Improved voltammetric methodology for chromium redox speciation in estuarine waters

Abstract

14Chromium is a toxic element naturally present in natural waters whose chemical speciation 15 regulates its cycling, mobility and bioavailability. We present here: 1-an improved analytical 16 method for chromium speciation (Cr(VI) vs Cr(III)) in estuarine samples by catalytic 17 adsorptive cathodic stripping voltammetric (cat-AdCSV) and 2-a study highlighting a 18 significant change of redox speciation during summer and winter. Initial measurements first 19 revealed that surface-active substances (SAS) present in estuarine samples strongly influenced 20 the analytical determination of Cr by partially masking the Cr peak through an increase of the 21 background current. We found that the application of a low negative accumulation potential (-22 1.65 V) resulted in much better voltammograms compared to those obtained using the usual 23 accumulation potential of -1.0 V . Using humic acid (HA) as a model SAS of natural origin, 24we show that this negative potential clearly prevents adsorption of SAS on the Hg-electrode 25 surface, which in turns benefits the adsorption of the in-situ formed Cr(III)-DTPA complex 26 and the resulting signal. The optimised method was applied to determine chromium redox 27 speciation and distribution along the 23 km long salinity gradient, well oxygenated, Krka 28 River estuary (Croatia). Cr(VI) was found to be the dominant redox species in both summer 29 and winter, with Cr(III) contribution being lower in summer (up to ~30%, average of ~5%) 30 than in winter (up to ~50%, average of ~30%). In summer, lower concentrations of Cr(VI) 31 were found in the freshwater end-member (2.5 nM) than in the seawater end-member (4-5 32 nM), while the opposite trend was found in winter. Hexavalent chromium exhibited a non-33 conservative behaviour along the salinity gradient for both seasons. Chromium predominantly 34 exists in dissolved phase, and contribution of particles reactive Cr(III) was minor. 35

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…”

Combined effects of nano-TiO2 and hexavalent chromium towards marine crustacean Artemia salina

“…Entry into seawater occurs either through natural [leaching from top soil and rocks] or anthropogenic sources [industrial establishments] (Oze et al, 2007;Tchounwou et al, 2012). Although their concentration in seawater remains very low [5.2 × 10 −6 mg/L -832 × 10 −6 mg/L], their toxic impact cannot simply be overlooked (Pađan et al, 2019). The determination of toxicity produced from such low concentrations of Cr (VI), along with a co-contaminant, such as nano-TiO 2 to marine organism is essential.…”

Inorganic Chromium Speciation in Geothermal Water of the Podhale Trough (Southern Poland) Used for Recreational Purposes

“…Its environmental presence is related to industrial activities (e.g., tanneries, chromium ore processing plants, slag-soil systems or deposition of steel production waste on landfills) [7,[71][72][73][74]. In particular, Cr(VI) in natural water may occur in surface water near which chromite-bearing formations are observed [5] The differences in chromium speciation ratio (Cr(III)/Cr(VI)) may be a result of seasonal changes [75].…”