Soluble Cd Research Articles

Reactivity, Exchangeability, and Solubility of Cu, Zn, and Cd in Various Soil Materials: Concepts and Evaluation

Six extractants (0.005 mole DTPA dm–3, pH 7.3; 1 mole CH3COONH4 dm–3, pH 7.0; 0.10 mole HNO3 dm–3; 0.10 mole HCl dm–3; 1 mole HNO3 dm–3 and 1 mole HCl dm–3) and three ratios (1 : 2, 1 : 5, 1 : 10) were applied for characterizing the reactivity, exchangeability, and solubility of Cu, Zn and Cd in media of contrasting origin: lacustrine sediments (LS), urban soils (US) and those impacted by copper ore processing, namely metallurgically impacted soils (MIS). Data revealed that soil materials differed in pH as follows: LS (6.99 ± 0.11–7.79 ± 0.28) > US (6.49 ± 0.32–7.23 ± 0.29) > MIS (5.68 ± 1.03–6.30 ± 0.66), for pHKCl and $${\text{p}}{{{\text{H}}}_{{{{{\text{H}}}_{{\text{2}}}}{\text{O}}}}}$$ , respectively. The DTPA test (reactivity) applied at ratios 1 : 5 and 1 : 10 showed the best extraction for Cu and Zn as confirmed by the coefficients of correlations (r) in the range 0.85*** 0.05). This implies that both extractants may be used interchangeably for extracting Cu and Zn in contrasting environmental media. On the basis of algorithms from the stepwise analysis, the evaluation of trace element (TE) extractability of ecosystems potentially contaminated by TE should pertinently involve two factors: acid-based extractants and cation exchange capacity (CEC). Organic matter appeared as a facultative parameter.

Cadmium solubility in paddy soil amended with organic matter, sulfate, and iron oxide in alternative watering conditions.

We successfully accounted for the dynamics of cadmium (Cd) solubility in paddy soil that contained a realistically low total Cd concentration (0.36 mg kg-1) after submergence and redrying by monitoring multiple chemical and microbial soil properties. The addition of rice straw promoted greater microbial iron reduction and induced a greater increase in soil pH after submergence, compared to the control and treatments with added gypsum or hematite. Consequently, dissolved Cd decreased to under the detection limit in one week in the straw-amended treatment but remained high even after eight weeks in the other three treatments. The Cd solubility strongly correlated with soil pH and was unlikely to decrease due to Cd precipitation in secondary iron minerals. After five weeks of redrying, the dissolved Cd content was still the lowest, and the putative iron-reducing bacteria Geobacter remained the most abundant in the straw-amended soil. The results suggest that the addition of organic matter can efficiently immobilize soil Cd at an environmentally realistic concentration by stimulating the microbial reduction of native oxidized soil components after submergence, while adding extra iron oxide or sulfate alone is not effective because it does not eliminate the limitation imposed by electron donors on microbial reduction.

Cadmium and zinc bioaccumulation by Phytolacca americana from hydroponic media and contaminated soils

Hydroponic, greenhouse and field experiments were conducted to explore the potential of pokeweed (Phytolacca americana L.) to accumulate Zn and Cd from nutrient solutions and contaminated soils. The hydroponic results confirmed that this native species is a strong Zn and Cd bioaccumulator that does not experience severe phytotoxicity until quite high root and shoot concentrations, approaching 4000 and 1600 mg kg−1 of Zn, and 1500 and 500 mg kg−1 of Cd, respectively. These high Zn and Cd concentrations were accompanied by increased sulfur and lower manganese in both shoots and roots. However, in field and greenhouse trials with soils historically contaminated by a number of heavy metals including Zn and Cd, concentrations of Zn and Cd in shoots of P. americana reached concentrations less than 30% and 10%, respectively, of those achieved with hydroponics. The main constraint to phytoremediation of soils by P. americana was the low concentrations of Zn and Cd in soil solution. Pretreatment of the metal-contaminated soil by oxalic acid increased soluble Cd and Zn but failed to increase plant uptake of either metal, a possible result of higher solubility of competing metal ions (Cu, Mn) or low bioavailability of Cd and Zn-oxalate complexes.

