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Minerals 2018, 8(3), 99; https://doi.org/10.3390/min8030099

Interaction of Freshwater Diatom with Gold Nanoparticles: Adsorption, Assimilation, and Stabilization by Cell Exometabolites

1
Instituto de Oceanografía y Cambio Global, IOCAG, Universidad de Las Palmas de Gran Canaria (ULPGC), 35001 Las Palmas, Spain
2
Géosciences Environnement Toulouse (GET), UMR 5563, CNRS-OMP-Université Toulouse, 14 Avenue Edouard Belin, 31400 Toulouse, France
3
BIO-GEO-CLIM Laboratory, Tomsk State University, Lenina 36, 634050 Tomsk, Russia
4
N. Laverov Federal Center for Integrated Arctic Research, Russian Academy of Science, 119991 Arkhangelsk, Russia
5
Tomsk branch of the Trofimuk Institute of Petroleum Geology and Geophysics, SB RAS, Tomsk, Akademichesky 4, 634055 Tomsk, Russia
6
UMR Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC) 5805, Aquatic Ecotoxicology, Université de Bordeaux, Place du Dr Peyneau, 33120 Arcachon, France
7
Institut de Chimie de la Matière Condensée de Bordeaux-UMR 5026 CNRS, 33600 Pessac, France
*
Author to whom correspondence should be addressed.
Received: 22 January 2018 / Revised: 27 February 2018 / Accepted: 1 March 2018 / Published: 5 March 2018
(This article belongs to the Special Issue Geomicrobiology and Biogeochemistry of Precious Metals)
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Abstract

The rising concern about the potential toxicity of synthetic gold nanoparticles (AuNPs) in aquatic environments requires a rigorous estimation of physico-chemical parameters of reactions between AuNPs and major freshwater microorganisms. This study addresses the interaction of 10-nm size, positively charged AuNPs with periphytic freshwater diatoms (Eolimna minima). The adsorption experiments on viable cells were performed in 10 mM NaCl and 5 mM NaCl + 5 mM NaHCO3 solution at a variable pH (3–10), at an AuNPs concentration from 1 µg/L to 10,000 µg/L, and an exposure time from a few minutes to 55 days. Three types of experiments, adsorption as a function of time (kinetics), pH-dependent adsorption edge, and constant-pH “Langmuirian” type isotherms, were conducted. In addition, long-term interactions (days to weeks) of live diatoms (under light and in the darkness) were performed. The adsorption was maximal at a pH from 3 to 6 and sizably decreased at a pH of 6 to 10. Results of adsorption experiments were modeled using a second order kinetic model, a Linear Programming Model, Freundlich isotherm, and a ligand binding equation for one site competition. The adsorption of AuNPs(+) most likely occurred on negatively-charged surface sites of diatom cell walls such as carboxylates or phosphorylates, similar to previously studied metal cations. Under light exposure, the AuNPs were stabilized in aqueous solution in the presence of live cells, probably due to the production of exometabolites by diatoms. The adsorbed amount of AuNPs decreased after several days of reaction, suggesting some AuNPs desorption. In the darkness, the adsorption and assimilation were stronger than under light. Overall, the behavior of positively charged AuNPs at the diatom–aqueous solution interface is similar to that of metal cations, but the affinity of aqueous AuNPs to cell exometabolites is higher, which leads to the stabilization of nanoparticles in solution in the presence of diatoms and their exudates. During photosynthetic activity and the pH rising above 9 in the vicinity of diatom cells, the adsorption of AuNPs strongly decreases, which indicates a decreasing potential toxicity of AuNPs for photosynthesizing cells. The present study demonstrates the efficiency of a thermodynamic and kinetic approach for understanding gold nanoparticles interaction with aquatic freshwater peryphytic microorganisms. View Full-Text
Keywords: AuNPs; freshwater diatoms; biofilm; adsorption; river; pollution AuNPs; freshwater diatoms; biofilm; adsorption; river; pollution
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González, A.G.; Pokrovsky, O.S.; Ivanova, I.S.; Oleinikova, O.; Feurtet-Mazel, A.; Mornet, S.; Baudrimont, M. Interaction of Freshwater Diatom with Gold Nanoparticles: Adsorption, Assimilation, and Stabilization by Cell Exometabolites. Minerals 2018, 8, 99.

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