Integrating voltammetry in ecotoxicology: Cu(II)-nitrocatechol complexes formation as a driver of Cu(II) and nitrocatechol toxicity in aquatic systems

Bakija Alempijević, Saranda; Vidović, Kristijan; Vukosav, Petra; Frka Milosavljević, Sanja; Kroflič, Ana; Mihaljević, Ivan; Grgić, Irena; Strmečki, Slađana (2025) Integrating voltammetry in ecotoxicology: Cu(II)-nitrocatechol complexes formation as a driver of Cu(II) and nitrocatechol toxicity in aquatic systems. Electrochimica Acta, 522 . ISSN 0013-4686

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Abstract

Nitrocatechols (NCs) are hazardous environmental pollutants that pose a significant risk to aquatic organisms. The toxicity of pollutants is determined by their speciation, which depends on interactions with coexisting inorganic and organic substances, emphasizing the need for detailed specific studies. Employing square wave and cyclic voltammetry, we investigated the complexation between NCs, specifically 4-nitrocatechol (4NC), 3-methyl-4-nitrocatechol (3M4NC), 3-methyl-5-nitrocatechol (3M5NC), and 4-methyl-5-nitrocatechol (4M5NC), and copper ions (Cu(II)), a micronutrient that is toxic at elevated concentrations. By confirming and following a quasi-reversible two-electron reduction of di-nitrocatecholate [Cu(NC)2]2- complexes in slightly alkaline solution (pH 8.2), we demonstrated fast complex formation in solution at different analyte concentrations and high kinetic stability. However, the pH lowering resulted in degradation of these complexes, yielding mono-nitrocatecholate [Cu(NC)] species and eventually uncomplexed Cu(II) ions. The chronic toxicity bioassays (AlgaeTox) with Scenedesmus subspicatus microalgae exposed to a mixture of Cu(II) and NCs at different concentrations showed decreased toxicity compared to the toxicity of individual Cu(II) and NCs. This decrease was linked to the formation of [Cu(NC)2]2- complexes, which was confirmed by the appearance of a corresponding voltammetric reduction peak. Conversely, increased toxicity was observed when the complexes were degraded, resulting in the presence of free/labile Cu(II) or NCs species in the solution. These results demonstrate that concentration-dependent complexation between pollutants significantly alters the toxicity profile of Cu(II)/NC systems. This study highlights the value of voltammetry with a mercury drop working electrode as a reliable method for studying pollutant complexation relevant to ecotoxicity in natural waters.

Item Type:	Article
Uncontrolled Keywords:	atmospheric organic pollutants; Cu(II) complexes; ecotoxicity; mercury electrode; nitrocatechols; pollutants interaction; voltammetry
Subjects:	NATURAL SCIENCES NATURAL SCIENCES > Interdisciplinary Natural Sciences NATURAL SCIENCES > Interdisciplinary Natural Sciences > Marine Science NATURAL SCIENCES > Interdisciplinary Natural Sciences > Environmental Science
Divisions:	Division for Marine and Enviromental Research
Projects:	Project title Project leader Project code Project type Biokemijski odgovori površinskog sloja oligotrofnog područja Jadranskog mora na atmosfersko taloženje-BiREADI Sanja Frka Milosavljević IP-2018-01-3105 HRZZ Pelud u Jadranskom moru: dinamika unosa, kemijska karakterizacija i utjecaj na primarnu produkciju Slađana Strmečki Kos IP-2022-10-6348 HRZZ
Depositing User:	Slađana Strmečki Kos
Date Deposited:	12 Nov 2025 08:59
URI:	http://fulir.irb.hr/id/eprint/10188
DOI:	10.1016/j.electacta.2025.145938

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