Tea bags as hidden source of micro- and nanoplastics: a systematic review for food safety.

Background: The release of micro- and nanoplastics (MNPs) from tea bags during brewing is a significant, recently identified source of potential human exposure. This systematic review collected global research published up to the end of 2025, indexed in PubMed, ScienceDirect, Web of Science, and Scopus, adhering to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Study objective was to systematically detect, quantify, and characterize MNPs released from various tea bag materials. The review focused exclusively on studies that directly measured MNPs release under brewing conditions. Methodology: A systematic literature search was conducted through specified databases. Inclusion criteria focused on studies quantifying MNPs release (by count or mass) from tea bags during brewing, irrespective of water temperature or time, but studies relying on in-vitro or in-vivo models, review/conference/retracted papers, or books/chapters were excluded. Data extraction included MNPs type, quantity, size range, tea bag material, brewing conditions, and detection methods. Main findings: Our systematic search identified 19 studies meeting the inclusion criteria. A significant finding is the substantial release of MNPs, often in billions of particles per bag, from plastic-containing tea bags (e.g., non-woven polypropylene, nylon) brewed in hot water (typically ≥95 °C). Released particles predominantly ranged from nano-to micrometer sizes. Release quantities were found to be influenced by tea bag material, water temperature, brewing duration, and mechanical agitation. While some materials like paper or woven nylon showed lower release rates, even composite or supposedly "eco-friendly" bags contributed measurable MNPs release. Limitations and gaps: Despite the direct evidence of MNPs release, some research gaps persist. Crucially, standardized methodologies for detection and quantification of MNPs, and human health risk assessment are lacking, obstructing comparability across studies. Furthermore, while our review focused on MNPs release, the in-vivo or in-vitro evidence regarding the biological implications remains largely outside the scope of this specific systematic review's direct findings, necessitating separate, targeted investigations. Current global exposure estimates are preliminary due to these methodological and data limitations. Conclusion: This systematic review confirms that tea bags, particularly those containing plastics, are a notable source of MNPs release into beverages and environment. While considerable quantities of MNPs are released, future systematic efforts should highlight developing and implementing standardized detection methodologies to improve the reliability of findings, alongside focused investigations into the biological and toxicological effects of MNPs and human health risk assessment. Furthermore, exploring and promoting innovative solutions, such as the use of biodegradable materials with minimal or without MNPs releasing and alternative brewing technologies, is crucial for mitigating MNPs contamination from tea consumption.