Proper Mode of Using Rice Straw Biochar To Treat Cd-Contaminated Irrigation Water in Mining Regions Based on a Multiyear in Situ Experiment

Biochar has been widely used for immobilizing heavy metals in soils due to its favorable sorption capacity. Previous investigations on heavy metal immobilization in waters by biochar are conducted in laboratory. Knowledge about the long-term effects of in situ biochar application on water bodies contaminated by heavy metals remains scarce. In this research, biochar was derived from cadmium (Cd)-accumulated rice straw. A 35-d laboratory simulation and a three-year field enclosure experiment were carried out to assess the impacts of biochar application on Cd behavior in a water–sediment system of a historically Cd-contaminated irrigation pond. Results indicated that the pH of sediment and overlying water increased with biochar addition in both the lab and field experiments. The rice-straw biochar transformed the Cd in sediments from the exchangeable to residual fraction, because biochar addition increased the pH values and organic matter contents in sediment, leading to the sorption, sequestration, and passivation of Cd by sediment. The Cd concentration in overlying water decreased with the increase in biochar addition, and it continuously decreased with repeated annual application. Overall, for long-term effects of biochar addition on soluble Cd concentrations, the repeated annual addition of 2% biochar exhibited better performance than the repeated annual addition of 1% biochar and one-time addition of 6% biochar. This study provided a proper mode of utilizing rice-straw biochar to treat Cd-contaminated irrigation water in mining regions.

Effect of biochar on Pb, Cd and Cr availability and maize growth in artificial contaminated soil

This study was performed to investigate the effect of biochar manufactured from agriculture residues for the stabilization of lead, cadmium and chromium (Pb, Cd and Cr) in artificially contaminated soil. A surface loamy sand soil was spiked with Pb, Cd and Cr at 200, 400 and 600 mg kg−1. Thereafter, the spiked soil was treated with biochar at different rates of 0.0, 1.0, 2.5, 5.0 and 10% (weight basis) and incubated for 30 days. The treated soil was cultivated with maize plant (Zea mays) lasting 30 days. Addition of biochar significantly increased the soil reaction (pH), organic matter (OM) and nutrient content of nitrogen, phosphorus and potassium (N, P and K). Moreover, the addition of biochar considerably decreased the solubility of Pb and Cd in terms of water soluble, exchangeable (extracted by ammonium nitrate), physiological based extraction test (PBET) and toxicity characteristics leaching procedure (TCLP) extracts. The highest reduction of expendable Pb and Cd were 28.68% and 85.14%, respectively. On the other hand, addition of biochar might facilitated Cr solubility through the transformation of Cr(III) into Cr(VI) due to increasing soil pH, and increased its uptake by maize plant. The phytotoxicity test revealed that biochar significantly increased maize biomass (shoots and roots), especially with applications of 5% and 10% treatments. Our findings provide evidence that biochar application decreased Pb and Cd toxicity by immobilizing them into more stable forms and improved soil quality. However, attention should be paid when treating the soil that is co-contaminated by Cr with biochar.

Serum IL-6 level may differentiate immune inactive phase from other phases in patients with chronic hepatitis B virus infection

Abstract Background and Aims Previous studies have found that serum level of IL-6 was increased in HBV-infected patients. Here we evaluate the impact of IL-6 levels according to the natural history of chronic hepatitis B(CHB) infection. Method Patients(n=71) with hepatitis B virus(HBV) were enrolled between September 2016 and Feb. 2018. Treatment-naïve chronic HBV carries were recruited. IFN-γ, TNF-α, IL-2, IL-6, and IL-17A were measured by a cytometric bead assay according to manufacturer’s instructions. Soluble PD-1 and soluble CD14 were made by the enzyme linked immunosorbent assay (ELISA) technique. The assay procedures were followed according to the manufacturer’s instructions. We studied patients with immune inactive phase (HBV DNA< 1,000 copies/ml, anti-HBe + and normal ALT, n=22), immune tolerant phase (HBV DNA > 10,000 copies/ml, HBeAg + and normal ALT, n=36), and immune active phase (elevated ALT and HBV DNA>10,000 copies/ml, n=13). Results Serum IL-6 levels in patients with immune inactive phase were significantly lower than patients with immune tolerant and immune active phases (267.3±245.6 pg/mL vs. 620.2±207.8 pg/mL and 1,815±803.2) (p<0.001). Serum TNF-α levels in patients with immune inactive phase was slightly lower than patients with immune tolerant and immune active phases (3.36±4.40 pg/mL vs. 8.74±12.91 pg/mL and 111.9±377.4) (p=0.079). However, other cytokines (serum IL-2, IL-17A, IFN-γ), soluble CD 14, and soluble PD-1 levels might not be significantly related to the natural history of CHB phase. Conclusion These results demonstrate the potential to apply serum IL-6 as a biomarker for differentiating immune inactive phase from other phases in patients with chronic HBV infection.

