Development of an In Situ Ion-Exchange Technique for the Determination of Free Cd, Co, Ni, and Zn Concentrations in Freshwaters

Abstract

It is now well established that the bioavailability of metals toward aquatic organisms varies as a function of the free metal concentration. The ion-exchange technique (IET), which consists of equilibrating a calibrated cation-exchange resin with the water sample, is one of the few existing speciation methods that provide sufficient sensitivity and specificity to measure free metals in natural waters. In the present study, we developed an in situ IET (field-IET) in which the resin was directly equilibrated on site using dialysis cassettes. The field-IET was tested in six Canadian Shield lakes and in the Athabasca River (AB, Canada) for Cd 2? , Co 2? (only in the Athabasca River), Ni 2? , and Zn 2? . Measurements were compared with those obtained on samples collected from the same sites with in situ diffusion samplers and analyzed in the laboratory (lab-IET). IET results were also compared with predictions from the Windermere Humic Aqueous Model [WHAM VII; the Co and Ni carbonato complex formation constants were updated according to the US National Institute of Science and Technology (NIST compilation)]. Good agreement was obtained between the field-IET and the lab-IET for Co 2? and Ni 2? concentrations, but field-IET Cd 2? and Zn 2? concentrations were systematically higher than the lab-IET results (factors of *1.59 and *2.49, respectively). Uncertainties in the field-IET resin calibration and a significant Zn contamination could explain these results. WHAM VII predicted the free metal concentrations reasonably well, except for Ni 2? concentrations in the lakes, probably due to inappropriate formation constants for complexation of Ni with Electronic supplementary material The online version of this article (dissolved organic matter. This study showed that the field-IET, with its relative simplicity and its low detection limits, could be a useful method for the determination of free metal concentrations in acidic to neutral freshwaters.

The longitudinal effects of early developmental cadmium exposure on conditioned place preference and cardiovascular physiology in zebrafish

“…Much less has been reported on surface waters since these tend to have levels below detection limits. However, general detectable concentrations reported are in the range of 0.05 to 0.65 μg/L (Cremazy et al 2015; Linnik et al 2015; Zhang et al 2016). These reported Cd concentrations are far lower than those used in our study (1.124 to 1124 μg/L).…”

Cadmium accumulation and toxicity in the unicellular alga Pseudokirchneriella subcapitata: Influence of metal‐binding exudates and exposure time

“…In a natural freshwater environment, metals such as Cd, Co, and Zn are typically found in large proportions as the free ion species [32][33][34] because of their relatively low affinity for dissolved organic matter, which poorly buffers the free metal ion concentrations. Hence, one might expect that metal-binding exudates produced by phytoplankton in oligotrophic, but particularly in eutrophic, systems would sometimes affect metal speciation, as suggested by several free metal ion measurements in ecosystems in different trophic states [35][36][37][38][39].…”

A review on electrochemical methods for trace metal speciation in environmental media

“…Thus, 40there is a need to design, develop, apply and interpret analytical techniques able to 41 provide reliable speciation information [5][6][7] that can be used by regulatory bodies. 42Although there are numerous non-electrochemical techniques [5][6][7][8][9][10][11][12][13], those that are 43 provide attractive possibilities such as speed of analysis, low-cost and miniaturization in 44 view to on-site (and in-situ) measurements [14], and can also provide thermodynamic 45 (i.e. equilibrium) information (such as the amount of the free metal, the amount of 46 complexing sites, the stoichiometry of complexes and their stability constants [15]) as 47 [16;17].…”