Aqueous Cd Research Articles

Microbial iron reduction as a method for immobilization of a low concentration of dissolved cadmium

Much attention has been paid to the relationship between microbial iron reduction and the behavior of cadmium (Cd) recently, but most previous research has employed unrealistically high Cd concentrations (e.g., 2–55 mg L−1) and has failed to consider the effects of iron oxides and microbial cells together. We investigated the reduction of lepidocrocite by Shewanella oneidensis MR-1 in the presence of a low concentration of Cd using batch reactor systems. The results showed that with 422 μg L−1 added dissolved Cd2+, an initial 137 μg L−1 decrease in aqueous Cd occurred due to adsorption onto lepidocrocite and that the further removal of remaining aqueous Cd occurred only in the system containing bacteria. This further decrease in aqueous Cd was unlikely to be caused by mineral transformation because the microbial reduction of lepidocrocite resulted in particle-size-increased (thus, specific-surface-area-decreased) lepidocrocite, and unlikely to be caused by the pH increase to 7.4 induced by iron reduction either because a pH-adsorption edge suggested that at pH 7.4, less than 60% of aqueous Cd can be adsorbed by lepidocrocite in the reactors. An adsorption isotherm showed a significant Cd adsorption capacity by S. oneidensis MR-1 cells, and we therefore attributed the further Cd removal to adsorption by S. oneidensis MR-1 cells. The results suggest that a realistically low concentration of Cd can be immobilized during microbial iron reduction by adsorption on iron oxides and microbial cells.

Synthesis of a bioadsorbent from jute cellulose, and application for aqueous Cd (II) removal

A low-cost, high-adsorption-capacity, eco-friendly bioadsorbent for removing Cd2+ from aqueous solution is reported. J-g-P(AM-co-AANa) was prepared by hydrolysis of the grafted copolymer, which was synthesized by free radical polymerization of acrylamide (AM) with jute fibers (JSE) pretreated by continuous screw-extrusion steam explosion. Fourier transform infrared and solid-state 13C nuclear magnetic resonance spectroscopies, confirmed that amino and carboxylate groups were introduced into J-g-P(AM-co-AANa). X-ray diffraction showed that the crystallinity of J-g-P(AM-co-AANa) was significantly lower than that of JSE. The surface morphology of bioadsorbent was investigated by scanning electron microscopy (SEM). The adsorption capacity of Cd2+ on J-g-P(AM-co-AANa) was evaluated for different solution pH values, contact times, and initial Cd2+ concentrations. The adsorption kinetics followed the pseudo-second-order kinetic model, and the rate controlling step was chemisorption. The adsorption isotherm was well fitted by the Freundlich model, and the adsorption process was multilayer adsorption. The maximum adsorption capacity was 344.8 mg/g, which indicated that the bioadsorbent was effective for removing Cd2+ from aqueous solution.

Comparing the adsorption mechanism of Cd by rice straw pristine and KOH-modified biochar

Biochar was considered as an effective and novel sorbent for cadmium (Cd) adsorption from aqueous solution. In this study, the adsorption isotherm investigations were conducted to examine the effect of biochar produced via pyrolysis from rice straw on removing aqueous Cd before and after modification by 2M KOH solution. Langmuir and Freundlich adsorption isotherms can preferably describe the adsorption process. Results showed that the highest adsorption capacity of pristine rice straw biochar was 12.17mgg-1. The chemically modified rice straw biochar showed greater Cd adsorption capacity of 41.9mgg-1, which was more than three times that of pristine biochar. Increase of surface area and changes of porous structure, especially the functional groups on the surface of modified biochar, were the major contributors to its more efficient adsorption of Cd. The possible mechanisms for Cd adsorption by biochar mainly involve (1) surface precipitation by forming insoluble Cd compounds in alkaline condition and (2) ion exchange for Cd with exchangeable cations in the biochar, such as calcium ions, which were confirmed by FTIR, XRD, SEM, and zeta potential determination.

