Cd Species Research Articles

Restriction of sulfate reduction on the bioavailability and toxicity of trace metals in Antarctic lake sediments

In this study, Acid-Volatile Sulfur (AVS), trace metals Cu, Cd and Zn and their chemical speciation based on BCR-sequential and simultaneous extraction (SEMs) in Antarctic lake sediments (Y2-1 and YO) were analyzed to investigate the restriction of sulfate reduction on the bioavailability and toxicity of trace metals. Much higher trace metals in Y2-1 indicating a primary source from penguin guano. The main chemical speciation of Cu and Cd in Y2-1 was their oxidizable fraction in contrast to those of weak-acid extraction in YO. Lower ratio of ΣSEM/AVS in Y2-1 indicating less toxicity of the trace metals. The main chemical speciation of Cd in Y2-1 was their oxidizable fraction in contrast to that exchangeable fraction in penguin guano, indicating that although amounts of Cd was transported from marine to lake by penguins, strong sulfate reduction in ornithogenic sediments restricts the bioavailability and toxicity of Cd through the formation of insoluble sulfide.

Mechanistic insights and multiple characterizations of cadmium binding to animal-derived biochar

Cattle-derived biochar (CB), which is derived from industrial pyrolysis of cattle carcasses in harmless treatment plants, is a naturally occurring mineral form of carbonate-bearing hydroxyapatite (CHAP) with a small amount of elemental carbon. CB has 4.02% of carbonate content, which falls under the B-type substitution of CHAP. In this work, the Cd(II) sorption capacity of CB was determined to be 0.82 mmol/g, with 97.6% of the Cd(II) uptake contributing to CHAP and only 2.36% of the Cd(II) uptake contributing to the elemental carbon component. The calculation and linear combination fitting (LCF) of Cd L3-edge X-ray absorption near-edge structure (XANES) analysis indicated that the contributions of Cd(II) species to CB presented the following order: ion exchange (57.6%–61.0%) > precipitation (24.4%–29.9%) > surface complexation (12.5%–13.4%). The depth dependent X-ray photoelectron spectroscopy (XPS) showed the presence of ion exchange, which is accompanied by intraparticle diffusion. LCF of XANES and Rietveld analysis of X-ray diffraction (XRD) demonstrated that Cd(II) was precipitated in the form of Cd5H2(PO4)4·4H2O on the CB surface. Furthermore, the precipitate was directly observed and identified by scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS). Consequently, we revealed the intricate binding mechanism of Cd(II) to CHAP-rich CB and confirmed the importance of surface precipitation.

Increased biomass and reduced tissue cadmium accumulation in rice via indigenous Citrobacter sp. XT1-2-2 and its mechanisms

Microbial remediation is a promising technique to remediate heavy metals contaminated soils. In this study, the cadmium (Cd)- resistant Citrobacter sp. XT1-2-2, isolated from heavy metals contaminated paddy soils, was investigated to evaluate the effect of this strain on soil Cd speciation, cellular Cd distribution, tissue Cd accumulation and rice biomass. The percentage of Cd2+ removal by Citrobacter sp. XT1-2-2 was up to 82.3 ± 2.1% within 240 min in the solution. The average content of soil soluble plus exchangeable and carbonate-bound fractions of Cd decreased, whereas Fe/Mn oxide-bound, organic matter-bound and residual fractions increased with bacteria inoculation. For the paddy soil inoculated with the XT1-2-2 strain, Cd concentrations of roots, culms, leaves and grains were significantly reduced by 24.1%, 46.9%, 41.5% and 66.7%, respectively. In addition, inoculation bacteria significantly increased the biomass of the roots, above-ground tissues and the rice grains. All results indicated that the XT1-2-2 strain had the ability to immobilize soil Cd and decrease Cd accumulation in rice grains. Therefore, the XT1-2-2 strain has potential for application to remediate Cd-contaminated paddy soils. It is possible to exploit a new bacterial-assisted technique for the remediation in Cd-contaminated paddy soils.

