The effects of solar irradiation on copper speciation and organic complexation

Abstract

Este trabalho teve como objetivo avaliar o efeito da irradiação solar na especiação do cobre em amostras de água coletadas em um reservatório eutrofizado e contaminado por metais. Voltametria de redissolução anódica e eletrodo de íon seletivo foram utilizados para determinação de cobre nas amostras irradiadas e não irradiadas. Os resultados demonstraram que após 7 h de irradiação solar, a matéria orgânica dissolvida (DOM) foi degradada promovendo aumento de cobre iônico livre, lábil e de carbono inorgânico dissolvido (DIC), e diminuição da concentração de ligantes disponíveis (C L ) e de carbono orgânico dissolvido (DOC). Os valores da constante de estabilidade condicional (logK') variaram em duas amostras, permanecendo constantes nas demais. Os resultados demonstraram que as reações fotoquímicas afetaram a especiação do cobre e as interações Cu-DOM, ressaltando implicações ecológicas da fotoxidação, como o aumento do cobre biodisponível e, desta forma, contribuindo para o entendimento do ciclo biogeoquímico desse metal.The aims of this research were to evaluate the effects of solar irradiation on copper speciation in water samples obtained in eutrophic and metal contaminated reservoir. Anodic stripping voltammetry and ion selective electrode were used for metal determinations of solar irradiated and non-irradiated samples. The results showed that after 7 h of solar irradiation, dissolved organic matter (DOM) was degraded promoting the increase of labile, free Cu 2+ ions and dissolved inorganic carbon (DIC). Decreases of ligand concentration (C L ) and dissolved organic carbon (DOC) were also observed. Conditional stability constant (logK') values varied for two sampling sites, but remained unchanged for the others. The present results demonstrated that photochemical reactions affected copper speciation and Cu-DOM interactions. This research is a contribution to the understanding of biogeochemical cycle of copper and highlights some ecological implications of photooxidation in freshwater ecosystems, such as the increase of copper bioavailability.Keywords: copper, freshwater, photooxidation, speciation, complexation IntroductionIn aquatic ecosystems, copper speciation is closely related to its uptake by the organisms. Natural DOM can be categorized as a complex mixture of organic compounds, each of which presenting unique elemental composition, molecular weight and a set of chemical and physical properties.7 These DOM properties can be affected by several factors, such as microbial degradation, temperature and photooxidation. [8][9][10] The importance of each of these processes depends on the characteristics of the environment and on the DOM origin. Nevertheless, DOM photooxidation in natural waters, which can produce environmentally and biologically important products, may modify the physicochemical properties of the DOM. 11Because in natural environments DOM is usually present in excess concentration of trace metals, it can regulate the chemical speciation of elements such as copper, providing natural waters wi...

Constraining the Global Ocean Cu Cycle With a Data‐Assimilated Diagnostic Model

“…The excess source here could be due to very weak biological removal combined with a yet undocumented source of dissolved Cu in the surface ocean. A candidate source mechanism is photochemical reactions in the surface ocean, which previous studies have shown can destroy or cleave Cu‐ligand complexes and increase the concentration of free Cu ions (Laglera & ven den Berg, 2006; Moffett & Zika, 1987; Shank et al, 2006; Tonietto et al, 2011). If Cu is photochemically solubilized from colloids or particles larger than 0.2–0.45 μm, this photodegradation could represent a source of dissolved Cu (smaller than 0.2–0.45 μm), as demonstrated by the photo‐dissolution of organic‐associated Cu from resuspended coastal sediments (Skrabal et al, 2018).…”

Marine Photochemistry of Organic Matter

“…Factors resulting in a negative or mixed effect include photochemical production of inhibitory substances such as hydrogen peroxide (Angel et al, 1999;Baltar et al, 2013;Farjalla et al, 2001;Gjessing and Källqvist, 1991;Kaiser and Sulzberger, 2004;Leunert et al, 2014;Lund and Hongve, 1994;Morris et al, 2011;Scully et al, 2003a;Tranvik and Kokalj, 1998;Weinbauer and Suttle, 1999), release of toxic metals (e.g., Pb, Cu, Ni, Cd, and Hg) from DOM complexes (Haverstock et al, 2012;Tonietto et al, 2011;Winch and Lean, 2005), photolysis of DOM to form substances that are both biologically and photochemically refractory (Kieber, 2000;Stubbins et al, 2010), deactivation of enzymes (Scully et al, 2003b;Vähätalo et al, 2003), changes in the BGE (Abboudi et al, 2008;McCallister et al, 2005;Mopper and Kieber, 2002;Pullin et al, 2004;Smith and Benner, 2005), changes in microbial populations (i.e., community structure) in response to photoproduced substrates or toxic substances (Abboudi et al, 2008;Calza et al, 2008;Lønborg et al, 2013;Piccini et al, 2009), and prior photochemical history, i.e., photon dose-related bleaching (Reader and Miller, 2014). In addition to the above factors, a negative or mixed effect on biological activity can result from reactions of biologically produced ROS, e.g., H 2 O 2 (Palenik and Morel, 1990;Diaz et al, 2013) with photochemically produced reduced metals, e.g., Fe(II), Mn(II), and Cu(I) (Barbeau, 2006;Brinkmann et al, 2003;…”

“…The photoproduction of labile substrates and mineral nutrients from humic substances may have been offset by the photodestruction of algal-produced DOM (Benner and Biddanda, 1998) or balanced by the photoproduction of toxic substances (Calza et al, 2008;Diamond, 2003;Haverstock et al, 2012;Ortega-Retuerta et al, 2007;Tonietto et al, 2011;Winch and Lean, 2005). Alternatively, carbon limitation may have been important.…”

Combined Effects of Trace Metals and Light on Photosynthetic Microorganisms in Aquatic Environment

“…The photo-induced transformations of DOM could results in: (i) a decrease of DOM concentrations or alteration of its structure and thus increase in the free metal ion concentration and bioavailability [34,50]; (ii) no change in the free metal ion concentrations, because of the production of low molecular weight dissolved organic acids able to scavenge dissolved metal [51]; (iii) an increase of the metal complexation because of a net production of functional groups on humic-like fractions that outcompete for the complexation by low molecular weight dissolved organic acids [34].…”