Entrapment of ball-milled biochar in Ca-alginate beads for the removal of aqueous Cd(II)

A novel adsorbent was synthesized through the entrapment of ball-milled biochar in Ca-alginate beads for the removal of aqueous Cd(II). Batch adsorption experiments were conducted to compare Cd(II) adsorption characteristics of ball-milled biochar (BMB), Ca-alginate (CA), and Ca-alginate entrapped ball-milled biochar (CA-BMB). All the tested adsorbents showed excellent sorption ability. The maximum Cd(II) adsorption capacity estimated with Langmuir isotherm modeling was 251.8mgg−1 for CA, 227.1mgg−1 for CA-BMB, and 40.0mgg−1 for BMB. The results demonstrate that entrapment of ball-milled biochar in Ca-alginate provides a low-cost and high-effective way for the removal of aqueous Cd(II).

Temporal Changes in Cadmium Speciation in Brazilian Soils Evaluated Using Cd LIII-Edge XANES and Chemical Fractionation.

Chemical speciation of soil cadmium (Cd) dictates its mobility and potential toxicity in the environment. Our objective was to compare temporal changes in speciation of Cd(II) reacted with samples from six Brazilian soils having varying Cd(II) sorption capacities. Cadmium L-edge X-ray absorption near edge structure (XANES) analysis showed there were short-term changes in speciation after reaction with 4.45 mmol Cd kg for 0.5 and 6 h. Chemical fractionation evaluated changes in Cd extractability after reaction with 89 μmol Cd kg for up to 4 mo. The XANES spectral fits suggested that Cd(II) bound with organic matter was a dominant species in all samples, along with Cd(II) bound with iron and aluminum oxides or montmorillonite. In several samples, CdCl apparently precipitated from aqueous Cd(II) during drying. The XANES spectral fits typically showed <25% change in speciation between 0.5 and 6 h of reaction, and chemical fractionation showed significant ( < 0.05) temporal changes in Cd extractability over time in two samples. Our results suggest that Cd(II) discharged into these soils, such as that occurring as a release into the environment, would bind with soil organic matter and oxide minerals or remain dissolved, with little change in speciation in the months following release.

Remediation of Cadmium Toxicity by Sulfidized Nano-Iron: The Importance of Organic Material

Nanozerovalent iron (nZVI) is widely used for its ability to remove or degrade environmental contaminants. However, the effect of nZVI-pollutant complexes on organisms has not been tested. We demonstrate the ability of a sulfidized derivative of nZVI (FeSSi) to sorb cadmium (Cd) from aqueous media and alleviate Cd toxicity to a freshwater alga for 32 days. FeSSi particles removed over 80% of the aqueous Cd in the first hour and nearly the same concentration of free Cd remained unbound at the end of the experiment. We found that FeSSi particles with Cd sorbed onto them are an order of magnitude more toxic than FeSSi alone. Further, algal-produced organic material facilitates safer remediation of Cd by FeSSi by decreasing the toxicity of FeSSi itself. We developed a dynamic model to predict the maximum Cd concentration FeSSi can remediate without replacing Cd toxicity with its own. FeSSi can remediate four times as much Cd to phytoplankton populations when organic material is present compared to the absence of organic material. We demonstrate the effectiveness of FeSSi as an environmental remediator and the strength of our quantitative model of the mitigation of nanoparticle toxicity by algal-produced organic material.

Simultaneous removal of aqueous Zn2+, Cu2+, Cd2+, and Pb2+ by zeolites synthesized from low-calcium and high-calcium fly ash