The optimum pH and Eh for simultaneously minimizing bioavailable cadmium and arsenic contents in soils under the organic fertilizer application

Cadmium (Cd) and arsenic (As) are usually found in contaminated soils. Their bioavailabilities are often related to pH and Eh, which indicate a generally contrasting or antagonistic effect. In this paper, the pH and Eh of soil samples were altered by adding organic fertilizer, and Tessier sequential extraction procedures were used to extract heavy metal speciation. With increasing pH and decreasing Eh, the content of the exchangeable, carbonate-bound, Fe-Mn oxide-bound, and organic-bound forms of the Cd decreased. The content of the residual form of Cd increased. The content of water-soluble Cd also increased. In terms of As, the content of the water-soluble, exchangeable, carbonate-bound, and organic-bound forms increased, and the content of the residual form decreased. Bioavailable forms contained water-soluble and exchangeable forms. With increasing pH or decreasing Eh, bioavailable Cd content linearly decreased, whereas bioavailable As content exponentially increased. The fitting curve showed that compared with 200 mV, the bioavailable Cd content decreased by 52.4%, and the bioavailable As content increased by 3.2 times at −400 mV. Finally, using the indicator of trade-off value, optimum pH = 7.31, and Eh = −130 mV, the bioavailable Cd and As contents were simultaneously maintained at a relatively low level. The novelty of this paper is studying the effects of different soil pH and Eh values changed by organic fertilizer on the speciation of Cd and As rather than the direct quantitative effects between organic fertilizer and the speciation of Cd and As, which can better explain the mechanism underlying the effect of organic fertilizer on the speciation of Cd and As.

Efficiency of lime, biochar, Fe containing biochar and composite amendments for Cd and Pb immobilization in a co-contaminated alluvial soil

Present study reports the laboratory and field scale application of different organic and inorganic amendments to immobilize cadmium (Cd) and lead (Pb) in a co-contaminated alluvial paddy soil. For that purpose, lime, biochar, Fe-biochar and two composite amendments (CA) composed of biochar, lime, sepiolite and zeolite (CA1: composite amendment 1) and manure, lime and sepiolite (CA2: composite amendment 2) were firstly tested in an incubation experiment to ameliorate Cd and Pb co-contaminated alluvial soil. It was observed that liming and CA2 elevated the soil pH and reduced DTPA extractable Cd and Pb in the incubated soil leading to higher metal immobilization. Therefore, efficiency of lime and CA2 was further investigated in field conditions with mid rice as the test crop to evaluate field scale immobilization and precise application rate for the tested soil type. DTPA and CaCl2 extractable Cd (46 and 51%) and Pb (68 and 70%) in field soil were decreased with applied treatments. Speciation of Cd and Pb also promoted conversion of metal exchangeable contents to less-available forms. Activated functional groups on amendments’ surface (_OH bonding, C_O and CO, -O-H, Si–O–Si, carboxylic and ester groups) sequestered metals by precipitation, adsorption, ion exchange or electro static attributes. Application of lime at 2400 kg/acre (T4) and CA2 at 1200 kg/acre was more effective in reducing rice shoot and grains metal contents. Moreover, obtained results in terms of pH, extractable content, speciation and yield, and microanalysis of amendments highlights the remarkable efficiency of lime and composite amendment to sorb Cd and Pb providing the key evidence of these amendments for metals immobilization and environmental remediation. Considering these results, lime and CA2 are potential amendments for co-contaminated rice field especially in context of alluvial soil.

Effects of cyanobacteria decomposition on the remobilization and ecological risk of heavy metals in Taihu Lake.

To investigate the relationship between cyanobacteria decomposition and the remobilization of heavy metals in Taihu Lake, the indoor simulation experiments were conducted. The areas of Taihu Lake that undergo harmful algal blooms mostly caused by excessive cyanobacteria have serious problems of heavy metal pollution. The results showed that cyanobacteria decomposition can release heavy metals into the water and change the total contents and chemical speciation of Cr, Ni, Cu, Zn, As, Cd, Hg, and Pb in sediment due to the change of physical and chemical properties in overlying water and sediment. The decomposition rate of cyanobacteria with sediment was clearly faster than that without sediment, and decomposition changed the pH and dissolved oxygen (DO) concentrations in overlying water. The cyanobacteria decomposition reduced the oxidation-reduction potential (ORP), and increased organic matter (OM) and total organic carbon (TOC) in the surface sediment. According to ecological risk assessment, the cyanobacteria decomposition increased the degree of heavy metal pollution and the potential ecological risk in sediment.

