Can gold assist in the global arsenic problem?: Insights from speciation and development of an on-site system

Lead Research Organisation: University of Liverpool
Department Name: Earth Surface Dynamics


Arsenic has been well known for its acute toxicity since the Middle Ages when poisoning occurred frequently. More recently, the debate around the death of Napoleon was a stark reminder of the harmful effect of this metalloid. Unfortunately, today, arsenic is not known for its acute toxicity but rather for its insidious chronic toxicity. In every continent, health problems related to arsenic are encountered. Absorbing high levels of arsenic during several years results in various cancers such as lung, bladder or skin cancer. The most recent and potentially catastrophic example of an on-going arsenic poisoning occurred in the 1970's, when millions of wells were drilled in Bangladesh and India to provide clean drinking water for the people. However, through dissolution processes of the arsenic naturally present in the bedrocks, millions of people are drinking contaminated water. This has been quoted as the biggest poisoning in human kind .Arsenic is present everywhere e.g. in food, water, soils, cigarettes or crops. The assessment of the toxicity of a sample is however difficult. Indeed, arsenic is found in the environment with four different valence states. Each of these can form complexes through association with other molecules and each of these complexes behaves differently in the environment: in terms of mobility, bioavailability (can they be absorbed with living organisms?) and toxicity. In order to be able to understand the toxicity of a sample, to predict the contamination of an area or to apply efficient technologies for the removal of arsenic in a contaminated site, we need to know what arseno species are present in this particular environment. There are different techniques currently used to perform such analysis. However, these techniques are all laboratory-based, generally very expensive and require a skilled operator. In addition, they cost both time and money: sampling, transport, storage and treatment of the sample have to be done before the measurement is finally achieved. Thus there is an incompatibility between the high demand on the number of samples to be analysed, especially in under-developed countries and the limited capacity of the few available (or affordable) measuring systems. The developments of cheap reliable systems that can be used on-site with a high spatial resolution are urgently needed to identify the contaminated sites and thus prevent potential intoxication.Very recently, in the group of Pr. van den Berg at the University of Liverpool, we developed a simple voltammetric method for the determination of the two main species of arsenic that are found in the majority of waters: arsenite and arsenate. The method was tested in marine samples of Liverpool Bay, in mineral water and tap water. This method is highly promising and has many advantages such as simplicity, sensitivity and reliability. The project intends to take further these advantages to optimise voltammetric procedures for the speciation of arsenic in natural systems: waters, plants and urine. This will include the development of smaller electrodes that are potentially much more efficient for the detection of As and other toxic metals of interest such as Mn, Sb or Hg. The optimised procedures/sensors will be tested on-site in a specifically designed analytical system that will be developed in collaboration with an industrial partner. This system should be reliable, robust, easy to use and battery powered to allow rapid on-site measurement. It is expected that a first commercial system will be available within two years.


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Description The first objective which consisted in further understanding of the analytical detection of arsenic in different types of water has been fulfilled. In particular, we published a new voltammetric method for the speciation of arsenic in groundwaters [1] that allowed the detection of arsenite at natural pH without oxygen removal and without any interference from antimonite. This work was novel in that the detection method was done by cathodic stripping voltammetry due to a novel process of adsorption of arsenite on the gold surface at neutral pH. This method was futher adapted to the conditions encountered in As contaminated areas such as West Bengal where high levels of Fe and Mn occur. In these conditions, addition of a strong complexing agent (EDTA) was required to remove Fe and Mn interferences. The method was successfully tested in a portable apparatus for the on-site (in the field) determination of arsenite [2]. In addition, methods were also developed for the simultaneous detection of total arsenic with copper Cu, lead Pb and mercury Hg [3] or for the detection of As(V) in conditions of neutral pH [4]. In this latter paper, we showed a novel electrochemical process whereby an intermediate cation (here Mn2+) can induce a chemical reduction of the pentavalent As(V). This method is promising as it should enable getting more insights into the mobility of arsenic in the environment ; An additional method for the detection of arsenite in seawater was also developed, again in conditions of neutral pH [5]. One of the most prominent interference in the electrochemical detection of arsenic is antimony. We found the region of pH and potential where Sb does not interfere with As detection and we also described the conditions where Sb detection is not interfered with As [6]. In focusing on this interference, a new cleaning procedure of the electrodes was developed [6]. Since using this cleaning procedure, reliability and reproducibility between different electrodes were significantly improved, greatly facilitating the efficient use of gold electrodes. This was a major finding. Together with the use of a small vibrating device on the working electrode, the resulting electrodes are very sensitive and efficient, suited for on-site analysis [2]. Within the course of this project, we extended the use of the vibrated electrode to other metals such as Cu[7,8], Pb and Cd on Bi film [9] and Pb on Hg film ([10],[11]).


