Impact of microplastics and nanoplastics on human health: Mechanistic insights and exposure pathways

Microplastics (MPs) and nanoplastics (NPs) have emerged as critical environmental contaminants with potential adverse effects on human health. This review examines the various ways MPs and NPs can be spread in the environment and their potential impact on humans. They can be introduced into the environment through multiple sources, like synthetic textiles, cosmetics, packaging, and industrial processes. These particles enter the human body through ingestion, inhalation, and skin contact, and they deposit in various tissues, including the lungs, kidneys, and gastrointestinal tract. Additionally, they can cross embryonic layers and reach the placenta. They can cause inflammation, oxidative stress, metabolic disorders, genotoxicity, and immunotoxic effects upon interaction, as confirmed by in-vivo and in-vitro studies. Furthermore, long-term exposure to MPs and NPs causes various complications to the human body, including metabolic disorders or even the development of cancers. Despite the presence of much evidence, a significant gap remains in fully understanding the mechanism of toxicity posed by MPs and NPs exposure and its long-term health outcomes. There is an urgent need for extensive investigations and improvement in standardized methods to evaluate the human health impact of MPs and NPs. This review explores current evidence on exposure pathways, bioaccumulation mechanisms, and health outcomes and identifies critical knowledge gaps.