Heavy metal pollution is a serious environmental problem. The presence of such metals in different areas of an ecosystem subsequently leads to the contamination of consumable products such as dietary and processed materials. Accurate monitoring of metal concentrations in various samples is of importance in order to minimize health hazards resulting from exposure to such toxic substances. For this purpose, it is essential to have a general understanding of the basic principles for different methods of elemental analysis. This article provides an overview of the most sensitive techniques of elementalanalysis such as atomic absorption/emission spectrometry, mass spectrometry, x-ray fluorescence, voltametry, and nuclear techniques. In addition, the article addresses some applications in a range of sample matrices.

Background: Traditional medicine mainly of herbal origin is widely used all around the world. Heavy metal contamination in such products is frequently reported. Accumulation of heavy metals in the human body leads to various health hazards. Thus, precise determination for such contaminants is required for safety assurance. Sample preparation is a significant step in spectroscopic analysis to achieve reliable and accurate results. Wet digestion methods are basically used for the dissolution of herbal product samples prior to elemental analysis.

Summary Sediment microbial fuel cells (SMFCs) are different from microbial fuel cells because they are completely anoxic and lack a membrane. SMFCs are a novel technology for the simultaneous production of renewable energy and bioremediation of heavy metals. Recently, SMFCs have attracted the attention of many researchers because of their moderate functioning parameters and ability to use a range of biodegradable substrates like glucose, glutamic acid, river water, cysteine, acetate, and starch. The inocula used in SMFCs include river sediment, marine sediment, and wastewater. For power generation, many exoelectrogens in SMFCs have the ability to transfer electrons from electrodes by using natural electron shuttles. Exoelectrogens use four primary pathways to transfer electrons to the electrodes, including short‐range electron transfer through redox‐active proteins, soluble electron shuttling molecules, long‐range electron transport by conductive pili, and direct interspecies electron transfer. The most dominant mechanism is long‐range electron transfer via conductive pili because pili have metal‐like conductivity. The powering by microbes is an emerging technique for the remediation of heavy metals from sediments. The pathways for transferring electrons in electrotrophs operate in the opposite direction from those in exoelectrogens. To further upgrade SMFC technology, this review targets the prototype, operating factors, working mechanisms, applications, and future perspectives of SMFCs. Copyright © 2017 John Wiley & Sons, Ltd.

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The industrial contamination of marine sediments with chromium, copper and nickel in Penang, Malaysia was addressed with bio-remediation, coupled with power generation, using in situ sediment microbial cells (SMFCs) under various conditions. The efficiency of aerated sediment microbial fuel cells (A-SMFCs) and non-aerated sediment microbial fuel cells (NA-SMFCs) was studied. The A-SMFCs generated a voltage of 580.5 mV between 50 and 60 days, while NA-SMFCs produced a voltage of 510 mV between 60 and 80 days. The cell design point for A-SMFCs was 2 kU, while for NA-SMFCs it was 200 U.In both SMFCs, the maximum current values relating to forward scanning, reverse scanning and oxidation/reduction peaks were recorded on the 80 th day. The anode showed maximum additional capacitance on the 80 th day (A-SMFC: 2.7 F cm À2; and NA-SMFC: 2.2 F cm À2). The whole cell electrochemical impedance using the Nyquist model was 21 U for A-SMFCs and 15 U for NA-SMFCs.After glucose enrichment, the impedance of A-SMFCs was 24.3 U and 14.6 U for NA-SMFCs. After 60 days, the A-SMFCs reduced the maximum amount of Cr(VI) to Cr(III) ions (80.70%) and Cu(II) to Cu(I) ions (72.72%), and showed maximum intracellular uptake of Ni(II) ions (80.37%); the optimum remediation efficiency of NA-SMFCs was after 80 days toward Cr(VI) ions (67.36%), Cu(II) ions (59.36%) and Ni(II) ions (52.74%). Both SMFCs showed highest heavy metal reduction and power generation at a pH of 7.0. SEM images and 16S rRNA gene analysis showed a diverse bacterial community in both A-SMFCs and NASMFCs. The performance of A-SMFCs showed that they could be exercised as durable and efficient technology for power production and the detoxification of heavy metal sediments. The NA-SMFCs could also be employed where anaerobic fermentation is required.

