Photoaging behavior and neurotoxic effects of shower gel-derived microbeads in Caenorhabditis elegans

Microplastics (MPs), particularly microbeads used in shower gel products, have garnered increasing attention due to their widespread presence in the aquatic environment and associated ecological risks. However, the photoaging behavior and toxicity of shower gel-derived microbeads (SGMBs) remain poorly understood. In this study, we investigated the aging characteristics and photoaging-induced neurotoxicity of microbeads isolated from shower gel products. The results demonstrated that the physicochemical properties of SGMBs changed progressively during photooxidation, accompanied by the generation of three environmentally persistent free radicals (alkyl, alkoxyl, and peroxyl radicals) and three reactive oxygen species (•OH, O₂^•-, and ¹O₂). Toxicity assays using Caenorhabditis elegans as a model organism revealed a significant decline in nematode motility upon exposure to 60-day photoaged SGMBs (SGMB-60), compared to those exposed to unaged SGMBs. Moreover, SGMB-60 exposure impaired serotonergic, glutamatergic, and GABAergic neurons, reduced the levels of serotonin, glutamate, and γ-aminobutyric acid (GABA), and downregulated the expression of neurotransmission-related genes mod-1, eat-4, unc-30, unc-46, and unc-49. Correlation analyses indicated that the expression of mod-1, eat-4, unc-30, and unc-49 was significantly associated with neurotransmitter levels and locomotor behaviors, underscoring the critical roles of these genes in SGMB-60-induced neurotoxicity. This study advances our understanding of the photoaging behavior and neurotoxic potential of microbeads in natural environments.