BCF) and translocation factor (TF) were found in Yunjing37 (YJ37) under Cd stress. At maturity, Cd stress inhibited the root length of Dianheyou34 (DHY34) the most and that of Dianheyou 918 (DHY918) the least, also affecting the root volume of DHY34 and Dianheyou615 (DHY615) the most and that of YJ37 and Yiyou 673 (YY673) the least; the inhibition rates were 41.80, 5.09, 40.95, and 10.51%, respectively. The exodermis showed the greatest thickening in YY673 and the lowest thickening in DHY615, while the endodermis showed the opposite result. The rates of change were 16.48, 2.45, 5.10, and 8.49%, respectively. The stele diameter of DHY615 decreased the most, and that of YY673 decreased the least, while the secondary xylem area showed the opposite result; the rates of change were -21.50, -14.29, -5.86, and -26.35%, respectively. Under Cd stress treatment at maturity, iron plaque was extracted using the dithionite-citrate-bicarbonate (DCB) method. The concentration of iron (DCB-Fe) was highest in YJ37, and the concentration of cadmium (DCB-Cd) was lowest in DHY34. YJ37 was screened as a low Cd-accumulating variety. The concentration of available Cd in the rhizosphere soil, iron plaque, root morphology, and anatomy affect Cd accumulation in rice with genotypic differences. Our screening of Cd-accumulating rice varieties provides a basis for the dry cultivation of rice in areas with high background values of Cd in order to avoid the health risks of Cd intake.

Synergistic effect between biochar and sulfidized nano-sized zero-valent iron enhanced cadmium immobilization in a contaminated paddy soil

Biochar-based sulfidized nano-sized zero-valent iron (SNZVI/BC) can effectively immobilize cadmium (Cd) in contaminated paddy soils. However, the synergistic effects between biochar and SNZVI on Cd immobilization, as well as the underlying mechanisms remain unclear. Herein, a soil microcosm incubation experiment was performed to investigate the immobilization performance of SNZVI/BC towards Cd in the contaminated paddy soil. Results indicated that the addition of SNZVI/BC at a dosage of 3% significantly lessened the concentration of available Cd in the contaminated soil from 14.9 (without addition) to 9.9 mg kg−1 with an immobilization efficiency of 33.3%, indicating a synergistic effect. The sequential extraction results indicated that the proportion of the residual Cd in the contaminated soil increased from 8.1 to 10.3%, manifesting the transformation of the unstable Cd fractions to the steadier specie after application of SNZVI/BC. Also, the addition of SNZVI/BC increased soil pH, organic matter, and dissolved organic carbon, which significantly altered the bacterial community in the soil, enriching the relative abundances of functional microbes (e.g., Bacillus, Clostridium, and Desulfosporosinus). These functional microorganisms further facilitated the generation of ammonium, nitrate, and ferrous iron in the contaminated paddy soil, enhancing nutrients’ availability. The direct interaction between SNZVI/BC and Cd2+, the altered soil physicochemical properties, and the responded bacterial community played important roles in Cd immobilization in the contaminated soil. Overall, the biochar-based SNZVI is a promising candidate for the effective immobilization of Cd and the improvement of nutrients’ availability in the contaminated paddy soil.Graphical

Biochar Derived from Urban Green Waste Can Enhance the Removal of Cd from Water and Reduce Soil Cd Bioavailability.

