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

Abstract

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...

The Crucial Role of Environmental Coronas in Determining the Biological Effects of Engineered Nanomaterials

“…Whilst in theory, an analogous framework is expected to exist in the environmental corona, with greater heterogeneity in the structure and components, a wider range of molecules of different molecular weights and compositions are competing for the surface of the ENM. [24,43] To date, the structure-activity relationships in environmental corona formation on ENMs is not well understood, as it is dependent on the physicochemical properties of ENMs and chemical reactivities of eco-molecules.…”

“…Unlike unicellular organisms such as bacteria and algae, particulate matter may be ingested and assimilated in the gastrointestinal tract of D. magna, helpful when assessing the bioavailability and biokinetic mechanism of exogenous particulates such as ENMs. [146][147][148] The mortality, survival rate, feeding rate, and locomotion of D. magna may be impacted by ENMs. [149][150][151] Again, most studies have ignored the presence of an environmental corona on ENMs, leading to proposals of theories that deviate from what is actually occurring in natural ecosystems.…”

Multigenerational Exposures of Daphnia Magna to Pristine and Aged Silver Nanoparticles: Epigenetic Changes and Phenotypical Ageing Related Effects

“…We have argued previously that the presence of biological macromolecules is essential for NP ecotoxicity assessment to allow formation of the eco‐corona and reduce the surface energy of the NPs as would occur instantaneously in the environment. [ 25–27 ] The present study investigates the effects of chronic (from 24 h old to 24–30 days) parental (F0) exposures, to both pristine and 6‐month aged uncoated Ag, PVP Ag and Ag 2 S NPs in a standard Daphnia culture medium (HH Combo) and in a synthetic European lowland water (Class V from [ 28 ] ) containing natural organic matter (NOM). The subsequent three generations (F1‐3) were split (from F1 onward) into two groups–half were continuously exposed for multiple generations (F1–F3 exp ) and half were removed from the maternal exposure and grown in NP‐free medium for 3 generations (F1–F3 rec ) to identify the potential recovery scenario, as shown schematically in Figure S13 in the Supporting Information.…”

Effect of the Albumin Corona on the Toxicity of Combined Graphene Oxide and Cadmium to Daphnia magna and Integration of the Datasets into the NanoCommons Knowledge Base

“…Indeed, it is well known that the protein content is a critical parameter for nanomaterial corona formation and their biological effects [ 5 , 48 , 80 ]. Thus, our findings highlighted the importance of developing a standard protocol for medium conditioning, medium supplementation with relevant biomolecules or pre-formation of coronas, as well as a need for advanced interlaboratory studies for a better characterisation and understanding of the impacts of the protein and metabolite eco-corona during Daphnia nanotoxicity testing and its implications for nanosafety regulation [ 81 ].…”