Mini review

The Importance of Chromium Speciation in Environmental Relevant Matrices

Spyros Foteinis¹*, Chatizisymenon² and Nikolaos G Kallithrakas Kontos³

¹Research Centre for Carbon Solutions, Heriot-Watt University, UK

²Senior Lecturer, School of Engineering, University of Edinburg, Scotland

³School of Mineral Resources Engineering, Technical University of Crete, Greece

Submission: April 24, 2021;Published: July 12, 2021

*Corresponding author: Spyros Foteinis, Research Centre for Carbon Solutions, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK

How to cite this article: Spyros F, Chatizisymenon, Nikolaos G Kallithrakas K. Clinical Benefits of Light Protection in a Human IVF Laboratory. Organic & Medicinal Chem IJ. 2021; 11(1): 555802. DOI: 10.19080/OMCIJ.2021.11.555802

Abstract

Chromium (Cr) is released to the environment by industrial activities such as metallurgy, power generation, leather tanning, and pigments. It typically occurs in its trivalent (Cr(III) or Cr³⁺) or hexavalent (Cr(VI) or Cr⁶⁺) form, with the first being an essential trace element and the latter being highly toxic, carcinogenic, mutagenic, and teratogenic even at trace concentrations. Therefore, chromium’s effects on living organisms grossly depend on its chemical form/species rather than its total concentration. For this reason, research has focus on Cr speciation in different environmental relevant matrices and particularly in water and foodstuffs. Online (usually HPLC/ICP-MS) and offline (e.g., ET-AAS, F-AAS, ICP-MS, and X-ray spectroscopy) analysis are employed, however the latter often requires a preconcentration/extraction step. During the past few years, simpler and/or more robust techniques based on electrochemical sensing, microfluidic paper-based analytical devices, polymer dots, solid-phase extraction, and colorimetric sensors have been also proposed or modified to improve Cr sensing and speciation.

Keywords: Chromium speciation; Environmental contamination or pollution; Cloud point microextraction; Dispersive micro-solid phase extraction (DMSPE); Analytical chemistry

Introduction

Chromium (Cr), from the Greek word ‘χρώμα’ (color), is a naturally occurring element that is encountered in its trivalent (Cr(III) or Cr³⁺) or hexavalent (Cr(VI) or Cr⁶⁺) form, which are its most stable valence states [1]. Other forms, such as Cr(II), Cr(IV), and Cr(V) are very unstable and they result from the oxidation and reduction reactions of Cr(III) and Cr(VI), respectively [2]. Owing to its unique properties, Cr(III) is widely used in electroplating, alloys, dyes, pigments, leather, anti-corrosion, and other industrial applications [3]. As such, large quantities of Cr have found their way into different environmental compartments, particularly after the industrial revolution [4]. In trace concentrations Cr(III) is considered an essential nutrient [5], since it helps regulate carbohydrate, lipid, and protein metabolism [6]. Nonetheless, in higher concentrations Cr(III) is considered an important environmental contaminant and has been linked with reproductive toxicity, embryotoxicity, dermatitis, carcinogenicity, and increase risks of diabetes and cardiovascular disease, along with DNA, protein, and lipid damage [3].

Nonetheless, the main problem lies with Cr(VI) occurrence in the environment, since even at trace concentrations Cr(VI) is a highly toxic, carcinogenic, mutagenic, and teratogenic [6]. Therefore, even though the estimation of the total Cr concentration is relatively simple to be determined [7], it does not provide insight since the effects of Cr contamination to living organisms are mainly linked to its species rather than its total concentration [2]. Cr is typically absorbed by living organisms either through inhalation (e.g., during coal combustion for power generation Cr(VI) can be generated and released to the atmosphere [4]) or the digestive tract (according to the World Health Organization (WHO) Cr(VI) concentration in drinking water should be 0.05 mg L−1 or below [8]) [1]. In terms of Cr speciation, foodstuffs such as plants, fish, boiled wheat, mushrooms, beer, and particularly meat, dairy products, bread, and tea which are considered as the main sources of Cr in human diet, have been examined [9]. Biological samples, including urine, whole blood, serum, plasma along with tissues, saliva and joint effusion have also been examined in terms of Cr species [1]. Cr speciation is achieved either using online (HPLC/ICP-MS) or offline (ET-AAS, F-AAS, ICP-MS) techniques, with research making large strides during the past few years in introducing new or optimising existing techniques.

Recent advances in Cr speciation

Cr is typically measured, at trace levels, using inductively coupled plasma mass spectrometry (ICP-MS) or optical emission spectrometry (ICP-OES), atomic absorption spectrometry (AAS), and spectrophotometry [8]. For trace elements analysis ICP-MS is considered as one of the most powerful technique, owing to fast and reliable ultra trace (sub-ppb) analysis and its multi-element capabilities [2,10]. However, it cannot distinguish between different element species [11] and therefore for online analysis ICP-MS is usually coupled with HPLC [2]. For offline analysis AAS, ICP-MS or OES, and spectrophotometry are typically used, however a preconcetration/extraction step is required for speciation analysis [12]. In foodstuffs Cr speciation is achieved through selective extraction, using alkaline media such as a mixture of NaOH/Na2CO3 or NaOH/NH4NO3, prior to determination by different online or offline analytical techniques [9]. This is also the case for Cr speciation in biological samples, however different exaction media are used coupled with offline analysis [1]. Cr speciation in coals has also been examined [4].

