European environmental regulation of nanomaterials: Inclusion of the eco-corona

Since the potential negative implications of nanomaterials (NMs) were first highlighted two decades ago, several European legislations have been revised to account for nano-specific properties NMs. NMs are materials with at least one dimension in the nanoscale (1-100 nm). Their small size gives them unique properties, such as high reactivity, making them useful in a wide range of applications. To support implementation of the legislations, test guidelines and regulatory guidance are being developed or adapted to assess NM environmental safety. Most tests, however, comprises of rather simple setups with use of pristine/”as-manufactured” NMs. This is in spite of the growing evidence that NMs undergo intricate interactions with the surrounding constituents upon environmental release, leading to a layer of biomolecules (such as natural organic matter (NOM), polysaccharides and proteins) forming around the NM. This layer is known as the eco-corona and has shown to change a range of characteristics of the NMs, such as particle size and surface composition, as well as the environmental behavior, -fate and ecotoxicity.

In this thesis, it was explored how consideration of eco-corona can be incorporated into European regulatory frameworks relevant to NMs, with a particular focus on the European chemicals legislation REACH. To do this, the scientific knowledge on eco-corona formation and impacts was investigated. Furthermore, the availability and suitability of methods for NM risk and safety assessment were analysed with a focus on inclusion of eco-corona aspects. The status of current NM regulatory frameworks was then discussed, and lastly, it was investigated how environmental safety assessment of NMs that include eco-corona consideration can be incorporated into NM regulatory frameworks.

It was found that the European Chemicals Agency’s (ECHA) guidance on NM ecotoxicity and fate testing, that aims to support implementation of REACH, highlights eco-corona formation as a relevant process to consider under the endpoint transformation. Yet, the guidance contains no advice on how to investigate eco-corona. To enhance implementation of REACH, it is recommended to include eco-corona testing in the forthcoming update of the guidance, e.g. by consideration of the methods provided in this thesis. Eco-corona considerations should be included for both assessment of transformation and of aquatic pelagic toxicity. Furthermore, the thesis found that to obtain insights into the characteristics and kinetics of eco-corona formation, data on especially time-dependent interaction/adsorption/-desorption between the NMs and the constituents of the medium (with and without presence of NOM/biomolecules) is of high relevance.

Lastly, it was found that there is a need for regulatory revisions as well as including addition of eco-corona as relevant process for transformation under the information requirement on degradation and exposure assessment in REACH. Since eco-corona formation can also affect NM ecotoxicity, it is recommended to increase environmental relevance in hazard assessment of NMs, more specifically in the PBT assessment. It is suggested to incorporate NOM/biomolecules in the persistency (P), bioaccumulation (B), and toxicity (T) testing of NM. Incorporating eco-corona aspects into hazard assessment will increase environmental relevance and thereby lower the uncertainties related to extrapolation which is especially challenging for NMs. For application of such additions to the PBT assessment, methods must be validated and further developed where needed to test P, B and T with inclusion of eco-corona.

As shown in this thesis, NM regulation must handle increasing complexity for more precise prediction of NM environmental behaviour, -fate and ecotoxicity. As it is recognised that development of NMs or advanced materials also continues to increase in complexity, regulatory frameworks need to adjust and develop accordingly to keep reflecting and managing currently unknown risks.