In this study, zeolites were synthesized from low-calcium (LCZ) and high-calcium (HCZ) fly ash, respectively. Subsequently, the zeolites were tested for their removal effectiveness for four aqueous cations, namely, Zn2+, Cu2+, Cd2+, and Pb2+, as a function of contact time, pH value, adsorbent dosage, and initial concentration of heavy metals. Both zeolites were characterized by X-ray diffraction, X-ray fluorescence spectrometry, scanning electron microscopy, specific surface area, and cation exchange capacity. The results show that HCZ mainly consists of an unnamed zeolite (Na6[AlSiO4]6·4H2O), whereas LCZ mainly consists of faujasite-type zeolite. The optimum sorption conditions were pH = 6.0; adsorbent dosage = 1.0 g·L-1; temperature = 25 °C; contact time = 100 min; and initial heavy metal concentration = 100 mg·L-1. The sorption kinetics of the four aqueous cations on both LCZ and HCZ followed the pseudo-second-order kinetic model, and the sorption isotherm data fitted well with the Langmuir isotherm model. For LCZ, the maximum adsorption capacities of Zn2+, Cu2+, Cd2+, and Pb2+ were 155.76, 197.86, 123.76, and 186.22 mg·g-1, respectively. For HCZ, the values were 154.08, 183.15, 118.91, and 191.94 mg·g-1, respectively. The zeolites were regenerated by NaCl solution (1 mol·L-1) and showed high removal efficiency. In conclusion, zeolites produced by fly ash are promising materials for removing Zn2+, Cu2+, Cd2+, and Pb2+ from wastewater.

Green-synthesized CdS nano-pesticides: Toxicity on young instars of malaria vectors and impact on enzymatic activities of the non-target mud crab Scylla serrata

Currently, nano-formulated mosquito larvicides have been widely proposed to control young instars of malaria vector populations. However, the fate of nanoparticles in the aquatic environment is scarcely known, with special reference to the impact of nanoparticles on enzymatic activity of non-target aquatic invertebrates. In this study, we synthesized CdS nanoparticles using a green protocol relying on the cheap extract of Valoniopsis pachynema algae. CdS nanoparticles showed high toxicity on young instars of the malaria vectors Anopheles stephensi and A. sundaicus. The antimalarial activity of the nano-synthesized product against chloroquine-resistant (CQ-r) Plasmodium falciparum parasites was investigated. From a non-target perspective, we focused on the impact of this novel nano-pesticide on antioxidant enzymes acetylcholinesterase (AChE) and glutathione S-transferase (GST) activities of the mud crab Scylla serrata. The characterization of nanomaterials was carried out by UV–vis and FTIR spectroscopy, as well as SEM and XRD analyses. In mosquitocidal assays, LC50 of V. pachynema-synthesized CdS nanoparticles on A. stephensi ranged from 16.856 (larva I), to 30.301μg/ml (pupa), while for An. sundaicus they ranged from 13.584 to 22.496μg/ml. The antiplasmodial activity of V. pachynema extract and CdS nanoparticles was evaluated against CQ-r and CQ-sensitive (CQ-s) strains of Plasmodium falciparum. IC50 of V. pachynema extract was 58.1μg/ml (CQ-s) and 71.46μg/ml (CQ-r), while nano-CdS IC50 was 76.14μg/ml (CQ-s) and 89.21μg/ml (CQ-r). In enzymatic assays, S. serrata crabs were exposed to sub-lethal concentrations, i.e. 4, 6 and 8μg/ml of CdS nanoparticles, assessing changes in GST and AChE activity after 16days. We observed significantly higher activity of GST, if compared to the control, during the whole experiment period. In addition, a single treatment with CdS nanoparticles led to a significant decrease in AChE activity over time. The toxicity of CdS nanoparticles and Cd ions in aqueous solution was also assessed in mud crabs, showing higher toxicity of aqueous Cd ions if compared to nano-CdS. Overall, our results underlined the efficacy of green-synthesized CdS nanoparticles in malaria vector control, outlining also significant impacts on the enzymatic activity of non-target aquatic organisms, with special reference to mud crabs.

Quantitative and spectroscopic investigations of the co‐sorption of myo‐inositol hexakisphosphate and cadmium(II) on to haematite

