Microplastics and Human Health: A Comprehensive Review on Exposure Pathways, Toxicity, and Emerging Risks

Microplastics (MPs) are considered to be dominant agents responsible for serious contamination in environmental and biological systems. Despite a huge increase in research on these contaminants, there are still considerable uncertainties and progress to be made on the exposure pathways of biological systems, modes of detection, and toxicity assessments. Therefore, developing a critical review of MPs is crucial due to growing evidence of their harmful effects on human health. In the current review, we aim to emphasize the potential toxic effects of MPs on different biological systems in humans, the mechanisms of their toxic effects, and gaps in our knowledge on risk assessment. Importantly, we focus on the risks posed by MPs for fetuses and child health. To ensure methodological rigor, the current review follows the PRISMA guidelines, explicitly detailing the literature search strategy and inclusion/exclusion criteria. The present review summarizes potential sources of MP generation, exposure pathways, quantitative analyses of dietary exposure, estimated daily intake, particle/leachate toxicity evidence, detection in different human organs, and potential toxic effects. MPs cause toxicity in several biological systems in humans, such as the gastrointestinal, nervous, hepatic, endocrine, respiratory, and reproductive systems. In addition, these particles are known to cause oxidative stress, alter metabolism, and affect gut microflora and gastrointestinal functions. Importantly, the current review also discusses the challenges encountered in conducting risk assessments for MPs and the approaches for counteracting these challenges. Finally, the review concludes by recommending future research directions in terms of counteracting the toxic effects of MPs on human health.