Naslov
Voltammetry in the study of unusual phenomena in the sea. Part II: Sulfur species characterization in the seawater anoxic conditions and aggregates of red tide blooms in the northern Adriatic

Autori
Mateša, Sarah ; Simonović, Niki ; Panagiotopoulou, Eleni ; Paliaga, Paolo ; Ciglenečki, Irena

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, prošireni sažetak, znanstveni

Izvornik
0th ISE Satellite Student Regional Symposium on Electrochemistry : Book of Abstracts / Marcinek, Saša ; Mikić, Dajana - Zagreb : Hrvatsko društvo kemijskih inženjera i tehnologa (HDKI), 2021, 17-18

ISBN
978-953-6894-79-6

Skup
10th Satellite Regional Symposium on Electrochemistry (ISE 2021)

Mjesto i datum
Online, 02.07.2021

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Podatak o recenziji nije dostupan

Ključne riječi
voltammetry ; unusual phenomena ; sulfur species ; Rogoznica Lake ; anoxic conditions ; red tide blooms

Sažetak
Sulfur (S), an ubiquitous element in the environment, occurs in different oxidation states from -2 (sulfide, S2-) to +6 (sulfate, SO42−). Reduced forms of S, i.e. reduced sulfur species (RSS: S2-, HS-, S0, SX2-, RSH), are important forms for processes related to S biogeochemistry and environmental quality [1]. Production of marine S species is mainly related to phytoplankton and mcrobial activities, as well as eutrophication phenomena and spreading of hypoxic– anoxic dead zones. A significant fraction of natural S emission occurs in the form of organic S, such as dimethylsulfide (DMS), produced by phytoplankton and zooplankton grazing activities. In different natural water systems, electroanalytical methods have been widely used for the characterization and determination of diferent S species, including dissolved and/or particulate inorganic and organic S forms [2- 5]. Electroanalytical determination of dissolved RSS on the Hg electrode is based on their interaction with the Hg, resulting in the Hg oxidation and the formation of insoluble mercury sulfide (HgS) at potentials more positive than -0.60 (vs . Ag / AgCl). The same process occurs during the interaction of Hg with organic and inorganic RSS that deposit HgS, which during the potential scan toward negative values are reduced, and reduction current at -0.68 V is directly proportional to the concentration of RSS in the sample. RSS that are adsorbed on the Hg surface, or form adsorbable RS– Hg complexes (in the case of DMS, DMDS, cysteine, glutathione) are reduced more positively (around - 0.5 vs. Ag/AgCl) [3-5]. By changing deposition potentials from - 0, 2 V to - 0, 4 V it is possible to make a rough distinction between organic and inorganic RSS that deposit HgS [4, and references therein]. In the presence of organic RSS, by measuring at Ed = -0, 4 V, the HgS reduction peak will decrease or completely disappear. Also, in the adopted electrochemical measurements of the RSS in natural samples, the acidification and purging step by N2 is used to make a distinction between the volatile and non- volatile fraction of the RSS [5]. Unusual phenomena in the sea, such as hypoxia, anoxia or intensive phytoplankton blooms as red tide, can occur as a consequence of environmental, i.e. meteorological conditions, lately highly impacted by climate change. In this paper, cyclic voltammetry (CV) at the Hg electrode was used for characterization of total RSS (RSSTOT) ; non- volatile RSS (RSSNV) and organic S compounds in natural samples collected during the red tide bloom, and in the stratified and holomictic conditions of the unique marine environment on the Adriatic coast (Rogoznica Lake, RL). During stratified conditions in the RL water column, the concentration of RSSTOT (mainly sulfide/S0-like compounds) detected with CV measurements was in the range between 20 nM (oxic layer) to 3 mM (anoxic layer), while concentration of RSSNV (S0- like compounds) ranged between 10 and 100 uM. Additionally, for the first time in the anoxic layer samples differential pulse voltammetry (DPV) was used for determination of polysulfides (SX2)-. The highest concentrations of SX2- (up to 0.1 mM) were determined about 1 m below the oxia/anoxia boundary (~10m) during summer months, when indirectly SX2 formation is proved to be connected by activities of purple phototrophic sulfur bacteria (PSB). In holomictic conditions, when stratification dissapeared, concentrations of both RSSTOT (~100 uM) and RSSNV (~10uM) were decreased and similar throughout the water column. In the same time presence of SX2- and PSB was not detected. Unlike RL samples, in samples of red tide blooms (mainly composed of Noctiluca scintillans), two RSS peaks were detected with CV measurments. First peak, at potential around - 0.5 V, confirms presence of organic S species (RS-Hg type) in the concentration range between 17- 45 nM [3-5]. Second peak at more negative potentials (around -0.68 V), confirms presence of inorganic RSS (sulfide/S0-like compounds) in the concentration range between 7 – 45 nM. Such results support the fact that dinoflagellates among other phytoplankton species contribute the most to the production of sulfur species in the sea [1, 3]. [1] Biogenic sulphur in the environment, E. S. Saltzman and W. J. Cooper (ed.), American Chemical Society, Washington, DC, USA, 1989. [2] I. Ciglenečki, D. Krznarić, G. R. Helz, Environ. Sci. Technol. (2005), 39, 7492. [3] I. Ciglenečki, B. Ćosović, Mar. Chem. (1996), 52, 87. [4] A. Cvitešić Kušan, S. Frka, I. Ciglenečki, Atmosphere (2019), 10, 674 [5] E. Bura-Nakić, G.R. Helz, I. Ciglenečki, B. Ćosović, Geochim. Cosmochim. Acta (2009), 73, 3738.

Izvorni jezik
Engleski

Znanstvena područja
Kemija, Biologija, Interdisciplinarne prirodne znanosti

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