Copper Isotope Fractionation during Equilibration with Natural and Synthetic Ligands

Abstract

As copper (Cu) stable isotopes emerge as a tool for tracing Cu biogeochemical cycling, an understanding of how Cu isotopes fractionate during complexation with soluble organic ligands in natural waters and soil solutions is required. A Donnan dialysis technique was employed to assess the isotopic fractionation of Cu during complexation with the soluble synthetic ligands ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA) and desferrioxamine B (DFOB), as well as with Suwannee River fulvic acid (SRFA). The results indicated enrichment of the heavy isotope ((65)Cu) in the complexes, with Δ(65)Cu complex-free values ranging from +0.14 to +0.84‰. A strong linear correlation was found between the logarithms of the stability constants of the Cu complexes and the magnitudes of isotopic fractionation. These results show that complexation of Cu by organic ligands can affect the isotopic signature of the free Cu ion. This free Cu is considered the most bioavailable species, and hence, our results highlight the importance of understanding fractionation processes in the uptake medium when using Cu isotopes to study the uptake mechanisms of organisms. These data contribute a vital piece to the emerging picture of Cu isotope cycling in the natural environment, as organic complexation plays a key role in the Cu cycle.

Persistence of deeply sourced iron in the Pacific Ocean

“…The binding strength of the Fe-ligand complex can modulate the magnitude of Fe isotopic fractionation, with stronger ligands-and thus stronger bonding environments-favoring larger equilibrium Fe isotopic fractionation factors. Analogous behavior has also been identified for Cu (35), which likely explains both the direction and magnitude of Cu isotopic fractionation between Fe−Mn crusts and seawater (36). The calculated value of Δ 56=54 Fe FeMn−SW of −0:77 ± 0:06‰ is essentially identical to the empirically determined Δ 56=54 Fe FeðIIIÞ−FeðsidÞ between inorganic dissolved Fe(III) and Fe-siderophore complexes of −0.60 ± 0.15‰ (32).…”

X-ray absorption spectroscopy study of Cu(II) coordination in the interlayer of montmorillonite

“…As an essential element for life, its toxicity as well as deficiency may cause acute and chronic problems to humans, animals, plants, and micro-organisms (Flemming and Trevors, 1989;Yruela, 2009;Ryan et al, 2014). Clay minerals play an important role as a natural scavenger of copper in controlling its mobility and fate in soil environments (Alvarez-Puebla et al, 2004;Brigatti et al, 2004;Schlegel and Manceau, 2013).…”

Response of copper concentrations and stable isotope ratios to artificial drainage in a French Retisol

“…Soil water samples were bulked to obtain a sufficient mass of Cu for isotope analysis. Bulking was done for the three different water types separately (piezometer, porous cup, and drain water samples) for two different time periods ( Ilina et al (2013), 9 Petit et al, 2013), 10 Vance et al (2008), 11 Balistrieri et al (2008), 12 Clayton et al (2005), 13 Pokrovsky et al (2008), 14 Li et al (2015), 15 Bigalke et al, 2010b), 16 Ryan et al, 2014), 17 Ehrlich et al (2004), 18 Zhu et al (2002), 19 Asael (2006), 20 Mathur et al (2005), 21 Mathur and Fantle (2015), 22 Mathur et al (2012). condition (Eh > 300 mV) were always lower than 40 μg L − 1 . Therefore, 40 μg L − 1 Fe was used as a threshold to separate between oxic and anoxic soil solution samples.…”

“…Sorption of Cu to Al and Fe (oxyhydr)oxides caused an enrichment of heavy Cu on the surface of the Fe (oxyhydr)oxides (Balistrieri et al, 2008;Pokrovsky et al, 2008). Sorption to organic ligands shows different fractionation factors depending on the type of organic ligand and pH (Bigalke et al, 2010b;Ryan et al, 2014). Lighter Cu isotopes are preferentially adsorbed on clay mineral surfaces (Li et al, 2015).…”