The beneficial utilization of potentially increasing urban green waste (UGW) is critical for sustainable urban development in China. In this study, UGW was pyrolyzed at different temperatures, and the resulting biochar was used to amend Cd-contaminated soils to grow cabbage. Our results showed that the Cd adsorption capacity of UGW-biochar was positively correlated with the surface area, O/C, and (O+N)/C value of biochar. Furthermore, UGW-biochar was incorporated into three Cd-contaminated soils, including one acidic soil and two neutral soils, to assess its impact on the availability of Cd. The most substantial reduction in the concentration of available Cd was observed in the acidic soil, of the three tested soils. In the neutral soils, a more substantial reduction was found in the heavily Cd-contaminated soil compared to the lightly Cd-contaminated soil. UGW-biochar amendments to the three Cd-contaminated soils resulted in an increase in the cabbage biomass in acidic soil, whereas in neutral soils, it increased in lightly contaminated soils but decreased in heavily contaminated soils. Additionally, the Cd bioaccumulation factor (BCF), translocation factor (TF), and removal efficiency (RE), as impacted by the biochar application, were calculated in the lightly Cd-contaminated soil-cabbage system. The BCF decreased from 5.84 to 3.80 as the dosage of the UGW-biochar increased from 0% to 3%, indicating that the UGW-biochar immobilized Cd and reduced its bioaccumulation in cabbage roots. Based on our investigations, UGW-biochar effectively immobilizes Cd by reducing its mobility and bioavailability in a lightly contaminated environment matrix.

Effects of stabilizing materials on soil Cd bioavailability, uptake, transport, and rice growth

Cadmium, a widespread toxic heavy metal in farmland soils, is harmful to human health. A field experiment was conducted to investigate the effects of biochar and biochar-based fertilizers on soil pH, organic matter, and available Cd, as well as rice Cd uptake and translocation. The results showed that rice biomass was significantly increased after both the application of biochar and high rate of biochar-based fertilizers at the tillering stage. The biomass and plant height of rice were improved at filling and maturity stages. Soil pH was significantly increased with the application of biochar but not with the biochar-based fertilizer. The amendments of biochar and biochar-based fertilizers had no significant (p < 0.05) influence on soil organic matter content. The concentration of available Cd in soil and the concentration of Cd in rice were decreased with the application of different amounts of biochar and biochar-based fertilizers in the mature stage. However, this effect was much greater under biochar amendment. Compared to the control, the concentration of available Cd in soil was reduced by 33.09% with the low application rate of biochar, while that was reduced by 18.06% with the high application rate of biochar. The lowest bioaccumulation factor was due to the high concentration of biochar and biochar-based fertilizers. It is concluded that biochar and biochar-based fertilizers particularly at a high addition rate are appropriate for decreasing Cd mobility and improve soil quality for contaminated paddy soils. The study showed a method for the safe production of rice in Cd-polluted farmlands by using a high application rate of biochar or carbon-based fertilizers.

Simultaneous reduction of available arsenic and cadmium in contaminated soil by iron-modified fly ash

ABSTRACT Arsenic (As) and cadmium (Cd) co-contamination in the soil is a serious global health concern. Three iron-modified fly ash (FA) composites were synthesised, including FA-supported nanoscale zero-valent iron (FA-nZVI), FA-supported FeCl3 (FA-FeCl3) and FA-supported Fe-oxyhydroxide sulphate (FA-FeOS) for remediation of As and Cd co-contaminated soil. Soil incubation experiments were conducted to evaluate the effects of iron-modified FA on the soil pH, availability and geochemical fractions of As and Cd. The results showed that FA and FA-nZVI significantly (P < 0.05) increased the soil pH, but FA-FeCl3 and FA-FeOS decreased the soil pH in general. FA, FA-nZVI, FA-FeCl3 and FA-FeOS decreased the concentration of available As by 15.13∼21.22%, 46.20∼46.66%, 30.02∼38.09% and 12.05∼30.50%, respectively. However, only FA and FA-nZVI decreased the concentration of available Cd by 4.85∼26.09% and 37.74∼52.18%, respectively. The results showed that FA-nZVI was the most effective amendment for simultaneous immobilisation of As and Cd. Besides, FA-nZVI stimulated the transformation of As and Cd from reactive states to less reachable states to decrease the toxicity of As and Cd in soil. In conclusion, FA-nZVI is a potential amendment for soil remediation in As and Cd co-contaminated soil.

