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Isotopically labeled nanoparticles: towards a better understanding of contamination mechanisms in aquatic environments

Manufactured nanoparticles (MNPs) are used in many everyday consumer products, thanks to their exceptional chemical, optical, magnetic or mechanical properties (as bleaching agents in paints or food products, as antibacterial agents, as UV absorbers in sun creams, to improve the color and brightness of illuminated displays or in solar panels, etc.).

Isotopically labeled nanoparticles: towards a better understanding of contamination mechanisms in aquatic environments

Publication date: 15/04/2019

Press, Research

Related themes : Earth System Science

The use and disposal of these products leads to the release of nanomaterials into wastewater or the environment. Manufactured nanoparticles have a potentially significant impact on the environment. It is therefore vital to gain a better understanding of how they are dispersed in aquatic environments.

Traditional analysis methods are unable to detect and analyse MNPs at very low concentrations, close to those found in natural environments. However, the concentration of MNPs in the environment is a parameter that strongly influences their fate (dissolution or aggregation, for example) in the environment.

In a study published on January 31st 2019, in the journal “Environmental Science and Technology”, a team of scientists from IPGP, Université Paris Diderot and IMPMC, proposes a new method, combining the use of non-traditional stable isotopes(111Cd, 77Se, 68Zn) as tracers incorporated into Quantum Dots type nanoparticles (known as “spiked”) and analysis by high-resolution plasma source mass spectrometer. These analyses enabled us to detect the constituent elements of the nanoparticles at concentration levels comparable to those found in other materials.
This experimental model therefore opens up a new avenue for better modelling of the fate of nanoparticles disseminated in natural aquatic environments.

Quantum dots (CdSe/ZnS) luminescent.

The transformations (e.g. dissolution, aggregation, sedimentation) of engineered nanoparticles (MNPs) in surface waters are affected by many factors such as pH, ionic strength, organic/inorganic phases, bacteria, algae, exopolysaccharides, as well as other metals and contaminants. However, the concentration of the MNPs themselves is another control factor, little discussed in the literature because of the difficulty of detecting these nano-objects in complex environments with high background noise (corresponding to the presence of the constituent elements of the MNPs in the environment at varying concentrations), which remains a real analytical challenge. The experimental use of isotopically labelled nanoparticles is one solution that could help to meet this challenge.

In this study, the limitations of such a technique were assessed. Nanoparticles labelled with non-traditional stable isotopes (or ‘spiked’) were used to complement high-resolution ICP mass spectroscopy (HR-ICP-MS): for the first time, multi-spiked 111Cd77Se/68ZnS quantum dots (QDs) coated with thioglycolic acid (TGA) were synthesised at a size of 7 nm and their dissemination in natural aquatic matrices (river, estuary and marine waters) was modelled at very low concentrations (from 0.1 to 5,000 ppm). The limits of quantification of the Qds (QD-LOQ) in each matrix were calculated as a function of the isotopic tracer. In ultrapure and simple media (HNO3 2%), Zn, Cd and Se from the Qds were quantifiable at concentrations of 10, 0.3 and 6 ppt, respectively, which are below the conventional quantification limits of a HR-ICP-MS. In aquatic matrices, QD-LOQs increased 10-, 130- and 250-fold for Zn, Cd and Se respectively, but remained relevant for environmental concentrations (3.4 ppt ≤ QD-LOQ ≤ 2.5 ppb).

These results validate the use of isotopically labelled MNPs at relevant concentrations and provide a framework for future experimental studies related to their fate, behaviour or toxicity in most aquatic matrices.

Ref: Isotopically Labeled Nanoparticles at Relevant Concentrations: How Low Can We Go? The Case of CdSe/ZnS QDs in Surface Waters, Nurul I. Supiandi, G. Charron, M. Tharaud, L. Cordier, J.-M. Guigner, M. F. Benedetti, and Y. Sivry, Environmental Science & Technology 2019 53 (5), 2586-2594, DOI: 10.1021/acs.est.8b04096

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