Embryotoxic effects of diflubenzuron active ingredient and commercial formulations: comparative insights from zebrafish model

Diflubenzuron (DFB) is a larvicide widely incorporated into pesticide product formulations (PPFs). In addition to the active ingredient (AI), PPFs contain inert substances and adjuvants that may interfere with the AI toxicity. This study aims to compare the embryotoxicity of a veterinary powder (VF; 3% DFB) and an agricultural water-soluble pellet (AF; 80% DFB) towards DFB, referred to as AI (purity > 99%). Zebrafish (Danio rerio) embryos were exposed to AI and both formulations at low (0.025 and 0.125 mg L− 1 of AI); intermediate (0.25 and 1.25 mg L− 1 of AI); and high (2.5 and 10 mg L− 1 of AI) concentrations, as well as a reconstituted water (fish medium) and DMSO (0.4% v/v) controls. Survival, hatching rates, pigmentation, and morphological biomarkers were monitored over 120 h post-fertilization (hpf). No significant effects on survival or hatching rates were observed. Morphological abnormalities, such as notochord deformities and yolk sac opacity, occurred at all concentrations, differing in frequency and intensity. AI showed stronger effects at lower and intermediate concentrations, whereas AF and VF exhibited stronger effects at higher concentrations. Oxygen consumption did not differ significantly from controls. Regarding morphometry, AF induced more pronounced alterations than both PPFs, mainly at intermediate and high concentrations, affecting sensory, physiological, skeletal, and muscle parameters. VF caused minor changes, AI showed no significant effects, and AF presented greater toxicity. AF caused an increase while AI and VF resulted in a slight decrease in body pigmentation. Our findings suggest that PPFs may enhance toxicity by increasing the AI solubility.