SummaryThe interactions between phosphates, both inorganic and organic ones, and heavy metals on mineral surfaces affect their environmental fate and transport. In this research, we investigated the co‐sorption of myo‐inositol hexakisphosphate (IHP) and cadmium (Cd(II)) on to haematite at various pHs in batch experiments, zeta (ζ) potential measurement and in situ attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. In the haematite–IHP binary system, IHP formed inner‐sphere complexes on haematite in which some phosphate groups of the IHP molecule bonded with the haematite surface, and other dissociated phosphate groups were ionized. In the haematite–IHP–Cd ternary system, the presence of aqueous Cd(II) increases IHP sorption and the ζ potential of haematite relative to that in the haematite–IHP binary system. The enhancement is more obvious at higher pHs, reversing the initial pH dependence of IHP sorption in the binary system. Similarly, the coexisting IHP promotes the retention of Cd(II) on haematite. The ATR‐FTIR spectroscopy indicates the formation of two structurally distinct ternary surface complexes (the Hm–IHP–Cd surface complex and the Hm–Cd–IHP–Cd surface complex). Our results suggest that simultaneous sorption not only increases the sorption density of IHP and Cd(II), but also changes the surface complex configuration of IHP and Cd(II) on haematite.Highlights The interactions between IHP and Cd(II) on haematite were investigated. The presence of Cd(II) increases IHP sorption and vice versa. IHP and Cd(II) co‐sorption is enhanced as pH increases. Two structurally distinct ternary surface complexes form on haematite surfaces.

Equilibrium Modelling for Adsorption of Aqueous Cd(II) onto Turmeric: Linear versus Nonlinear Regression Analysis

Adsorption parameters determined from equilibrium modelling provides a powerful tool to understand adsorbate-adsorbent interaction mechanism but there is an on-going debate about pros and cons of linearizing isotherm equations. Therefore, in the present study, linear and nonlinear regression forms of Langmuir, Freundlich, D-R and Temkin equilibrium models were applied on experimental data obtained from batch adsorption of aqueous Cd(II) onto turmeric. Five error functions i.e. Marquardt’s PSD, Least Absolute Errors (LAE), Sum of Squared Residuals (SSR), Chi-square test (χ 2 ), Average Percent Error (APE) for nonlinear optimization were also applied to determine best fit adsorption model. Linearized as well as nonlinearized Freundlich model provided better fit as compared to other applied equilibrium models. Nonlinear error analysis further validated Freundlich isotherm as best fit model for experimental data. Comparison of linear and nonlinear regression suggested that nonlinearized isotherm equations provided more reliable fit for the adsorption data but it is more appropriate to evaluate goodness of fit after comparison between linearized and nonlinearized modelling parameters.

Cadmium ion adsorption by amine-modified activated carbon.

Cadmium (Cd) is one of the most toxic metals found in water and sediments. In the effort to develop an effective adsorbent for aqueous Cd removal, activated carbon (AC) was modified with an amino-terminated organosilicon (3-aminopropyltrimethoxysilane, APS). Response surface methodology was used to optimize selected operational parameters of adsorption of aqueous Cd by considering a central composite design with three input variables, temperature of the mixture solution, the contact time and feed ratio (APS/AC), on the surface modification. Results demonstrated that the strong Cd-binding amine ligands were effectively introduced onto the AC surfaces through the silanol reaction between carbon surface functional groups (-COOH, -COH) and APS molecules. The optimized preparation condition is 77 °C, 4 h and 2.1 ratio. The adsorbent presented a favorable adsorption of the aqueous Cd(II).

Growth and biochemical constituents of an indigenous cyanobacterium affected by heavy metal stress

A cyanobacterium having high relative abundance in sewage irrigated soil was isolated and identified as Lyngbya contorta. The species was tested for tolerance towards heavy metals, Cu2+, Zn2+, Ni2+and Cd2+ (0.5 to 10 mg/L) in single metal systems under controlled laboratory conditions. Our results show that the studied strain has a distinctive response towards each heavy metal, it was most affected by Ni2+ followed by Cu2+, Zn2+, Cd2+ ions. The studied strain showed better response as indicated by higher concentrations of sugar, proteins and photosynthetic pigments in aqueous Cd2+ solutions as compared to that at control. The incubation of cyanobacterial cells with lower concentrations of heavy metals (Cu2+, Zn2+, Ni2+) enhanced the growth rate, soluble proteins and photosynthetic pigments, while elevated concentrations were observed to be inhibitory. The present study demonstrates the capability of isolated indigenous species to withstand heavy metal stress at low concentrations and can be utilized for bioremediation of contaminated lands.