Effect of biochar on the form transformation of heavy metals in paddy soil under different water regimes

ABSTRACT To ascertain the effect of biochar on remediation of paddy soil contaminated by heavy metals under different irrigation regimes (flooding irrigation (FI), intermittent irrigation (II) and wet irrigation (WI)), rice straw biochar (RSB) and rice husk biochar (RHB) were applied into soil contaminated by Cd and Cu. The concentrations of available Cd and Cu were significantly reduced by RSB, and decreased by 6.8–15.9%, 11.1–20.0% and 6.8–18.2%, and 6.2–12.9%, 7.0–14.8% and 5.6–17.7% under FI, II and WI regimes, respectively. The application of RHB generally reduced the content of acid extractable and reducible Cd under FI and II regimes, and promoted its transformation to oxidizable and residual form. Similarly, both biochars reduced the acid extractable Cu in paddy soil and promoted its transformation to reducible and oxidizable form under three irrigation regimes (especially in II). This is significantly related to the increase of soil pH, organic matter content and cation exchange capacity by biochar. The preliminary results of this study indicate that biochar application combined with intermittent irrigation could be an effective measure to enhance the paddy soil quality. However, future studies are still needed to evaluate the long-term impact of biochar on heavy metal bioavailability under different water conditions.

Biochar alleviates metal toxicity and improves microbial community functions in a soil co-contaminated with cadmium and lead

Soil amendment with biochar alleviates the toxic effects of heavy metals on microbial functions in single-metal contaminated soils. Yet, it is unclear how biochar application would improve microbial activity and enzymatic activity in soils co-polluted with toxic metals. The present research aimed at determining the response of microbial and biochemical attributes to addition of sugarcane bagasse biochar (SCB) in cadmium (Cd)-lead (Pb) co-contaminated soils. SCBs (400 and 600 °C) decreased the available concentrations of Cd and Pb, increased organic carbon (OC) and dissolved organic carbon (DOC) contents in soil. The decrease of metal availability was greater with 600 °C SCB than with 400 °C SCB, and metal immobilization was greater for Cd (16%) than for Pb (12%) in co-spiked soils amended with low-temperature SCB. Biochar application improved microbial activity and biomass, and enzymatic activity in the soils co-spiked with metals, but these positive impacts of SCB were less pronounced in the co-spiked soils than in the single-spiked soils. SCB decreased the adverse impacts of heavy metals on soil properties largely through the enhanced labile C for microbial assimilation and partly through the immobilization of metals. Redundancy analysis further confirmed that soil OC was overwhelmingly the dominant driver of changes in the properties and quality of contaminated soils amended with SCB. The promotion of soil microbial quality by the low-temperature SCB was greater than by high-temperature SCB, due to its higher labile C fraction. Our findings showed that SCB at lower temperatures could be applied to metal co-polluted soils to mitigate the combined effects of metal stresses on microbial and biochemical functions.

Risk assessment of heavy metals in soils and edible parts of vegetables grown on sites contaminated by an abandoned steel plant in Havana.

Food production in areas contaminated by industrial wastes poses a serious risk to farmers and consumers. Here, we evaluate Cd, Cr, Ni, and Pb concentrations in the soils and the edible parts of lettuce, chives, tomatoes, pepper, and cassava plants grown by small farmers in areas contaminated by slag from an abandoned steel plant in Havana, Cuba. The total, environmentally available, and bioavailable concentrations of metals in the soils and the metals bioconcentration factor in the plants were determined. The risks to human health from food and soil ingestion were estimated. The total and environmentally available concentrations of Cd, Cr, and Pb were above values considered safe by international standards, with likely adverse effect on human health. Cadmium was the most bioavailable metal, reflected in the highest accumulation in the crops' edible parts. Even with negligible DTPA-available Cr concentrations in soils, the Cr concentrations in edible parts of the crops exceeded regulatory levels, suggesting that rhizosphere mechanisms may increase Cr availability. The consumption of vegetables represented 70% of the daily intake dose for Cr, Cd, and Ni, while accidental ingestion of contaminated soil is the predominant human exposure route for Pb. Our results demonstrated the health risks associated with cultivating and consuming vegetables grown on metal contaminated soils in Havana and can assist public policies capable of guaranteeing the sustainability of urban agriculture and food security.

