126 How could the OECD-CBC adapt the assessment of human health impact for micro- and nanoplastics? Fit-for purpose test materials, in-vitro and in-vivo test guidelines

Abstract Inhalation of air-borne micro- and nanoplastics (MNPs) can potentially be associated with adverse effects. The Chemicals and Biotechnology Committee (CBC) at OECD held a workshop in November 2025 and initiated a process, led by South Korea, on the Safety Testing of Nanoplastics specifically. But one can hardly identify a scenario of human exposure to nanoplastics without the concomitant exposure to the size continuum from microplastics to dissolved oligomers or other plastics-associated chemicals. Test Guidelines established for chemicals, or for other types of particles, especially nanomaterials, may be applicable, or may need to be adapted. For orientation, we tested the applicability of both in vivo and in vitro guidelines on PA and PS nanoplastics. We thus report on the applicability of TGs 407, 412, 439, 487, 120, 125. In support of the first and second phase of the tentatively drafted OECD project –consisting of the test material generation, aging and fragmentation– the present study established a workflow to generate and characterize MNPs which mimic those found in the environment. We generated particles of PET, PBAT and three versions of PA, representing post-consumer textile fragments, biodegradable agroplastics and degraded fishing gear, respectively. The workflow includes controls for aging-induced effects, specifically the isolation of aged MNP particles from the mixture with UV-degradation-generated oligomers. In support of the third phase of the OECD project –consisting of toxicity testing– the present study addressed the potential lung toxicity and the alveolar uptake of respirable MNP particles by applying two low-tier in vitro methods. A549 cells, cultivated at the air-liquid interface on permeable membranes were applied to analytically quantify the uptake of MNPs across a biological barrier by pyGCMS. Metabolic activity as well as release of lactate dehydrogenase and cytokines (IL-6, IL-8) were assessed to detect an impaired barrier integrity. In the Alveolar Macrophage Assay (AMA), which was developed to identify harmful particles posing a risk to human health, rat alveolar macrophages (NR8383) were exposed to MNP dispersions to assess activation, inflammation and cytotoxicity. In total, eight different MNPs were synthesized via several approaches and subsequently characterized regarding descriptors of molecular identity and of physical structure. This approach will help to provide fit-for-purpose reference MNPs, applicable for toxicological assessments. In parallel, the adaptation of low-tier in vitro assays to MNP testing depicts a crucial step towards a better understanding of how the diverse particle properties determine potential adversity. As a result of the overall process, test materials can be developed into reference materials, and test guidelines can be adapted to enlarge the applicability domain to MNPs.