Chronic toxicity of antibiotics and global warming in Danio rerio: Biomarker responses and toxicological effects

The combined influence of multiple stress factors on natural ecosystems is a critical concern, as neglecting their effects could compromise essential biological functions. However, limited studies have explored the combined effects of antibiotics and global warming on aquatic ecosystems, leaving a gap in understanding their interaction. This study aimed to assess the toxicity of environmentally relevant concentrations of sulfamethoxazole (SMX: 150 μg/L), trimethoprim (TRIM: 30 μg/L), and their mixture (MIX: 150 μg SMX/L + 30 μg TRIM/L) on Danio rerio at three temperature conditions: standard (26 °C), moderately high (28 °C), and high (32 °C) temperatures. A multi-biomarker approach was used to evaluate the organism's biological status (e.g., antioxidant/detoxification defense enzymes, lipid peroxidation, cholinergic neurotransmission, energetic metabolism, DNA damage). Results indicated that rising temperatures influenced the toxicity level of each antibiotic differently to D. rerio. At 26 °C, all the antibiotics were marginally toxic, and major alterations were observed (oxidative stress and neurotoxicity). Increasing temperature to 28 °C, the toxicity increased, with SMX and MIX exhibiting moderate toxicity, and severe alterations (neurotoxicity and DNA damage). In contrast, TRIM showed only slight toxicity and recorded negligible alterations (antioxidant defense alterations). At higher temperature (32 °C) individual antibiotics revealed slightly toxic with negligible alterations. However, MIX at 32 °C was more toxic, and severe damage was observed (e.g., higher DNA damage). These findings reveal a pressing and alarming threat: combined contaminants impact and climate change could drive aquatic ecosystems toward collapse. Understanding how these stressors interact is critical to preventing potentially irreversible damage to aquatic life.