Following the inadequacy of global plastic pollution control measures, microplastic (MP) pollution is posing new challenges to human health. In recent years, MPs have been detected in various human tissues, including their first identification in human kidneys in 2023. MPs can reach the kidneys through inhalation, oral ingestion, and intravascular injection, and they can be excreted via urine. Based on the latest research, this article reviews the nephrotoxicity of MPs and proposes a filtration-reabsorption-translocation hypothesis regarding the potential renal excretion mechanism of MPs. Short-term exposure to MPs can induce oxidative stress, resulting in endoplasmic reticulum (ER) stress, inflammatory responses, and lipid metabolism disorders, while long-term exposure may result in renal fibrosis mediated by ferroptosis. The nephrotoxicity of MPs is associated with particle size, though not in a linear manner. A specific size range appears to exhibit more significant kidney toxicity. Furthermore, oral exposure may activate the complement system in the kidneys through the gut-kidney axis, with the C5a/C5aR pathway playing an important role in this process. In conclusion, MPs present a substantial threat to human kidney health. Considering the existing research limitations, it is imperative to urgently investigate the effects of MPs at realistic environmental exposure concentrations on human kidneys and to explore strategies for mitigating their nephrotoxicity.