Another objective was the development of small gold electrode structures that could potentially be used as voltammetric sensors. A scheme which enables a routine generation of small scaled metal structures was developed further [12]. Based on the electrochemical deposition of metal templated by patterned self-assembled monolayers (SAMs) and transfer of the electrode structure to another substrate, the main points were to reduce electrode dimensions, to extend the scheme to the generation of gold electrodes suitable for sensing and elucidate the complex relationship between SAM architecture, deposition parameters and quality of the electrode structures. Due to the different deposition characteristics of gold, SAM molecules different from those used previously for the deposition of copper had to be used which in turn required a change in deposition parameters. Line electrodes of 15 ?m wide, up to 3 mm long and contact pad areas of 200x400 ?m2 were successfully generated. Notably, simultaneous electrochemical metal deposition onto areas with very different geometries, i.e. pads and lines with grossly different length to width ratio was accomplished. Electrode structures in the sub-micrometre range required a change in SAM patterning technique from microcontact printing (?CP) used for the micrometre sized line electrodes to electron beam lithography. The deposition-lift off scheme was successfully extended to electrode structures with features around 100 nm in size [13]. An important finding relevant for future applications was that transfer of the electrode structures from the original to another substrate occurs with very high fidelity thus making metal nucleation and the initial stages of growth on the SAM modified master electrodes the step which determines the achievable resolution. In order to improve control over metal deposition, means to influence nucleation were investigated by varying the SAM terminating moieties. The specific architecture used for these SAMs turned out to allow for a systematic variation of functionality without compromising the structural quality [14]. This result is of fundamental importance for the generalisation of the deposition scheme as the SAM property can be matched to the specific requirements of the metal to be deposited.

The third objective was to assess the chemical speciation of As in xylem sap, the main question being to understand/assess a potential complexation of arsenite. The study was done on cucumbers due to their relative ease in producing xylem sap. They were hydroponically grown and a method was specifically developed to collect the sap [15]. Two different methods were used to investigate arsenic transport/speciation through the xylem sap which had never been done before. The first one consisted in looking at changes in the metabolic profile of the sap before and after short term stress with different As species[16]. It was clearly shown that upon As stress, the amount of produced sap decreased with levels of stress and that the amount of arsenic transported from roots to shoots decrease as arsenate stress levels increased. This way of mitigation or self-protection by shutting down sap transport processes under high stress is a mechanism that is not known but concurs with other observations. In addition, it was found that four organic compounds were up-regulated (i.e. increased) in presence of As(V) stress while one compound, identified as isoleucine, was down regulated [16].
Based on the knowledge gained on the analytical detection of arsenite, the method was adapted for the speciation of Sb(III) in pentavalent antimonial solutions which are widely used for the treatment of leischmaniasis which affect 2 million new people every year, with an estimated death toll of 50,000/y. We identified an instability of the Sb(III) species in acidic conditions which explains the wide disparity of the results found in the literature [17]. Moreover, the Sb(III) levels found in the solutions were much higher than previously reported which brings new insights into the mode of action of this medication towards leischmaniasis[17].