Sorption Process of Date Palm Biochar for Aqueous Cd (II) Removal: Efficiency and Mechanisms

Date palm biochar (BC) was prepared at two pyrolysis temperatures of 300 °C (BC-300) and 700 °C (BC-700) as sorbents for removing Cd from aqueous solutions in batch experiments. The results indicated that Cd removal efficiency was significantly affected by the initial pH (2–7) of aqueous solutions, with the lowest Cd adsorption at initial pH of 2. BC-700 was more effective in removing Cd from aqueous solution than BC-300. The maximum adsorption capacity of 43.58 mg g−1 was observed for BC-700 based on the Langmuir model, which was 1.6 times higher than that of BC-300 (26.96 mg g−1). Mechanistic evidences of Cd sorption onto BCs were identified by using the instrumental techniques of XRD and SEM or predicted from sorption isotherm and kinetic models. The Cd sorption onto BCs followed the pseudo-second order kinetics, suggesting chemisorption as one of the possible mechanisms of Cd interaction with BCs. However, XRD and SEM analyses of BCs before and after Cd sorption indicated that ion exchange and surface complexation could be the controlling mechanisms of Cd adsorption onto BC-300, while precipitation (as CdCO3) could be the operating mechanism of Cd sorption onto BC-700. Date palm waste, therefore, could possibly be converted to BC as an efficient sorbent for removal of Cd from aqueous media. However, the removal efficiency of BCs varies with different pyrolysis temperatures.

Structures of the Subnanometer Clusters of Cadmium Sulfide Encapsulated in Zeolite Y: Cd4S6+ and Cd(SHCd)46+

The structures of the subnanometer clusters of CdS that form in zeolite Y (FAU), prepared as follows, have been determined. A single crystal of Cd2+-exchanged zeolite Y was prepared by the exchange of Na75–Y (|Na75|[Si117Al75O384]–Y with aqueous Cd(NO3)2 at 294 K, followed by vacuum dehydration at 723 K (crystal 1). A second crystal, similarly prepared, was exposed to 6.7 × 104 Pa of dry H2S(g) for 6 h at 294 K and evacuated (crystal 2). Their structures were determined crystallographically using synchrotron X-rays and were refined using all data to the final error indices (calculated using only Fo > 4σ(Fo)) of R1/wR2 = 0.040/0.156 and 0.049/0.186, respectively. In crystal 1, Cd2+ ions primarily occupy sites I and II. In crystal 2, |Cd27(Cd4S6+)0.6(Cd(SHCd)46+)0.9H12|[Si117Al75O384]–FAU, tetrahedral Cd4S6+ ions center about 7.5% of the sodalite cavities and tetrahedral Cd(SHCd)46+ ions center about 11% of the supercages. In Cd(SHCd)46+, a Cd2+ ion at the center of a supercage bonds tetrahedrally to four S...

Characterization, dissolution and solubility of cadmium–calcium hydroxyapatite solid solutions at 25 °C

A series of cadmium–calcium hydroxyapatite solid solutions [Cd–Ca-HAP, (Ca1−xCdx)5(PO4)3(OH)] was synthesized and characterized, and then the dissolution of the prepared solids in aqueous solutions was experimentally studied. The element concentrations in the aqueous solutions were considerably influenced by the Cd/(Cd+Ca) atomic ratio of the Cd–Ca-HAP solids (XCd). For solids with high XCd (>0.6), the aqueous Ca2+ concentration increased gradually with time and reached a stable state after approximately 5040h of dissolution; the aqueous Cd2+ concentration increased rapidly with time and reached a peak value within 480–720h, and then decreased gradually and attained a stable state after 5040h of dissolution. For solids with low XCd (≤0.6), the aqueous Ca2+ concentration increased rapidly with time and reached a peak value after approximately 240–360h of dissolution, and then decrease slightly and are relatively stable after 720h; the aqueous Cd2+ concentration increased quickly with time and attained a peak value within 1h and then decreased gradually and attained a stable state after 480h of dissolution. The dissolution process of the solid samples with high XCd (>0.6) was different from that of the solids with low XCd (≤0.6), which can be related to a slight tendency of Cd2+ in preferring the M(2) sites and Ca2+ in occupying the M(1) sites in the apatite structure. The average solubility products (Ksp) were estimated for Cd5(PO4)3OH to be 10–64.62 (10–64.53–10–64.71) at 25°C and for Ca5(PO4)3OH to be 10–57.65 (10–57.56–10–57.79) at 25°C. The corresponding free energies of formation (ΔGfo) were −3970.47kJ/mol and −6310.45kJ/mol. The solubility of the solid solution (CdxCa1−x)5(PO4)3(OH) decreased with increasing XCd. For the dissolution at an initial pH of 2 and 25°C, plotting of the experimental data on the Lippmann diagram indicated that (Cd0.71Ca0.29)5(PO4)3(OH) dissolved stoichiometrically during the initial period and approached gradually up to the Lippmann solutus before overshooting it. Finally, the data points moved along the Lippmann solutus curve from right to left. The Cd5(PO4)3(OH)-rich solid phase was in equilibrium with the Cd-poor aqueous solution. These findings provided a better understanding of the processes controlling the solubility, transport and distribution of cadmium in the environment.