Effects of nearly four decades of long-term fertilization on the availability, fraction and environmental risk of cadmium and arsenic in red soils

Fertilizers are important for agricultural production because they can effectively promote crop productivity. However, long-term fertilization can cause heavy metal accumulation in soils and crops. This study utilized sequential extraction, the diffusive gradient in the thin films (DGT) technique and risk assessment models to estimate the effects of the longest long-term fertilization (38 years) in China on cadmium (Cd) and arsenic (As) accumulation in soils. The treatments included no fertilization (CK); inorganic nitrogen, phosphorus, and potassium fertilization (NPK); manure fertilization (M); and NPK plus M cofertilization (NPKM). The results indicated that the soils treated with NPKM, M and NPK had significantly increased total and available concentrations of Cd and As after 38 years of long-term fertilization. Cd mainly originates from cattle manure, while As originates from phosphate fertilizer. Sequential extraction results indicated that the application of manure increased the acid/exchangeable fraction (F1) and organic matter-bound fraction (F3) of Cd and As. The risk assessment results showed that the environmental risks of both Cd and As increased during long-term fertilization, and Cd contamination in the soil was at a moderate-high level, while As remained at a relatively low level. According to the calculations of the maximum numbers of years of soil productivity and rice production, Cd was labile and accumulated in the soils, and As was more labile than Cd in terms of accumulating in rice, indicating that the true risk from As in rice is higher than that from Cd. Controlling the heavy metals in fertilizers, mitigating effective amendments, and identifying plant types that accumulate low amounts of contaminants may be good choices for cleaner crop production.

Remediation of heavy metal-polluted alkaline vegetable soil using mercapto-grafted palygorskite: effects of field-scale application and soil environmental quality.

Remediation materials are the most critical factors for in situ immobilization of soil contaminated by heavy metals. In this study, in order to improve the performance of palygorskite (Pal), a new remediation material, mercapto-grafted palygorskite (MPal) was synthesized by grafting mercapto groups onto the surface of Pal. The results of field application in northern China showed that at a dosage of 0.12-0.23 kg m-2, MPal significantly reduced the available concentrations of Cd, Pb, and Cr in the soil by 52.2%, 29.9%, and 46.2%, respectively. Concurrently, Cd, Pb, and Cr concentrations in the shoots of head lettuce also decreased significantly, with the highest reduction being 44.0%, 61.5%, and 50.0%, respectively. At the same dosage, MPal had a better immobilization effect than Pal. There was no significant change in the pH of the vegetable soil, while the zeta potential decreased significantly, indicating that the MPal did not immobilize the heavy metals by increasing the pH, making it suitable for alkaline farmland soil. In addition, soil environmental quality was improved overall. MPal increased the activities of urease, β-glucosidase, cellulase, and catalase by 15.4%, 56.5%, 7.8%, and 14.9%, respectively. It increased the number of fungi and actinomycetes by 4.5% and 23.1%, respectively. MPal, as a new remediation material for soil contaminated by heavy metals, could achieve efficient remediation effects when applied in small doses. Compared with Pal, it is environmentally friendly, is low cost, and is more suitable for the treatment of heavy metal pollution in large areas of farmland.

Laboratory versus field soil aging: Impacts on cadmium distribution, release, and bioavailability.