Potential application of a recombinant bacterial strain carrying a groEL promoter as a whole-cell microbial biosensor for detecting bioavailable cadmium

Abstract In this study, we investigated the response to heavy metals of recombinant E. coli NovaBlue strains carrying plasmids harboring different Cupriavidus taiwanensis LMG19424-derived groEL promoter fragments fused to the lacZ reporter gene. Four recombinant plasmids (designated G14, G26, G27 and G28) were transformed into E. coli and screened for the ability to indicate the presence of heavy metals on Luria–Bertani (LB) agar. Only the G28 biosensor exhibited reproducible results, with an observed limit of Cd detection of 3 μ g/mL. In LB broth, the NovaBlue host strain was able to grow and tolerate in the presence of 50 μ g/mL As, Cd, Co, Ni, Pb and Zn but was susceptible to 6.2 μ g/mL Cr. The β -galactosidase ( β -gal) reporter activity was reduced when the concentration of heavy metals increased, with observed detection limits, as indicated by the blue color, of 25 μ g/mL for CdCl2, CdSO4, and CdCO3; 50 μ g/mL for As (III) and ZnSO4; and 100 μ g/mL for CoCl2 and NiSO4. The specificity of the induction ratio and metal concentration was highest for Cd, with R2 values of 0.9196 and 0.9164 for CdCl2 and CdSO4, respectively. When the ratio of β -gal activity and growth was compared between NovaBlue strains carrying G28 or pETBlue-2 (containing an E. coli promoter), the G28 biosensor exhibited a significantly higher ratio than the strain carrying pETBlue-2 at 0.8–6.3 μ g/mL CdCl2. The results demonstrated that the certain concentration range corresponded to Cd induction of G28. The G28 biosensor were immobilized on paper discs and tested using the most toxic and soluble Cd compound (CdCl2) at 0–0.8 μ g/mL on LB agar. The G28 biosensor developed a blue color only in the absence of CdCl2. However, when testing soil extracts contaminated with low, medium or high levels of total Cd or those spiked with CdCl2 (up to 40 μ g/mL), all the G28 biosensor discs showed a similar growth pattern with a spotted blue color compared with the even blue color of the control disc. Due to the complexity of environmental samples, several factors may interfere with the metal response of the G28 biosensor. However, the G28 biosensor exhibited different behaviors in the presence of specific types and concentrations of metals. Thus, combinations of G28 and more specific promoters should be further investigated to improve the sensitivity and specificity of the groEL promoter for detecting Cd and other heavy metals in contaminated samples.

Water management impacts on the solubility of Cd, Pb, As, and Cr and their uptake by rice in two contaminated paddy soils

Agricultural soil contaminated with heavy metals and the subsequent heavy metals uptake by rice have increasingly been reported in the last few decades. In this study, pot experiments with two contaminated soils (acidic soil from Jiangxi Province and slightly alkaline soil from Hunan Province) were conducted to investigate the effects of water management (flooding and aerobic treatment) on the uptake of cadmium (Cd), lead (Pb), arsenic (As), and chromium (Cr) by rice (Oryza sativa L.). The pore water contents of these heavy metals were determined during the growing season. Flooding the soil decreased Cd, Pb, and Cr in soil pore water, but increased As in the soil solution. Relative to the aerobic treatment, flooding decreased the Cd in the soil solution by 17.3–94.5% and 54.7–88.3% in acidic and slightly alkaline soils, respectively. The total As in the soil solutions increased by 0.2–20.9 and 0.1–15.2 times throughout the growing season in acidic and slightly alkaline soils, respectively. In acidic soil, flooding significantly decreased the Cd contents in iron plaque and rice tissues, significantly increased the Cr content in iron plaque, slightly decreased the Cr uptake by rice, and decreased the Pb content in the aboveground parts of rice, and increased the Pb content in rice roots and iron plaque. Relatively fewer changes were observed in rice grown in slightly alkaline soil. Results suggested that flooding the acidic soil had mixed results on heavy metal bioavailability, and the bioavailability in slightly alkaline soil was not notably impacted by flooding.