1. Gibbon-Walsh K, Salaün P, van den Berg CMG (2010) Arsenic speciation in natural waters by cathodic stripping voltammetry. Anal Chim Acta 662 (1):1-8. doi:10.1016/j.aca.2009.12.038
2. Gibbon-Walsh K, Salaün P, Uroic MK, Feldmann J, McArthur JM, van den Berg CMG (2011) Voltammetric determination of arsenic in high iron and manganese groundwaters. Talanta 85 (3):1404-1411. doi:10.1016/j.talanta.2011.06.038
3. Alves GMS, Magalhaes JMCS, Salaün P, van den Berg CMG, Soares HMVM (2011) Simultaneous electrochemical determination of arsenic, copper, lead and mercury in unpolluted fresh waters using a vibrating gold microwire electrode. Anal Chim Acta 703 (1):1-7
4. Gibbon-Walsh K, Salaün P, van den Berg CMG (2012) Determination of arsenate in natural pH seawater using a manganese-coated gold microwire electrode. Anal Chim Acta 710:50-57. doi:10.1016/j.aca.2011.10.041
5. Salaün P, Gibbon-Walsh KB, Alves GMS, Soares HMVM, van den Berg CMG (2012) Determination of arsenic and antimony in seawater by voltammetric and chronopotentiometric stripping using a vibrated gold microwire electrode. Anal Chim Acta 746:53-62. doi:10.1016/j.aca.2012.08.013
6. Salaün P, Gibbon-Walsh K, van den Berg CMG (2011) Beyond the Hydrogen Wave: New Frontier in the Detection of Trace Elements by Stripping Voltammetry. Anal Chem 83 (10):3848-3856. doi:10.1021/ac200314q
7. Gibbon-Walsh K, Salaün P, van den Berg CMG (2012) Pseudopolarography of copper complexes in seawater using a vibrating gold microwire electrode. The journal of physical chemistry A 116 (25):6609-6620
8. Chapman CS, Cooke RD, Salaün P, van den Berg CMG (2012) Apparatus for in situ monitoring of copper in coastal waters. Journal of environmental monitoring : JEM 14 (10):2793-2802. doi:10.1039/C2EM30460K
9. Bi Z, Chapman CS, Salaün P, van den Berg CMG (2010) Determination of Lead and Cadmium in Sea- and Freshwater by Anodic Stripping Voltammetry with a Vibrating Bismuth Electrode. Electroanalysis 22 (24):2897-2907. doi:10.1002/elan.201000429
10. Bi Z, Salaün P, Van den Berg CMG (In press) Study of bare and mercury coated vibrated carbon, gold and silver microwire electrodes for the determination of lead and cadmium in seawater by anodic stripping voltammetry. Electroanalysis
11. Bi Z, Salaün P, Van den Berg CMG (Submitted) Determination of lead and cadmium in seawater using a vibrating silver amalgam microwire electrode. Anal Chim Acta
12. She Z (2012) Generation of Micro/Nano Metallic Nanostructures using Self-Assembled Monolayers as Template and Electrochemistry. University of Saint Andrews,
13. She Z, DiFalco A, Haehner G, Buck M (2012) Electron-beam patterned self-assembled monolayers as templates for Cu electrodeposition and lift-off. Beilstein Journal of Nanotechnology 3:101-113. doi:10.3762/bjnano.3.11
14. She Z, Lahye D, Champness NR, Buhl M, Hamoudi H, Zharnikov M, Buck M (submitted).
15. Uroic MK (2011) The impact of arsenic species on the production and composition of xylem sap. University fo Aberdeen,
16. Uroic MK, Salaun P, Raab A, Feldmann J (2012) Arsenate Impact on the Metabolite Profile, Production, and Arsenic Loading of Xylem Sap in Cucumbers (Cucumis sativus L.). Frontiers in physiology 3:55-55
17. Salaün P, Frezard F Unexpectedly high levels of antimony (iii) in the pentavalent antimonial drug glucantime: insights from a new voltammetric approach . Anal Bioanal. Chem., DOI 10.1007/s00216-013-6947-5
Exploitation Route The findings obtained during the fellowship have contributed to the commercialisation of a gold wire electrode by an international company called Metrohm LTD. Metrohm is selling an adapted version of the gold wire electrode. We were however not involved in the development but our work is cited in their application procedure that can be found at:
Sectors Environment

Description Few analytical methods have been developed for the determination of arsenic and other metals. Up to now, the findings published in the scientific journals have been used in a research context. A potential contribution of the findings is in the commercialisation of a new sensor for arsenic based on the voltammetric detection on a gold wire. It is currently commercialised by Metrohm Ltd, international company. The sensor is named: scTrace Gold. The suggestion that our work has had some inputs into this development is based on the application published by Metrohm where our first paper on the detection of arsenic is cited. A company based in Australia called MEP Instruments ( is advertising the electrode that we developed for the on-line monitoring of trace metals. In March 2016, further funding from EPSRC through an Impact Acceleration Account grant was received to work with a UK company (Modern Water) in developing reproducible electrode sensors for the on-line unattended detection of trace metals. The sensors have been fabricated with a company based in Middlesex (ICT) and are currently being tested in laboratory conditions using the portable voltammetric system that is sold by Modern Water. These sensors will soon be tested in the fully automated system that is sold by Modern Water for long term monitoring of trace elements. It is hoped that they will display long term resilience and sensitivity to measure low arsenic levels (as well as other elements such as Hg, Cu or Sb).
Sector Environment
Impact Types Societal

