Daphnia magna are an important environmental indicator species who may be especially sensitive to nanoparticles (NPs) as a result of being filter-feeders. This paper demonstrates for the first time that proteins released by Daphnia magna create an eco-corona around polystyrene NPs which causes heightened uptake of the NPs and consequently increases toxicity. The secreted protein eco-corona also causes the NPs to be less efficiently removed from the gut of D. magna and NPs remaining in the gut of D. magna affected the rate of subsequent feeding. Thus, fate of NPs in the environment should be evaluated and monitored under more realistic exposure scenarios.

Nanomaterials (NMs) are particles with at least one dimension between 1 and 100 nm and a large surface area to volume ratio, providing them with exceptional qualities that are exploited in a variety of industrial fields. Deposition of NMs into environmental waters during or after use leads to the adsorption of an ecological (eco-) corona, whereby a layer of natural biomolecules coats the NM changing its stability, identity and ultimately toxicity. The eco-corona is not currently incorporated into ecotoxicity tests, although it has been shown to alter the interactions of NMs with organisms such as Daphnia magna (D. magna). Here, the literature on environmental biomolecule interactions with NMs is synthesized and a framework for understanding the eco-corona composition and its role in modulating NMs ecotoxicity is presented, utilizing D. magna as a model. The importance of including biomolecules as part of the current international efforts to update the standard testing protocols for NMs, is highlighted. Facilitating the formation of an eco-corona prior to NMs ecotoxicity testing will ensure that signaling pathways perturbed by the NMs are real rather than being associated with the damage arising from reactive NM surfaces "acquiring" a corona by pulling biomolecules from the organism's surface.novel and unique qualities that are not traditionally exhibited by bulk material of the same composition. NMs have been at the core of novel research for two decades and are incorporated into products spanning a range of industrial fields. For example, NMs properties are exploited in cancer research, such as the utilization of surface plasmon resonance properties of gold (Au) NMs; here the NMs are conjugated to antibodies complementary to antigens on cancer cells and are thereby internalized, following which oscillation of the Au electron cloud at a specific wavelength of light converts the absorbed light into localized heat to specifically destroy cancer cells. [1] Another example is exploitation of the antimicrobial properties of silver (Ag) NMs which undergo high dissolution to release Ag + ions [2] and where the dissolution site, rate (and thus toxicity) can be adjusted depending on the surface coating. [3] Considering that NMs are becoming so widely used, their release into the environment is inevitable. Despite this, considerably less research has focused on the implications of NMs on environmental organisms, especially under realistic conditions, than on development of their applications. NMs may enter freshwater systems from industrial effluent, where, for example, the concentrations of zinc oxide (ZnO) NMs, widely used in sunscreens and paints, in river waters has been found to be as high as 150 ng L −1 , [4] while gold (Au) NMs excreted following use in medical applications into surface waters have been predicted to be 470 pg L −1 [5] With deposition of NMs into environmental waters increasing, concerns regarding the potential for toxicity posed by NMs have demanded action, although the standard testing approaches h...

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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.

A key hypothesis in nanosafety assessment is that the NP core chemistry and eco-corona are primary factors controlling toxicity.

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The ingestion and digestion of Escherichia coli by the ciliated protozoan, Tetrahymena thermophila, was investigated after an initial exposure to either water-soluble single-walled carbon nanotubes (SWNT) or to carbon black (CB). Both SWNT and CB were internalised and visible in food vacuoles of ciliates. When presented with E. coli expressing green-fluorescent protein (GFP), these ciliates internalised bacteria as well. However, ciliates that had first internalised SWNT but not CB subsequently externalised or egested vesicle-like structures with fluorescent bacteria inside. These egested bacteria were viable and less susceptible than planktonic E. coli to killing either by the antibiotic, chloramphenicol or the disinfectant, glutaraldehyde. These results suggest that SWNT can alter the intracellular trafficking of vesicles within ciliates, leading to bacterial prey being packaged externally and protected for a time from environmental killing, which could have implications for sewage treatment and for public health.