Enhancing the effectiveness of zinc, cadmium, and lead phytoextraction in polluted soils by using amendments and microorganisms.

For remediating polluted soils, phytoextraction of metals received considerable attention in recent years, although slow removal of metals remained a major constraint in this approach. We, therefore, studied the effect of selected organic and inorganic amendments on the solubility of zinc (Zn), cadmium (Cd), and lead (Pb) in polluted soil and enhancing the efficacy of phytoextraction of these metals by Indian mustard (Brassica juncea cv. Pusa Vijay). For this purpose, a greenhouse experiment was conducted using a metal-polluted soil to evaluate the effect of amendments, viz. green manure (T2), EDTA (T3), sulfur (S)+S oxidizing bacteria (Thiobacillus spp.) (T4), metal-solubilizing bacteria (Pseudomonas spp.) (T5), and green manure + metal-solubilizing bacteria (T6), on solubility and bioavailability of Zn, Cd, and Pb. Distribution of metals in different soil fractions revealed that Cd content in water soluble + exchangeable fraction increased to the extent of 34.1, 523, 133, 123, and 75.8% in T2, T3, T4, T5, and T6 treatments, respectively, over control (T1). Cadmium concentrations in soil solution as extracted by Rhizon sampler were recorded as 3.78, 88.1, 11.2, 6.29, and 4.27μgL-1in T2, T3, T4, T5, and T6, respectively, whereas soil solution concentration of Cd in T1 was 0.99μgL-1. Activities of Cd (pCd2+) in Baker soil extract were 12.2, 10.9, 6.72, 7.74, 7.67, and 7.05 for T1, T2, T3, T4, T5, and T6, respectively. Cadmium contents in shoot were recorded as 2.74, 3.12, 4.03, 4.55, 4.68, and 4.63mgkg-1 in T1, T2, T3, T4, T5, and T6 treatments, respectively. Similar trend in Zn and Pb content with different magnitude was also observed across the different amendments. Cadmium uptake by shoot of mustard was enhanced to the extent of 125, 62.5, 175, 175, and 212% grown on T2-, T3-, T4-, T5-, and T6-treated soil, respectively, over T1. By and large, free ion activity of metals as measured by Baker soil test proved to be the most effective index for predicting Zn, Cd, and Pb content in shoot of mustard, followed by EDTA and DTPA. Among the metal fractions, only water soluble + exchangeable metal contributed positively towards plant uptake, which explained the variation in shoot Zn, Cd, and Pb content to the extent of 74, 81, and 87%, respectively, along with other soil metal fractions. Risk to human health for intake of metals through the consumption of leafy vegetable (mustard) grown on polluted soil in terms of hazard quotient (HQ) ranged from 0.64 to 1.10 for Cd and 0.11 to 0.34 for Pb, thus rendering mustard unfit for the human consumption. Novelty of the study mainly consisted of the use of natural means and microorganisms for enhancing solubility of metals in soil with the ultimate aim of hastening the phytoremediation.

Relevance of dissolved organic matter generated from green manuring of Chinese milk vetch in relation to water-soluble cadmium.

Dissolved organic matter (DOM) can become a carrier of soil contaminants. Therefore, an understanding of the evolution and characteristics of DOM produced by Chinese milk vetch during green manuring is crucial. In this study, DOM solutions from 28days' manuring with three different organic materials were characterized using three-dimensional fluorescence excitation-emission matrix (3D-EEM) with parallel factor (PARAFAC) analysis, and ultraviolet-visible spectroscopy. With the green manuring milk vetch at flowering period (MVFP), the DOC and water-soluble cadmium (WS-Cd) in soil solution reached 1875mg/l and 2.64μg/l, respectively, on day 6 after manuring. The PARAFAC analysis modeled three components: protein-like (tryptophan) and two humic-like components (humic acid and fulvic acid); DOM produced by MVFP was primarily protein-like during the early stage of decomposition. The aromaticity and molecular weight of DOM in the MVFP treatment was lower than in the other treatments, which could promote the release of soil particle-adsorbed Cd to soil solution. Principal components analysis showed that aromaticity was the main factor affecting Cd solubility, and the negative linear correlation of aromaticity with WS-Cd reached 0.4827. The results of this study supported the idea that manuring with MVFP might accelerate Cd infiltration to deep soil with water under gravity.

