Fabrication of a novel polyvinylpyrrolidone/chitosan-Schiff base/Fe2O3 nanocomposite for efficient adsorption of Pb(II) and Hg(II) ions from aqueous solution.

A novel magnetic polyvinylpyrrolidone/chitosan-Schiff base/Fe2O3 (PVP/CS-SB/Fe2O3) adsorbent was prepared by one-pot facile co-precipitation route for adsorption of Pb(II) and Hg(II) ions from aqueous solution. Fourier transform infrared-spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and Brunauer-Emmett-Teller (BET) were used to characterize the synthesized PVP/CS-SB/Fe2O3. The results predicted that the successfully synthesis of magnetic CSSB-PVP@Fe2O3. The effects of important factors such as pH solution, contact time, concentration of metal ions, adsorbent dose and co-existing ions on Pb(II) and Hg(II) adsorption were investigated. The maximum adsorption capacities of Pb(II) and Hg(II) ions at optimal conditions were 120 mg/g and 102.5 mg/g, respectively. The kinetic studies predicted that the adsorption followed the pseudo-second-order (PSO) model as chemisorption using the coordination of active sites of PVP/CS-SB/Fe2O3 with the metal ions and also n-π interactions. Reproducibility results predicted that the excellent regeneration ability after 6 adsorption cycles. According to the results of this work, the PVP/CS-SB/Fe2O3 nanocomposite is promising for Pb(II) and Hg(II) ions adsorption and can be potential as a simple, low-cost, high-efficient adsorbent for decontamination of other heavy metal ions from aqueous solution.

Identification of metal binding motifs in protein frameworks to develop novel remediation strategies for Hg2+ and Cr(VI).

Amino acid sequences in metal-binding proteins with chelating properties offer exciting applications in biotechnology and medical research. To enhance their application in bioremediation studies, we explicitly aimed to identify specific metal-binding chelating motifs in protein structures for two significant pollutants, such as mercury (Hg2+) and chromium Cr(V1). For this purpose, we have performed an extensive coordination chemistry approach by retrieving Hg2+ and Cr(V1) binding protein structures from the protein database and validated using the B-factor, a term defining uncertainty of the atoms and with occupancy to obtain the best binding motifs. Our analysis revealed that acidic amino acids like aspartic acid, glutamic acid, and basic amino acids such as cysteine and histidine are predominant in coordinating with these metals. The order of preference in Hg2+-bound structures is predicted to be Cys > His > Asp > Glu, and for Cr(V1) is His > Asp > Glu. Examination of the atomic coordinates and their distance from each metal revealed that the sulfur atoms of cysteine showing more preference towards Hg2+coordination with an atomic distance ranging from 1.5 to 2.9 Å. Likewise, oxygen atoms of aspartic acid, glutamic acid and nitrogen atoms of histidine are within 2 Å of Cr(V1) coordination. Based on these observations, we obtained C-C-C, C-X(2)-C-C-(X)2-C, H-C-H motifs for Hg2+, and D-X(1)-D, H-X(3)-E motif for Cr(V1) to be shared within the coordination space of 3 Å. As a future scope, we propose that the identified metal-binding chelating motifs are oligopeptides and can display on the surface of microorganisms such as Escherichia coli and Saccharomyces cerevisiae for effective removal of natural Hg2+ and Cr(V1) through biosorption. Hence, our results will provide the basis for futuristic bioremediation.

Levels of heavy metals in soil and vegetables and associated health risks in Mojo area, Ethiopia.