The impact of fermentation on the distribution of cadmium in cacao beans.

A large fraction of the South-American cacao production is affected by new cadmium (Cd) regulations in cacao. This work was set up to characterize the distribution and speciation of Cd within the cacao fruit and to monitor potential Cd redistribution during cacao fermentation. In cacao fruits from four locations, Cd concentrations decreased with testa > nib ~ placenta ~ pod husk > mucilage. The distribution of Cd within cacao beans was successfully visualized using laser ablation inductively coupled plasma spectrometry (LA-ICP-MS) and confirmed higher Cd concentrations in the testa than in the nib. Speciation analysis by X-ray absorption spectroscopy (XANES) of unfermented cacao beans revealed that Cd was bound to O/N-ligands in both nib and testa. Fermentation induced an outward Cd migration from the nibs to the testa, i.e. against the total concentration gradient. This migration occurred only if the fermentation was sufficiently extensive to decrease the pH in the nib to <5.0, likely as a result of increased Cd mobility due to organic acid penetration into the nibs. The change in dry weight based nib Cd concentrations during fermentation was, on average, a factor 1.3 decrease. We propose that nib Cd can be reduced if the nib pH is sufficiently acidified during fermentation. However, a balance must be found between flavor development and Cd removal since extreme acidity is detrimental for cacao flavor.

Cd uptake by Phytolacca americana L. promoted by cornstalk biochar amendments in Cd-contaminated soil

Cadmium (Cd) contamination is the most extensive pollution in China farmland. A greenhouse pot trial was conducted to investigate the effects of cornstalk biochar on Cd accumulation by Phytolacca americana L. (pokeweed) in Cd-contaminated soil. The Cd concentration increased in leaves, shoots, and roots of plants amended with 5% biochar by 79%, 113%, and 32%, respectively, compared with the pokeweed without biochar. The Cd availability, soil Cd speciation, soil fertility, root biomass, and Cd chemical forms in root were investigated to explore the mechanism by which Cd uptake increased in presence of biochar. The extractability of Cd by DTPA decreased in presence of biochar by 30% compared with that of soil without biochar. The increases occurred with dose of biochar increased in available phosphorus, labile organic carbon, and C/N atom ratio. Although, the dry weight of the aboveground part of the pokeweed decreased by 38.5%, however, the weight of roots increased by 20.8%. Root biomass and microbial activity reached maximum in the treatment that recieved 5% biochar. Cd forms extracted by NaCl and acetic acid (HAc) were predominant in root. When 5% biochar applied to soil, HAc-extracted Cd took up maximum of the increase in root.

Distribution, transfer, and time-dependent variation of Cd in soil-rice system: A case study in the Chengdu plain, Southwest China

Heavy metal contamination in soil has been a major environmental concern and affected agricultural safety, and it is generally believed that the risk of heavy metals in soil is associated critically with their forms. This study was carried out to identify the distribution of cadmium (Cd) speciation in paddy soil of Chengdu Plain and its time-dependent variation during rice growing process and to determine the controls of soil Cd fractions on their accumulation in rice. The speciation of Cd in soil was analysed by Community Bureau of Reference (BCR) sequential extraction method. The result showed that the Cd concentration range in study fields was 0.54 mg/kg ˜ 1.65 mg/kg and the distribution order of Cd in soil was basically: residua > exchangeable ≈ reducible > oxidizable. Cd accumulation and distribution in rice largely depended on non-residual fraction Cd, rather than the total Cd, especially exchangeable fraction Cd having a linear relationship with total Cd in grain within a use limit value of Cd concentration in soil. In the process of rice growth, the distribution of Cd in rhizosphere soil was changed, and the relatively high percentage of non-residual fraction Cd was reached before heading, which suggested that the amount of Cd took up by paddy roots during the time of tillering was more than at any other period. Overall, this study provided a basis for exploring more appropriate risk assessment and heavy metal contaminated soil remediation.

