Original Research ArticlePhaeophyceae and rhodophyceae macroalgae from the Antarctic: A source of selenium
Graphical abstract
Introduction
Macroalgae are aquatic organisms found in marine environments, such as water, soils, rocks and snow (Maehre et al., 2014). The accumulation of trace metals by macroalgae means these organisms are useful bioindicators of metal contamination in the marine environmental (Farias et al., 2018). In addition, macroalgae present bioactive compounds, such as polyphenols, carotenoids, vitamins and minerals, which are responsible for their antibacterial, antiviral, antifungal and antioxidant properties (Battu et al., 2011; Rabanal et al., 2014; Musbah et al., 2019; Pereira et al., 2017; Pandian et al., 2011).
Although the antioxidant activity of microalgae can be associated mainly with the presence of polyphenolic compounds (Pinteus et al., 2017), the contribution of other compounds should not be overlooked. In this context, selenium (Se) is an essential micronutrient for many organisms, and its actions have been implicated as essential for defence against various diseases (Combet and Grey, 2019). Its presence, biochemical association and chemical form in macroalgae have been reported (Schiavon et al., 2017). According to Zhong et al. (2015), Se can improve the activity of glutathione peroxidase, catalase and peroxidase. These associations between Se and the antioxidant enzymes play a pivotal role in the biological functions related to the body's defence mechanism against the oxidative damage caused by free radicals (Silva et al., 2011; Chatterjee et al., 2001).
This globally distributed metalloid is mobilized and released into the environmental via both anthropogenic (industrial and agricultural activities) and natural sources due to its tendency to bioaccumulate and biomagnify in the food chain (Yu et al., 2015). While Se is of nutritional importance because of its physiological functions, its bioaccumulation in aquatic food chains can cause toxicity, and it can persist in the food chain for decades, highlighting the importance of accurate methods for its quantification. To date, Se has been determined mainly by spectrometric techniques (Castilho et al., 2014; Ródenas de la Rocha et al., 2009). Despite the underutilisation of voltammetry to quantify Se in macroalgae samples, it is known that this technique combines low detection limits and multi-element capabilities with cost- effectiveness in various matrices, including macroalgae (Hasan, 2017; Almeida et al., 2017). The electrochemistry of Se at mercury electrodes has been widely discussed. Most of the electrochemical stripping techniques concern inorganic selenium species, such as Se(IV) which is irreversibly reduced to HgSe at the mercury electrode in acidic media (Zelić et al., 1985; Hasan, 2017). Among the techniques applied to macroalgae digestion, the microwave-assisted digestion (MAD) offers several advantages as a simple and rapid method, employing small volumes of reagents with low risk of contamination (Soares et al., 2012; Almeida et al., 2017).
To the best of our knowledge, the Se levels in macroalgae from the Antarctic have not yet been investigated. Considering the Se diverse interactions and impacts of Se, the possibility of using macroalgae as a source of this element and the advantages of voltammetric techniques, this study aimed to develop a voltammetric method for Se determination in macroalgae from the Antarctic, after MAD of the samples.
Section snippets
Reagents and samples
The reagents used in this work were analytical grade: HNO3 65 % (Vetec, Brazil), H2SO4 98 % (Neon, Brazil), HCl 37 % (Synth, Brazil), H3PO4 85 % (Vetec, Brazil). All standard solutions were prepared using ultrapure water obtained from a Milli-Q system (Resistivity 18.2 MΩ cm, Milli-Q Direct-Q UV3, Germany). For the development of the work, a stock solution of 1000 mg L−1 Se(IV) (GQ, Belgium) was used. Standard solutions of 1000 mg L−1 Fe (II), Zn(II), Mn(II), Cr(III), Sn(II), As(III), Cd(II),
Evaluation of Cu concentration, electrolyte composition and concentration
It is known that the determination of Se in the presence of Cu2+ ions provides higher currents peaks, better sensitivity (resulting in lower detection limits), and it is less susceptible to metallic ion interference when compared with measurements without Cu2+ ions (Ferri et al., 2007). Hence, the effect of Cu2+ concentration on the Se voltammetric response by DPCSV was evaluated. It can be observed in Fig. 1 that without Cu2+ (continuous line), the peak presents poor resolution. However, when
Conclusion
This paper discusses the development of a voltammetric method applied to determination of Se in Phaeophyceae and Rhodophyceae macroalgae from the Antarctic after MAD. The developed method was considered adequate, based on the systematic evaluation of the influence of electrolyte and voltammetric parameters in the Se determination. The amount of Cu had strong influence on the Se determination and, despite the matrix complexity, the method presented high accuracy, and a low concentration of Se
CRediT authorship contribution statement
Juliana Rocha Guilherme: Formal analysis, Validation, Writing - review & editing. Bruna Pacheco: Formal analysis, Validation. Bruno Meira Soares: Validation, Writing - review & editing. Claudio Martin Pereira de Pereira: Funding acquisition, Writing - review & editing. Pio Colepicolo: Funding acquisition, Writing - review & editing, Supervision, Writing - review & editing. Daiane Dias: .
Declaration of Competing Interest
The authors declare that they have no conflict of interest.
Acknowledgements
The researchers gratefully acknowledge the financial support to the Brazilian Foundations CAPES, FAPESP (no 2016/06931-4) and CNPq (ProAntar no 407588/2013-2). We would like to thank CAB English Lessons for the English correction.
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