Microplastic in milk and dairy products: Research quality, abundance, sources, and transfer mechanisms

Microplastics (MPs), as emerging contaminants, have been widely detected in milk and dairy products. However, current studies lack systematic evaluation regarding data reliability, variations in MPs abundance across different dairy products, and the underlying sources and transfer mechanisms. This review applies an experimental quality assurance and quality control scoring to assess the quality of existing literature and identifies common methodological issues in milk and dairy product research. Evidence from published studies reveals varying degrees of MPs contamination from raw milk to milk powder, with the latter exhibiting the highest levels. To clarify the sources of MPs, this review investigates potential contamination pathways during packaging, processing, transportation, and farm environment. Further analysis indicates that MPs can enter dairy cattle through drinking water, feed, air, and dermal exposure, subsequently reaching the mammary gland via blood circulation. Once internalized by mammary epithelial cells, MPs may be secreted into milk. This review specifically highlights the long-overlooked but critical transfer pathway of MPs from environmental exposure through dairy cattle to raw milk. By elucidating this key contamination route, the study provides a theoretical foundation and research direction for risk assessment and mitigation strategies related to MPs in dairy products, offering valuable insights for ensuring milk quality and food safety.