Enhanced photocatalytic performance of CdO-WO3 composite for hydrogen production

Considering the renewability and cleanness of hydrogen generation system, the photocatalytic H2 evolution through water splitting with assistance of Earth abundant co-catalysts has become a scientific hotspot. Efficient and visible light driven CdO-WO3 composites with versatile properties have been fabricated through hydrothermal approach for H2 evolution. X-ray diffractometer, scanning electron microscope, UV-Vis absorption spectroscopy, photoluminescence emission spectroscopy and photocatalytic activity test were employed to investigate different properties like crystallography, morphology, optical and photocatalytic properties. The effect of CdO concentration on the grain size indicated the reduction of bad gap energy of the WO3. The concentration of CdO nanoparticles in WO3 directly effect on the morphology of the particles that are in the form of nanorods. The atoms of CdO makes the WO3 nanoparticles more effective and efficient up to 4% of CdO but when coupling amount increases then the CdO-WO3 nanoparticles exhibited less photocatalytic performance to evolve H2 energy. Results shown that 4% content in WO3 had exceptional photocatalytic activity for water splitting when compared to other samples. The improved hydrogen production was allied with formation of active Cd species during the photocatalysis process, which has the ability to promote the interfacial charge-separation and concurrently may cause to reduce the over potential of hydrogen evolution, thus boosting the photocatalytic activity over the hybrid sample. The improved photocatalytic activity of composites could be accredited to extended absorption region of visible light, efficient separation of charge carrier's and suppress recombination of electron-hole pairs. The current work not only shows a prospect for the utilization of low cost CdO as a co-catalyst in photocatalytic hydrogen generation but also shows a substantial enhancement in H2 evolution, first time, using CdO-WO3 hybrid photocatalyst.

The Speciation of Cd in Cd–Fe Coprecipitates: Does Cd Substitute for Fe in Goethite Structure?

Anthropogenic inputs of Cd into environments through various industrial and agricultural activities cause wide concerns around the world. The fate and toxicity of Cd in soils is substantially affected by its association with various iron (hydr)oxides via adsorption, isomorphous substitution, and/or coprecipitation mechanisms but the Cd speciation in Cd–Fe coprecipitates during Fe (hydr)oxides formation is rarely studied. In the present study, Cd–Fe coprecipitates during goethite formation were obtained and sequentially treated with acidic ammonium oxalate and nitric acid, and then the Cd speciation in these treated samples were determined by a combination of acidic dissolution kinetics, powder X-ray diffraction, transmission electron microscopy, Fe and Cd K-edge extended X-ray absorption fine structure spectroscopy, and the atomic pair distribution function analysis. The acidic ammonium oxalate-treated samples (NCd_o, N = 1–6) contain some ferrihydrite besides goethite, and the amount of ferrihydrite increases with increasing Cd content. Accordingly, more Cd is accumulated in ferrihydrite rather than goethite, and minor Cd(OH)2 precipitate probably exists in the NCd_o samples with high Cd content. In the NCd_o sample with the highest Cd content (6.9 ± 0.2 mol %), ferrihydrite proportion can be as high as one-third and retains almost one-half of the total Cd. Further treatment of these NCd_o samples with nitric acid solution almost totally removes the 2-line ferrihydrite, finite goethite particles and the Cd associated with them. The thus obtained Cd–Fe coprecipitates (NCd_n, N = 1–6) are probably Cd-substituted goethites with Cd uniformly distributed in the mineral structure with a slightly enrichment in interior regions. These results help to have a better understanding of the Cd speciation in iron (hydr)oxides and the transformation and fate of Cd in polluted soils enriched in iron oxide minerals and also provide a useful strategy to investigate the speciations of heavy metals in complex matrixes.

Characterization of quantum dots in cancer cytosol using ICP-MS-based combined techniques

Knowledge of the intracellular behavior of quantum dots (QDs), which encompasses the antiproliferative effect on living cells, is still limited. For this reason, the transformations of CdSeS/ZnS-based QDs in cancer cytosol were examined using capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) hyphenated with inductively coupled plasma MS (ICP-MS). CE-ICP-MS method revealed the dose- and time-dependent speciation changes of QDs in the cytosol, while HPLC-ICP-MS (in the size-exclusion chromatography mode) allowed further characterization of the resulting Cd species. In such an appraisal, the decent CE advantage of high resolution is well complemented by higher sensitivity of HPLC (LOD 4.0 × 10−10 and 5.4 × 10−12 mol/L Cd, respectively). Additionally, the influence of serum protein corona on the surface of QDs on their uptake by Hep G2 cancer cells was investigated by direct ICP-MS analysis that revealed that the conjugated proteins greatly reduce the particle internalization.