Health implications to the population due to the consumption of contaminated vegetables has been a great concern all over the world. In this study, the levels of heavy metals (Cr, Cd, Zn, Fe, Pb, As, Mn, Cu, Hg, Ni and Co) in soil and commonly consumed vegetables from Mojo area in central Ethiopia have been determined using Inductively Coupled Plasma Optical Emission Spectrophotometer (ICP-OES) and possible health risks due to the consumptions of the vegetables have also been estimated. The levels of As, Pb, Cd, Zn, Cu, Hg and Co were exceeded the reference level in agricultural soil. Likewise, As, Pb, Cd, Cr and Hg levels exceeded the recommended values in vegetable samples with concentrations ranging from 1.93-5.73, 3.63-7.56, 0.56-1.56, 1.49-4.63 and 3.43-4.23 mg/kg, respectively. It was observed that leafy vegetable (cabbage) has accumulated heavy metals to greater extent compared with tomato. The estimated daily intake (EDI) of toxic metals due to the consumption of the vegetables were below the maximum tolerable daily intake (MTDI). However, the total health quotient (THQ), calculated based on EDI of the heavy metals were found > 1 for As and Hg due to tomato consumption and for As, Hg and Co due to cabbage consumption, suggesting significant health risk. The health index (HI) due to the intake of toxic metals from the consumption of both vegetables were much > 1, with HI values of 7.205 and 15.078 due to tomato and cabbage consumption, respectively. This clearly suggests the possible adverse health effect to adult population from the consumption of tomato and cabbage from the study area. The total cancer risk (TCR) analysis have also revealed the potential adverse cancer risk induced by As, Cd, Hg, and Ni from the consumption of both tomato and cabbage as their TCR values were above the threshold level. Based on the results of this study, there would be a significant health risk (both non-carcinogenic and carcinogenic) to the consumer associated with the consumption of cabbage and tomato being cultivated in Mojo area. Consequently, we recommend a strict regulatory control on the safety of vegetables originated from the study area.

Studying absorbance properties and mercury remediation capabilities of gold-graphene oxide-iron oxide (Au-GO-Fe3O4) nanoparticle systems.

Mercury pollution is a rampant problem in many economically significant Philippine freshwater ecosystems. Communities dependent on these freshwater sources are therefore at risk for exposure to harmful levels of mercury. Various formulations of a novel gold-graphene oxide-iron oxide (Au-GO-Fe3O4) hybrid nanoparticle system were created and subjected to UV-Vis spectroscopy to determine optimal formulations that would best serve as potential substrates for Surface-Enhanced Raman Spectroscopy (SERS) detection of mercury. Optimal formulations of Au-GO-Fe3O4 were also introduced into mercury-polluted environments to evaluate its ability to remove mercury from both water and biological tissues. Spectroscopic analysis revealed that Fe3O4-rich formulations of Au-GO-Fe3O4 had the greatest potential to boost Raman signal intensities of mercury due to red shifting of absorbance peaks and overall increased absorbance across visible wavelengths resulting in the inclusion of greater areas underneath absorbance peaks. Mercury remediation experiments likewise demonstrated Au-GO-Fe3O4 to significantly reduce average concentrations of mercury from 1.67 to 0.82 ppm in polluted water samples - corresponding to a mercury removal efficiency of 50.9% and a mercury adsorption capacity of 5.89 mg/g. The results highlight the viability of Au-GO-Fe3O4 to function as both substrate for SERS detection of mercury and as effective adsorbent for mercury remediation.

One-pot synthesis of multi-functional and environmental friendly tannic acid polymer with Fe3+ and formaldehyde as double crosslinking agents for selective removal of cation pollutants.

A novel multi-functional and environmental friendly tannic acid polymer (Fe3+-TA-HCHO) with Fe3+ and formaldehyde as double crosslinking agents together with cysteine as heteroatom source was prepared by a one-pot hydrothermal method. Characterization with transmission electron microscope (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR), and elemental analysis demonstrated that the Fe3+-TA-HCHO possessed uniform structure and particle size as well as plentiful functional groups. The resulted Fe3+-TA-HCHO material as a adsorbent to remove methylene blue, sunset yellow, Pb2+, Hg2+, and AsO33- from water. The results suggested that Fe3+-TA-HCHO polymer (pHpzc is 2.33) showed different adsorption properties for anionic pollutants (sunset yellow and AsO33-) and cationic pollutants (methylene blue, Pb2+, and Hg2+). The material exhibited remarkable selectivity for adsorption and separation of pollutants. The maximum adsorption capacities calculated from Langmuir model for methylene blue, Pb2+, and Hg2+ were 154.32, 819.67, and 699.30 mg g-1, respectively. This is the first time that tannic acid polymer is synthesized by double crosslinking method, which not only developed a promising adsorbent for selective removal of cation pollutants, but also opened up a new avenue for synthesis and application of tannic acid polymer.

A sulfur-resistant CuS-modified active coke for mercury removal from municipal solid waste incineration flue gas.

