Rifampicin Co-Exposure Increases the Acute Toxicity of Chlorantraniliprole to Zebrafish (Danio rerio)

Pesticides and antibiotics frequently co-occur in aquatic environments, yet their combined effects on aquatic life remain poorly understood. We evaluated whether antibiotic co-exposure alters pesticide toxicity in juvenile zebrafish (Danio rerio). Five pesticides—chlorantraniliprole (CAP), chlorpyrifos (CPF), buprofezin (BPF), difenoconazole (DFZ), and boscalid (BO)—were tested alone and with rifampicin (RIF), ampicillin (AMP), and tetracycline (TET); DFZ and BO were tested only with RIF and AMP, and ternary mixtures were tested only for CAP, CPF, and BPF. Based on nominal concentrations, adding RIF (50 mg/L) increased CAP toxicity, lowering its 96 h LC50 from 61.85 to 40.72 mg/L (LC50 ratio, LCR = 1.52); this increase was no longer observed when AMP or TET was also added. For CPF, only the ternary mixture with RIF and AMP slightly reduced toxicity (LCR = 0.95). For BPF, only co-exposure with TET increased toxicity (LCR = 1.18). DFZ and BO showed reduced toxicity with RIF or AMP (LCRs of 0.80–0.91). Except for CAP + RIF, changes were small (≤20%). These varied responses suggest that antibiotic–pesticide interactions are chemical-specific. Because the antibiotic concentration was high relative to environmental levels and exposure concentrations were not analytically verified, the findings indicate possible interactions under the experimental conditions rather than environmental mixture risk and suggest that single-compound toxicity data may be insufficient for assessing pesticide hazards in multi-contaminant environments.