Inclusion of eco-corona formation and biotransformation in regulatory nanomaterial ecotoxicity and fate testing: review and insights from the MISTRA environmental nanosafety project

Journal article, 2025

Background: The eco-corona, consisting of environmental biomolecules formed around engineered nanomaterials (ENMs) when released to the environment, has gained increasing focus in the scientific literature and its role for ENM fate and toxicity is now widely acknowledged. The European chemicals legislation, REACH, entails reporting requirements when it comes to the transformation of nanoforms. Guidance provided by the European Chemicals Agency (ECHA) highlights eco-corona and biotransformation as relevant transformation processes. Still, no specific advice is given on how to test these processes. Based on the findings from the MISTRA Environmental Nanosafety project, we here map out methods to characterise ENM eco-corona and biotransformation and assess their effects. Furthermore, the regulatory relevance of the methods is evaluated. Results: We identified methods to assess both eco-coronas formed ex vivo (by interaction with natural organic matter-based solutions or solutions with animal secretes) and bio-coronas formed in vivo (via biotransformation, i.e., filtration of ENMs through living organisms). We recommend implementing these methods and methodological considerations in a future update of ECHA’s guidance on ENM ecotoxicity and fate testing, both in the sections on transformation and aquatic pelagic toxicity. When exploring the characteristics and kinetics of eco-corona formation, various data are needed, including data on time-dependent interaction/adsorption/desorption between ENM and constituents in the medium (both with and without the addition of natural organic matter/biomolecules). It is, furthermore, proposed that environmental relevance is enhanced for hazard assessment of nanoforms in REACH. This can be done by incorporating eco-corona considerations in the persistency, bioaccumulative, and toxicity (PBT) assessment. Conclusions: We here propose to update ECHA 's guidance on ENM ecotoxicity testing and the PBT assessment required under REACH to include eco-corona considerations. If updated, this will aid in implementing information requirements on ENM transformation, increase the environmental relevance of ENM ecotoxicity tests, and reduce uncertainties in the extrapolation of ENM ecotoxicity data.