Environmental exposure to microplastics: a scoping review on human health effects

Background: Microplastics are omnipresent environmental contaminants leading to unavoidable human exposure. However, little is known about the health effects of microplastics exposure on humans. This review explored the existing evidence for the potential adverse effects of microplastics and research gaps. Methods: An electronic search of published articles was conducted in PubMed, Scopus, EMBASE, Cochrane databases, and Google Scholar using a combination of subject heading and text word terms for microplastics and human health effects with specific inclusion and exclusion criteria. Letters, comments or notes, conference abstracts, and editorials were excluded. Additional keywords were developed after the preliminary screening to incorporate relevant articles. Google Scholar search, followed by a focused search, was performed to gather grey literature. The initial search resulted in 16,983 and 23 published articles and grey literature, respectively. A total of 4,817 unique citations were retrieved after filtering out duplicates. The title and abstract screening process resulted in 119 articles. After full article review and investigating their references, 63 articles were finalized. Every document was reviewed by at least two of the researchers. Results: Literature has reported that exposure to microplastics might occur through ingestion, inhalation, and dermal contact due to its presence in foods, air, and consumer products. Microplastics exposure might cause particle toxicity through oxidative stress, inflammatory lesions, and increased uptake or translocation. Failure of the immune system to eliminate synthetic particles might lead to chronic inflammation and increase cancer risk. Moreover, microplastics have been found to release their constituents, pathogenic organisms, and adsorbed contaminants. Conclusion: Knowledge regarding microplastic toxicity is still limited and primarily influenced by exposure concentration, particle components, adsorbed contaminants, organs involved, and individual susceptibility. Further research is warranted to understand the risk of human health due to exposure to microplastics, which requires human exposure assessment, understanding of pathogenesis, and quantifying the effects.