Adsorption is a typical method for air pollutant removal from flue gas. A CuS-modified active coke (CuS/AC) sorbent was developed to improve the elemental mercury removal efficiency from municipal solid waste incineration (MSWI) flue gas. The influences of the loading amount of CuS, reaction temperature, and flue gas components including O2, SO2, H2O, and HCl on Hg0 removal efficiency were investigated, respectively. The results showed that the mercury adsorption capacity of CuS/AC(20%) sorbent was about 7.17 mg/g with 50% breakthrough threshold, which is much higher than that of virgin active coke. The analysis of XPS indicated that HgS was the main species of mercury on spent CuS/AC, which implied that adsorption and oxidation were both included in Hg0 removal. S22- played a vital role in the oxidation of physically adsorbed Hg0. Meanwhile, the common components of MSWI flue gas exhibited no significant inhibition effect on Hg0 removal by CuS/AC sorbent. CuS/AC sorbent is a promising sorbent for the mercury removal from MSWI flue gas.

Application of Iron-Based Materials for Remediation of Mercury in Water and Soil.

Mercury contamination in soil and water has become a major concern to environmental quality and human health. Among the existing remediation technologies for mercury pollution control, sorption via iron-based materials has received wide attention as they are environmental friendly and economic, and their reactivity is high and controllable through modulating the morphology and surface properties of particulate materials. This paper aimed to provide a comprehensive overview on environmental application of a variety of iron-based sorbents, namely, zero valent iron, iron oxides, and iron sulfides, for mercury remediation. Techniques to improve the stability of these materials while enhancing mercury sequestration, such as nano-scale size control, surface functionalization, and mechanical support, were summarized. Mechanisms and factors affecting the interaction between mercury and iron-based materials were also discussed. Current knowledge gaps and future research needs are identified to facilitate a better understanding of molecular-level reaction mechanisms between iron-based materials and mercury and the long-term stability of the immobilized mercury.

An electrochemical sensor for attomolar determination of mercury(II) using DNA/poly-L-methionine-gold nanoparticles/pencil graphite electrode.

The present work describes an ultrasensitive electrochemical sensor for determination of mercury(II) using deoxyribonucleic acid/poly-L-methionine-gold nanoparticles/pencil graphite electrode (DNA/PMET-AuNPs/PGE). To fabricate this biosensor, L-methionine (L-MET) was electropolymerized on the PGE surface followed by simultaneous electrochemical entrapment of AuNPs. Next, DNA was immobilized on the PMET-AuNPs/PGE by applying a 0.5 V potential. The surface area of modified and unmodified electrodes was determined by chronocoulometric technique. Hg2+ was detected in the linear dynamic range of 0.1 aM to 0.1 nM, and the detection limit was determined as 0.004 aM using square wave anodic stripping voltammetry (SWASV) under optimized conditions. The DNA/PMET-AuNPs/PGE demonstrated good selectivity toward Hg2+ against other metal ions such as V4+, Pb2+, Cr3+, Cd2+, Cu2+, Zn2+, Sn2+, In3+, Ge4+, and Fe3+. Real samples studies were carried out in sea water and fish samples.

Criminal mercury vapor poisoning using heated tobacco product.

We report an unusual case of mercury vapor poisoning from using a heated tobacco product. The suspect had added grains of mercury into 20 cigarettes in a pack. When a 36-year-old Japanese man inserted one of these cigarettes into the battery powered holder, it was heated to a temperature of 350 °C, and he inhaled vaporized mercury. After using 14 of the cigarettes over 16 h, he noticed he had flu-like symptoms so he visited the hospital. Although no physical abnormalities were revealed, 99 µg/L of mercury was detected in his serum sample. His general condition improved gradually and his whole blood mercury level had decreased to 38 µg/L 5 days later. When the remaining six cigarettes in the pack were examined, many metallic grains weighing a total of 1.57 g were observed. Energy dispersive X-ray fluorescence spectrometry confirmed the grains as elemental mercury. Accordingly, the victim was diagnosed with mercury poisoning. Because the mercury was incorporated into cigarettes, an unusual and novel intoxication occurred through the heating of the tobacco product. Both medical and forensic scientific examination confirmed this event as attempted murder.

