Toxicity, Bioaccumulation and Biotransformation of Glucose-Capped Silver Nanoparticles in Green Microalgae Chlorella vulgaris

Abstract

Silver nanoparticles (AgNPs) are one of the most widely used nanomaterials in consumer products. When discharged into the aquatic environment AgNPs can cause toxicity to aquatic biota, through mechanisms that are still under debate, thus rendering the nanoparticles (NPs) effects evaluation a necessary step. Different aquatic organism models, i.e., microalgae, mussels, Daphnia magna, sea urchins and Danio rerio, etc. have been largely exploited for NPs toxicity assessment. On the other hand, alternative biological microorganisms abundantly present in nature, i.e., microalgae, are nowadays exploited as a potential sink for removal of toxic substances from the environment. Indeed, the green microalgae Chlorella vulgaris is one of the most used microorganisms for waste treatment. With the aim to verify the possible involvement of C. vulgaris not only as a model microorganism of NPs toxicity but also for the protection toward NPs pollution, we used these microalgae to measure the AgNPs biotoxicity and bioaccumulation. In particular, to exclude any toxicity derived by Ag+ ions release, green chemistry-synthesised and glucose-coated AgNPs (AgNPs-G) were used. C. vulgaris actively internalised AgNPs-G whose amount increases in a time- and dose-dependent manner. The internalised NPs, found inside large vacuoles, were not released back into the medium, even after 1 week, and did not undergo biotransformation since AgNPs-G maintained their crystalline nature. Biotoxicity of AgNPs-G causes an exposure time and AgNPs-G dose-dependent growth reduction and a decrease in chlorophyll-a amount. These results confirm C. vulgaris as a bioaccumulating microalgae for possible use in environmental protection.

Surface Coating-Modulated Phytotoxic Responses of Silver Nanoparticles in Plants and Freshwater Green Algae

“…Several studies have reported a decrease in chlorophyll content upon exposure to uncoated AgNPs in freshwater algae C. vulgaris [ 18 , 34 ], P. oedogonia and Chara vulgaris [ 27 ], and C. reinhardtii [ 31 ], as well as vascular plants, e.g., rice [ 141 , 162 ] and A. thaliana [ 163 ]. A decline in chlorophyll content was also observed upon exposure to AgNPs stabilized with different surface coatings, e.g., in freshwater algae Scenedesmus after exposure to AgNP-PVA [ 26 ], C. vulgaris treated with AgNP-glucose [ 35 ] and AgNP-citrate [ 22 ], and in A. thaliana exposed to AgNP-citrate [ 90 ]. AgNP-induced reduction of carotenoid content has also been reported upon treatment of A. thaliana with AgNP-citrate [ 90 , 92 ] and in O. sativa exposed to uncoated AgNPs [ 141 ].…”

Nanotechnology for Environmental and Biomedical Research

“…The authors reported a broad spectrum of genetic, molecular, cellular, morphological and behavioral effects, involving a wide range of organisms, such as algae, duckweed, amphipods, daphnids, chironomids, terrestrial plants, nematodes and earthworms. It is interesting to note that, having reported values mainly for aquatic ecotoxicity, the most sensitive test turned out to be the algae assay, and the most toxic nanomaterials were composed of silver, reinforcing the impact of the contribution by Mariano et al [4]. The other review, by Zahra et al [10], mainly focused on the aspect of environmental safety, and gave an overview of the potential exposure route of titanium dioxide nanoparticles from industrial applications to wastewater treatment, and the impact of this on the agro-environment.…”

Toxicity and Molecular Mechanisms of Actions of Silver Nanoparticles

“…The bioaccumulation of AgNPs can occur through various routes, including ingestion, inhalation, and dermal exposure. Once inside the organism, AgNPs can interact with biological molecules and cause toxicity and adverse effects [65] [66] [67].…”