Aged microplastics-induced growth inhibition via DNA damage, GH/IGF-1 and HPT axes disruption in zebrafish larvae

The escalating use of microplastics (MPs) has led to the widespread exposure of aquatic organisms. The associated toxicities of MPs may be influenced by photoaging. However, the toxicity of aged MPs at environmentally relevant concentrations to aquatic organisms remains unclear. Therefore, our study focused on assessing the effects of aged polystyrene microplastics (PS-MPs) on the development of zebrafish. Here, using simulated sunlight, we investigated the endocrine and developmental toxicity of embryo-larvae exposed to pristine PS-MPs (1 μm) and aged PS-MPs at environmentally relevant concentrations of 0.1-100 μg/L. The alterations in PS-MPs characteristics using photoaging were investigated through scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The results suggested that photoaging altered physicochemical characteristics of PS-MPs. The assessment of physiological indicators revealed that exposure to aged PS-MPs significantly inhibited the growth of larval zebrafish compared to pristine PS-MPs with endpoints of body length, heartbeat rate and tail coiling frequency. Bioinformatics analyses indicated that aged PS-MPs exposure perturbed the hormones levels (GH, IGF-1, T3 and T4) and gene expression (e.g., gh, igf1, trh and ugt1ab) related to growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis, and the hypothalamic-pituitary-thyroid (HPT) axis. Moreover, 8-OHdG levels were significantly altered in zebrafish larvae exposed to aged PS-MPs, and Pearson correlation results showed significant associations between 8-OHdG levels and GH/IGF-1 and HPT axis-related genes. Overall, these results indicated that the growth inhibition of larval was attributed to DNA damage, HPT and GH/IGF axes disruption, providing new insights into the environmental effects and health risks of MPs.