Simple synthesis and characterization of l-Cystine functionalized δ-FeOOH for highly efficient Hg(II) removal from contamined water and mining waste.

l-Cystine functionalized δ-FeOOH nanoparticles (Cys-δ-FeOOH) were prepared by a cheap and straightforward method for using as an adsorbent of Hg(II) in aqueous solution. X-ray diffraction (XRD), attenuated total reflectance infrared spectroscopy (ATR-IR), and Raman spectroscopy confirmed that Cys-δ-FeOOH was successfully synthesized. Cys-δ-FeOOH with 14 nm crystal size, 34 m2 g-1 surface area, and 9 nm pore size were produced. The functionalization of the δ-FeOOH surface with cysteine decreases the point of zero charge of the iron oxyhydroxide from 8.4 in δ-FeOOH to 5.7 in Cys-δ-FeOOH, which is beneficial for the adsorption of Hg(II) near neutral pH. The maximum Hg(II) adsorption capacity of the δ-FeOOH and Cys-δ-FeOOH at pH 7 were found to be 35 mg g-1 and 217 mg g-1, respectively. The kinetics data were best fitted by a pseudo-second-order model, suggesting chemical adsorption on the surface and pores of Cys-δ-FeOOH nanoparticles. Finally, δ-FeOOH and Cys-δ-FeOOH filters were constructed for purifying mercury-contaminated water. The filters were highly efficient to treat mercury-contaminated water from a Brazilian river, reducing the concentration of mercury in water to values below the allowed limits by the current legislation.

Stability of mercury on a novel mineral sulfide sorbent used for efficient mercury removal from coal combustion flue gas.

Nano-structured zinc sulfide (Nano-ZnS) has been demonstrated to be a promising alternative to activated carbon (AC) for controlling mercury emission from coal combustion flue gas. The ultimate fate of the mercury-laden Nano-ZnS after mercury capture is mostly disposed in landfill with fly ashes. Thus, the stability of mercury adsorbed on the Nano-ZnS is of considerable significance in the secured disposal of fly ash after mercury removal and in the commercial application of the Nano-ZnS sorbent for removal of mercury from coal combustion flue gas. In this work, a modified toxicity characteristic leaching procedure (TCLP) was conducted to evaluate the leachability of mercury on the Nano-ZnS. The effects of leachate pH value, leaching time, liquid-to-solid ratio, and acid rain types on mercury leaching from the mercury-laden Nano-ZnS were systematically investigated. The TCLP results show that the concentration of mercury in leachate was far below the safe limit (200 µg/L) as imposed by the US Environmental Protection Agency (EPA) for classifying a material as a hazardous waste. All the key parameters that generally affected metal leaching rate exhibited slight effect on mercury leaching from the mercury-laden Nano-ZnS. Leaching tests at various highly severe conditions resulted in less than 0.01% mercury leaching from the mercury-laden Nano-ZnS. Sequential selective extraction tests demonstrated that mercury sulfide (HgS) was the dominant adsorption product on the Nano-ZnS, which guaranteed the excellent stability of mercury adsorbed on the Nano-ZnS. Graphic abstract ᅟ.

Synthetic coal fly ash-derived zeolites doped with silver nanoparticles for mercury (II) removal from water.

Coal fly ash-derived zeolites have attracted considerable interest in the last decade due to their use in several environmental applications such as the removal of dyes and heavy metals from aqueous solutions. In this work, coal fly ash-derived zeolites and silver nanoparticles-impregnated zeolites (nanocomposites) were synthesized and characterized by TEM/EDX, SEM/EDX, XRD, XRF, porosimetry (BET), particle size analysis (PSA) and zeta potential measurements. The synthesized materials were used for the removal of Hg2+ from aqueous solutions. The results demonstrated that nanocomposites can remove 99% of Hg2+, up to 10% and 90% higher than the removal achieved by the zeolite and the parent fly ash, respectively. Leaching studies further demonstrated the superiority of the nanocomposite over the parent materials. The Hg2+ removal mechanism is complex, involving adsorption, surface precipitation and amalgamation.

Insight into elemental mercury (Hg0) removal from flue gas using UV/H2O2 advanced oxidation processes.

Elemental mercury (Hg0) emitted from coal-fired power plants and municipal solid waste (MSW) incinerators has caused great harm to the environment and human beings. The strong oxidized •OH radicals produced by UV/H2O2 advanced oxidation processes were studied to investigate the performance of Hg0 removal from simulated flue gases. The results showed that when H2O2 concentration was 1.0 mol/L and the solution pH value was 4.1, the UV/H2O2 system had the highest Hg0 removal efficiency. The optimal reaction temperature was approximately 50 °C and Hg0 removal was inhibited when the temperature was higher or lower. The yield of •OH radicals during UV/H2O2 reaction was studied by electron paramagnetic resonance (EPR) analysis. UV radiation was the determining factor to remove Hg0 in UV/H2O2 system due to •OH generation during H2O2 decomposition. SO2 had little influence on Hg0 removal whereas NO had an inhibitory effect on Hg0 removal. The detailed findings for Hg0 removal reactions over UV/H2O2 make it an attractive method for mercury control from flue gases.

