SciRAPplastic and plasticCRED: tailoring existing tools to assess micro- and nanoplastics (eco)toxicity studies

There is a rapid increase in scientific studies on the environmental and health effects of microplastics and nanoplastics (MNPs), with potential to inform risk assessment. However, regulatory uptake of scientific evidence depends on the reliability and relevance, often referred to as the regulatory adequacy, of the studies. This regulatory adequacy may be challenged by, for example, insufficient characterization of test materials, and lack of transparency and reporting in experimental setup, methods, and analytics. While frameworks exist for evaluating the regulatory adequacy of (eco)toxicity data for chemicals and nanomaterials, they do not fully account for the unique characteristics and challenges associated with MNPs. Therefore, there is a need to provide further guidance specifically tailored to MNP studies. The aim of this paper was to review and synthesize the state of knowledge regarding key physicochemical parameters and experimental considerations critical to evaluating the regulatory adequacy, defined in terms of reliability and relevance, of MNP (eco)toxicity studies. Building on this comparative review, existing criteria were identified, adapted and aligned to support the development of structured tools embedded within the SciRAP and CRED frameworks. A literature review revealed the importance of, for example, polymer identity, size and shape distribution, surface chemistry, additive content, dispersion behaviour, background contamination control, description of sample preparation, and characterization of the test item. Based on these findings, relevant criteria were identified from existing frameworks and literature and subsequently adapted or extended and built into the SciRAP and CRED frameworks, to address the specific challenges of MNP research, supporting structured evaluation of study reliability and relevance. By promoting better reporting practices and attention to MNPs specific test considerations, the proposed frameworks, SciRAPplastic (in vivo and in vitro) and plasticCRED (ecotoxicity), can strengthen the scientific foundation for environmental and health risk assessments of MNPs. Furthermore, they may support the regulatory uptake of data generated in emerging non-standard MNP (eco)toxicity studies.