For Cr speciation in water ultrasound assisted microextraction coupled with AAS [13] or graphite furnace AAS (GFAAS) [14] has been proposed. Cloud point extraction (CPE) in the presence of unmodified silver nanoparticles [15] or when using graphene oxide [16] can also be used for ultra-trace Cr speciation in aqueous samples. Dispersive micro-solid phase extraction (DMSPE), using an aluminum oxide supported on graphene oxide (Al2O3/GO) nanocomposite, is also promising [17]. A new extractant was synthesized and used as adsorbent (solid phase extraction) in combination with HPLC/ICP-MS for Cr speciation in wastewater [18]. For offline analysis of water with ICP-MS a carboxyl-functionalized column [11], an amine- and carboxyl-biofunctionalized hybrid column [19], and carboxyl-group functionalized mesoporous silica [10] have been proposed. These adsorbents can assist the separation of chromium species, as Cr(III) can be selectively collected by chelation. A colorimetric lab-on-a-disc sensor gave a 4-ppb minimum detection limit for Cr(VI) in water [20], thus enabling on-site measurements. Microfluidic paper-based analytical devices (mPADs) [21] and polymer dots (PDs) [12] have been also proposed for Cr speciation in water. For Cr(III) and Cr(VI) speciation in water a simple and rapid approach, based on electro dialytic ion preconcentration for the rapid transfer of chromium ions into respective acceptors and coupled to ICP-MS was proposed [22].

For noninvasive analysis of the Cr(VI)/Cr ratio in different types of plastics the X-ray emission spectroscopy (XES) and synchrotron-based X-ray absorption fine structure (XAFS) appears to be promising [23]. Cr speciation in water can be also achieved using resonant inelastic X-ray scattering under total reflection geometry (TRIXS) combined with principal component analysis and linear discriminant analysis, with the added benefit of manganese determination [24]. For rapid detection of Cr(VI) in food and water samples sandwich structured (triadic silica gel-supported) copper sulfide (CuS) nanocomposites were used as the solid phase extraction adsorbent for Cr(VI), followed by FAAS analysis [25]. A custom-built HPLC/ICP-MS system, using a metal-free HPLC-DAD system and a sector-field ICP-MS detection (ICFsfMS) with desolvating injection and optimization of sample handling, was proposed to improve ICP-MS sensitivity, dynamic range, and mass resolution and address the problems of interferences. This system was tested for Cr speciation in protein and pigments and results ate ultrarace levels were obtained [26].

For portable Cr(III) determination in water a miniaturized immune-barometer sensor (IBS), able to detect pressure changes induced when gold core platinum shell nanoparticles decompose H₂O₂ to generate O₂ in a sealed chamber, was proposed for cost effective and environmentally friendly Cr(III) analysis and tested in tap and river water (LOB 0.35 ppb) [3]. An indirect photoelectrochemical sensing platform for Cr(VI) determination in water, based on Cr(VI) inhibition by quercetin oxidation at a titanium dioxide modified glassy carbon electrode in the presence of solar irradiation, was proposed and verified using GFAAS [27]. Similarly, for Cr(VI) sensing in water, graphite printed macroelectrodes, based on the electrochemical reduction of Cr(VI), were also proposed achieving detection limits as low as 0.19 ppb with the added benefits of portability and low cost [28].

Gold nanoparticle-decorated titania nanotube arrays have been used for Cr(VI) electrochemical sensing in tap and lake water, leading to a 23-fold improvement of peak current compared to polycrystalline gold electrodes, thus achieving the detection limit suggested by WHO [27]. A few years later, an activated glassy carbon electrode was proposed for the electrochemical determination of Cr(III) and Cr(VI) in different kinds of samples (e.g., drugs, different heavy metals, and/or biological samples), with the added benefit of signal amplification compared to conventional glassy carbon electrodes, however more research is need on identifying the mechanisms that govern the different activation methods [29]. Finally, a dual channel structured ion imprinted fluorescent sensor was proposed for the simultaneous determination of both Cr(III) and Cr(VI) in river water, without the need for to Cr(VI) reduction or to Cr(III) oxidation, and its sensitivity in Cr(VI) detection was on par or higher with previously reported fluorescent sensors (results were verified using ICP-MS) [30].

Conclusion

The effects of Cr contamination to living organisms are mainly linked to its chemical form rather than its total concentration. Even at trace levels Cr(VI) is highly toxic, carcinogenic, mutagenic, and teratogenic and therefore research has focus on Cr speciation rather than in identifying its total concertation in environmental relevant matrices. Online analysis using HPLC/ICP-MS is typically used for Cr speciation, while preconcentration/extraction followed by offline analysis (e.g., AAS and ICP-MS) is also used. Future research should focus introducing simple, fast, cost-effective, and sensitive techniques for Cr speciation, focusing on on-site (portable) applications.

Chromium (Cr) speciation in environmental relevant matrices is a perquisite to safeguard human health and the environment, since the effects of Cr contamination to living organisms are mainly linked to its chemical form/species rather than its total concentration. However, Cr speciation remains challenging, particularly in real environmental matrices. Many analytical techniques have been developed or improved in recent years, with particular emphasis on optimizing the minimum detection limit, portability (on-site determination), speed, cost, and avoidance of interferences. Overall, key points on the recent advances on Cr speciation in environmental matrices were given and discussed, focusing on Cr speciation in aqueous samples.

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