To date, most studies about the aging of metals in soil were based on the controlled laboratory experiments, and few works have attempted to investigate how aging process influences the distribution and bioavailability of metals in soil under the field condition. The purpose of this study was to compare the aging of cadmium (Cd) in soils under the controlled laboratory and the field by monitoring time-dependent soil Cd speciation changes, Cd release kinetics, and Cd bioavailability to plant through the 438-day aging experiments. During the aging process, the proportions of Cd associated with the most weakly bound fraction tended to decrease, with corresponding increases in the more stable binding fractions. After aging, a higher concentration of available Cd was found in the field aging soil (0.74mgkg-1) than the laboratory aging soil (0.65mgkg-1). The Elovich equation was the best model to describe the soil available Cd aging process. The constant b in the Elovich equation, which was defined as the transformation rate, was in the order of laboratory aging soil > field aging soil. Moreover, higher Cd release amounts were found for the field aging soil (2.74mgkg-1) than the laboratory aging soil (2.57mgkg-1) at the end of aging. Additionally, higher body Cd concentrations were found for the vegetables grown in the field aging soils (1.49mgkg-1, fresh weight) than those grown in the laboratory aging soils (1.32mgkg-1, fresh weight). Therefore, this study indicated that the metal distribution process and its bioavailability may be overestimated or underestimated if research data from the laboratory experiments are used to derive soil quality criteria or investigate soil metal bioavailability.

Cadmium uptake and transfer by Sedum plumbizincicola using EDTA, tea saponin, and citric acid as activators

Sedum plumbizincicola (S. plumbizincicola) is known as a sufficient plant for phytoremediation of cadmium (Cd) polluted soils. This study aimed to investigate the effects of ethylene diamine tetraacetic acid (EDTA), tea saponin (TS), and citric acid (CA) on Cd uptake and translocation by S. plumbizincicola. To do so, using a pot experiment, we set four concentration levels of activators (1, 3, 5, and 10 mmol L−1) and a control (CK). Results showed that none of the applied activators had significant impact on soil pH. Except for CA-10, the concentration of available Cd in Cd polluted soils increased by 65.8–72.9% compared with CK. The EDTA-1, CA-1, and TS-5 treatments caused significant increases of 52.3, 67.2, and 38.4%, respectively, in the biomass of aerial parts of S. plumbizincicola (p < 0.05) compared with CK. Except for CA-3, activators increased Cd accumulation in the aerial parts of plants by 47–124% compared with CK. Of all activators, EDTA-3 caused the highest Cd accumulation of 6.64 g pot−1 in the aerial plant tissues followed by CA-10 (6.25 g pot−1) and TS-1 (5.48 g pot−1). Finally, our results suggested that the application of S. plumbizincicola together with different activators sufficiently reduced soil total Cd by 4.64–48.4% compared with CK. These findings suggest that appropriate application of EDTA, TS, and CA can promote phytoremediation of Cd contaminated soils by hyper-accumulators. In particular, the combined use of EDTA and S. plumbizincicola is an affordable and promising strategy for remediation of Cd contaminated soil. Novelty statement: Sedum plumbizincicola (S. plumbizincicola) is a well-known hyper-accumulator plant for remediation of cadmium (Cd) and zinc (Zn) contaminated soils. In addition, low molecular rganic acids and macromolecular chelating agents can improve the solubility and leaching of soil heavy metals. In the present work, we examined the combined effects of three activators (EDTA, tea saponin, and citric acid) with S. plumbizincicola to remediate a Cd contaminated soil in Anhui Province, East China. Our results indicated the effectiveness of these activators to increase soil available Cd, as well as improving the biomass of S. plumbizincicola and its Cd uptake. We believe that this study provides an efficient approach to increase the uptake of Cd by S. plumbizincicola, restoring Cd contaminated soils. Nevertheless, excessive activators may have adverse effects on soil aggregates and soil microorganisms. Therefore, it is necessary to control the amount of chelating agents and subsequently the deterioration of soil quality.

