Comprehensive review of ecological risks and toxicity mechanisms of microplastics in freshwater: Focus on zebrafish as a model organism

Abstract

Zebrafish, as a model organism, exhibit high sensitivity to environmental pollutants and has been widely used in microplastics (MPs) toxicology studies. However, the mechanisms underlying MPs' effects on zebrafish have yet to be comprehensively summarized. This review systematically explores the sources, pollution status of freshwater MPs and their biological toxicity mechanisms using zebrafish as a model organism. This analysis reveals that the primary sources of MPs include sediment release, natural degradation of plastic products, and precipitation-mediated transport. Freshwater MPs predominantly comprise of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyvinyl chloride (PVC). These MPs typically appear transparent, white, black, or blue, and predominantly exist as fibers, films, fragments, foams, and particles. The concentration, size, shape, type, aging status, and loading capacity of MPs can induce developmental malformations in zebrafish embryos, including pericardial and yolk sac edema. In adult zebrafish, MPs cause intestinal injuries characterized by increased permeability, impaired barrier function, and microbiota dysbiosis. MPs exposure also induces behavioral abnormalities such as reduced locomotion and anxiety-like responses, while simultaneously provoking oxidative stress and immune-inflammatory reactions. The physical mechanism of MPs-induced toxicity in zebrafish involves particle accumulation and tissue abrasion. In contrast, physiological and molecular mechanisms encompass interactions between MPs' surface functional groups and biological tissues, alterations in oxidative stress markers, enzymatic activity and cytokine profiles, and modulation of gene expression patterns. This review synthesizes current knowledge on the ecological risks of freshwater MP pollution and its toxicological impacts on zebrafish, thereby providing a comprehensive framework for understanding MP toxicity mechanisms.

Keywords: Danio rerio; Molecular actions; Physical action; Physiological; Pollution status; Sources.