New guidance brings clarity to environmental hazard and behaviour testing of nanomaterials

Manufactured nanomaterials (MNs) may have novel or enhanced properties compared to bulk materials with the same elemental composition, enabling a range of product applications in multiple sectors. With the potential for widespread usage of MNs in products, it is essential to reproducibly assess their potential for ecological and human health risks and environmental fate during a product’s life cycle1. However, the unique properties and dynamic behaviours of MNs hinder the attainment of consistent environmental hazard and fate results. Regulatory agencies often require standardized test methods to assess the potential aquatic toxicity hazards of substances and their environmental behaviours. Most methods for ecotoxicological testing were designed for dissolved substances; depending on the protocol, this may involve intentional removal of solid-phase particulates and thus exclusion of potential ‘physical effects’, or insufficient characterization to understand the relative contribution of solid particulates versus soluble fractions on the overall hazard3. While there is an Organisation for Economic Co-operation and Development (OECD) guidance document (GD) for evaluating the ecotoxicity of ‘difficult to test substnces’2, that GD was not designed to consider MNs and could be interpreted to intentionally exclude particulate materials (that is, MNs) from aquatic toxicity exposures. Thus, one of the early questions in nanotechnology environmental health and safety research was to what extent currently available standard methods can be used to assess the ecotoxicological risks and environmental behaviours of MNs4. An OECD workshop (Berlin 20135) concluded that new MN-specific test guidelines (TGs) and GDs were required to address the fundamentally different environmental behaviour (for example, agglomeration, dissolution, transformation) of MNs in standardized testing. It was also concluded that standard ecotoxicological test methods should be acceptable to evaluate MNs after certain amendments6,7, but additional discussion was needed to reach consensus on what modifications are required or allowed. To fulfil this need, international groups of scientists worked together from 2014 to 2020 to develop specific GDs and TGs to quantify the dispersion stability and dissolution of MNs, and to guide the use of OECD aquatic toxicity test methods for water column organisms (for example, algae, fish, zooplankton) and sediment organisms with MNs. This resulted in a publication in 2015 describing initial guidance on this topic for ecotoxicity testing3, followed by the release in July 2020 of two new GDs: OECD GD 317 titled Guidance document on aquatic and sediment toxicological testing of nanomaterials8 and OECD GD 318 titled Guidance document for the testing of dissolution and dispersion stability of nanomaterials and the use of the data for further environmental testing and assessment strategies.