Adsorption of Cadmium and Arsenic by Corn Stalk Biochar Solidified Microorganism

Immobilization of bacteria on biochar can improve the performance of the soil complex polluted with cadmium (Cd) and arsenic (As). In this study, bacteria (Delftia sp. B9, B9), biochar (corn stalks biochar, CSB), and biochar-bacteria complexes (B-CSB) were used as adsorption materials to explore the adsorption characteristics of Cd and As. The effects of pH on the adsorption performance of Cd and As and the ion removal from the aqueous solution were investigated, and the adsorption behaviors were simulated using an isothermal adsorption model. The changes in Cd and As speciation with the addition of B9, CSB, and B-CSB to As and Cd-contaminated soil were explored. The results showed that the Cd-saturated adsorption capacities of B9, CSB, and B-CSB were 49.43, 82.68, and 75.38 mg ·g-1, respectively; the As-saturated adsorption capacities were 24.67, 42.92, and 34.03 mg ·g-1, respectively. The concentration of available Cd and As significantly decreased, whereas the residual fraction increased after the addition of B-CSB. B-CSB was shown to be an effective material for the remediation of soil complexes polluted with Cd and As.

The Availability and Accumulation of Heavy Metals in Greenhouse Soils Associated with Intensive Fertilizer Application.

In China, greenhouse agriculture, which provides abundant vegetable products for human consumption, has been rapidly developed in recent decades. Heavy metal accumulation in greenhouse soil and products obtained have received increasing attention. Therefore, the availability and accumulation of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) and their association with soil pH, soil organic matter (SOM), inorganic nitrogen (IN), total nitrogen (TN), available phosphorus (AP), and planting year (PY) in greenhouse soils were analyzed. The results showed that the mean concentrations of available Cd, Cu, Ni, Pb, and Zn were 17.25 μg/kg, 2.89, 0.18, 0.36, and 5.33 mg/kg, respectively, while their suggested levels in China are 0.6, 100, 100, 120, and 250 mg/kg. Cd, Cu, and Zn might be mainly originated from fertilizer application. A lower soil pH significantly increased the available Cu, Ni, and Zn concentrations and reduced Cd, Cu, Ni, and Zn accumulation. A higher AP significantly increased the proportions of available Cu, Ni, and Zn and elevated Cd, Cu, and Zn accumulation. There was a strong positive correlation between Cd, Pb, and Zn availability and TN, while IN was negatively related to the availability and accumulation of Cu and Zn. It was concluded that chemical fertilizer application increased the availability of Cu, Ni, Pb, and Zn and the accumulation of Cd, Cu, and Zn. Manure application clearly elevated the accumulation and availability of Cd and Zn in greenhouse soil.

Goethite modified biochar as a multifunctional amendment for cationic Cd(II), anionic As(III), roxarsone, and phosphorus in soil and water

Abstract Environment-friendly, function tunable, and low-cost adsorbents/amendments from agricultural residue-derived biochar show enormous potential for mitigating the environment problems. A series of nano-sized goethite modified biochar (GMB) material were synthesized by co-precipitating with crop residue-derived biochar and could be used for amelioration of cation, anion, antibiotics, and non-point source pollutant in both soil and water. The GMB materials were characterized by SEM-EDS, BET, FTIR, XRD, VSM, and XPS analysis. Their adsorption performance for cationic Cd(II), anionic As(III), antibiotics roxarsone (ROX), and non-point source pollutant phosphorus in water was evaluated by adsorption kinetics and equilibrium experiments. Based on Langmuir model, the maximum adsorption capacities of Cd(II), As(III), ROX, and phosphorus were 31.9, 65.3, 66.5, and 42.7 mg/g, respectively, which were enhanced by 135%, 6279%, 961%, and 2437% compared to pristine biochar. The adsorption behavior of GMB can be explained by non-specific adsorption (electrostatic interaction and physical adsorption), specific adsorption (hydroxyl complex, π-π interaction, surface complexation, ion exchange, etc.), and chemisorption induced by goethite nanoparticles on the GMB. Moreover, GMB (1 wt%) also performed well for immobilization of these four contaminants in soil. After GMB treatment, the concentrations of available Cd, As, ROX, and phosphorus in soil decreased by 74.1%, 58.7%, 70.8%, and 29.1%, respectively. This study proposed that the scalable GMB can be considered as a sustainable multifunctional material for soil and water decontamination.