Adsorption of mercury by activated carbon prepared from dried sewage sludge in simulated flue gas.

Conversion of sewage sludge to activated carbon is attractive as an alternative method to ocean dumping for the disposal of sewage sludge. Injection of activated carbon upstream of particulate matter control devices has been suggested as a method to remove elemental mercury from flue gas. Activated carbon was prepared using various activation temperatures and times and was tested for their mercury adsorption efficiency using lab-scale systems. To understand the effect of the physical property of the activated carbon, its mercury adsorption efficiency was investigated as a function of its Brunauer-Emmett-Teller (BET) surface area. Two simulated flue gas conditions, (1) without hydrogen chloride (HCl) and (2) with 20 ppm HCl, were used to investigate the effect of flue gas composition on the mercury adsorption capacity of activated carbon. Despite very low BET surface area of the prepared sewage sludge activated carbons, their mercury adsorption efficiencies were comparable under both simulated flue gas conditions to those of pinewood and coal activated carbons. After injecting HCl into the simulated flue gas, all sewage sludge activated carbons demonstrated high adsorption efficiencies, that is, more than 87%, regardless of their BET surface area. IMPLICATIONS: We tested activated carbons prepared from dried sewage sludge to investigate the effect of their physical properties on their mercury adsorption efficiency. Using two simulated flue gas conditions, we conducted mercury speciation for the outlet gas. We found that the sewage sludge activated carbon had mercury adsorption efficiency comparable to pinewood and coal activated carbons, and the presence of HCl minimized the effect of physical property of the activated carbon on its mercury adsorption efficiency.

Evaluation of porogen factors for the preparation of ion imprinted polymer monoliths used in mercury removal.

In the present study, ion imprinted polymer monoliths (IIPMs) were developed to overcome the limitations of ion imprinted polymer particles (IIPPs) used for the removal of Hg(II) ions from waste water samples. The adsorbents preparation, characterization and Hg(II) removal were very well reported. The IIPMs on porogen optimization was prepared using the molding technique with Hg(II) as a template ion, [2-(methacryloyloxy)ethyl]trimethylammonium cysteine (MAETC) as ligand, methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylamide (EGDMA) as cross-linker, benzoyl peroxide as an initiator and methanol and acetonitrile as porogen in the polypropylene tube (drinking straw) as mold. The IIPMs prepared with higher volumes of porogen were indicated to have a good adsorption rate for the Hg(II) removal along with good water permeability and larger porosity as compared to a lower volume of porogen. The IIPMs prepared using the binary porogen were able to improve the porosity and surface area of the monolithic polymers as compared to the single porogen added IIPMs. Finally, we indicate from our analysis that the IIPM having the efficient capacity for the Hg(II) ions is easy to prepare, and has higher water permeability along with high porosity and high adsorption capacity and all these factors making it one of the suitable adsorbent for the successful removal of Hg(II) ions.

l-Cysteine functionalized bagasse cellulose nanofibers for mercury(II) ions adsorption.

Presence of mercury ions in water, even in trace amounts, is a serious environmental hazard. Hence, there is imperative need to develop innovative and environmentally-friendly materials for their removal from wastewaters. In the present study, cellulose nanofibers (CNFs) extracted from bagasse was esterified with l-cysteine to yield thiol and amine functionalized green material (Cys-CNFs) for removal of Hg2+ ions. The Cys-CNFs were well characterized by SEM, TEM, FTIR, EDS and XRD and evaluated for selective removal of Hg2+ ions from the simulated wastewater. It was observed that Cys-CNFs adsorb Hg2+ ions even at a very low concentration of 1.0mg/L and it exhibited a maximum adsorption capacity of 116.822mgg-1. Kinetic analysis of the data revealed that pseudo-second order kinetics and Langmuir isotherm were followed for adsorption of Hg2+ ions.

Purification of Hg0 from flue gas by wet oxidation method and its mechanism: a review.