Iron-Manganese (Oxyhydro)oxides, Rather than Oxidation of Sulfides, Determine Mobilization of Cd during Soil Drainage in Paddy Soil Systems.

The preharvest drainage of rice paddy fields during the grain filling stage can result in a substantial mobilization of Cd in soil and, consequently, elevated grain Cd concentration. However, the processes controlling the mobilization of Cd remains poorly understood. Using 12 field-contaminated paddy soils, we investigated the factors controlling the temporal changes in Cd solubility in paddy soils that were incubated anaerobically for 40 d followed by a 20 d oxidation period. Soluble and extractable Cd concentrations decreased rapidly upon flooding but increased during the oxidation phase, with Cd solubility (aqueous Cd/soil Cd) largely depending upon porewater pH. Furthermore, inhibiting sulfate reduction or inhibiting oxidation dissolution of Cd-sulfides had little or no effect on the mobilization of Cd in the subsequent oxidation phase. Both sequential extraction and X-ray absorption spectroscopy (XAS) analyses revealed that changes in Cd solubility were largely dependent upon the transformation of Cd between the Fe-Mn (oxyhydro)oxide fraction and exchangeable fraction. Mobilization of Cd upon soil drainage was caused by a decrease in soil pH resulting in the release of Cd from Fe-Mn (oxyhydro)oxides. Taken together, Fe-Mn (oxyhydro)oxides play a critical (and prevalent) role in controlling the mobilization of Cd upon soil drainage in paddy systems.

Growth, Properties, and Structure of Cadmium Sulfamate Cd(NH2SO3)2 · 2H2O

The temperature dependence of the solubility of Cd(NH2SO3)2 compound in the range from 25 to 80°C has been determined. It is found that Cd(NH2SO3)2 · 2H2O and Cd(NH2SO3)2 are crystallized from aqueous solution below and above 40°C, respectively. Cd(NH2SO3)2 · 2H2O single crystals are obtained, their structure is solved, and some physicochemical properties are investigated.

Studies on the formation and properties of polypyrrole doped with ionised β-cyclodextrins: influence of the anionic pendants

Polypyrrole films doped with sulfonated β-cyclodextrin (PPy/sβ-CD) and carboxymethyl β-cyclodextrin (PPy/CMβ-CD) were formed on electropolymerisation of pyrrole in a solution of the cyclodextrin sodium salts. Lower rates of electropolymerisation were evident with the carboxymethyl β-CD and this was attributed to protonation of the carboxylate groups due to an increase in the interfacial pH at the electrode–solution interface. The PPy/sβ-CD and PPy/CMβ-CD films showed cation exchange behaviour with the ingress of Na+ and its associated water molecules on reduction. The PPy/CMβ-CD film showed less electroactive behaviour which may be related to the lower number of anionic pendants on the CMβ-CD or to the possible precipitation of the less soluble neutral CD which arises due to the protonation of the carboxylate groups. The PPy/sβ-CD showed a high capacitance of 6.0 mF cm−2 corresponding to a specific capacitance of 71 F g−1 over a wide potential range extending from − 0.60 to 0.60 V vs SCE. Over-oxidation was observed at relatively low potentials, at about 0.60 V vs SCE. A diffusion coefficient of 6.47 × 10−6 cm2 s−1 and a rate constant of 3.73 × 10−2 cm s−1 were obtained for the ferricyanide redox couple at the PPy/sβ-CD, indicating little or no inhibition of the ferricyanide redox reaction.

Study of urinary interferon gamma-induced protein 10 (IP-10) and urinary soluble CD 25 (sCD25) as markers of lupus nephritis and their relation to histological class

