Ecotoxicological insights into UV-P-induced immunotoxicity and bacterial infection risk in marine medaka (Oryzias melastigma).

Abstract

Benzotriazole ultraviolet stabilizers (BUVs) are widespread and bioaccumulative aquatic contaminants. However, their immunotoxicity and underlying molecular mechanisms remain largely unexplored. In this study, we measured the concentrations of ten BUVs in the East China Sea and selected UV-P for further study based on its highest detected concentration. Consequently, marine medaka (Oryzias melastigma) were exposed to an environmentally relevant concentration (3.5 μg/L) and two elevated concentrations (35 and 350 μg/L) of UV-P for 28 days. Immunological parameters, histopathological alterations, and transcriptomic profiles were examined at the end of exposure. Additionally, bacterial challenge tests using Pseudomonas fluorescens were performed to assess host resistance. The results revealed an initial increase in the levels of alkaline phosphatase, immunoglobulin M, C-reactive protein, and complement component 3, followed by a significant decrease with increasing UV-P concentration. Histopathological damage was observed in immune tissues, including the liver, intestine, kidney, and gills. Transcriptomic analysis indicated significant enrichment of differentially expressed genes in multiple immune-related pathways following UV-P exposure. The key pathways affected mainly included cytochrome P450-mediated metabolism and the complement and coagulation cascades. The 24-h post-infection assessment revealed dose-dependent increases in bacterial loads and mortality rates in UV-P-exposed fish. Collectively, these findings demonstrate that UV-P induces immunotoxicity and increases the risk of bacterial infection in marine medaka. This study highlights the potential ecological threats posed by BUVs and offers valuable insights into the immunotoxic mechanisms of these contaminants.