Biotoxic effects of microplastics and nanoplastics across biological systems: A systematic review and meta-analysis

Micro plastics (MPs) and nano plastics (NPs) are new emerging contaminants of concern in the environment and to human health. Although there was growing experimental evidence, there was no quantitative synthesis available regarding their biological toxicity in various experimental systems. The purpose of the current systematic review and meta-analysis was to assess and quantify the toxic effects of MPs and NPs on various biological systems. The review was conducted based on PRISMA 2020 guidelines and a PROSPERO registration was done in advance (CRD420251166074). Literature search was systematically done in PubMed, Scopus, Web of Science, Embase, Google Scholar and Cochrane library till November 2025. Reported experimental in vivo and in vitro quantitative toxicological results from exposure to MP/NP were eligible. A total of 212 studies were included in qualitative synthesis, of which 174 studies were quantitatively analysed. Standardised mean difference (SMD) was pooled using a random effects model. Subgroup analysis and meta-regression were performed to investigate the impact of particle size, polymer type and exposure time. The I² statistic was used to assess the heterogeneity of the studies. The meta-analysis showed that the MP/NP exposure significantly influenced oxidative stress and biological functions (pooled SMD = −0.45; 95% CI: −0.71 to −0.19; p < 0.001). Toxic effects were more severe with smaller sized nanoplastics and greater exposure times. The polystyrene particles had the greatest effect sizes of all the polymer types. There was moderate heterogeneity (I² = 52–68%) which may have been attributed to differences in experimental design, exposure levels, and biological models. Some of the limitations were significant differences in exposure conditions and particle characterization between the studies. In general, MPs and NPs cause oxidative stress, growth defects, and reproductive impairment in a variety of biological systems. These results can contribute to better environmental risk assessment, and indicate the need for standardisation of testing protocols and for studies to be conducted under environmentally relevant exposure conditions in the future.