Abstract
Nanomaterials (NMs) are particles with at least one dimension between 1 and 100nm 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.
Highlights
This review explores the range of biomolecules available to form an eco-corona, and the impacts that acquisition of an eco-corona can have on the toxicity of NMs to organisms, utilizing Daphnia magna (D. magna) as a representative freshwater species
Environmental waters contain a wide variety of biological constituents such as proteins, carbohydrates, and natural organic matter (NOM), as well as a multitude of small molecules and metabolites, all of which have a tendency to adsorb to the surface of NMs that are deposited into
NMs may already have surface coatings when they are deposited into environmental waters, which may get replaced in part or fully by biomolecules existing within the water
Summary
Despite it being widely recognized that NOM is a sink for a range of pollutants, including metals and organics, and influences their bioavailability,[31,32,33] interactions with NOM are not considered as part of standard toxicity testing, nor in modeling of pollutant fate and behavior. As per the well-known Vroman effect,[35,36] biomolecules in high abundance may bind initially to be subsequently replaced by molecules with a higher affinity for the NM surface, as shown schematically in Figure 1; evolution of the NMs corona in this manner can result from NMs uptake and transport to new locations with different biomolecule availability,[37] or from cellular secretions in response to the NMs presence which can alter the corona composition.[38] evolution of the NM (eco)corona is an area of active research, both experimentally and through development of predictive models based on affinities.[39] These biological and environmental constituents, whose molecular weights span from 10–2 000 000 Da, have the ability to adsorb onto NM surfaces and create a layer around the NM termed the "corona," or "eco-corona" to emphasize that it is composed of environmental biomolecules. It is worth highlighting that the majority of these studies were conducted without the presence of biomolecules (unless otherwise stated), so that these values may be altered under realistic conditions
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