Updating traditional regulatory tests for use with novel materials: Nanomaterial toxicity testing with Daphnia magna

Abstract Nanomaterials (NMs) are being widely incorporated into a variety of fields such as medicine, cosmetics and electronics, due to the exceptional qualities provided by their small size and high surface area to volume ratio. Increased use of NMs leads to their deposition into environmental waters where they interact with organisms such as the fresh water zooplankton Daphnia magna (D. magna). D. magna is an ideal candidate for fresh water toxicity testing and a central study species used by the Organization for Economic Cooperation and Development (OECD) which sets the gold standard for regulatory testing protocols. The ecotoxicity protocols using D. magna were originally designed for bulk chemicals though have been deemed acceptable for NM testing, despite NMs existing as suspensions rather than dissolved chemicals. These protocols fail to account for key exposure features of NMs such as the fact that the natural clearance processes in these organisms require food to push out previously accumulated matter, and that under realistic exposure scenarios, NMs will have acquired a biomolecule corona that changes their identity, stability, uptake and excretion. Thus, the lack of biomolecules added to the medium and lack of feeding can lead to significant over or underestimation of the amount of NMs taken up by, or retained within, D. magna leading to uncertainty of dose and ultimately miscalculation of NMs toxicity and the risks posed by these materials. Herein we present evidence to support the call for revised guidelines for D. Magna acute and chronic toxicity tests for hazard and risk assessment of NMs.