Effects of Mn(II) on the Oxidation of Fe in Soils and the Uptake of Cadmium by Rice (Oryza sativa)

Soil properties affect the bioavailability of cadmium (Cd). In general, soils in southern China are rich in iron (Fe) and contain manganese (Mn), which form ferromanganese nodules through biological or chemical reactions. In this study, it is hypothesized that the formation of Fe/Mn oxides can reduce the bioavailability of Cd and play an important role in reducing the uptake of Cd by rice. In this study, the effects of Fe and Mn on the contents of Fe (II)-oxidizing bacteria (FeOB) communities, Fe oxides, and Cd speciation in Cd-contaminated paddy soils were studied in a pot experiment. Results showed that, compared with the CK treatment, the addition of Mn (II) increased the abundance of FeOB (Thiobacillus sp.) in the soil, thereby increasing the content of amorphous Fe oxides in the rhizosphere. Amorphous Fe oxides effectively immobilized Cd in the soil, that is, with an increasing content of Cd bound to amorphous Fe/Mn oxides in the rhizosphere and non-rhizosphere soils, the mobility and bioavailability of Cd were reduced. After the addition of Mn (II) and Fe (II), the Fe content in the root Fe plaque of rice increased significantly, while the Cd content decreased significantly. The increase of Fe in the root Fe plaque inhibited rice uptake of soil Cd; thus, the Cd content in rice shoots was significantly lower than the Cd content in the CK treatment. Compared with the addition of Fe (II), the addition of Mn (II) effectively reduced the Cd content in rice shoots. These findings suggested that the addition of Mn (II) can promote the formation of Fe oxides in soils and reduce the Cd content in rice. These research results provide support for using Mn-based soil remediation materials to remedy Cd-contaminated soils.

Degradation of 2,4-dichlorophenol by a novel iron based system and its synergism with Cd(II) immobilization in a contaminated soil

Nowadays, the remediation of heavy metals and organic compounds contaminated soil has been greatly growing attentions. In this paper, the feasibility of a novel biochar-supported zero valent iron (B-nZVI) based system for the degradation of 2,4-Dichlorophenol (2,4-DCP) and immobilization of Cd(II) in contaminated soil was firstly investigated. The most relevant findings revealed that persulfate (PS) could obviously improve the degradation of 2,4-DCP by B-nZVI process. Within 240 min, nearly 91% of 2,4-DCP degradation could be reached at reaction conditions of 40 mg kg−1 2,4-DCP, 6 mM PS, 3.0 g L−1 B-nZVI and pH 4.51. A much higher performance on the 2,4-DCP degradation was observed at acidic and aerobic conditions. A lower concentration of ethylene diamine tetraacetic acid (EDTA) exhibited a slight improvement of 2,4-DCP degradation, whereas humic acids (HA) exhibited a significant inhibitory effect on that. Radical scavenging tests revealed that SO4− was primarily involved in degradation reaction of 2,4-DCP by B-nZVI/PS process. A total of five intermediate products including 2-chlorohydroquinone, 3,5-dichlorocatechol, phenol, fumaric acid and acetic acid were generated in 2,4-DCP degradation process, whereas two Cd species such as Cd(OH)2 and CdO were identified in Cd(II) immobilization process. A possible mechanism for the 2,4-DCP degradation and Cd(II) immobilization by B-nZVI/PS process was proposed.

Bidens pilosa L. hyperaccumulating Cd with different species in soil and the role of EDTA on the hyperaccumulation.

Investigating whether the same hyperaccumulator shows a high accumulation potential for different species of the same heavy metal in the soil has rarely been considered until now. In this experiment, Cd accumulation by a hyperaccumulator Bidens pilosa L. from soils spiked with 3 and 9mgCdkg-1 in the form of Cd(NO3)2, CdCl2, CdBr2, CdI2, CdSO4, CdF2, Cd(OH)2, CdCO3, Cd3(PO4)2, and CdS and effect of soil amendment with EDTA were determined. The results showed that the Cd concentrations in B. pilosa for high-solubility species were basically higher. But the enrichment factors (EFs) (shoot to soil Cd concentration ratio) and translocation factors (TFs) (shoot to root Cd concentration ratio) of low-solubility Cd species were all greater than 1, either indicating that there was a high Cd hyperaccumulative potentials of B. pilosa without considering on Cd species in soil. EDTA significantly improved B. pilosa Cd hyperaccumulation, especially for low-solubility Cd forms in soils. These results can perfectly explain the accumulation properties of one hyperaccumulator to different species of the same heavy metal. Phytoremediation may be applied for a wide scope for different Cd species-contaminated soil. Moreover, the total amount of Cd in soil was important when assessing the risk of Cd-contaminated soils.

