Trends in quality and risk assessment applicability of microplastic ecotoxicity studies

• Using the ToMEx 2.0 database, 286 microplastic ecotoxicity studies were evaluated based on technical quality and risk assessment applicability. • While most studies reported basic technical criteria reliably, less than half met key requirements for applicability to ecological risk assessment. • Quality scores varied significantly among taxa: studies on crustaceans, molluscs, and annelids generally scored higher, whereas fish studies tended to perform worse on both technical and risk-related criteria. • Study quality has not improved significantly over time, likely reflecting a lag in integrating recently published quality frameworks into experimental design and reporting. The Toxicity of Microplastics Explorer 2.0 (ToMEx 2.0) aquatic organism database contains 286 microplastic ecotoxicity studies that have been scored for quality and applicability to risk assessment. The overall reporting quality of microplastic effects studies was assessed, and the relationships between quality scores and various factors, including time, taxonomic group were evaluated. Data uploaded into ToMEx were first evaluated against quality assurance and quality control criteria for the requirements of the database. Each study was given at least three total scores related to: technical quality, applicability to risk assessment, and overall study quality, which is the sum of scores for all criteria. While most studies reliably reported technical criteria, the majority of studies were not rated as applicable to risk assessment. Overall, study quality scores and reporting of technical criteria have not changed over time. However, a weak but significant decline in applicability to risk assessment was observed over time. Additionally, there was a weak, significant positive trend between study quality score and journal impact factors, but no significant correlation between study quality and whether a study found a significant effect. Quality scores varied significantly depending on species, with fish studies generally having lower risk applicability criteria scores and studies with crustaceans, molluscs, and annelids generally having higher scores. This analysis highlights uncertainties underlying the current state of knowledge regarding microplastic ecotoxicity, data gaps in the microplastic ecotoxicity literature, and provides a framework for assessing aggregated microplastic ecotoxicity data quality and their applicability to risk assessment.