Determination of sub-picomolar levels of platinum in the pristine Krka River estuary (Croatia) using improved voltammetric methodology

Abstract

Environmental contextPlatinum concentrations in natural waters such as oceans, rivers and lakes are extremely low, hindering studies of Pt distributions and biogeochemical cycles. An improved electrochemical method was used to reliably determine Pt in estuarine conditions at trace concentrations. Platinum displayed a near-conservative behaviour along the salinity gradient of the estuary, with about 90% remaining in the dissolved form. AbstractExtremely low concentrations of platinum in natural waters require very sensitive analytical techniques, with adsorptive cathodic stripping voltammetry (AdCSV) being one of the most frequently used techniques. A ‘fine tuning’ of the voltammetric parameters, along with advanced data treatment based on derivative transformations, allowed us to determine reliably Pt levels down to 50 fM (0.05 pM). By using short modulation and interval times of the differential pulse stripping waveform, and applying a 4th derivative transformation to the voltammograms, the limit of detection (LOD) was lowered down to 10 fM. Although very small concentrations of surface-active substances (e.g. 0.025mgL−1 fulvic acid) strongly influenced the method sensitivity, recoveries of spiked samples were not impacted (~100%). The application of a desorption step (Eds=−1.35V; tds=2s) at the end of the accumulation significantly improved the sensitivity, presumably through the removal of adsorbed surface-active substances. Using this optimised methodology, we determined the Pt distribution in the pristine Krka River estuary in the winter and summer periods by performing both horizontal transects and vertical profiles (salinity ~1 to 39). In surface waters, dissolved Pt concentrations gradually increased towards the seawater end-member (from ~0.15 to ~0.3 pM). A small deviation from the conservative mixing line was observed at salinities below 10, which may reflect changes in Pt redox speciation. In bottom waters, the trend was opposite with dissolved Pt concentrations increasing towards the freshwater end-member, probably owing to progressive accumulation related to seawater residence time. On average, 90% of Pt was present in the dissolved form.

Trace Metal Partitioning in the Salinity Gradient of the Highly Stratified Estuary: A Case Study in the Krka River Estuary (Croatia)

“…The Krka River estuary is a very interesting system for the investigation of trace metal partitioning, since for most of the year it features a pristine environment with low organic content. Namely, due to the scarce vegetation, the absence of significant anthropogenic influence and self-purifying ability of the Krka River, the estuary, as well as the coastal sea, are unusually clean in terms of trace elements, terrigenous material and biomarkers [8,[25][26][27][28][29][30]. The only concern presents the seasonal anthropogenic pressure related to increased boat traffic and touristic activities [8,31].…”

Dissolved organic matter dynamics in the pristine Krka River estuary (Croatia)

“…Under the conditions of small terrestrial and negligible anthropogenic input (Cindric et al, 2015;Legovic et al, 1994), photochemical and biological processes are expected to strongly affect DOM pool, while the permanent stratification could further influence DOM distribution and dynamics (Santinelli et al, 2013). While the Krka River estuary is in general well characterized on its hydrology, biological status and trace metals behavior (Cetinic et al, 2006;Cindric et al, 2015;Knežević et al, 2019;Legovic, 1991;Pađan et al, 2019a;Pađan et al, 2019b;Supraha et al, 2014;Svensen et al, 2007;Zutic and Legovic, 1987), the organic matter dynamics has been only sporadically studied and to the best of our knowledge, no information about CDOM and FDOM dynamics is reported. In this study, we investigated DOM dynamics in the Krka River estuary during two contrasting periods of the year; February 2019, characterized by low production and high riverine input…”

Redox Speciation of Vanadium in Estuarine Waters Using Improved Methodology Based on Anion Exchange Chromatography Coupled to HR ICP-MS System

“…Halocline is usually positioned between 1.5 and 3 m, with the thickness of the halocline layer varying between a few cm up to 1 m [ 12 , 54 ]. Special characteristics make this sampling location ideal for evaluating the mobility and fate of trace metals and natural organic matter [ 12 , 53 , 55 , 56 , 57 ]. Trace metals have been previously studied, although mainly in reference to their total concentrations [ 12 , 51 ].…”