Are Environmental Levels of Nonsteroidal Anti-Inflammatory Drugs a Reason for Concern? Chronic Life-Cycle Effects of Naproxen in Zebrafish

The nonsteroidal anti-inflammatory drug naproxen (NPX) is among the most consumed pharmaceuticals worldwide, being detected in surface waters within the ng to μg/L range. Considering the limited chronic ecotoxicity data available for NPX in aquatic ecosystems, the present study aimed at evaluating its impact in the model organism <i>Danio rerio</i>, following a full life-cycle exposure to environmentally relevant concentrations (0.1 to 5.0 μg/L). An integration of apical endpoints, i.e., survival, growth, and reproduction, with gonad histopathology and gene transcription (RNA-seq) was performed to provide additional insights into the mode of action (MoA) of NPX. NPX decreased zebrafish growth and reproduction and led to histopathological alterations in gonads at concentrations as low as 0.1 μg/L. At the molecular level, 0.7 μg/L of NPX led to a disruption in gonads transcription of genes involved in several biological processes associated with reproduction, mainly involving steroid hormone biosynthesis and epigenetic/epitranscriptomic machineries. Collectively, these results show that environmentally realistic concentrations of NPX affect zebrafish reproduction and associated signaling pathways, indicating that current hazard and risk assessment data for NPX underestimate the environmental risk of this pharmaceutical.