ObjectiveTo study the role of urinary interferon gamma-induced protein 10 (IP-10) and urinary soluble CD 25 (sCD 25) as diagnostic and prognostic markers of lupus nephritis (LN) and their relation to the LN class in renal biopsy. Subjects and methodsThis study included 45 lupus patients fulfilling the Systemic Lupus International Collaborating Clinics (SLICC) classification criteria: 25 patients with active LN during activity and during follow up (3 months later) as [group A] and 20 patients without any signs of activity [group B]. (20) age and sex matched healthy subjects were enrolled as control group [group C]. Urine samples were collected at baseline and at follow up. Urinary IP-10 and sCD25 were measured by ELISA. ResultsUrinary IP-10 and sCD25 levels were higher in group A compared to groups B and C (P < 0.001 for both). In patients with active nephritis, urinary IP-10 and sCD25 correlated positively with serum creatinine (P < 0.001 for both), proteinuria (p = 0.010; p = 0.007), anti ds-DNA (p = 0.002; p < 0.001), SLEDAI score (global) (P < 0.001 for both), and renal SLEDAI score (p = 0.002; p < 0.001) respectively. The urinary IP-10 and sCD25 levels were highest in patients with class (IV) LN and lowest in class (II) patients with a statistically significant difference. In patients achieving remission with treatment, both markers decreased significantly. ConclusionUrinary IP-10 and sCD25 are potential biomarkers for early recognition and follow up of LN.

Dietary strategies to reduce the oral bioaccessibility of cadmium and arsenic in rice.

The study aims to seek the dietary strategies to reduce the bioaccessibility of Cd and As in contaminated rice. A total of 12 selected food matrices were assayed by using the in vitro gastrointestinal digestion models. The results showed that tomato, carrot, water spinach, and spinach reduced the solubility of Cd by 45-78%, 50-71%, 53-70%, and 45-71%, respectively. Meanwhile, tomato, carrot, potato, and sweet potato reduced the solubility of As by 53-79%, 50-80%, 40-71%, and 36-76% in aqueous solution, respectively. In both gastric and gastrointestinal phases, Cd and As bioaccessibility decreased as the amount (100, 200, or 400mg) of food matrices increased (except for As in water spinach). These results suggested that the uses of some foodstuffs may be a good dietary strategy to reduce Cd and As bioaccessibility, although in vivo studies are required to confirm their suitability.

Sodium hydrosulfide alleviates cadmium toxicity by changing cadmium chemical forms and increasing the activities of antioxidant enzymes in salix

Cadmium (Cd) is a highly toxic element for plant. In order to reveal the effects of NaHS on Cd uptake, physiological and molecular responses of salix to Cd toxicity, NaHS-mediated hydroponics of salix under Cd stress was performed. The addition of NaHS reduces the salix biomass reduction caused by Cd poisoning. NaHS did not obviously reduce the total Cd level absorbed by salix, but significantly reduced the soluble Cd fractions and increased the insoluble Cd fractions in salix leaves and roots. NaHS reduced the distribution of Cd in organelles and vacuoles and increased the distribution of Cd in the cell wall of salix leaves and roots. NaHS promotes the level of antioxidant enzyme activities and gene expression of salix, and reduces the accumulation of MDA and H2O2 caused by Cd. NaHS increases the content of GSH and endogenous H2S in salix leaves and roots. The addition of NaHS can reduce the toxicity of Cd to salix without obviously reducing the Cd uptake by salix, thus improving the application of salix in phytoremediation to Cd.

Soil properties and agronomic factors affecting cadmium concentrations in cacao beans: A nationwide survey in Ecuador

Recent cadmium (Cd) regulation in chocolate threatens the sustainability of cacao production in Southwest America. Cadmium contamination in cacao beans has not been assessed at a country level. A nationwide survey was conducted in Ecuador to identify the spatial distribution of Cd in cacao beans, as well as soil and agronomic factors involved. Paired soil and plant samples (pods and leaves) were collected at 560 locations. Information on agronomic practices was obtained through a prepared questionnaire for farmers. Total soil Cd averaged 0.44 mg kg−1 which is typical for young and non-polluted soils. Mean Cd concentration in peeled beans was 0.90 mg kg−1 and 45% of samples exceeded the 0.60 mg kg−1 threshold. Bean Cd hotspots were identified in some areas in seven provinces. Multivariate regression analysis showed that bean Cd concentrations increased with increasing total soil Cd and with decreasing soil pH, oxalate-extractable manganese (Mnox) and organic carbon (OC) (R2 = 0.65), suggesting that Cd solubility in soil mainly affects Cd uptake. Bean Cd concentration decreased a factor of 1.4 as the age of the orchard increased from 4 to 40 years. Bean Cd concentration was inconsistently affected by genotype (CCN-51 vs. Nacional), pruning or application of fertilizers. It is concluded that the relatively larger bean Cd concentrations in Ecuador are related to the high Cd uptake capacity of the plants combined with their cultivation on young soils, instead of Cd depleted weathered soils. Mitigation strategies should consider the application of amendments to modify such soil properties to lower soil Cd availability. There is scope for genetic mitigation strategy to reduce bean Cd, but this needs to be properly investigated.