Achieving the safe use of Cd- and As-contaminated agricultural land with an Fe-based biochar: A field study

A field study was conducted to investigate the effect of Fe-based biochar application on the extractability and availability of Cd and As, as well as its impact on crop growth and yield under a two-years wheat-rice rotation system. The Fe-based biochar was applied to the soil at 1.5 and 3.0 t ha–1, manure compost was also applied as a comparison, as well as a non-treated control. The application of the Fe-based biochar significantly (p < 0.05) increased the crop yields for the rice season in the first year, but the both treatments had no significant effect on the crop yields in the others cultivation seasons, compared to the control. The concentrations of available Cd and As significantly (p < 0.05) decreased after either higher or lower dose of Fe-based biochar addition, especially with lower rate in the second year. In the second year, the soil extractable Cd and As reduced by 57% and 18%, respectively, in the wheat season and 63% and 14%, respectively, in the rice season, after the lower dose of Fe-based biochar was applied. The lower dose of the Fe-based biochar treatment showed higher efficiency for decreasing Cd and As availability in soil than the higher one, the control and manure compost treatment. Additionally, both the higher and lower doses of the Fe-based biochar treatments significantly decreased Cd and As uptake by wheat and rice plants. Overall, the Fe-based biochar showed effective immobilization at an application of 1.5 t ha–1, making the use of the Fe-based biochar feasible as an amendment for the safe use of agricultural land contaminated by Cd and As.

Evaluation of different amendments and foliar fertilizer for immobilization of heavy metals in contaminated soils

PurposeThe aim of this study was to evaluate the effectiveness of soil amendments and foliar fertilizer on Cd and Pb immobilization in contaminated soils.Materials and methodsA field experiment was conducted in contaminated soils, wherein four amendments (sepiolite (SE), single superphosphate (SSP), triple super phosphate (TSP), calcium magnesium phosphate (CMP)) in combination with one foliar fertilizer (ZnSO4) were investigated to reduce Cd and Pb bioavailability in calcareous soils. Total Cd and Pb concentrations in wheat, soil, and amendments were determined using inductively coupled plasma mass spectrometry. Available concentrations of Cd and Pb in soils were extracted using diethylenetriamine pentaacetic acid.Results and discussionThe results indicated that application of these amendments and foliar fertilizer significantly decreased Cd availability in soils and Cd accumulation in wheat (P < 0.05); however, the soil amendments plus Zn fertilizer did not significantly decrease Cd and Pb concentrations in wheat. Compared with the control, application of soil amendments effectively reduced the available Cd and Pb in soils by 25.69~54.13% and 9.86~42.14%, respectively. Accordingly, the reduction of Cd and Pb concentrations in wheat grain by the soil amendments was 20.68~41.38% and 23.68~55.26%, respectively.ConclusionsAmong all the treatments, the addition of SE + SSP and SE + CMP exhibited the most efficiency in reducing Cd and Pb availability, respectively, in the soil.

Assessment of cadmium content of potato grown in Weining County, Guizhou Province, China.

A total of 54 soil and 54 potato samples have been collected from Weining County to evaluate the accumulation of cadmium in potatoes. The concentrations of the total Cd and the available Cd in the soil samples have been detected. The total concentrations of Cd were from 0.41 to 10.0mg/kg with an average value of 2.60mg/kg in soil. The concentrations of available Cd in the soil were 0.07 to 3.47mg/kg with an average value of 0.59mg/kg. The concentration of the available Cd showed a good linear positive correlation with the total Cd content in the soil. For the 54 potato samples, the Cd concentrations were from 0.023 to 0.18mg/kg with an average value 0.083mg/kg (fresh weight).The bioconcentration factor (BCF) values of Cd in potatoes, based on dry weight, were from 0.02 to 0.96 with an average value 0.24. The uptake of cadmium by plants is dependent on various soil and environmental factors. A regression model to predict the concentration of cadmium in Weining potatoes based on soil properties and elevation was developed. The results showed the elevation and the soil pH played an important role and had a negative influence on the uptake of Cd by potato in Weining County. The mean intake of Cd by adults through consumption of potato from Weining would be 5.9μg/day, and it is well below the provisionally tolerable daily intake for Cd (70μg/day).