Effects of the acanthocephalan Polymorphus minutus and the microsporidian Dictyocoela duebenum on energy reserves and stress response of cadmium exposed Gammarus fossarum.

Amphipods are commonly parasitized by acanthocephalans and microsporidians and co-infections are found frequently. Both groups of parasites are known to have severe effects on their host. For example, microsporidians can modify host sex ratio and acanthocephalans can manipulate the behavior of the amphipod to promote transmission to the final host. These effects influence host metabolism in general and will also affect the ability of amphipods to cope with additional stressors such as environmental pollution, e.g., by toxic metals. Here we tested the effects of sub-lethal concentrations of cadmium on glycogen and lipid levels, as well as on the 70kDa heat shock protein (hsp70) response of field collected Gammarus fossarum, which were naturally infected with microsporidians and the acanthocephalan Polymorphus minutus. Infected and uninfected G. fossarum were exposed to a nominal Cd concentration of 4 µg/L, which resembled measured aqueous Cd concentration of 2.9 µg/L in reconstituted water for 7 d at 15 °C in parallel to an unexposed control. After exposure gammarids were snap frozen, weighed, sexed and tested for microsporidian infection by PCR. Only individuals containing the microsporidian Dictyocoela duebenum were used for the further biochemical and metal analyses. P. minutus infected amphipods were significantly smaller than their uninfected conspecifics. Mortality was insignificantly increased due to cadmium exposure, but not due to parasite infection. Microsporidian infection in combination with cadmium exposure led to increased glycogen levels in female gammarids. An increase of glycogen was also found due to interaction of acanthocephalan and microsporidian infection. Elevated lipid levels were observed in all groups infected with microsporidians, while acanthocephalans had the opposite effect. A positive correlation of lipid and glycogen levels was observed. The general stress response measured in form of hsp70 was significantly increased in microsporidian infected gammarids exposed to cadmium. P. minutus did not affect the stress response of its host. Lipid levels were correlated negatively with hsp70 response, and indicated a possible increased stress susceptibility of individuals with depleted energy reserves. The results of our study clearly demonstrate the importance of parasitic infections, especially of microsporidians, for ecotoxicological research.

Adsorption of aqueous Cd(II) and Pb(II) on activated carbon nanopores prepared by chemical activation of doum palm shell.

Non-uniformly sized activated carbons were derived from doum palm shell, a new precursor, by carbonization in air and activation using KOH, NaOH and ZnCl2. The activated carbon fibres were characterised by X-ray diffraction, N2 adsorption–desorption, scanning electron microscopy, particle size analysis and evaluated for Cd(II) and Pb(II) removal. The 40–50 nm size, less graphitic, mesoporous NaOH activated carbon yielded high adsorption efficiency, pointing largely to the influence surface area. The performance of the KOH based activated carbon was arguably explained for the first time in terms of crystallinity. The efficiencies of the mesoporous ZnCl2-formulated activated carbon diminished due to the presence of larger particles. Batch adsorption of divalent metals revealed dependence on adsorbent dose, agitation time, pH and adsorbate concentrations with high adsorption efficiencies at optimum operating parameters. The equilibrium profiles fitted Langmuir and Freundlich isotherms, and kinetics favoured pseudo-second order model. The study demonstrated the practicability of the removal of alarming levels of cadmium and lead ions from industrial effluents.

