Dissolution of Silver Nanoparticles in Stratified Estuarine Mesocosms and Silver Accumulation in a Simple Planktonic Freshwater Trophic Chain

Camille Guilleux,Zhongzhi Chen,Peter G C Campbell,Claude Fortin

doi:10.3390/environments9020020

Camille Guilleux, Zhongzhi Chen + Show 2 more

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https://doi.org/10.3390/environments9020020

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Abstract

The increasing presence of nanomaterials in consumer products has led the scientific community to study the environmental fate of these contaminants of emerging concern. Silver nanoparticles, used mainly for their antibacterial properties, are among the most common nanomaterials. Understanding their transformations and interactions with living organisms, especially under environmentally relevant conditions that can modify metal bioavailability, is a crucial step in the study of their impacts on aquatic ecosystems. In the present study, citrate-coated silver nanoparticles (20 nm; 10 µg/L) were added to the surface freshwater layer of mesocosms simulating a stratified estuary. The investigation by dialysis of the nanoparticle dissolution showed that a large amount of total silver was found in the freshwater layer (and a very low amount in the seawater layer) and that 5–15% was in the form of dissolved silver. These results indicate that the halocline, separating fresh water from seawater, acted as a strong density barrier limiting the sedimentation of the nanoparticles. A simple trophic chain, composed of the freshwater alga Chlamydomonas reinhardtii and the invertebrate Daphnia magna, was used to determine silver bioavailability. This study suggests that citrate-coated silver nanoparticles do not significantly contribute to Ag accumulation by algae but may do so for invertebrates.

Highlights

More than 50% of biocidal silver products such as nanotextiles, registered by the United States Environmental Protection Agency (USEPA), contain silver nanoparticles (AgNPs) [1]
Because Ag in the mesocosms was not significantly accumulated by Chlamydomonas reinhardtii, but quantified in daphnids, these results suggest that the daphnids likely took up Ag from abiotic particles
A longer exposure time of the algae to the nanoparticles might have provided a quantifiable accumulation in Chlamydomonas reinhardtii and, in on average versus 20 nm here), their concentration (1000 μg/L AgNPs) and the exposure time of the algae to the nanoparticles (12 h) were much greater than in the experiment presented here (3.0–3.5 μg/L and 1 h of exposure, respectively, in this study)

Summary

Introduction

More than 50% of biocidal silver products such as nanotextiles, registered by the United States Environmental Protection Agency (USEPA), contain silver nanoparticles (AgNPs) [1]. There are still no fully developed analytical techniques that can detect anthropogenic nanoparticles in complex matrices such as a natural environment [2,3]. Gottschalk et al predicted that silver nanoparticle concentrations would be between 0.09 and 0.43 ng/L and between 0.59 and 2.16 ng/L in U.S. and European surface waters, respectively [5]. The transformations of silver nanoparticles in the environment, mainly aggregation and dissolution [6], were reviewed recently [2,7,8]

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