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Summary Performance of sediment microbial fuel cells (SMFCs) with aerated (A‐SMFC) and nonaerated (NA‐SMFC) cathodes was evaluated at different operating conditions in toxic metal removal and power generation. The A‐ and NA‐SMFC open‐circuit voltages were respectively about 665 and 275 mV, with quite steady performances for 120 days. The cell design points of both SMFCs were calculated by implementing polarization curves, and they were at 1 kΩ (power density 8.1 mW/m2 and current density 0.0504 mA/m2 with voltage 150 mV) for NA‐SMFC and 100 Ω (power density 252.81 mW/m2 and current density 0.954 mA/m2 with voltage of 275 mV) for A‐SMFC, respectively. Cathode potentials were at 30 kΩ 290 mV (NA‐SMFC) and 500 mV (A‐SMFC). As to the anode, at 30 KΩ, it was −180 mV (NA‐SMFC) and 190 mV (A‐SMFC). The voltammetry profiles of A‐SMFC showed maximum current (forward scan, 22.7 μA; reverse scan, −19.4 μA) followed by NA‐SMFC (forward scan, 11.3 μA; reverse scan, −9.5 μA). The cell design points of A‐SMFC and NA‐SMFC were altered after pH and temperature amendments at 200 and 700 Ω, respectively. As to metal removal rate, the maximum arsenic cadmium and lead removal was observed in A‐SMFC at pH 7.0 (77.70%, 90.86%, and 83.91%) and 45°C (66.22%, 79.03%, and 71.17%). Scanning electron microscopy confirmed, at pH 7.0 and 45°C, an optimal biofilm growth at cathode and anode graphite of both SMFCs. After 120 days of operation, genomic DNA was extracted from biofilms and analyzed for rDNA 16S sequences. Similarity search was performed by using Basic Local Alignment Search Tool algorithm against the National Center for Biotechnology Information Gen Bank showing Pseudomonas spp. dominance at both anode and cathode. The results revealed that the A‐SMFC system could be employed as an effective and long‐term tool for power generation as well as stimulated bioremediation of the polluted sediments.

The industrial contamination of marine sediments with mercury, silver, and zinc in Penang, Malaysia was studied with bio-remediation coupled with power generation using membrane less open (aerated) and closed (non-aerated) sediment microbial fuel cells (SMFCs). The prototype for this SMFC is very similar to a natural aquatic environment because it is not stimulated externally and an oxygen sparger is inserted in the cathode chamber to create the aerobic environment in the open SMFC and no oxygen supplied in the closed SMFC. The open and closed SMFCs were showed the maximum voltage generation 300.5 mV (77.75 mW/m2) and 202.7 mV (45.04 (mW/m2), respectively. The cyclic voltammetry showed the oxidation peak in open SMFCs at +1.9 μA and reduction peak at -0.3 μA but in closed SMFCs oxidation and reduction peaks were noted at +1.5 μA and -1.0 μA, respectively. The overall impedance (anode, cathode and solution) of closed SMFCs was higher than open SMFCs. The charge transfer impedance showed that the rates of substrate oxidation and reduction were very low in the closed SMFCs than open SMFCs. The Nyquist arc indicated that O2 act as electron acceptor in the open SMFCs and CO2 in the closed SMFCs. The highest remediation efficiency of toxic metals [Hg (II) ions, Zn (II) ions, and Ag (I) ions] in the open SMFCs were 95.03%, 86.69%, and 83.65% in closed SMFCs were 69.53%, 66.57%, and 65.33%, respectively, observed during 60–80 days. The scanning electron microscope and 16S rRNA analysis showed diverse exoelectrogenic community in the open SMFCs and closed SMFCs. The results demonstrated that open SMFCs could be employed for the power generation and bioremediation of pollutants.