Competitive and Noncompetitive Batch Sorption Studies of Aqueous Cd(II) and Pb(II) Uptake ontoCoffea canephoraHusks,Cyperus papyrusStems, andMusaspp. Peels

Coffea canephora,Cyperus papyrus,andMusaspp. were studied for competitive and noncompetitive removal of aqueous Cd2+and Pb2+. The optimal conditions were pH 4.5 and agitation time 3.0 hours. Biomass constituent ions showed no interference effects whereas cation exchange capacity values corresponded to the sorption efficiencies. XRD spectroscopy revealed surface oxygen and nitrogen groups that provide binding sites for metal ions. The maximum sorption efficiency ranges for metal ions in noncompetitive media were 95.2–98.7% forC. canephora, 42.0–91.3% forC. papyrus,and 79.9–92.2% forMusaspp. and in competitive sorption 90.8–98.0% forC. canephora, 19.5–90.4% forC. papyrus,and 56.4–89.3% forMusaspp. The Pb2+ions uptake was superior to that of Cd2+ions in competitive and noncompetitive media. In competitive sorption synergistic effects were higher for Cd2+than Pb2+ions. The pseudo-second-order kinetic model fitted experimental data with0.917≤R2≥1.000for Pb2+ions and0.711≤R2≥0.999for Cd2+ions. The Langmuir model fitted noncompetitive sorption data with0.769≤R2≥0.999; moreover the Freundlich model fitted competitive sorption data with0.867≤R2≥0.989. Noncompetitive sorption was monolayer chemisorption whereas competitive sorption exhibited heterogeneous sorption mechanisms.

Facile preparation of highly luminescent CdTe quantum dots within hyperbranched poly(amidoamine)s and their application in bio-imaging

A new strategy for facile preparation of highly luminescent CdTe quantum dots (QDs) within amine-terminated hyperbranched poly(amidoamine)s (HPAMAM) was proposed in this paper. CdTe precursors were first prepared by adding NaHTe to aqueous Cd2+ chelated by 3-mercaptopropionic sodium (MPA-Na), and then HPAMAM was introduced to stabilize the CdTe precursors. After microwave irradiation, highly fluorescent and stable CdTe QDs stabilized by MPA-Na and HPAMAM were obtained. The CdTe QDs showed a high quantum yield (QY) up to 58%. By preparing CdTe QDs within HPAMAM, the biocompatibility properties of HPAMAM and the optical, electrical properties of CdTe QDs can be combined, endowing the CdTe QDs with biocompatibility. The resulting CdTe QDs can be directly used in biomedical fields, and their potential application in bio-imaging was investigated.

Modification of metal bioaccumulation and toxicity in Daphnia magna by titanium dioxide nanoparticles

Titanium dioxide (TiO2) nanoparticles are widely used in water treatments, yet their influences on other contaminants in the water are not well studied. In this study, the aqueous uptake, assimilation efficiency, and toxicity of two ionic metals (cadmium-Cd, and zinc-Zn) in a freshwater zooplankton, Daphnia magna, were investigated following 2 days pre-exposure to nano-TiO2. Pre-exposure to 1 mg/L nano-TiO2 resulted in a significant increase in Cd and Zn uptake from the dissolved phase. After the nano-TiO2 in the guts were cleared, the uptake rates immediately recovered to the normal levels. Concurrent measurements of reactive oxygen species (ROS) and metallothioneins (MTs) suggested that the increased metal uptake was mainly due to the increased number of binding sites provided by nano-TiO2 presented in the guts. Consistently, pre-exposure to nano-TiO2 increased the toxicity of aqueous Cd and Zn due to enhanced uptake. Our study provides the evidence that nano-TiO2 in the guts of animals could increase the uptake and toxicity of other contaminants.