Subcellular distribution, chemical forms and thiol synthesis involved in cadmium tolerance and detoxification in Siegesbeckia orientalis L.

ABSTRACTSiegesbeckia orientalis L. is a promising species for cadmium (Cd) phytoextraction with large biomass and fast growth rate, while little information about their intracellular mechanisms involved in Cd tolerance and detoxification has been explored. A soil pot experiment with total target Cd concentrations of 0, 10, 50, 100, and 150 mg kg−1 were designed to investigate the subcellular distribution, chemical forms and thiol synthesis characteristics of Cd in S. orientalis. More than 90% of Cd was bound to the soluble fractions (48.4–76.5%) and cell walls (19.9–46.3%). Increasing soil Cd concentrations enhanced Cd sequestration into the cell walls. Most of the Cd (69.8–82.7%) in the plant organ was mainly in the forms of pectate and protein integrated Cd and undissolved Cd phosphate, while a minor portion (6.8–20.9%) was in the forms of the inorganic Cd and the water soluble Cd. Nonprotein thiols and phytochelatins significantly increased with increasing soil Cd treatment levels, while glutathione concentrations had no obvious change trends. Therefore, intracellular detoxification mechanisms of Cd in S. orientalis mainly rely on formation of less toxic Cd chemical forms, store of a large amount of Cd in cell wall and synthesis of thiol compounds.

Effect of modified coconut shell biochar on availability of heavy metals and biochemical characteristics of soil in multiple heavy metals contaminated soil

On account of the potential in immobilizing metals and improving soil environment, various biochar materials have been extensively applied in environmental remediation. The purpose of this experiment was to evaluate the effect of modified coconut shell biochar (MCSB) on the availability of metals and soil biological activity in multi-metals (cadmium (Cd), nickel (Ni) and zinc (Zn)) contaminated soil. MCSB was obtained from coconut shell biochar (CSB) by hydrochloric acid pickling and ultrasonication, which has significantly improved its surface functional groups and microcosmic pore structure. Sandy soil samples were incubated at 25 °C amended with MCSB or CSB by 0%, 2.5% and 5% addition for 63 days, respectively. The results showed that the acid soluble Cd, Ni and Zn decreased by 30.1%, 57.2% and 12.7%, respectively, in groups with 5% MCSB addition, which indicated MCSB had a better effect on immobilizing metals compared with CSB. In addition, higher soil biological activities were detected in different treatments compared with control (CK). Especially, the maximum bacterial number was found in 5% MCSB treatment, which increased by 149.43% compared with CK. Accordingly, our results suggested that MCSB could be used as an ameliorant to immobilize heavy metals in contaminated soils and improve soil physicochemical and biological properties.

Optimization of flocculation conditions for soluble cadmium removal using the composite flocculant of green anion polyacrylamide and PAC by response surface methodology

In this work, we describe a flocculation performance evaluation of a novel anionic polyacrylamide (APAM) synthesized using low dose γ-ray initiation. The APAM structure and morphology were characterized using Fourier transform-infrared spectroscopy (FTIR), High performance liquid chromatography (HPLC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) techniques. In comparison to commercially purchased APAM (Mw = 1.0 × 107), γ-ray initiation was demonstrated to be a more effective method to increase molecular weight, decrease the residual acrylamide monomer, and improve thermal stability. Flocculant performance was evaluated by assessing their ability to remove Cd(II) from water. We utilized the Plackett-Burman (PB), steepest ascent, and response surface methodology (RSM) experimental design to identify the optimal flocculating conditions for the removal of soluble Cd(II). Under optimal conditions [26.84 mg L−1 CaO, 71.28 mg L−1 polyaluminium chloride (PAC) and 2.87 mg L−1 APAM], the maximum percent removal of Cd(II) was observed to reach 93.65%. A potential flocculation mechanism for the Cd(II) removal from water was further studied by evaluating the colloid Zeta potential. Results from these studies demonstrated that PAC had a greater capability to change the Zeta potential of collide under alkaline conditions, while APAM played a critical role in the bridging, enmeshment, and sweeping effect. The composite of two types of predominance makes considerable sense in regards to enhancing flocculating efficiency, decreasing secondary pollution, and reducing flocculant cost.