Description Impact Acceleration Account Grant (IAA)
Amount £19,958 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 03/2016 
End 03/2017
Description Collaboraiton with Soares 
Organisation University of Porto
Country Portugal 
Sector Academic/University 
PI Contribution Training of Georgina Alves, PhD student at the University of Porto, during her 3 month visit in Liverpool. Georgina was formally supervised by Helena Soares.
Collaborator Contribution Analysis of samples. Development of new analytical method for the simultaneous determination of As, Hg, Pb and Cu in freshwater systems
Impact G.M.S. Alves, J.M.C.S. Magalhaes, P. Salaün, C.M.G. van den Berg, and H.M.V.M. Soares, Simultaneous electrochemical determination of arsenic, copper, lead and mercury in unpolluted fresh waters using a vibrating gold microwire electrode. Analytica Chimica Acta 703 (2011) 1-7. P. Salaün, K.B. Gibbon-Walsh, G.M.S. Alves, H.M.V.M. Soares, and C.M.G. van den Berg, Determination of arsenic and antimony in seawater by voltammetric and chronopotentiometric stripping using a vibrated gold microwire electrode. Analytica Chimica Acta 746 (2012) 53-62.
Start Year 2009
Description Collaboration Brest - Waeles 
Organisation University of Western Brittany
Country France 
Sector Academic/University 
PI Contribution Implementation of the analytical detection method in Brest for the detection of arsenic Supervision of PhD students during visits Contribution in analysis and write up of research papers
Collaborator Contribution Sample collection Improvement and developement of new analytical application for sulfide analysis in marine waters Write up of papers
Impact M. Waeles, J. Vandenhecke, P. Salaün, J.Y. Cabon, and R.D. Riso, External sources vs internal processes: what control As speciation and concentrations in the Penze estuary. Journal of Marine Systems 109-110 (2013) S261-S272 V. Aumond, M. Waeles, P. Salaun, K. Gibbon-Walsh, C.M.G. van den Berg, P.-M. Sarradin, and R.D. Riso, Sulfide determination in hydrothermal seawater samples using a vibrating gold micro-wire electrode in conjunction with stripping chronopotentiometry. Analytica Chimica Acta 753 (2012) 42-7.
Start Year 2008
Description Collaboration Frezard 
Organisation Federal University of Minas Gerais
Country Brazil 
Sector Academic/University 
PI Contribution Development of speciation methods for antimony in meglumine antimoniate, medication used for the treatment of leishmaniasis
Collaborator Contribution Provided sample and original idea for the work
Impact Salaun P, Frezard F (2013) Unexpectedly high levels of antimony (III) in the pentavalent antimonial drug Glucantime: insights from a new voltammetric approach. Anal Bioanal Chem 405 (15):5201-5214. doi:10.1007/s00216-013-6947-5 Kato KC, Morais-Teixeira E, Reis PG, Silva-Barcellos NM, Salaun P, Campos PP, Correa-Junior JD, Rabello A, Demicheli C, Frezard F (2014) Hepatotoxicity of Pentavalent Antimonial Drug: Possible Role of Residual Sb(III) and Protective Effect of Ascorbic Acid. Antimicrobial Agents and Chemotherapy 58 (1):481-488. doi:10.1128/aac.01499-13
Start Year 2011
Description Weiss-Imperial 
Organisation Imperial College London
Country United Kingdom 
Sector Academic/University 
PI Contribution Develop the analytical detection of arsenic on gold wire electrodes. Provide scientific support to the 2 PhD students regarding arsenic detection. Provide electrodes for analysis.
Collaborator Contribution Develop a highly specific adsorbent for arsenic. Provided water samples from Geotraces cruises for analysis Participates in measurements.
Impact "Molecular recognition and scavenging of arsenate from aqueous solution using bimetallic receptors", Chris D. Moffat, Dominik J. Weiss, Arun Shivalingam, Andrew J.P. White, Pascal Salaün, Ramon Vilar, Chemistry: A European Journal - Paper Accepted
Start Year 2009