Potential toxicity of microplastics on vertebrate liver: A systematic review and meta-analysis

Microplastics (MPs) pollution is emerging as a significant environmental concern, threatening human and animal health. Liver, as an important organ, plays an important role in the metabolism and detoxification of pollutants. Many studies have suggested that the liver is a potential target organ for MPs. However, the extent and consequences of the impacts of MPs on the liver reported in studies remain inconsistent. We categorized vertebrates into fish, mammals, and birds and performed a meta-analysis to comprehensively examine the effects of MPs on the liver. Hedges' g values were calculated to evaluate effect sizes. To further explore the sources of heterogeneity among the studies, we conducted subgroup analyses focusing on life stage, MPs type, MPs size, and exposure duration. Additionally, we normalized the MPs concentrations and conducted meta-regression analyses to explore the relationship between MPs concentrations and their hepatotoxic effects. A total of 118 studies were included in this meta-analysis. By quantifying 19 indicators, the results showed that MPs could damage the liver by altering liver morphology, inducing oxidative stress, producing intracellular toxicity, altering biotransformation processes, and disturbing lipid metabolism. Intracellular toxicity, followed by oxidative stress, had the greatest impact. Organisms are more sensitive to MPs under the following conditions: longer exposure duration, smaller MPs sizes, and earlier life stages. As the concentration of MPs increases, the levels of several liver indicators, including catalase, glutathione S-transferase, reactive oxygen species, and alkaline phosphatase, progressively increase. This study provides a comprehensive understanding of the effects of MPs on the liver and suggests the underlying mechanisms of MPs hepatotoxicity.