The Combination of DGT Technique and Traditional Chemical Methods for Evaluation of Cadmium Bioavailability in Contaminated Soils with Organic Amendment.

Organic amendments have been proposed as a means of remediation for Cd-contaminated soils. However, understanding the inhibitory effects of organic materials on metal immobilization requires further research. In this study colza cake, a typical organic amendment material, was investigated in order to elucidate the ability of this material to reduce toxicity of Cd-contaminated soil. Available concentrations of Cd in soils were measured using an in situ diffusive gradients in thin films (DGT) technique in combination with traditional chemical methods, such as HOAc (aqua regia), EDTA (ethylene diamine tetraacetic acid), NaOAc (sodium acetate), CaCl2, and labile Cd in pore water. These results were applied to predict the Cd bioavailability after the addition of colza cake to Cd-contaminated soil. Two commonly grown cash crops, wheat and maize, were selected for Cd accumulation studies, and were found to be sensitive to Cd bioavailability. Results showed that the addition of colza cake may inhibit the growth of wheat and maize. Furthermore, the addition of increasing colza cake doses led to decreasing shoot and root biomass accumulation. However, increasing colza cake doses did lead to the reduction of Cd accumulation in plant tissues, as indicated by the decreasing Cd concentrations in shoots and roots. The labile concentration of Cd obtained by DGT measurements and the traditional chemical extraction methods, showed the clear decrease of Cd with the addition of increasing colza cake doses. All indicators showed significant positive correlations (p < 0.01) with the accumulation of Cd in plant tissues, however, all of the methods could not reflect plant growth status. Additionally, the capability of Cd to change from solid phase to become available in a soil solution decreased with increasing colza cake doses. This was reflected by the decreases in the ratio (R) value of CDGT to Csol. Our study suggests that the sharp decrease in R values could not only reflect the extremely low capability of labile Cd to be released from its solid phase, but may also be applied to evaluate the abnormal growth of the plants.

Cadmium, lead, and zinc mobility and plant uptake in a mine soil amended with sugarcane straw biochar.

Accumulation of heavy metals in unconsolidated soils can prove toxic to proximal environments, if measures are not taken to stabilize soils. One way to minimize the toxicity of metals in soils is the use of materials capable of immobilizing these contaminants by sorption. Biochar (BC) can retain large amounts of heavy metals due to, among other characteristics, its large surface area. In the current experiment, sugarcane-straw-derived biochar, produced at 700 °C, was applied to a heavy-metal-contaminated mine soil at 1.5, 3.0, and 5.0% (w/w). Jack bean and Mucuna aterrima were grown in pots containing a mine contaminated soil and soil mixed with BC. Pore water was sampled to assess the effects of biochar on zinc solubility, while soils were analyzed by DTPA extraction to confirm available metal concentrations. The application of BC decreased the available concentrations of Cd, Pb, and Zn in the mine contaminated soil leading to a consistent reduction in the concentration of Zn in the pore water. Amendment with BC reduced plant uptake of Cd, Pb, and Zn with the jack bean uptaking higher amounts of Cd and Pb than M. aterrima. This study indicates that biochar application during mine soil remediation could reduce plant concentrations of heavy metals. Coupled with this, symptoms of heavy metal toxicity were absent only in plants growing in pots amended with biochar. The reduction in metal bioavailability and other modifications to the substrate induced by the application of biochar may be beneficial to the establishment of a green cover on top of mine soil to aid remediation and reduce risks.