Cd(II) retention and remobilization on δ-MnO2 and Mn(III)-rich δ-MnO2 affected by Mn(II)

Birnessite owing to its negative surface charge and defective structure exhibits high sorption affinities for Cd(II). However, Mn(II) can not only compete for the sorption sites with Cd(II), but also react with structural Mn(IV) in birnessite to form Mn(III), and thus, affect Cd(II) immobilization by birnessite. Herein, we investigate effects of Mn(II) on Cd(II) retention and remobilization on two birnessite δ-MnO2 and Mn(III)-rich δ-MnO2 (denoted as HE-MnO2). At pH 5.5, Cd(II) sorption to birnessite was inhibited by Mn(II) addition. Mn(II) addition to δ-MnO2 led to Cd(II) migration from vacant sites to edge sites, forming double-corner sharing (DCS) complexes. Mn(II) introduction to δ-MnO2 led to less stable Cd(II) species formed on birnessite, indicating that Cd(II) was more firmly bound to vacant sites than edge sites of birnessite. Cd(II) formed double-edge sharing (DES) and DCS complexes on HE-MnO2. Mn(II) addition to HE-MnO2 increased the CdMn distance in DES complexes. The stability of adsorbed Cd(II) on HE-MnO2 was slightly elevated due to Mn(II) addition. At pH 7.5, Mn(II) had no effect on Cd(II) sorption and desorption amounts on birnessite. However, low concentration of Mn(II) added to δ-MnO2 induced partial migration of Cd(II) from vacant sites to edge sites while high concentration of Mn(II) added to birnessite led to the formation of amorphous Cd(II)-Mn(III) coprecipitate. These findings imply that aqueous Mn(II) is an important factor in influencing Cd(II) immobilization by birnessite in the environment.

Implementing chemical mass balance model and vulnerability the theories to realize the comprehensive evaluation in an abandoned battery plant

In China groundwater contamination has become a serious problem. The assessment and remediation of contaminated sites are greatly important. Moreover, only few studies deal with the influence of metal speciation on human health risk assessment. This paper proposed a comprehensive assessment methodology combined human health risk assessment and groundwater vulnerability assessment for contaminated area, exploring a more reasonable model for the Cd morphology simulation, and utilizing accurate method to calculate the average daily dose by the weight analysis. PHREEQC and Visual MINTEQ were applied and compared to the morphology simulation, the modified of average daily dose and non-modified of average daily dose was investigated, carcinogenic and non-carcinogenic risks were calculated subsequently. The groundwater vulnerability was assessed by the DRASTIC model, the DRASTIC index as the indicator of groundwater vulnerability. The morphology simulation results showed 20 and 13 metal species which were simulated by PHREEQC and Visual MINTEQ, respectively. Cd2+ and CdCl+ were the primary species of Cd in groundwater. The modified average daily dose showed less than the average daily dose in results. The carcinogenic risks showed the species of Cd2+ and CdCl+ were simulated by PHREEQC which were harmful to human health. The DRASTIC index was ranged from 109 to 134 in the studied area, which showed that the area was susceptible to pollution. This method provided a more effective risk assessment model and supplied a fundamental advice for government policy-making and site remediation.

Profiling of main metabolites in root exudates and mucilage collected from maize submitted to cadmium stress.

