Silver nanoparticle toxicity and association with the alga Euglena gracilis

Abstract

Impact of silver nanoparticles (AgNP) on aquatic algae has largely been studied with model species that possess a rigid cell wall. Here we explored the interactions of AgNP with Euglena gracilis, a green alga having no cell wall but a pellicle. The toxicity and silver uptake upon 1-2 h exposures to various concentrations of AgNO3 and AgNP, having a mean size of 47 nm measured in the exposure medium, were examined. The photosynthetic yield decreased in a concentration-dependent manner and AgNP were less toxic than AgNO3 based on total silver added. Cell morphology was significantly altered by AgNP and AgNO3. Damaging effects of AgNP on photosynthesis and morphology were completely prevented by cysteine, suggesting that the toxicity of AgNP was mediated by dissolved Ag. Indeed, the maximal cell-associated silver was higher in AgNP compared to AgNO3 exposures, amounting to 5.1 × 10 -4 mol Lcell -1 and 1.4 × 10 -4 mol Lcell -1 for AgNP and AgNO3, respectively. However, the difference was not caused by cellular uptake of AgNP, but strong sorption of AgNP to the pellicle. Nano ImpactOne of the most controversial issues in algal nanotoxicology is whether nanoparticles can be internalized and if internalization is a prerequisite for toxicity. Here, we examined the interactions of AgNP with the algae, Euglena gracilis, possessing a proteinaceous pellicle instead of a typical cell wall, which we considered as a barrier against nanoparticle uptake. This study provides evidence that AgNP were not internalized but strongly adsorbed on the pellicle. The toxicity of AgNP to algae merely resulted from the dissolved silver released from the nanoparticles.

Nanomaterials in the environment: Behavior, fate, bioavailability, and effects—An updated review

“…More systematic studies are required to resolve the extent to which plant cell walls act as a barrier and for which NMs. Focusing on the interaction of Ag NMs with unicellular algae, Piccapietra et al () and Li et al () confirmed a strong interaction of particles with the cell surface of Chlamydomonas reinhardtii and Euglena gracilis , respectively, but with negligible uptake. The comparatively thick cell wall of algae appears to be a significant barrier to NM uptake.…”

“…Nano‐CuO sulfidation also occurs over several days with the initial formation of copper (I) sulfide (Cu 2 S) and possible transformation to CuS (Ma et al ). Unlike nano‐Ag and nano‐ZnO, the sulfidized form of the original nano‐CuO has greater solubility and releases more Cu 2+ than the parent NM (Ma et al ); as a consequence, the sulfidized form has been shown to be more toxic to aquatic biota (Li et al ).…”

Co, Zn and Ag-MOFs evaluation as biocidal materials towards photosynthetic organisms

“…Most of the literature has established that the biocidal activities of metallic nanomaterials are due to the dissolved metal ions (Aruoja et al, 2009;Li et al, 2015;Navarro et al, 2008;Wyszogrodzka et al, 2016), however, in some cases, direct contact between the organism and the material could be also responsible of the observed toxicity (Rodea-Palomares et al, 2011;Zhuang et al, 2012). To determine the contribution of dissolved metals to MOFs toxicity, MOF filtrates experiments were performed.…”

Assembly of CdTe Quantum Dots and Photosystem II Multilayer Films with Enhanced Photocurrent

“…[30] Previous report also showed that free nanoparticles could be toxic to plant and algae by strong sorption of nanoparticles onto the pellicle. [31] In the meantime, the shading of light absorption by QDs may lead to decreased light absorption by PSII, this may also contribute to the decreased photocurrent density. To avoid the toxicity and make effective use of QDs, CdTe QDs were first immobilized onto ITO substrates through the LbL assembly technique, which has been well developed by our group.…”