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

Abstract

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 NaHCO 3 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.

When Environmental Chemistry Meets Ecotoxicology: Bioavailability of Inorganic Nanoparticles to Phytoplankton

“…[12] Multiple examples demonstrate the adsorption of metallic and metal oxide nanoparticles (NPs) to freshwater microalgae. Platinum nanoparticles (PtNPs) were shown to adhere to the surface of the green algae Pseudokirchneriella subcapitata and Chlamydomonas reinhardtii, [17] palladium (Pd) NPs [17b] and four iron-containing particles [18] to C. reinhardtii; silver (Ag) NPs to Euglena gracilis [19] and C. reinhardtii, [17b] gold (Au) NPs to the diatom Eolimna minima [20] and C. reinhardtii. [17b] Titanium dioxide (TiO 2 ) NPs aggregates trapped different phytoplankton species, including the green alga Raphidocelis subcapitata, the diatom Fistulifera pelliculosa, and the cyanobacterium Synechocystis sp.…”

Molecular investigation to RNA and protein based interaction inducedin vivobiocompatibility of phytofabricated AuNP with embryonic zebrafish

“…In vitro and in vivo studies in mammalian cell lines and live models like mouse, rat has been performed in order to address the cytotoxicity of these nanoparticles in relevance of clinical aspects [8,9]. Moreover, attention has been also focused towards assessment of toxicity on aquatic biotic bodies for environmental concerns [10,11]. The accumulation of the nanoparticles in aquatic system after being washed out as waste after use is a serious threaten for the aquatic bodies.…”

Editorial for Special Issue “Geomicrobiology and Biogeochemistry of Precious Metals”

“…Natural nanoparticle mobility of precious metals and the increasing anthropogenic use of gold and silver can lead to the large-scale release into the environment. Therefore, ecotoxicological pathways need to be studied, as was done by González et al [18], who studied gold nanoparticle toxicity in freshwater diatoms. The results suggested that cell photosynthesis can lead to a decrease in gold nanoparticle adsorption and uptake by cells.…”