The vast majority of Hg2+ can be removed while elemental mercury (Hg0) can hardly be removed due to its characteristic of high volatility and insolubility in water. Till now, how to oxidize Hg0 to Hg2+ is the key for the purification of Hg0, especially when there are others pollutants, such as HCl, SO2, and NOx. In this review, the method and mechanism of Hg0 purification from flue gas by H2O2, KMnO4, NaClO2, and O3 are reviewed comprehensively. It is concluded that the oxidation of Hg0 mainly depends on the electronic supply efficiency from the solution. The Fenton reagent, composed of H2O2 and metal cations, is superior to O3 and the solution of KMnO4 and NaClO2. Moreover, HCl, SO2, and NOx in the flue gas can influence the oxidation and purification mechanism of Hg0. It is found that HCl in flue gas had obvious auxo-action on the oxidation of mercury, and SO2 and NOx have different effects on the oxidation of Hg0 with the change of compositions and concentration of pollutants in the flue gas. In general, SO2 and NOx can slightly promote the oxidation of Hg0 due to the synergistic effect.

A portable RGB sensing gadget for sensitive detection of Hg2+ using cysteamine-capped QDs as fluorescence probe.

A facile one-pot method was proposed to synthesis cysteamine capped CdTe QDs with a high quantum yield 30%. In the synthesis process, nitrogen protection, ultrasonic treatment, and light irradiation were unnecessary. Additionally, potassium tellurite was used instead of Te powder as Te source, avoiding of the time-consuming Te powder dissolution process. The prepared QDs were found to be Hg2+ sensitive. The detection linear range for Hg2+ was from 5 to 300nM, and the detection limit was calculated to be 1nM. The detection mechanism was mainly ascribed to the electron transfer from cysteamine capped QDs to Hg2+, resulting in a fluorescence quenching phenomenon. In addition, we developed a portable RGB sensing gadget with the QDs as fluorescence probe for Hg2+ detection, and the linear range was from 5 to 200nM. Furthermore, the gadget was applied for Hg2+ detection in tap water sample. The results showed that the average recoveries in real tap water sample were in the range from 97.2% to 115.3%, which indicated that accuracy and precision were satisfactory for practical application requirements.

Facile Chip-Based Array Monolithic Microextraction System Online Coupled with ICPMS for Fast Analysis of Trace Heavy Metals in Biological Samples.

Trace heavy metals have great impact on biological system; therefore, it is essential to develop suitable analytical methods for the determination of trace heavy metals in biological samples to elucidate their biochemical and physiological functions in organisms. Herein, we presented a chip-based array monolithic microextraction system and combined it with inductively coupled plasma mass spectrometry (ICPMS) for online analysis of trace Hg, Pb, and Bi in real-world biological samples. Six ethylenediamine modified poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (poly(GMA-co-EDMA-NH2)) capillary monolithic columns were embedded parallelly in microchannels of a microfluidic chip for array monolithic microextraction. Various parameters affecting the chip-based array monolithic microextraction of target metals were investigated. The sample throughput of the proposed method was 16 h-1, with the limits of detection for Hg, Pb, and Bi of 23, 12, and 13 ng L-1, respectively. The developed method was validated by the determination of trace Hg, Pb, and Bi in HepG2 cells and human urine samples, and the recoveries for the spiked samples were in the range of 90.4-102%. This chip-based array monolithic microextraction system is easy to prepare, and the proposed online analytical system provides a new platform for trace elements analysis in biological samples with the merits of high sample throughput, high sensitivity, and low sample/reagents consumption.

Functional characterization of Gram-negative bacteria from different genera as multiplex cadmium biosensors.

Widespread presence of cadmium in soil and water systems is a consequence of industrial and agricultural processes. Subsequent accumulation of cadmium in food and drinking water can result in accidental consumption of dangerous concentrations. As such, cadmium environmental contamination poses a significant threat to human health. Development of microbial biosensors, as a novel alternative method for in situ cadmium detection, may reduce human exposure by complementing traditional analytical methods. In this study, a multiplex cadmium biosensing construct was assembled by cloning a single-output cadmium biosensor element, cadRgfp, and a constitutively expressed mrfp1 onto a broad-host range vector. Incorporation of the duplex fluorescent output [green and red fluorescence proteins] allowed measurement of biosensor functionality and viability. The biosensor construct was tested in several Gram-negative bacteria including Pseudomonas, Shewanella and Enterobacter. The multiplex cadmium biosensors were responsive to cadmium concentrations ranging from 0.01 to 10µgml-1, as well as several other heavy metals, including arsenic, mercury and lead at similar concentrations. The biosensors were also responsive within 20-40min following exposure to 3µgml-1 cadmium. This study highlights the importance of testing biosensor constructs, developed using synthetic biology principles, in different bacterial genera.