Shape and Charge of Gold Nanomaterials Influence Survivorship, Oxidative Stress and Moulting of Daphnia magna

Abstract

Engineered nanomaterials (ENMs) are materials with at least one dimension between 1–100 nm. The small size of ENMs results in a large surface area to volume ratio, giving ENMs novel characteristics that are not traditionally exhibited by larger bulk materials. Coupled with large surface area is an enormous capacity for surface functionalization of ENMs, e.g., with different ligands or surface changes, leading to an almost infinite array of variability of ENMs. Here we explore the effects of various shaped (spheres, rods) and charged (negative, positive) gold ENMs on Daphnia magna (D. magna) in terms of survival, ENM uptake and production of reactive oxygen species (ROS), a key factor in oxidative stress responses. We also investigate the effects of gold ENMs binding to the carapace of D. magna and how this may induce moulting inhibition in addition to toxicity and stress. The findings suggest that ENM shape and surface charge play an important role in determining ENM uptake and toxicity.

Nanomaterials in the Environment Acquire an “Eco‐Corona” Impacting their Toxicity to Daphnia Magna—a Call for Updating Toxicity Testing Policies

“…Figure shows that differently shaped (sphere, short rod, and long rod) Au NMs incubated in D. magna conditioned medium all acquired different proteins in their coronas, as evidenced by polyacrylamide gel electrophoresis (SDS‐PAGE) indicating that corona formation is morphology‐dependent as they all had the same core composition and the same surface charge. It has previously been shown that these differently shaped NMs prompted different amounts of ROS formation in D. magna and that the D. magna were able to recover to different degrees from this; while the negatively charged Au NMs did not cause significant ROS formation, recovery, defined as the ability of the organism to return to steady‐state ROS levels, was better when exposed to spheres compared to short rods . Identical Au NMs with positive charges prompted a much higher degree of ROS formation with much poorer recoveries .…”

“…It has previously been shown that these differently shaped NMs prompted different amounts of ROS formation in D. magna and that the D. magna were able to recover to different degrees from this; while the negatively charged Au NMs did not cause significant ROS formation, recovery, defined as the ability of the organism to return to steady‐state ROS levels, was better when exposed to spheres compared to short rods . Identical Au NMs with positive charges prompted a much higher degree of ROS formation with much poorer recoveries . NMs of different shapes that were originally stable in fresh medium were found to agglomerate to different degrees in medium containing biomolecules specifically from D. magna ; for example, long rods remained stable for up to 8 h whereas both spheres and short rods agglomerated, with size increasing up to fivefold, indicating that the presence of secreted biomolecules has a destabilizing effect on smaller NMs .…”

“…Identical Au NMs with positive charges prompted a much higher degree of ROS formation with much poorer recoveries . NMs of different shapes that were originally stable in fresh medium were found to agglomerate to different degrees in medium containing biomolecules specifically from D. magna ; for example, long rods remained stable for up to 8 h whereas both spheres and short rods agglomerated, with size increasing up to fivefold, indicating that the presence of secreted biomolecules has a destabilizing effect on smaller NMs . The effect of this agglomeration of the smaller spherical NMs, due to the destabilization resulting from the acquisition of the corona, caused an increase in D. magna mortality upon exposure.…”

“…D. magna also undergoes asexual (parthanogenetic) reproduction when in ideal environmental conditions, which ensures the offspring are genetically identical, ultimately decreasing variation in experimental studies, but also providing a strong indication of the presence of pollution when the exposed organisms produce male offspring and resting eggs . Several studies pertaining to the toxicology of chemicals and NMs have used D. magna as the indicator species due to the variety of end‐points that can be measured when exposed to a stimulus, including heart rate, appendage movement, brood number release, male neonate production, ROS formation, morphological deformation, spin rate, and moulting pattern . These studies are conducted in a range of approved biological media, although the medium is generally free of any biological material such as NOM or biomolecules such as proteins or polysaccharides that would naturally be present in real environmental scenarios, at least at the outset.…”

The Toxicity of Nonaged and Aged Coated Silver Nanoparticles to Freshwater Alga Raphidocelis subcapitata

“…The impact of NPs on organisms depends on their intrinsic properties (Fröhlich 2012;Silva et al 2014;Kwok et al 2016;Nasser et al 2016;Saei et al 2017), fate, and transport in the environment (Levard et al 2012;Seitz et al 2015;Metreveli et al 2016). Once present in the environment, the NPs are transformed, having significantly different physicochemical characteristics from fresh ones (Mudunkotuwa et al 2012;Mitrano et al 2015).…”