Abstract
The difficulties when studying the behavior of engineered nanoparticles (ENPs), and the subsequent metal speciation in aquatic ecosystems, at concentrations relevant of environment (i.e. ppt level) are often related to the occurrence of ENPs constitutive elements at high concentrations as a background in aquatic media (i.e.). In this study, the physico-chemical behavior of CdSe/ZnS quantum dots (QDs) when spread at very low concentration in surface waters was investigated. The above-mentioned issues were overcome with the use of isotopically labeled QDs, separated by centrifugal ultrafiltration (CU) and measured by HR-ICP-MS, combined with the detection of free and labile metal ions by Scanned Stripping ChronoPotentiometry (SSCP). They firmly provided a thorough comprehension regarding the transformation of QDs in surface waters. The physicochemical conditions of the medium including the presence of an analogue of natural organic matter and a mineral (i.e. fulvic acid, goethite), the manufactured coating of the QDs (here thioglycolic acid), and the occurrence of added Zn in the medium, were considered in the study. The overall results show that, in the absence of mineral/organic matter, the TGA ligands in solution detached from the QDs surface after dissolution control the metal ions speciation, especially for Cd. Conversely in a more representative aquatic ecosystem conditions (i.e. with Zn in the background media together with fulvic acid and goethite), almost no Zn nor Cd dissolution from the QDs is detected. SSCP measurements reveal that the Zn complexes formed with the organic/mineral material in the system are inert, whereas the speciation model calculations indicated that Cd2+ is bound to TGA ligands in solution and organic/inorganic matter – therefore suggesting that, under the studied conditions, aquatic organisms will be exposed to a very low concentration of free and labile metal ions issued from the QDs.
Highlights
The progress of nanotechnology led to numerous applications of engineered nanoparticles (ENPs), which results in the increase of studies concerning their fate and behavior in environmental compartments, as well as their potential toxic effects
The difficulties when studying the fate of quantum dots (QDs) in aquatic water systems at ppt-level concentrations and the subsequent metal speciation were surmounted by the combination of the two mentioned methods, isotopically labeled QDs/centrifugal ultrafiltration (CU) and scanned stripping chronopotentiometry (SSCP)
The QD behavior in aquatic systems is affected by various factors: (i) the physicochemical conditions of the medium including the presence of natural organic and mineral matter, (ii) the presence of the manufactured coating of the QDs, and (iii) the interaction of the metal ions in the medium with the coating itself
Summary
The progress of nanotechnology led to numerous applications of engineered nanoparticles (ENPs), which results in the increase of studies concerning their fate and behavior in environmental compartments (e.g., wastewater treatment plants, surface water, sediments, and soils), as well as their potential toxic effects. Most of these studies are often carried out at conditions far QDs Geochemistry in Surface Waters from the ones expected in the environment, mostly for two main reasons. Cd and Pb metal ions were shown to interact with CdTe/CdS NPs, influencing their dissolution and metal ion speciation (Cd and Pb) and their environmental fate (Domingos et al, 2015)
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