The aim of this study was to characterize qualitatively and quantitatively the composition of the main rhizodeposits emitted from maize (Zea mays) under Cd stress, in order to discuss their role in Cd availability and tolerance. Maize was grown for 6weeks in sand at four Cd exposure levels (0, 10, 20, and 40μM Cd in nutrient solution) and two types of rhizodeposits were collected at the end of cultivation period. Mucilage and other molecules adhering to rhizospheric sand were extracted with a buffer before root exudates were collected by diffusion into water. Total carbon, proteins, amino acids, and sugars were analyzed for both rhizodeposit types and about 40 molecules were identified using GC-MS and LC-MS. Cadmium effect on plant morphology and functioning was slight, but consistent with previous works on Cd toxicity. However, rhizodeposition did tend to be impacted, with a decrease in total carbon, sugars, and amino acids correlating with an increasing Cd content. Such a decrease was not noticeable for proteins in root exudates. These observations were confirmed by the same trends in individual compound contents, although the results were generally not statistically significant. Many of the molecules determined are well-known to modify, whether directly or indirectly, Cd speciation and dynamics in the soil and could play a role in Cd tolerance.

In-situ trace metal (Cd, Pb, Cu) speciation along the Po River plume (Northern Adriatic Sea) using submersible systems

Information on the distribution and speciation of trace metals is of critical importance for our ability to interpret the links between the bioavailability and uptake of an element, and its biogeochemical cycle in coastal environments. Within the framework of the European Project “In-situ automated Monitoring of Trace metal speciation in Estuaries and Coastal zones in relation with the biogeochemical processes (IMTEC)”, the chemical speciation of Cd, Pb and Cu was carried out along the Po River plume in the period 27 October – 2 November 2002. During the cruise, five Voltammetric In-situ Profiling systems and one Multi Physical Chemical Profiler, as well as conventional voltammetric instruments, were successfully applied in order to evaluate the distribution of Cd, Pb and Cu between different fractions (free ion, dynamic, colloidal, dissolved and particulate fractions) and to assess the evolution of these fractions during estuarine mixing and in the water column. Dynamic concentrations were 0.05–0.2 nmol L−1 Cd, 0.02–0.2 nmol L−1 Pb, and 0.15–4.0 nmol L−1Cu. Cd was mainly present as dynamic fraction (40–100% of the dissolved Cd). High proportions of Pb (~70%) and Cu (~80%) were present as colloids probably of biogenic origin. Principal components analysis reveals a strong influence of the Po River discharge on the spatial and vertical distributions of metal species. Almost all the metal fractions globally decreased following the salinity gradient. Metal concentrations are far below (at least one order of magnitude lower) the Environmental Quality Standard established by the Italian law. However, the Cu dynamic fraction showed concentrations likely to be toxic to sensitive phytoplankton community and to have negative effects on larva development of coastal macroinvertebrate species (toxicity data extracted from literature).

Expression of the Tobacco Non-symbiotic Class 1 Hemoglobin Gene Hb1 Reduces Cadmium Levels by Modulating Cd Transporter Expression Through Decreasing Nitric Oxide and ROS Level in Arabidopsis.

Hemoglobin (Hb) proteins are ubiquitous in plants, and non-symbiotic class 1 hemoglobin (Hb1) is involved in various biotic and abiotic stress responses. Here, the expression of the tobacco (Nicotiana tabacum) hemoglobin gene NtHb1 in Arabidopsis (Arabidopsis thaliana) showed higher cadmium (Cd) tolerance and lower accumulations of Cd, nitric oxide (NO), and reactive oxygen species (ROS) like hydrogen peroxide (H2O2). NtHb1-expressing Arabidopsis exhibited a reduced induction of NO levels in response to Cd, suggesting scavenging of NO by Hb1. In addition, transgenic plants had reduced accumulation of ROS and increased activities of antioxidative enzymes (catalase, superoxide dismutase, and glutathione reductase) in response to Cd. While the expression of the Cd exporters ABC transporter (PDR8) and Ca2+/H+ exchangers (CAXs) was increased, that of the Cd importers iron responsive transporter 1 (IRT1) and P-type 2B Ca2+ ATPase (ACA10) was reduced in response to Cd. When Col-0 plants were treated with the NO donor sodium nitroprusside (SNP) and H2O2, the expression pattern of Cd transporters (PDR8, CAX3, IRT1, and ACA10) was reversed, suggesting that NtHb1 expression decreased the Cd level by regulating the expression of Cd transporters via decreased NO and ROS. Correspondingly, NtHb1-expressing Arabidopsis showed increased Cd export. In summary, the expression of NtHb1 reduces Cd levels by regulating Cd transporter expression via decreased NO and ROS levels in Arabidopsis.